Can Geology Tell Us What is Warming the Climate?

On Monday this week, and rather late in the day, Dr Colin Summerhayes from the Scott Polar Institute, Cambridge University, left this lengthy comment at the end of the thread on Prof. Richard Lindzen’s post called Global Warming and the Irrelevance of Science. I wanted to respond to some of the points raised but did not want to do this at the end of an old comment thread, and so asked if I may publish the comment as a guest submission. Dr Summerhayes responded by expanding on the comment and submitting the Opinion Piece that is published below.

Here are some of the highlights from Dr Summerhayes’ CV:

  • April 2010: Emeritus Associate, Scott Polar Research Institute
  • January 1 2004 part time, and full time from April 1 2004- April 9 2010: Executive Director, International Council for Science’s Scientific Committee on Antarctic Research (SCAR)
  • 1997-2004: Director Global Ocean Observing System (GOOS) Project Office; UNESCO’s Intergovernmental Oceanographic Commission, Paris
  • 1995-1997: Southampton Oceanography Centre; Deputy Director, and Head of Seafloor Processes Division.
  • 1988-1995: Director, Natural Environmental Research Council’s Institute of Oceanographic Sciences Deacon Laboratory, Wormley, Surrey.
  • 1982-1988: BP Research Centre. (A) 1982-1985: Research Associate; (B) 1985-88: Senior Research Associate and Manager, Stratigraphy Branch.
  • 1976-1982: Research Associate and Project Leader; Petroleum Geochemistry Branch, Exxon Production Research Co, Houston, Texas.

Comments will be strictly moderated. Additional commenting guidelines are given at the end of the post.


Despite the world’s politicians finally agreeing, in Paris in December 2015, on what to do about global warming, many scientists still reject the evidence for it being caused by humans, or question that it is a significant problem.

For example, Dr Lindzen (2016) agrees that although carbon dioxide (CO2) is a greenhouse gas, which absorbs and re-emits infrared radiation from the Earth’s surface, the increase in its concentration in the atmosphere is not important because its climate sensitivity (the amount by which temperature will rise for a doubling of CO2) is low. This common rejection of the anthropogenic global warming theory ignores the evidence from the Earth science community about the causes of climate change in the past (for summaries see e.g. Ruddiman, 2013; Hay 2013; Summerhayes, 2015). The chapter on Palaeoclimate in the report on the science of climate change by Working Group 1 (WG1) of the Intergovernmental Panel on Climate Change (IPCC) summarizes some of this evidence (Masson-Delmottee et al, 2013), but almost nobody reads it, and the media largely ignores it. If we want to know what causes climate change at any one time we have to divide the climate signal into its constituent parts and look at the forcing provided by each element.

John Tyndall, the experimentalist who discovered that carbon dioxide, methane and water vapour act as what we now call greenhouse gases (Tyndall, 1861), considered that his discovery opened the way to understanding the wanderings of Earth’s climate uncovered by geologists. One of the first geologists to take him seriously was a Swede, Arvid Hogböm, who asked Svante Arrhenius if he could calculate whether fluctuations in atmospheric CO2 might account for glacial to interglacial changes of the Ice Age (Arrhenius, 1896). Yes, said Arrhenius, who later coined the term ‘Hothouse [now Greenhouse] Climate’ (Arrhenius, 1908). Geologist T.C. Chamberlin converted Arrhenius’s findings into a geologically based conceptual climate model (Chamberlin, 1897, 1899). Volcanoes emitted CO2, which was extracted from the air by chemical weathering. Imbalances over time between the volcanic source and the chemical weathering sink accounted for periods of warming or cooling.

For a full accounting of the effects of CO2 we had to wait until its spectrum had been established by the investment of the US military in large spectrophotometers in the early 1950s. Physicist Gilbert Plass used the new data to confirm that fluctuations in CO2 had likely contributed to the variability of the climate of the Ice Age (Plass, 1956). Roger Revelle was convinced it was important to measure CO2, and set about finding funds for Charles Keeling to set up a CO2 measuring facility on Mauna Loa in 1957 (Revelle and Suess, 1957). Keeling ignored CO2 measurements from sites close to industrial plants or cities where CO2 was being emitted. He wanted background air (Keeling, 1960).

Charles Lyell was among the first to note that Earth had experienced a ‘Great Cooling’ since Cretaceous times (Lyell, 1830), and it was soon realized that there had been a previous glaciation in Carboniferous-Permian times (Ramsay, 1855). During Lyell’s Great Cooling, plate tectonic processes were moving the continents apart from one another, eventually isolating Antarctica at the South Pole 90 million years ago.

In the late 20th century, geochemist Bob Berner (Berner, 1999, 2004), and palynologists like Dana Royer and Dave Beerling (Beerling and Royer, 2011), confirmed that the Great Cooling was likely driven, as T.C. Chamberlin had suggested, by changing atmospheric CO2 through time (Royer et al., 2004). Plate tectonics processes provide abundant CO2 from volcanic activity (the source) associated with phases of rapid seafloor spreading, and soak up CO2 during phases of mountain building that enhance chemical weathering (the sink) (Berner, 1999). We now have various ways of estimating the likely abundance of CO2 in the air in past times (e.g. see Beerling and Royer, 2011). This modern understanding is remarkably similar to T C Chamberlin’s conceptual model.

Chemical weathering works by atmospheric CO2 combining with H2O vapour to form a weak acid that attacks silicate and carbonate minerals exposed by mechanical weathering in mountains, and the silicates of flood basalts. It absorbs CO2 from the atmosphere (Kent and Muttoni, 2013). The products of chemical weathering, including that CO2, are taken to the sea by rivers, consumed by plankton, and used to build soft organic tissue and calcium carbonate skeletons (Berner, 1999). Much of this is recycled in the water column when organisms die, but some falls to the seafloor to be preserved as sediment (another CO2 sink).

About half of the CO2 put into the air dissolves in the ocean to enable these two ‘fluids’ to stay in chemical equilibrium. Dissolution of CO2 in the ocean makes it slightly more acid, which makes deep bottom waters corrosive to sediments rich in CaCO3 skeletal remains. The boundary below which carbonate cannot accumulate is termed the carbonate compensation depth (CCD), and is a marker for the amount of CO2 dissolved in the ocean. When CO2 is abundant the CCD is shallow, as it was in Eocene times some 50 million years ago (Pälike et al., 2012).

When rates of seafloor spreading are high (hence CO2 is abundant and the climate is warm), the ocean becomes depleted in magnesium (Mg), which favours deposition of low-Mg-Calcite. When rates of seafloor spreading are low (hence CO2 is less abundant and the climate is cool), the ocean becomes enriched in Mg, which favours the deposition of Aragonite (Müller et al, 2013). The oscillation between these two types of calcium carbonate (from Calcite to Aragonite) is known as the calcite metronome (Zalasiewicz And Williams, 2012), and is an indirect reflection of (though not caused by) the abundance of CO2 in the atmosphere.

Deep sea cores contain records of a massive emission of carbon at the Palaeocene-Eocene boundary, 55 million years ago. It caused a rise in temperature of 5-6°C, and acidified the deep ocean, raising the CCD by about 2 km and killing off deeper water organisms with carbonate skeletons (Zachos et al., 2010). Sea level rose by 10-12 m. New work shows that this emission occurred in two very closely spaced events in which the rise in CO2 was almost as abrupt as it is today (Bowen et al, 2015), making this a possible natural analog for what we are now doing to the climate.

Deep sea cores also show that around 34 million years ago the production of cold Antarctic Bottom Water began (Kennett 1977, Zachos et al., 2001). That in turn suggested that gaps had opened between Antarctica and Tasmania and Tierra del Fuego, permitting the formation of the Antarctic Circumpolar Current (ACC) driven by westerly winds, and thermally isolating the continent (Kennett 1977). It has also been suggested that the gradual decline in atmospheric CO2 cooled the continent leading to the growth of ice caps and then, 34 million years ago, to the formation of a major ice sheet (DeConto and Pollard, 2003; Pollard and DeConto, 2005). Supporting evidence for the CO2 hypothesis comes from Southern Ocean sediments containing debris from Antarctic glaciers in the Eocene, before the ACC developed (Barrett, 1999).

There is also evidence, from bubbles of fossil air in ice cores, that rising temperature increases atmospheric CO2. When temperature rose, so did the CO2, which emerged from the ocean as it warmed, as expected from the operation of the Gas Laws. That rise in CO2 warmed temperatures further through positive feedback. When the CO2 signal was found in the Vostok ice core, it appeared that the CO2 signal lagged the temperature signal (Petit et al., 1999). But, in 2013, Frederic Parrenin showed that during the last glacial termination CO2 changed with temperature (Parrenin et al., 2013). The apparent delay at Vostok now seems to be an illusion generated by the age model for the air in ice core bubbles.

During the Ice Age of the past 2.6 million years our climate was predominantly cool, interrupted by brief warm intervals (interglacials), like the one we are now living in. This pattern is caused by regular periodic changes in the Earth’s orbit and the tilt of the Earth’s axis, which change the amount of incoming solar radiation (insolation). The changes in that insolation are not large enough to account for the amount of warmth in interglacials. The extra warmth most likely comes from the release of CO2 from the oceans as they warm (Petit et al, 1999).

In the last interglacial, 120,000 years ago, temperatures were 2-3°C warmer than today, and sea level rose 4 to 9 metres above today’s level (Kopp et al., 2009). Geology is telling us that if we raise our temperature that much, our coasts will be inundated, as they were then. We should be concerned about that.

Insolation peaked around 11,700 years ago, melting the great North American and European ice sheets and parts of West and East Antarctica. Since then, insolation has declined (Berger and Loutre, 2002). As a result, Earth’s climate cooled over the past 10,000 years (Marcott et al., 2013; see also the PAGES 2k Consortium, 2013, for the past 2000 years). The cooling trend culminated in the Little Ice Age of 1350-1850.

Orbital calculations show that we should remain in this cold condition for the next 5,000 years (Berger and Loutre, 2002). So, why are we not still in the Little Ice Age? Has the sun suddenly gotten hotter? No. The latest data on sunspots (Clette et al, 2014) show that there were about the same peak numbers of sunspots in the 1980s-90s as there were in the 1780s or the 1840s-60s, during the Little Ice Age. Indeed, the number of sunspots has been declining since 1990 (Clette et al, 2014; Lockwood, 2010), so our climate should be cooling from that cause too. Why is it not?

What reversed the cooling trend of the past 10,000 years, if it was not the Sun? The finger points clearly at the rise in our emissions of CO2 and related greenhouse gases (especially methane and nitrous oxide). Data from ice cores show that the abundance of CO2 in the atmosphere increased from 280 ppm to 400 ppm, starting in about 1770 (Wolff, 2011). That’s when James Watts’ steam engines started burning coal in abundance, kicking off the industrial revolution. The rise in CO2 was exponential, starting slow, taking off as we entered the 20th century, and increasing even faster after about 1955. Not surprisingly, given what we know from geology and from basic physics, temperature increased along with it. Proof that the source is the burning of fossil fuel comes from carbon isotopes, which show an increase in the concentration of the 12C as opposed to the 13C carbon isotope.

Couldn’t the present warming be something like that which caused the Medieval Warm Period (MWP)? We can answer that question with recourse to the record of beryllium-10 (10Be) and carbon-14 (14C) isotopes in (e.g.) tree rings (Steinhilber et al., 2012). Cosmic rays create these isotopes in the upper atmosphere. The two isotopes were abundant when the Sun’s output was weak, and the climate was cool, and rare when the Sun’s output was strong, and the climate was warm. The Sun’s output follows the 208-year Suess Cycle and the 88-year Gleissberg Cycle. The isotopic patterns show that these cycles should have made the climate warm during the MWP, but not as warm as the mid 20th century (Steinhilber et al., 2012). Equally, these patterns show that the Little Ice Age was not uniformly cold, but characterized by a series of cold peaks (solar minima), separated by warm periods. The last such cold peak was the Gleissberg Minimum in about 1900, after which the Sun’s activity rose to a broad peak between 1960 and 1990, followed by a decline (Lovelock, 2010; Clette et al., 2014). These solar effects are smaller in magnitude than those caused by orbital insolation. So the curve of declining temperature with time over the past 2,000 years is driven primarily by orbital change, superimposed on which are small warmings (like the MWP), and coolings (like those of the solar minima of the Little Ice Age) (Summerhayes, 2015). The current warming is now back at about the level of the Roman Warm period. It is most extreme in the Arctic, where plants that last saw daylight several thousand years ago are emerging from beneath Canadian Ice Caps. The modern warmth of the eastern Canadian Arctic now exceeds the peak warmth of the early Holocene, when summer insolation across the region was 9% greater than present (Miller et al., 2013).

Why is there not a perfect 1:1 relationship between the subsequent rises in temperature and CO2? Small periodic natural fluctuations in the climate system, like warm El Niño events followed by cold La Niña events, temporarily disrupt the basic temperature-CO2 link. Another such fluctuation is the Pacific Decadal Oscillation, which warms the Pacific slightly for 20-25 years, then cools it for as long (Chavez et al., 2003). Since about the year 2000 we have been in the negative (cool) phase of the PDO. It has operated like a prolonged La Niña event, keeping Earth slightly cooler than it would otherwise have been (Fyfe et al., 2016). In a few years from now the PDO will revert to its positive (warm) phase, and operate like a prolonged El Niño, warming the planet once more. These relatively small natural fluctuations are superimposed on the underlying trend driven by the CO2-temperature relationship that, along with orbital change, has modulated our climate for millions of years. We are now perturbing it.

What can geology tell us about the climate sensitivity? The PALEOSENS Project, comprising a large group of climatologists and palaeoclimatologists (PALEOSENS Project Members, 2012) calculated that over the past 65 million years the climate sensitivity for a doubling of atmospheric CO2 was between 2.2–4.8°C, which agrees reasonably well with calculations for the modern climate system by the Intergovernmental Panel on Climate Change (IPCC) (Solomon et al., 2007).

With rising emissions of CO2, geology tells us that that the planet will continue to warm, driving a long-term rise in sea level (Clark et al, 2016). The rise of sea level will take much longer to reach equilibrium than the rise in surface air temperature. For example, although warming due to orbital effects ceased 11,700 years ago, sea level continued to rise by 45m over the next 5,000 years (Clark et al., 2016). We would not expect such a large rise in the next few hundred years, because we no longer have large northern hemisphere ice sheets. But we have begun a process that will inevitably continue, melting parts of Greenland, Antarctica, and mountain glaciers, and affecting coastlines in the millennial time frame.

In summary, Earth’s history confirms that CO2 does change temperature, and that temperature does change CO2, and that we cannot blame the Sun for where we are now. All that we can blame are our emissions. Let’s get on with improving the long-term chances for survival of our species. Alarm is misplaced, but we should be seriously concerned about what global warming driven by our emissions will do to the climate that our children and their children will inherit.


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Supplementary Commenting Guidelines

My objective for this thread is to have a high level exchange of views on a number of key technical issues that divides sceptical opinion from main stream climate science. All comments should be of a technical nature and where possible backed by data, scientific principles and sources. Primary comments that don’t meet this standard will be deleted. Responses to primary comments are a little more tricky to manage. Please understand that comment moderation is a difficult issue to manage.

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219 Responses to Can Geology Tell Us What is Warming the Climate?

  1. Euan Mearns says:

    Figure 1 The carbon cycle from IPCC AR5.

  2. Peter Lang says:

    Dr Summerhayes

    Thank you for this excellent post. This is a much clearer and simpler explanation than IPCC WG1.

    Despite the world’s politicians finally agreeing, in Paris in December 2015, on what to do about global warming, many scientists still reject the evidence for it being caused by humans, or question that it is a significant problem.

    I am a geologist and an engineer. I am aware of and already accept most of what you state about the science in this post. However, I am not persuaded that human caused GHG emissions are a significant risk. I am persuaded that the policies advocated to reduce GHG emissions are likely to cause significant economic damage to the economies of the countries that participate and therefore to the global economy. This will slow the rate that living standards are raised and people: are lifted out of poverty, get better education and health services and longer more fulfilling lives. Proper economic, cost-benefit, risk and decision analysis are what is needed to demonstrates whether or not we should proceed with the policies being advocated. But scientis’ knowledge of the inputs that policy analysts need for such analyses, such as the damage function, is almost non-existent. The information science should be providing for policy analysis is not more information about temperature changes, we’ve had 30 years of that and it’s going nowhere relevant; the estimates of ECS haven’t changed since the start. Some of the other inputs needed and the uncertainties are explained in my recent article:

    Deep sea cores contain records of a massive emission of carbon at the Palaeocene-Eocene boundary, 55 million years ago. It caused a rise in temperature of 5-6°C, and acidified the deep ocean, raising the CCD by about 2 km and killing off deeper water organisms with carbonate skeletons (Zachos et al., 2010). Sea level rose by 10-12 m. New work shows that this emission occurred in two very closely spaced events in which the rise in CO2 was almost as abrupt as it is today (Bowen et al, 2015), making this a possible natural analog for what we are now doing to the climate.

    What was the atmospheric CO2 concentration at the start of those events? And what was the average global temperature at their start? If the CO2 concentration and the global average temperature were not similar to now (which I understand they were not), how can it be considered a relevant analogue for human caused emissions today and for the hypothesized damages of our GHG emissions?

    The apparent delay at Vostok now seems to be an illusion generated by the age model for the air in ice core bubbles.

    I wasn’t aware of that. I’ll watch to see how that develops over the next few years.

    Geology is telling us that if we raise our temperature that much, our coasts will be inundated, as they were then. We should be concerned about that.

    Why should we be concerned about that? Over what period will the hypothesized sea level rise occur? People move in hours and infrastructure is replaced about every 50 years or so. There is no shortages of arable land or food supply to feed a world population of 10 billion people. The shortages are caused by poor infrastructure, poor governance, and lack of law and order and security for workers. This will improve fastest if we do not damage the global economy. The economic cost of sea level rise is trivial, about $1 trillion over 85 years ‘Economic impacts of substantial sea-level rise . Most of the world’s economy is unaffected by it. It’s an unpersuasive argument to use to justify polices that will do far more harm than good.

    Orbital calculations show that we should remain in this cold condition for the next 5,000 years (Berger and Loutre, 2002).

    The last few glacial cycles have been about 100,000 years between peaks and troughs, so why are you suggesting just 5000 years of cooling?

    So, why are we not still in the Little Ice Age? Has the sun suddenly gotten hotter? No.

    What reversed the cooling trend of the past 10,000 years, if it was not the Sun? The finger points clearly at the rise in our emissions of CO2 and related greenhouse gases (especially methane and nitrous oxide).

    To answer these questions, the scientists need to explain what caused the other similar warm periods when there was no human caused CO2 emissions: Holocene Optimum, Minoan, Roman, Medieval warm periods. I understand the warm periods since the Holocene maximum occurred with a period of about 900 years. The explanation you have written is too hard to follow without charts showing the actual data and hypothesized causes. However, from a policy perspective these changes in temperature are trivial and irrelevant because we don’t know whether GHG emissions are doing more harm than good. Temperature, itself, is not a measure of good or harm.

    over the past 65 million years the climate sensitivity for a doubling of atmospheric CO2 was between 2.2–4.8°C

    That is one analysis. But there are many. If we pick others, e.g. Nic Lewis and co-workers, is getting central estimates for ECS around 1.7. Furthermore, it is TCR not ECS that is relevant for policy analysis, and TCR is around 1.3. Nothing scary about any of this.

    Let’s get on with improving the long-term chances for survival of our species. Alarm is misplaced, but we should be seriously concerned about what global warming driven by our emissions will do to the climate that our children and their children will inherit.

    There is nothing in this post to support or justify this call to action. And nothing that is relevant for policy analysis. But the damage the advocated policies would do – the damage to human well-being and the debt that our children and grand-children will inherit as a result of such policies – is not taken into consideration. See my article linked above for some examples of what is relevant for policy analysis.

    Judith Curry’s testimony to the US Congress is a coherent, rational and persuasive summary of the current state of relevant climate science:

    • Greg Kaan says:

      I believe this is the paper referred to by Dr Summerhayes regarding the Vostok ice cores. The assertion is that the CO2 bubbles will diffuse upwards through the ice pack until the ice builds up to be firm enough to lock the bubbles to a fixed depth and this movement is enough to remove the 800 year lag between temperature rise and atmospheric CO2 concentration increase..

      There appear to be many assumptions and suppositions in the modelling but perhaps this is normal in ice core analysis. Hopefully you and others can make more of this

    • Reply to peter lang

      Bowen et al 2014, report that CO2 rose from 700 ppm to 1820 ppm during the 55 million year old carbon event.

      Zachos et al 2010, report that temperature went, as a result, from 8.5°C to 14°C

      Why should we be concerned about sea level rise? Because much human activity is concentrated in the coastal zone, as are most major cities. If sea level rises by a metre this century, there will be a distinct cost to re-engineering their coastal defences. Equally, in areas where it is too expensive to protect the coast, valuable land will be flooded. Sea level will go on rising long after 2100, even if global warming stops then, and may reach between 2 and 5 m depending on what our eventual emissions are. As to plants, they are already moving. This will change agriculture. Yes we can adapt in the temperate zone, but farmers elsewhere (in poor regions) may find it difficult to do so because of growing drought. In addition, don’t forget that warming also affects the hydrological cycle. By removing glaciers from the Andes and Himalayas, warming will deprive poor nations of regular summer melt supplies of water. You also seem to have forgotten that adding CO2 to the atmosphere also adds it to the ocean, which makes it more acid. Over long periods of slow change, organisms can adapt, but we are now changing it fast, making adaptation difficult. Some of the first affected animals will be calcium carbonate shelled plankton (coccolithophores and pteropods) in polar oceans. These are at the base of the food chain, leading to concerns about the future viability of the food chain there.

      5,000 years merely indicates that the Little ice Age conditions forecast by orbital calculations will last at least that long. The current interglacial will last very much longer.

      My article explains that we have in the past 2,000 years had a succession of cool and warm periods driven by solar variation that were superimposed on a cooling trend driven by declining insolation. The solar variations are small compared with the orbital effect. I would dispute your statement that temperature is not a measure of good or harm. If it causes sea level to rise to unacceptable levels, we will not be happy.

      You can if you wish stick with Nic Lewis’s estimate of climate sensitivity, but what I am pointing out is that estimates like his are well outside the mainstream. It’s your choice.

      You may think that what I have said is not a call to action. Others may think differently. That’s what politics is all about. Ultimately, as you say, it is about risk. Lord Stern had a lot to say about that – but it’s not my field.

      Perhaps you like Judith Curry’s views because they chime with your own. I note that since her testimony we have had the warmest year yet (2015) in the past few hundred. In my view she should not have started with 1998 which was an El Nino peak – one of the largest El Ninos in memory. What she should have done was take a long term running mean to eliminate the up and down wiggles caused by alternating El Ninos and La Ninas, which distort the underlying trend. Equally, 2015 sea ice in the Arctic has continued the downward trend in Arctic sea ice. She did not show that. Equally, Antarctic sea ice showed a big downward swing in 2015, taking it back to the levels of the early 1980s. She did not show that. The problem with Antarctic sea ice is that its distribution is complicated by the effects of the ozone hole, which help to keep sea ice widespread. Once the ozone hole disappears the true global warming signal will re-emerge. Her and Lewis’s estimate of climate sensitivity did not take into consideration the geological evidence as far as I am aware. Are climate models running too hot, as she suggests? I don’t know – I confine myself to what I can learn from geological data. I am surprised at her announcement that Arctic ice will recover. I have just been at an Arctic science meeting in Fairbanks where the assembled scientists were all talking about the continued decline. I wonder what she knows that they don’t. That there may well be a forthcoming grand solar minimum is on the cards, as I point out in my book “Earth’s Climate Evolution” in 2015. I would estimate it as probably occurring between 2070 and 2160, but its effects are likely to be small, and to be compensated for by continually rising greenhouse gas emissions. Regarding the source or ‘alarm’, it is not the UNFCCC, but the multitude of climate scientists who are the source, because they have been studying the matter in depth since at least the 1890s. Anyway, I’m happy to see that she concluded by saying there is reason to be concerned about climate change, which is, after all, my message too.

      • Peter Lang says:


        The concentrations and the average surface temperature at start and peak of the PETM you quote from the two references you picked are not consistent with what I understand is the consensus from IPCC. For example, you say:

        Zachos et al 2010, report that temperature went, as a result, from 8.5°C to 14°C

        The current average surface temperature is about 15C. Do you believe the global surface temp before the PETM was colder than the current average surface temperature?

        Given that the planet has been much hotter in the past and life thrived during those periods, even if some species became extinct, this demonstrates that much warmer temperatures than our GHG emission can cause will not be catastrophic for life on Earth.

        Can you compare the proportion of species that became extinct during the PETM with proportion that became extinct during rapid cooling events? And can you compare the mass of carbon tied up in the biosphere in hot and cold times? Please provide quotes to authoritative studies that address these two questions. If these questions haven’t been addressed, you might like to explain why they haven’t. Surely these should be important questions we need answers to before embarking on hugely expensive global abatement policies.

        You say:

        Why should we be concerned about sea level rise? Because much human activity is concentrated in the coastal zone, as are most major cities. If sea level rises by a metre this century, there will be a distinct cost to re-engineering their coastal defences.

        True, there is a cost. But the relevant point is that the cost is trivial compared with the cost of GHG emissions abatement. The cost of all the estimated damages from human caused GHG emissions, including sea-level rise, is much less than the projected abatement cost. Therefore, the advocated abatement policies cannot be justified, on a rational basis. The link I gave explains . And note that the projected benefits are based on inputs that are more alarmist than the IPCC central estimates, and the costs of the advocated abatement policies are likely to be much higher than estimated. Also note that the key inputs are highly uncertain. The uncertainties of the various inputs cascade.

        • Apologies, the Zachos paper refers to a change in the temperature of bottom water. Today’s deep ocean bottom water is around 2 dec C.

          You are right, a rise in temperature globally of say 3 deg will not be detrimental to life. Our planet has been hotter than that before now. The question is – what will it do to our ability to farm, globally?

          The PETM was accompanied by a mass extinction of 35-50% of benthic foraminifera (especially in deeper waters) over the course of ~1,000 years – the group suffering more than during the dinosaur-slaying K-T extinction. Contrarily, planktonic foraminifera diversified, and dinoflagellates bloomed. Success was also enjoyed by the mammals, who radiated extensively around this time. So, not all bad news.

          I am not sure where you got your figures about costs, but my reading of Lord Stern’s report is that there will be a considerable eventual cost to doing nothing. So perhaps one’s reading of what we ought to do depends on which economists one trusts.

          • Euan Mearns says:

            Colin, you are bound to know more about this than I. But is it not the case that seawater reaches maximum density at about 2˚C and then sinks. Hence, for so long as we have ice at the poles, polar water will sink and produce bottom water that is close to 2˚C?


            Does it not follow from this that the volume of seawater cooled to 2˚C that sinks must impact the average temperature of the oceans? This sets up ocean convection. And Houghton tells me that atmospheric convection is the principle way of removing heat from Earth’s surface to the tropopause where the density of CO2 becomes too low to trap IR by radiative transfer and the energy is lost to space?

          • Peter Lang says:

            Dr Colin Summerhayes,

            Thank you for your reply.

            The question is – what will it do to our ability to farm, globally?

            Indeed that is the key question. Or, stated more generally, what is the damage function – i.e. what is the net benefit or net damage per 1C or warming or cooling. This is the point i’ve been making Scientist need to stop focusing on temperature changes – they are irrelevant unless we know the damage function – and focus instead on providing policy analyst’s with the information they need for policy analysis. Did you read this: ?

            I’d suggest we know that planetary cooling is very damaging, potentially catastrophic, because we’ve been there and the planet has previously encountered many phases of snow-ball earth. We know that warming has been very beneficial for the past 1C of warming. It strains credulity to believe the benefits of warming we’ve experienced over the past 1C temperature rise will suddenly turn negative just when we happen to be living on the planet. It’s like believing we are at the centre of the universe – unless we have good evidence to support it, which we don’t. That’s why we need c=scientists to focus on providing the inputs needed for policy analysis, not keep regurgitating temperature data analyses for another 30 years.

            I am not sure where you got your figures about costs, but my reading of Lord Stern’s report is that there will be a considerable eventual cost to doing nothing.

            As my paper explains, I got my figures from William Nordhaus’s analysis for AR5 WG3. The model is published, available for download and has an informative ‘Introduction and User’s Manual‘ here: . I used the model as downloaded with all the default input values. I added a seventh policy scenario, the red line, for ‘1/2 the Copenhagen participation rate’. It’s all explained in the paper I linke=ked in my previous comment.

            Stern’s report has been discredited. It is loved by the climate alarmists but widely discredited by Economists. Notice the line for Stern analysis line on the chart in my paper – it is anomalous and clearly not realistic (notice how it start with enormously negative benefits). Here is what William Nordhaus had to say ( , p167):

            To begin with, the Stern Review should be read primarily as a
            document that is political in nature and has advocacy as its
            purpose. The review was officially commissioned when
            British chancellor of the exchequer Gordon Brown “asked Sir
            Nick Stern to lead a major review of the economics of climate
            change, to understand more comprehensively the nature of
            the economic challenges and how they can be met, in the UK
            and globally.”7 For the most part, the Stern Review accurately
            describes the basic economic questions involved in global
            warming. However, it tends to emphasize studies and findings
            that support its policy recommendations, while reports with
            opposing views about the dangers of global warming are

            Putting this point differently, we might evaluate the
            Stern Review in terms of the ground rules of standard science
            and economics. The central methodology by which science,
            including economics, operates is peer review and reproducibility.
            By contrast, the Stern Review was published without
            an appraisal of methods and assumptions by independent
            outside experts, and its results cannot be easily reproduced.

            These may seem minor points, but they are fundamental
            for good science. The British government is not infallible in
            questions of economic and scientific analysis of global warming,
            any more than it was in its assessment of weapons of mass
            destruction in Iraq.8 External review and reproducibility cannot
            remove all errors, but they are essential for ensuring logical
            reasoning and a respect for opposing arguments.

            There are many other sever critiques discounting the Stern report.

          • Euan Mearns says:

            Peter, your comment went to moderation. Don’t know why, sometimes my own comments go to moderation too. Do yo want me to publish the second comment you wrote?

            So far, the only costs of man made climate change to the UK are futile attempts to prevent it from happening. Its just possible that beyond the visible costs of electricity infrastructure and prices that there are hidden costs by way of lowered GDP stemming from the misallocation of vast sums of capital. This enterprise is a tax on the British people for which there are zero rewards. Osborne should take note.

          • Peter Lang says:


            Thank you for the explanation. I understand. No need to post my second attempt to make the same points.

            I agree with your comments about the costs and benefits of mitigation for UK. I did analyses of the costs of the Australian carbon price and posted it several places. A short article explains the cost to the individual, per family, per worker, and as a discounted payment in 2013 versus pay it yearly through to 2050:

      • clivebest says:

        It is estimated the PETM released 3000 GT carbon. Mankind has so far released about 700GT C. If we were to burn all the estimated known reserves of fossil fuels then we might be able to release an equivalent amount to PETM . Zebe et al. (2009) estimated that CO2 levels after PETM rose from 1000 ppm to 1700 ppm. The direct radiative CO2 forcing of such an increase is only about 2.8 W/m2 or a temperature rise of < 1C. Even if climate sensitivity from feedbacks is more like 2-3C this still cannot explain the observed rise of ~ 6C. If you believe CO2 alone was responsible for the temperature rise then Paleocene CO2 levels have to be much assumed lower than 1000 ppm and PETM release at least more than double the evidence at 6000 GT C.

        So PETM is really not that well understood.

        source : Paleoclimate – Micheal L. Bender

        • polarscientist says:

          According to Bower et al 2015 (see my list of references) the rates of release during the PETM were probably within
          an order of magnitude of, and may have approached, the 9.5 Pg/yr associated with modern anthropogenic carbon emissions. And as we now know there were in fact two bursts of emissions (Bowen et al), closely spaced in time. So the total emitted is likely to have been significantly more than Zeebe et al imagined in 2005 from less well-resolved stratigraphic rewcords. In estimating what this means for warming one has to estimate both the climate sensitivity (how much warming for a doubling of CO2) plus the effects of added water vapour from increased evaporation caused by warming. We are getting better at understanding the PETM.

          • Peter Lang says:

            In estimating what this means for warming one has to estimate both the climate sensitivity (how much warming for a doubling of CO2) plus the effects of added water vapour from increased evaporation caused by warming.

            There is a more important point that you seem to not recognise or be unwilling to acknowledge. I pointed out in one of my early comments and you responded with incorrect figures – later acknowledged after I questioned your figures but you did not acknowledge the key point.

            The key point is that the rapid carbon release that caused the PETM occurred when the planet was already at near it’s highest temperature which was around 11 C warmer than now (Hansen and Sato,, Fig 1). We are currently at a cold period (we are in about the third coldhouse phase in the past 1/2 billion years; for 75% of that time there have been no polar ice caps – this is a very cold time!). The point is that talking about the consequences of the rapid C releases during the PETM is not a good analogue of the consequences of them being released now. The reality is we do not know whether human caused GHG emissions are doing more harm than good and we do not know if we are reducing or increasing the risk of climate damages. You seem very reluctant to acknowledge that reality,

  3. Euan Mearns says:

    Colin, many thanks for this comprehensive and well referenced review of the geology and geochemistry processes surrounding CO2. I want to begin by picking up on this notion of a rock weathering sink. We had several posts here on this and related topics in the carbon cycle and I summarised my views in this post:The Carbon Cycle: a geologist’s view. From your text:

    Plate tectonics processes provide abundant CO2 from volcanic activity (the source) associated with phases of rapid seafloor spreading, and soak up CO2 during phases of mountain building that enhance chemical weathering (the sink) (Berner, 1999). We now have various ways of estimating the likely abundance of CO2 in the air in past times (e.g. see Beerling and Royer, 2011). This modern understanding is remarkably similar to T C Chamberlin’s conceptual model.

    Chemical weathering works by atmospheric CO2 combining with H2O vapour to form a weak acid that attacks silicate and carbonate minerals exposed by mechanical weathering in mountains, and the silicates of flood basalts. It absorbs CO2 from the atmosphere (Kent and Muttoni, 2013). The products of chemical weathering, including that CO2, are taken to the sea by rivers, consumed by plankton, and used to build soft organic tissue and calcium carbonate skeletons (Berner, 1999).

    Curiously, we have similar backgrounds in geology and geochemistry, but manage to reach very different conclusion. I will assert that there is no such thing as a chemical weathering sink for CO2. If there is, then I have never seen it.

    What you describe correctly is the process of CO2 going into solution with water that on a global scale is dominated by sea water. The carbonic acid formed in fresh water certainly facilitates weathering but I very much doubt that d_weathering rate has any significant impact upon the atmospheric CO2 budget. Accelerated weathering may occur with elevated CO2 and temperature. Hence, going from warm high CO2 Cretaceous to colder and lower CO2 Tertiary, I’d expect chemical weathering rates to decline – all other variables being equal.

    You also correctly describe the real  sink which is ocean life and I will return to that in a moment. So, in my opinion, you are correctly describing the physical processes but giving it a very strange name that seems to have become engrained in the climate science vocabulary.

    What we need to focus on here are the physical processes that control the uptake of CO2 by water, mainly the oceans. And the key variables here are CO2 concentration in the atmosphere and in the surface water (partial pressure of CO2) and temperature. If temperature rises, so will CO2 in the atmosphere and vice versa.

    So what is / are the sinks for CO2? I have viewed hundreds of miles of cores from oil wells in the N Sea and globally and can use my eyes to see where the C / CO2 goes. It ends up as coal, oil, gas, disseminated organic matter and carbonate minerals formed by organisms, soil processes and by limestone formation.

    Far and away the most important process is photosynthesis both on land (forests) and at sea (phytoplankton).

    CO2 + H2O + photons ——– CH2O + O2

    The CH2O ends up as coal, oil, gas, kerogen, elephants and zooplankton. I don’t see that rock weathering has anything to do with this at all and will only begin to accept the existence of a rock weathering sink when someone takes me on a field excursion and shows me it.

    It’s also important to look at the magnitude of rock weathering in relation to other processes. The IPCC carbon cycle shows annual exchanges in GtC of the order:

    Ocean – atmosphere 80
    Land photosynthesis 120
    Rock weathering 0.4

    The weathering effect is minuscule and I fail to see how changing this minuscule variable will have any impact at all upon atmospheric CO2 that is dominated by ocean and land plant exchanges.

    So, if it is not rock weathering that changed CO2 and climate from the Cretaceous into the Tertiary, what did? Here I need to go skating on the thin ice of speculation.

    The plate tectonic maps show a great period of upheaval as we leave the Cretaceous marked mainly by the break up of the super continent Pangea and the opening of the Atlantic Ocean. I think we can say with a high degree of certainty that this will have impacted Earth’s climate. But how? I will venture two important processes:

    1) is the eventual establishment of thermohaline circulation (I don’t know a version of this existed in the Cretaceous)

    2) a change in atmospheric circulation forced by the uplift of high mountain belts. Elevated land will eventually encourage the formation of ice caps.

    It is perhaps the former that is more important, moving warm water away from the tropics where it eventually cools so much at the poles that is sinks locking in cold water in the ocean depths. We can see how changes in ocean temperature record the glaciations of the last 2.6 million years, locked into the d18O records of carbonate fossils.

    The LR04 d8O stack for benthic foraminifera. Click for large version.

    And we also know that the closure of the Panama Isthmus about 4.6 m ago may be implicated in the eventual onset of glaciation.

    Nature 393, 673-676 (18 June 1998) | doi:10.1038/31447; Received 28 July 1997; Accepted 14 April 1998

    Effect of the formation of the Isthmus of Panama on Atlantic Ocean thermohaline circulation

    The Late Cenozoic closure of the seaway between the North andSouth American continents is thought to have caused extensive changes in ocean circulation and Northern Hemisphere climate1, 2. But the timing and consequences of the emergence of the Isthmus of Panama, which closed the seaway, remain controversial1, 2, 3, 4, 5. Here we present stable-isotope and carbonate sand-fraction records from Caribbean sediments which, when compared to Atlantic and Pacific palaeoceanographic records, indicate that the closure caused a marked reorganization of ocean circulation starting 4.6 million years ago. Shallowing of the seaway intensified the Gulf Stream and introduced warm and saline water masses to high northern latitudes. These changes strengthened deep-water formation in the Labrador Sea over the next million years — as indicated by an increased deep-water ventilation and carbonate preservation in the Caribbean Sea — and favoured early Pliocene warming of the Northern Hemisphere. The evaporative cooling of surface waters during North Atlantic Deep Water formation would have introduced moisture to the Northern Hemisphere. Although the pronounced intensification of Northern Hemisphere glaciation between 3.1 and 2.5 million years ago substantially lagged the full development of North Atlantic Deep Water formation, we propose that the increased atmospheric moisture content was a necessary precondition for ice-sheet growth, which was then triggered by the incremental changes in the Earth’s orbital obliquity.

    And so to wrap up this lengthy comment. I think we agree that plate tectonics plays a major role in climate change since the Cretaceous, I fail to see or be persuaded that this has anything at all to do with rock weathering rates. Rather, I see plate reconfiguration changing the climate via changes in ocean and atmosphere circulation that had an overall cooling effect that would eventually draw down atmospheric CO2. Of course the change in CO2 then has a feedback on cooling. What came first? The climate chicken or the CO2 egg will be a recurring theme in comments.

    • Euan Mearns says:

      As a possible correction to the above, it may be more appropriate to view d_weathering in relation to C sequestration rates:

      Marine biota 13 GtC / annum
      Burial 0.2 GtC per annum
      Land plants and soils – I can’t work that out from the C cycle graphic

      Any change in these rates is still likely to swamp any change in the rate of weathering. Colder ocean, more plankton, faster rate of CO2 removal from surface waters.

    • Building upon the work of Harold Urey, Garrels documented the equations explaining how CO2 in rainwater created the acidity needed to dissolve the silicate rocks of mountain belts, pointing out that the CO2 extracted from the air in this way would eventually be restored, for instance by reactions in the oceans and sediments, not to mention via eruption from volcanoes. Below is a typical equation for the effect of atmospheric CO2 on silicate rocks in the presence of water.
      Mg2SiO4 + 4CO2 + 4H2O ↔ 2 Mg2+ + 4HCO3-+ H4SiO4.

      One can replace the magnesium silicate by a calcium silicate, CaSiO3, to produce calcium carbonate and silica, CaCO3 + SiO2. These two equations are commonly called the ‘Urey Reactions’, following their description by Harold Urey. When the bicarbonate ions reach the ocean they combine with calcium ions to produce calcium carbonate, water and carbon dioxide, thus:

      4HCO3- + 2Ca2+ → 2CaCO3 + 2H2O + 2CO2.

      Marine organisms use the CaCO3 to build skeletons made of calcite or aragonite, which ends up as carbonate ooze before hardening to limestone. Half of the original 4CO2 is thus prevented from returning rapidly to the atmosphere.

      So the ultimate sink is the sediment, but the process of chemical weathering is an integral part of feeding that sink, and the entire process ALSO delays the return of CO2 immediately to the atmosphere.

      The rates of these reactions double with a 10°C rise. When CO2 increases in the air, so does the temperature, increasing the rates of reaction so that more CO2 is consumed by weathering. That keeps the CO2 from expanding out of hand. Here we have Earth’s natural thermostat.

      These equations conceal the voyage of a typical molecule of CO2 from its emission in volcanic gas to its solution in a bead of rainwater, to its impact on an exposed mountainside and its subsequent transfer through rivers to the sea, where it gets absorbed by plankton to form organic matter that is eaten by zooplankton, incorporated into their CaCO3 skeletons, and ends up as calcareous ooze on the ocean bed awaiting transformation to limestone and the repeat of the cycle.

      A further point concerns your table showing ocean atmosphere exchange = 80; land photosynthesis = 120; rock weathering = 0.4. But what you seem to forget is that the first two are annual, while the last one is cumulative.

      The ocean circulation in the Cretaceous was haline – driven by salt rather than by temperature. Much the same characterizes the Eastern Mediterranean today.

      Mountain building with its attendant effect on climate was not well developed in Cretaceous or Palaeocene times.

      We cannot call on ocean circulation or mountain building to explain the cooling from the mid Cretaceous onwards. As in the model of T C Chamberlin (1899), volcanism (from what we now know was a rapid expansion of plate tectonics) supplied abundant CO2, resulting in warming. There are abundant examples of tests of this hypothesis (see “Earth’s Climate Evolution”). Gradually plate processes slowed, and mountain building took over, which enhanced the chemical weathering that led to CO2 being transferred from the atmosphere to the ocean then to ocean sediments. The loss of CO2 cooled the atmosphere to the point where a large ice sheet ice could form on Antarctica 34 million years ago.

      As I said in my response to the Lindzen piece, the development of northern hemisphere glaciation from the Pliocene onwards was connected to the rise of the isthmus of Panama, which prevented the former movement of warm surface water from the Atlantic to the Pacific through the Caribbean, and diverted warm water north and south towards the poles. A parallel result was that cold water moved through the Bering Strait to cool the Arctic enough to aid the development of the Greenland Ice Cap.

      • Jim Steele says:

        polarscientist, argues “Half of the original 4CO2 is thus prevented from returning rapidly to the atmosphere.”

        But you only cherry pick a subset of all chemical reactions.

        For example,the theorized CO2 concentrations required to maintain the Cretaceous warmth means increased ocean acidification that would dissolve calcium carbonate shells and release CO2 back to the atmosphere..

        • polarscientist says:

          Dear Mr Steele,

          I was asked what chemical weathering does, and I supplied the answer. That does not constitute cherry picking. Indeed I am sure you are correct in assuming that the high CO2 concentrations of CO2 in the Cretaceous atmosphere, which kept it warm, mean that the ocean contained high levels of dissolved CO2, which dissolved deep ocean carbonate and raised the level of the CCD (carbonate compensation depth). However, that does not mean that such a process released CO2 back into the atmosphere. As far as I am aware, dissolving deep ocean carbonate does not simply fill the ocean with dissolved CO2. You would need to look carefully at the various equations for carbonate dissolution in a high CO2 world to figure out precisely what the result was..

      • Jim Steele says:

        polarscientist simply asserts, “The ocean circulation in the Cretaceous was haline – driven by salt rather than by temperature….
        We cannot call on ocean circulation or mountain building to explain the cooling from the mid Cretaceous onwards. ”

        Astronomical factors will always dictate a temperature gradient from the equator to the poles which in turn will always produce powerful easterly winds like the trades that are observed today. Those equatorial winds drive ocean circulation that pushes warmer equatorial waters poleward as witnessed in the Gulf Stream and Kuroshio Current. To dismiss that circulation is utter nonsense. Haline circulation affects the depths of overturning circulation with an insignificant contribution to poleward heat transport.

        polarscientist repetitively asserts it is CO2 that warmed the Cretaceous but models require either higher CO2 concentrations or a greater climate sensitivity than proxy evidence supports. Furthermore the warm humid Cretaceous climate suggests a much lower climate sensitivity to CO2 back scattering analogous to what is observed today in the tropics today.

        As the IPCC states, “In the humid equatorial regions, where there is so much water vapour in the air that the greenhouse effect is very large, adding a small additional amount of CO2 or water vapour has only a small direct impact on downward infrared radiation.”

        Claiming CO2 warmed the Cretaceous is nothing more than empty assertions.

        • polarscientist says:

          Well, there we go again, more insults from Mr Javier. Now I am full of empty assertions about Cretaceous warming!

          Notice that Mr Javier does not himself take the time to tell us what it was that made the world significantly hotter in the Cretaceous.

          Geochemists have done a considerable amount of work on understanding the origins of our warm Cretaceous climate. We know from the chemistry of bottom sediments (which record chemical changes in the ocean that are related to chemical changes in the atmosphere) that the Cretaceous ocean was both warm and rich in CO2 (see Muller reference in my post). We know from proxies for CO2 that this gas was high in the atmosphere (see Royer reference in my post). And we know from geochemical models of the carbon cycle that CO2 was abundant at the time (see Berner references in my post). So my comments are far from being assertions. They are based on the work of many geochemists and palynologists and others over several decades.

          Equally we know from the distribution of bottom temperatures in deep Cretaceous seas that primary circulation in the narrow, early opening Atlantic was driven by haline circulation in which evaporation in coastal seas created dense and oxygen-poor warm bottom water – much as happens in the eastern Mediterranean today (Brass et al., Nature 296, 1982).

          The overall wind patterns at the time were likely to be less strong than they are today, because in a more or less ice-free Cretaceous world, the equator-to-pole thermal gradient was much less steep than it is today, and it is that which drives the winds. Equally, the currents driven by the winds would have been less effective. The major current movements were east-west, from the Pacific through the Tethyan seaway between India and Asia to the Atlantic, and onwards to the Pacific again. There was no significant northern transport of heat through the Atlantic to the Arctic, because the gap between Greenland and Norway was not open.

          Modelling carried out by Eric Barron and others at NCAR helped to establish the role of CO2 in governing the Cretaceous climate. If you read the three paleoclimate reviews referenced in paragraph 2 of my submission, you will get a very different impression from that given by Mr Javier.

          • Euan Mearns says:

            That’s a reply to Jim Steele. The comments are by and large very civil. One thing you need to understand is that you make a large number of claims backed up by literature citation which is fine, but a lot of those claims some of us simply find difficult to understand or accept. That is why there is a controversy. And there is a controversy, despite claims that there isn’t.

            By way of example, I fully understand the process of carbonic acid assisting rock weathering. But find it difficult to accept that this moves the CO2-ocean equilibrium. It simply moves a tiny amount of CO2 into the ocean via a different route. What you seem to be saying is that without weathering that CO2 would still be in the atmosphere. Why would it not just go into solution in fresh or seawater?

            My view is that the controlling factor is the real sink rate. The rate of removal of CO2 from shallow seawater by plankton and from the atmosphere by trees. I simply don’t understand why anyone would want to invoke rock weathering as the control knob.

            And in a comment close by you say that the temperature gradient between tropics and poles controls atmosphere circulation rate. Most commenters will agree with that but then wonder why we are continually told that a warmer world, especially one where the Arctic is deemed to be warming the most, will become stormier. This is one point made by Dick Lindzen.

            In fact, I believe, climate science needs to be careful in using the term “storm” because there are two distinctly different types. I will accept that thunder storms would be more common in a warmer world, since increased convection is a natural response to more warming. But I’d then add that this increased convection will cool the surface keeping temperature in check. Cyclonic storms on the other hand should become reduced with reduced temperature gradient. And yet we have Dame Slingo (UK MET) telling us that recent winter storms in the UK could be down to CC. For many of us much of the climate science narrative just doesn’t stack up.

            I’ve not walked away from providing my alternative explanation for warming since 1850, I’m away to hunt for your comment.

    • Peter Shaw says:

      Dr Summerhayes – Thank you for a brisk and informative summary.

      Euan –
      I think the “carbon-sinks” issue needs a little clarification, so offer the following:
      If you argue that all fixed CO2 (as biomass or carbonate minerals) naturally and inevitably returns to the biosphere by divers means, so can’t be a permanent sink, you’re undoubtedly correct. However, fixed CO2 on the seabed takes around 10 million years before it ‘s erupted from a volcano near a destructive plate margin, while its lifetime in the biosphere is decades to millenia; the fraction we study is tiny. Any imbalance between sequestration and re-release rates can produce large and (geologically) rapid biosphere changes. Recall the argument (elsewhere on this blog) that oil production and consumption are so closely-coupled that any imbalance produces large price excursions.
      So, perhaps you differ principally on timescale; you’re taking the long view, where Dr Summerhayes is considering the excursions at (say) < 10 Ma (although neither of you seem to specify ;)).
      The WG1 carbon-cycle diagram (Euan Mearns March 18, 2016 at 11:13 am) is importantly incomplete (for the simple reason that we don't yet have the data); it has no mid-ocean ridge (MOR). The significance is that basalt is altered by water successively to serpentine and talc, and each step produces magnesium – as carbonate if CO2 is present, or hydroxide if not. A paper (apologies, link mislaid) on core mineralogical analyses from the mid-Atlantic ridge shows this – carbonate in upper parts, but hydroxide below from water locally depleted in CO2 . Alteration can extend at least 500 m down. The initial magnesium carbonate ends up as limestone incorporating varying amounts of magnesium (the process summarised by Dr Summerhayes above). The chemistry is such that if this process went to completion, it could fix all the biosphere's CO2 (!). I'm not sure how seafloor spreading rate change would affect the CO2 removal rate.
      It seems that hydrothermal circulation in fractured seabed continues off-ridge. I conclude that MOR chemistry may be an important missing piece (perhaps more than terrestrial weathering), both for steady-state carbon cycling as in the WG1 diagram, and for "short-term" excursions.

  4. Euan Mearns says:

    The Vostok Ice Core: Temperature, CO2 and CH4

    In Vostok, T and CH4 are well aligned:

    T and CO2 are not.

    Following the Eemian inter-glacial the time lag is about 8000 years. It is not credible to argue that this is a gas age calibration issue. Full glacial conditions were established with interglacial CO2 concentrations.

    Figure 6 Detail of the last 150,000 years showing how CO2 lags temperature by about 8,000 years following the Eemian inter-glacial. Full glacial conditions were established with inter-glacial CO2 concentrations.

    If the gas age calibration is revised then this will completely destroy the beautiful alignment between T and CH4.

    How do we explain this? CH4 is probably linked to methane clathrate formation and melting. The permafrost responds instantaneously to changes in T.

    CO2 on the other hand needs planktonic activity to increase in order to remove CO2 from surface water eventually pumping down the atmosphere. And this needs to fight CO2 being liberated from dying land plants and soils. At the terminations, CO2 and T are more closely aligned since this is a simple ocean warming and degassing process.

    • The delay of 600 years or so between CO2 and temperature applies to periods of temperature rise. That has now been shown by Parrenin to be an illusion (see above).

      CO2 and CH4 do follow one another closely during warming. The CH4 is derived from the development of wetlands as sea level rises, and the CO2 is expelled from seawater as it warms due to rising orbital insolation.

      During cooling the situation is different. The CH4 declines rapidly as sea level falls and wetlands consequently decrease. The CO2 does not fall as fast. This is most likely because as sea level falls with cooling, there is less area of seawater to soak up the CO2, and the cooling encourages the formation of sea ice in polar regions, further limiting the area of exposed sea through which ocean-atmosphere exchange can take place.

      • Euan Mearns says:

        Most of us will accept that the 600 or so year time lag is within error of dating. But there is no way out of the 8000 year time lag I detail at the inception. And there is no way of getting away from that full glacial conditions were established with inter-glacial CO2 concentrations.

        Given this information, it is therefore strange to me that an argument should be made that CO2 reinforces orbital forcing since the data shows that we go from interglacial to full glacial with CO2 playing no role at all.

        The data are most consistent with temperature change controlling CO2, a point I believe you agree with.

        • polarscientist says:

          Hi Euan,

          First I will reply to a point you made above on the same day, where there was no ‘reply’ box.

          You say I “make a large number of claims backed up by literature citation which is fine”. But the literature is what science is all about – that’s where the results of investigations get reported. My (self-imposed) task is to bring that literature out of the dusty shelves of library journals and to the attention of the public, who otherwise might not know it even existed. It took me 4 years of research to produce my book “Earth’s Climate Evolution” summarizing everything I had learned from a wide reading of oceanography, meteorology, climatology, geology, geochemistry, glaciology, and solar studies – including reading the views of and speaking to and exchanging correspondence with what one might call climate change contrarians. I wish you would read my book to get an appreciation of how all this information from widely diverse fields hangs together.

          You say “but a lot of those claims some of us simply find difficult to understand or accept”. But in my experience that is commonly because people do not have the time or will not take the trouble to undertake the kind of broad ranging survey that I did for my book. There is a common tendency to latch on to one or other particular point as if it is a show stopper. But the climate story is built on solid foundations of understanding that go right back to the likes of Fourier in the early 1800s and Lyell from 1830 onwards. Time and the arrival of new technologies of analysis have deepened our understanding of how the system works. But very few people realise how far back all this goes, and how many branches of science back the story up.

          You say “What you seem to be saying is that without weathering that CO2 would still be in the atmosphere. Why would it not just go into solution in fresh or seawater?” The standard ocean-atmosphere exchange keeps CO2 in equilibrium between the two. If you increase CO2 in the atmosphere the ocean absorbs some to maintain the equilibrium (which is of course modified by temperature – warming lets more CO2 out of the ocean, cooling takes it in). Chemical weathering is independent of this process. It extracts CO2 from the ocean and leads to it being stored in sediments. Eventually, it makes the ocean more acid, and deep ocean sediments dissolve releasing their CO2. But that process is on the 10,000 year time scale. The equations speak for themselves. Read Berner’s 2004 book (in my reference list) for the chemical details.

          You say “My view is that the controlling factor is the real sink rate. The rate of removal of CO2 from shallow seawater by plankton and from the atmosphere by trees. I simply don’t understand why anyone would want to invoke rock weathering as the control knob”. But, what plankton and trees to is ‘eat’ CO2 to grow, then release it when they die and decompose. That process is the fast carbon cycle, which for most plants takes one year. In geology we are concerned with the slow carbon cycle, which takes many thousands to millions of years. See Berner, 2004.

          I have no easy answer for why some climate forecasts tell us that warming will lead to more storminess. My focus is on what the geology has to tell us about our possible future(s). When Dame Julia Slingo talks about storms becoming more frequent recently, part of the reason may simply be the positioning of the storm tracks across the North Atlantic, which are ultimately steered by the pressure differences between Iceland and the Azores within what is called the North Atlantic Oscillation. But I am not a meteorological expert on recent climate matters.

          With regard to your later response, just above, it does look as if Parrenin et al (2013) may prove to be right about the lack of a time ;lag between temperature and CO2 at glacial terminations, as I have mentioned in one of my replies. Equally, I have addressed in another reply the delay (which you quantify as 8000 years) between the fall of temperature and the fall in CO2 going from interglacial to glacial. The explanation I provided is that insolation is the main driver of change. CO2 follows it as temperatures warm, but when insolation causes temperature to form it also (i) lowers sea level, providing less ocean area for the ‘normal’ amount of air-sea exchange, (ii) starts expanding polar sea ice, which further prevents the ‘normal’ amount of air sea exchange; and (iii) starts increasing the areas of snow and ice, which increases albedo, which causes temperature to drop faster. Hence as others have pointed out in fact we need two CO2 sensitivities for the Ice Age: (1) for increasing insolation, and (2) for decreasing insolation. The face that this is complicated leads to a great deal of misunderstanding – especially when people think that the CO2-temperature relationship is ‘supposed to be’ direct.

          As a result, Petit et al found that the CO2-temperature correlation for Vostok was about 70%, while Parrenin et al found that for the last glacial termination is was 90+%. That’s because Parrenin et al were not mixing the apples of glacial terminations with the oranges of the onset of glacial cooling.

    • steve says:

      Euan, this conversation is a good antidote to the Sunday morning god slot when Nicky had an audience of Green activists bury Piers Corbyn with the usual settled science 97% of scintists stuff. I had thought that the Danish ice core graphs, showing a lag of about 800 years behind warming and cooling, were convincing evidence for the Skeptic side. To read that this has been corrected, along with temperatures and sea levels is not surprising. So the gas bubbles in the ice core have somehow dispersed or perhaps moved through the ice core back in time 800 years to make the graphs match.

      I am not a scientist but have a question. Back in time is downwards or deeper. How to gas bubbles sink down through ice at a speed of one layer of yearly ice per year for 800 layers, or perhaps 800x 5cm? Or have I got the wrong end of the hockey stick?

      • polarscientist says:

        No the gas bubbles didn’t move or disperse. What changed was the way of estimating their age in relation to the age of the surrounding ice. The key paper on this is by Parrenin et al 2013 (see the reference in my post at the top of the site).

        • steve says:

          Not being a clever scientist, I still don’t get it. So the gas bubbles don’t move and were captured at the same time as the ice formed. But the way that the bubbles and ice are dated has changed and now they are 600 years or so younger. So if they are in fact younger, how did they get into that piece of ice at the same time that it froze?

  5. JerryC says:

    In summary, Earth’s history confirms that CO2 does change temperature, and that temperature does change CO2, and that we cannot blame the Sun for where we are now. All that we can blame are our emissions.

    That’s pretty reductionist. Are we to believe that the sun and “our emissions” are the only two variables affecting the earth’s climate? Not sure how this is any different from the 70s global cooling scare stories that told of a coming ice age driven by our sun-blocking particulate emissions.

    Furthermore, the idea of assigning blame for a minor temperature shift seems normative and unscientific. Why the anti-warmth bias? Most people prefer it to cold, and for good reason.

  6. A C Osborn says:

    There is so much data presented here, much of it total Supposition and Estimations about the planet’s history, especially in regards to Solar Output. Even today Solar Scientists cannot accurately predict what the mechanism of the Sun will do in the next ten years (as they couldn’t for the previous ten years). Sun Spots being a very crude appriximation for what is actually happening.
    But to debate this raft of data and correct some items is going to take a long time.
    But I will start with this simple statement.
    “Another such fluctuation is the Pacific Decadal Oscillation, which warms the Pacific slightly for 20-25 years, then cools it for as long (Chavez et al., 2003). Since about the year 2000 we have been in the negative (cool) phase of the PDO.”

    When the Scientists first detected this period they assumed that the first 2 periods of 20-25 years of shift would hold up. But it has not, so despite Dr Summerhayes categorically stating that it is 20-25 and has entered a cooling phase which should last 20-25 years it has in fact not done so.
    According to the NOAA data here

    You can clearly see that the relationship has broken down and since 2000 we have in fact had 2 cool and 2 warm periods and are currently in a warm period since 2013. The Settled Science of 20-25 year periods has now been overthrown due to it now being periods of 4 years and of lesser magnitude.
    A minor detail I know but still very telling about our supposed understanding of the Ocean Cycles.

  7. Leo Smith says:

    Philosophy of AGW, trumps philosophy of Science!

    “If none of the reasons fit the facts, the first reason that you haven’t completely eliminated yet that could fit the facts, must be the Truth”

  8. Phil Chapman says:

    A close reading of the technical sections of the IPCC’s AR5 yields a surprise: the analyses do not express serious concern about the consequences of anthropogenic global warming (AGW), at least for human welfare. Almost all the issues reduce to economic effects, such as the costs incurred in adapting farms to higher temperatures and longer growing seasons, moving people from areas adversely affected to those where warming is beneficial, providing adequate water supplies (perhaps by desalination of seawater), etc. While these costs may be significant, Chapter 10 (Key Economic Sectors and Services) of the AR5 WG2 volume (Impacts, Adaptation, and Vulnerability) says that “for most economic sectors, the impact of climate change will be small relative to the impacts of other drivers (medium evidence, high agreement). Changes in population, age, income, technology, relative prices, lifestyle, regulation, governance, and many other aspects of socioeconomic development will have an impact on the supply and demand of economic goods and services that is large relative to the impact of climate change.” In other words, adapting the infrastructure of our society to a warmer world in coming decades will be a relatively small part of the effort needed to maintain economic growth so as to permit a decent living for the growing, increasingly urban global population.

    There is however a disconnect in AR5 WG2 between the technical chapters and the material that is widely published. Section B.2 of the Summary for Policymakers of this volume says “Throughout the 21st century, climate-change impacts are projected to slow down economic growth, make poverty reduction more difficult, further erode food security, and prolong existing and create new poverty traps, the latter particularly in urban areas and emerging hot spots of hunger (medium confidence). Climate-change impacts are expected to exacerbate poverty in most developing countries and create new poverty pockets in countries with increasing inequality, in both developed and developing countries ”

    This claim, which is of course all that politicians and the public are likely to see, is deliberately deceptive: it implies that failure to control AGW would be a serious impediment to economic progress, while the actual conclusion by IPCC analysts is that the projected warming is a relatively minor economic problem.

    A second major area of concern is the damage to vulnerable ecosystems that AGW might inflict. The basic position, which the IPCC shares with many environmental groups such as the World Wildlife Fund, seems to be that we have an ineluctable responsibility to do whatever it takes to prevent the extinction of any existing plant or animal species, and also to preserve their present geographic distributions. A similar principle is adopted explicitly in the US Endangered Species Act, whose stated purpose is “to protect and recover imperiled species and the ecosystems upon which they depend.” An endangered species means one that “is in danger of extinction throughout all or a significant portion of its range.” All species of plants and animals, except pest insects, are eligible for listing as endangered, without any discrimination on the basis of economic value, scientific interest, aesthetic appeal or any other criterion.

    The idea that we must protect all existing species is a debatable ethical opinion, not a law of nature. Any climate change will of course affect the habitats of some plants or animals; some species might benefit from the change, but others might become extinct because they fail to migrate or adapt. Ecological niches vacated due to the emigration or extinction of the occupants are soon filled by others, perhaps allowing the evolution of new species. That is how the world has worked, ever since the only life was pond scum. There are of course many species that we should protect for aesthetic or scientific reasons, but it is neither possible nor desirable to maintain a rigid, comprehensive status quo.

    Satellite observations demonstrate beyond dispute that the planet is becoming greener because anthropogenic CO2 is enhancing photosynthesis, especially in semi-arid areas. See, for example, Liu, Y.Y. et al, “Recent reversal in loss of global terrestrial biomass,” Nature Climate Change 5, 470–474 (2015). An abstract is at

    There is no doubt that the biosphere as a whole could thrive in a warmer world with more CO2 in the atmosphere, as it often has in the geologic past. In the lush world of the Middle Jurassic, for example, 170 million years ago, the CO2 concentration was at least five times greater than now, and the global temperature was almost 10 deg C higher. On what basis should we conclude that the present worldwide assortment of species is somehow superior to those that would eventually evolve in a warmer climate?

    Whatever individual opinions may be about these issues, is AGW a major threat to existing species? According to the Encyclopedia of Earth, “Proximate causes of endangerment include loss of habitat, overexploitation, habitat fragmentation, pollution and introduction of alien species. Chief among reasons for habitat loss and fragmentation are conversion of natural habitats to agriculture, with ancillary drivers being deforestation and urbanization. Overexploitation may take the form of overgrazing, overfishing, clear-cutting of forests or hunting fauna to a point near the minimum viable population size in a given region.” Conspicuously missing from this list is any mention of climate change. Of course it is true that human activities can be and often are destructive, but the claim that anthropogenic emissions of CO2 are one of the worst offenders is yet another example of the misrepresentation that has destroyed the credibility of the anti-AGW campaign.

    • Peter Lang says:

      Phil Chapman,

      This is a clear and succinct comment. It makes all the most relevant and important points I strongly agree with. Thank you. If only the IPCC would write as succinctly and clearly?

      I can put some figures on your comment about the economic effects of AGW and the advocated abatement strategies, You said:

      … This claim, which is of course all that politicians and the public are likely to see, is deliberately deceptive: it implies that failure to control AGW would be a serious impediment to economic progress, while the actual conclusion by IPCC analysts is that the projected warming is a relatively minor economic problem.

      The chart below is a replot of analyses by Professor William Nordhaus for IPCC AR5 WG3. I replotted to show the net benefits of proposed emissions abatement policies for this century only, and also added the red line on the chart. This is the nearest policy scenarion to being possible, but I doubt any policies that significantly increase the cost of energy are achievable or politically sustainable for the time needed.
      Explanation here:

      The paper points out that the inputs used are on the alarmist side of the IPCC central estimates and the uncertainties on the inputs are very high. The total net benefit for the red line for the remainder of this century is – $33 trillion (in 2010 US$) – i.e. the abatement costs exceeds the benefits of avoided climate damages by $33 trillion this century.

    • It will not have escaped your attention that my post concerned the evidence for CO2 and warming linkages in the geological record. It was intended to widen the debate about the causes of climate change. I am not an expert in what continued warming will do to ecosystems. But as an informed layman in such matters it seems obvious to me that a continued rise sea level will (i) put coastal populations in danger, and damage coastal farmland; (ii) diminish mountain glaciers, creating problems for lowland populations that depend on the slow melt of highland ice and snow to provide them with water for drinking and irrigation; (iii) expand already dry areas and prolong droughts, bringing problems to farmers. Affecting farming will affect food supplies. Equally, ocean acidification is already affecting the skeleton-building capacity of planktonic organisms at the base of the ocean food chain in the polar oceans, which again would seem to put food supplies potentially in jeopardy. While we might fondly imagine that warming may move the Canadian wheat belt north into unpopulated land, much of that land lost the sediment that would make good soil, when it was covered by the Laurentide ice sheet. None of this has anything to do with saving species, but it does seem rather important for the future of mankind.

      • Doug Brodie says:

        Polarscientist: I note that you have not responded to my rebuttal (March 19 3:57) of your earlier comment. I have still had no credible answer to my simple question: where is the evidence that there has been ANY man-made global warming to date caused by man-made CO2 emissions (shorthand for man-made greenhouse gas emissions).

        In this comment you employ the usual warmist misdirection of conflating the effects of natural global warming with alleged but, I assert, non-existent man-made global warming (excluding minor impacts due to land use changes, urban heat island effects, etc). Sea levels have been rising for centuries, since well before any man-made CO2 emissions. Similarly glaciers have receded then sometimes expanded again over centuries. Your talk of “continued warming” is meaningless without any justification of what you base your prediction on. Relying on the UN IPCC’s failed prediction of 0.2degC of man-made CO2 forced warming per decade is just not good enough any longer (although it unfortunately seems to be good enough for our ignorant politicians).

        Obviously we can do nothing about conditions resulting from natural global warming, other than to adapt.

        I’m afraid it will be at least two days before I can respond again due to travelling and other commitments.

        • polarscientist says:

          Contrary to your assumption about sea level, the sea level experts point out that ocean volumes remained nearly constant from 2000-3000 years ago until the onset of the modern rise about 100 years ago (Lambeck et al., 2010, in Church et al., 2010, Understanding sea level rise and variability. Wiley Blackwell). The points I made in my discussion piece are all well supported by documentation (see reference list). Those papers and many like them provide the justification you seek. Incidentally, I am not relying on the IPCC for anything. My piece is entirely about what the geological record tells us, and my concluding inference is that since that record tells us that CO2 has caused warming and sea level rise and ocean acidification in the past, it is highly likely to do so in the future if we continue to put CO2 into the atmosphere. What we are doing now is emulating what nature did in the past. You are assuming that the current warming is all natural, but without providing any proof that such is the case.

          • Doug Brodie says:

            polarscientist, sorry for the delayed response. You say:

            “You are correct that solar input was at a century high late in the 20th century, but what you need to recognise is that it was no higher than it was in the 1780s or the 1840s-60s, when the climate was significantly colder.”

            The Wiki graph I link to (which you say is out of date) and your 2014 Clette at al graph, see, both show that solar SSN activity was indeed higher in the late 20th century than during the LIA.

            Perhaps of much greater significance (if the following graph is correct), the earth’s magnetic field was at a 2000-year high in the late 20th century, see

            According to Hendrik Svensmark (ignored by the UN IPCC), a higher magnetic field gives greater shielding of the Earth from cosmic rays, leading to fewer clouds being seeded. This could explain the stronger El Nino events in this period and hence the natural global warming of the 80s and 90s. This is supported (admittedly not very scientifically) by a study of paintings referenced in Brian Fagan’s book The Little Ice Age: “Hans Neuberger studied the clouds shown in 6,500 paintings completed between 1400 and 1967 from forty-one art museums in the United States and Europe. His statistical analysis revealed a slow increase in cloudiness between the beginning of the fifteenth and the mid-sixteenth centuries, followed by a sudden jump in cloud cover … After 1850, cloudiness tapers off slightly.”

            You also say:

            “To really understand what’s going on [with global temperatures] you need to do a 16 month running mean, or a 32 month running mean through the data from 1900 onwards. What you will see emerge is the underlying trend that runs through all the wiggles caused by things like El Nino”

            Well I’ve done that and it shows an underlining trend which does nothing for your AGW arguments. Here it is as a modification of my original graph:


            This graph weakens your AGW argument. It shows the period of steady warming from about 1910 to the mid 40s (comparable to the warming of the 80s and 90s) which climate scientists don’t like to talk about because it must have been natural as atmospheric CO2 levels at that time were too low. So why shouldn’t the warming of the 80s and 90s also have been natural, nothing to do with man-made CO2? It still shows the global cooling period from the mid 40s to the mid 70s and the global temperature standstill from around 1998.

            The fact that the climate establishment is so duplicitous and downright dishonest all the time should set alarm bells ringing for any dispassionate observer. You say I have no proof that global warming has been natural. You may deem it so, but the evidence I put up to support that assertion is surely more credible to an objective observer than the unconvincing evidence put up by the climate establishment, e.g. ongoing adjustments of temperature records to show ever-worsening warming, pretending that IPCC climate science is comprehensive when they are only mandated to study alleged man-made impacts, invoking on-off-on aerosol cooling to explain any temperature trend which goes against the narrative, dismissing the effects of the natural PDO warm phase and solar effects. Don’t forget that AGW is just a politically-motivated theory, with no backing of any empirical evidence.

      • Peter Lang says:


        But as an informed layman in such matters it seems obvious to me that a continued rise sea level will (i) put coastal populations in danger, and damage coastal farmland; (ii) diminish mountain glaciers, creating problems for lowland populations that depend on the slow melt of highland ice and snow to provide them with water for drinking and irrigation; (iii) expand already dry areas and prolong droughts, bringing problems to farmers.

        You have taken no account of the time scales involved for the changes and the rate the human populations adapt, move, migrate. We migrate for better jobs and better opportunities. There is no issue about the planet being able to feed future populations. The rate of sea level rise is irrelevant compared with the rate we adapt. The costs are trivial.

        I’ve always found that one of the advantages geologists bring to debates such as this is their understanding of time scales. The other important context that is needed is a proper understanding of the context of economics to allow a rational discussion about whether or not abatement policies are justified (on rational grounds).

        • louploup2 says:

          There is no issue about the planet being able to feed future populations.

          I do not believe the best available science supports this conclusion. Current food production is heavily dependent on both petroleum and natural gas (for nitrogen fixing). Euan Mearns and others here can address the problems that dependency far better than I can. Also, we are not recycling phosphorus and will start running short of readily accessible supplies in a few decades. Without phosphorus, large scale agriculture becomes ‘difficult.’

          It seems to me that AGW (or just GW—does the cause really matter?) is only one of a few serious problems caused by human failure to behave as if there are limits to growth.

          I’m not sure if Schramski 2015 ( has been cited here lately (I haven’t visited in a while), but the authors indicate we are running out of time to voluntarily reduce our global footprint. If anyone has cogent responses challenging that study’s conclusions, I’d like to read them.

          • Peter Lang says:


            I do not believe the best available science supports this conclusion.

            There is very little “available science” that addresses the issue. And what there is seems to have been designed to support the consensus.

            However, economics seems to show that has been enormous improvements in productivity such that we are using less land area to supply food for an increasing world population. The land area under cropping is decreasing as population increases (I don’t have links to hand). Part of the increase in productivity is due to advances in technology, fertilizer and fossil fuels. But part is also due to increasing CO2 concentration in the atmosphere and warming.

            Richard Tol, Figure 2 here (although now superseded) is interesting: ‘The economic impact of climate change in the 20th and 21st centuries’

            This, although not completely relevant to your point or my response is also interesting:
            Humanity Unbound: How Fossil Fuels Saved Humanity from Nature and Nature from Humanity

            It seems to me, GW is doing much more harm than good. Furthermore, given that climate changes abruptly, always has and always will, our concerns should be about abrupt climate changes not slow steady changes, especially abrupt cooling events. GHG emissions are delaying the time to the next abrupt cooling event and reducing its severity. Some argue humans have, perhaps inadvertently, been practicing excellent climate change risk mitigation.

          • A C Osborn says:

            Peter, don’t you mean
            “It seems to me, GW is doing much more good than harm.”?

          • Peter Lang says:

            A C Osborne,

            Yes. Thanks for picking up that mistake. I meant to say “GW is doing more good than harm”.

          • louploup2 says:

            Thanks for your response Peter Lang. I believe there is a great deal of BAS (and improving all the time) regarding the capacity of agricultural systems to provide sufficient calories for expected populations. You have focused on impacts of climate change; I do not believe GW is the biggest near term (decadal) problem although there is a considerable body of literature indicating that changing temperature and hydrology regimes are worrisome. See the conclusions and reference list at doi:10.7930/J02Z13FR (Chapter 6 of U.S. National Climate Assessment).

            A major ag sustainability problem that came to my attention while learning about peak oil is peak phosphorus, an element essential to food production. Before concluding that there is “no issue” please read up on that subject. Here are some references I’ve found:

            Similarly, even aside from biodiversity the global decrease in total biomass is very worrisome. Did you note in particular figure 5 (“Number of years of phytomass food potentially available to feed the global human population.”) in the Schramski paper? If you have some information or references to counter their analysis, I’d like to see it. It’s one of the scariest analyses I’ve read in a while, and I see very little critique, discussion, or follow up.

            Your reference to “enormous improvements in productivity” brings to mind Norman Borlaug’s Nobel Peace Price acceptance (he was the main ‘author’ of the so-called Green Revolution), wherein he said: There can be no permanent progress in the battle against hunger until the agencies that fight for increased food production and those that fight for population control unite in a common effort. Rather optimistic to think we have much control over long term trends of either at this point.

            Euan Mearns consistently and accurately points out that food production (and energy and almost everything else) has become very dependent on fossil carbon: So the question is how to care for all these people without FF. But that is not the subject for discussion here.

          • Peter Lang says:


            Thank you for your reply. I’ll respond to a few of your points.

            I don’t try to follow the details of individual scientific studies into specific impacts. I am interested in the total consequences (net benefit globally or regionally) per degree of average global warming AND cooling. I am interested in the damage function as an input to economic cost-benefit analyses of the net benefit (or cost) of abatement policies, where ‘benefit’ means ‘reduced climate damages’. My key point is that after some 30 years of scientific research and the ‘climate industry’ now spending $1.5 trillion per year, we have very little relevant information on the damage function. Therefore, there is no valid justification for the huge expenditure on the ‘climate industry’. In my opinion, it is an enormous waste of money and is driven by ideological beliefs, not objective research. The waste of money is damaging the global economy and retarding development. It is slowing the rate that standard of living improves globally, especially for the poorest people.

            there is a considerable body of literature indicating that changing temperature and hydrology regimes are worrisome.

            What does “worrisome” mean? Worrisome to whom? (those with an ideological agenda?). How do you quantify “worrisome”? When terms like “worrisome” are used it suggests advocacy and spin rather than objective analysis.

            The research papers and reports into the consequences of global warming that I have looked at seem to be biased and cherry picked. Some economists, like Richard Tol, have made a genuine attempt to do objective analysis to determine the global costs and benefits of GW. Bjorn Lomborg has pulled a lot together. I am strongly persuaded there is no rational justification for wasting money on abatement policies that do not deliver substantial economic benefits over the short and medium term. This explains why economically irrational policies will not succeed:

            decrease in total biomass is very worrisome

            I’d be very interested in a link to an authoritative reference with figures or a chart showing carbon tied up in biomass versus global average surface temperature. I recall that IPCC AR4, WG1, Chapter 6 (I think from memory) stated that the mass of carbon tied up in biomass was much higher when the planet was warmer than now and much less when the planet was colder. This is the opposite of what you suggest.

            Regarding the references you asked me to look at, I can’t read everything everyone suggests I read. I am interested in the total damage function firstly for the whole planet and secondly for regions. I am not interested in looking at studies of part of the answer – there are thousands or millions of them – e.g. “ A (Not Quite) Complete List Of Things Supposedly
            Caused By Global Warming

            You quoted the author of “the Green Revolution” and commented as follows:

            “There can be no permanent progress in the battle against hunger until the agencies that fight for increased food production and those that fight for population control unite in a common effort.” Rather optimistic to think we have much control over long term trends of either at this point.

            I am not saying we have control. I am saying I am not persuaded global warming or GHG emissions will have a significant net negative impact on food production, in fact trends to date are that warming and increasing CO2 concentrations are net beneficial. I’ve seen nothing persuasive to suggest the trend will change direction. Most of the down-in-the-weeds studies seem biased and selected to support the advocacy for CAGW and “we must do something” (no matter what the cost or whether or not it will deliver any measurable benefits).

          • louploup2 says:

            Peter Land, lots to unpack there.

            I find it ironic that you challenge Colin’s speaking outside his expertise while stating there is no valid justification for the huge expenditure on the ‘climate industry’. In my opinion, it is an enormous waste of money and is driven by ideological beliefs, not objective research. The waste of money is damaging the global economy and retarding development. It is slowing the rate that standard of living improves globally, especially for the poorest people.

            This is itself a pretty ideologically driven conclusion to reach while at the same time refusing to read or cite to any evidence in support. Do you suppose it is difficult to determine how many cities, or portions of cities, or populations generally, live at specific elevations from sea-level? You don’t need a Ph.D. in oceanography to look up that basic demographic data.

            I do have a meeting to attend (I’m on the Pacific Coast, U.S.), so I’ll need to respond to your concerns about use of “worrisome” etc later (if at all).

          • Peter Lang says:


            This is itself a pretty ideologically driven conclusion to reach while at the same time refusing to read or cite to any evidence in support.

            Neither you nor Dr Colin Summerhayes have said anything that suggests you understand what is relevant and how to go about estimating the net benefits of a policy to abate GHG emission. Dr Colin Summerhayes last reply to me is personal opinion, innuendo and supposition. He clearly doesn’t understand the subject of policy analysis but states his beliefs and opinions. It’s the type of scare mongering that has discredited climate science and climate scientists.

            You said I didn’t cite any evidence. That is disingenuous. I gave you the evidence but you haven’t referred to it and apparently haven’t read it or haven’t understood it. If you took the time to digest it and also go to the other references I sited you might begin to understand what is required. At the moment you clearly don’t have any expertise in the matter. Furthermore, you cited references but gave no description explaining how they are relevant. This suggest you don’t understand what is relevant and shows you do not understand the subject you are trying to talk about.

            Do you suppose it is difficult to determine how many cities, or portions of cities, or populations generally, live at specific elevations from sea-level? You don’t need a Ph.D. in oceanography to look up that basic demographic data.

            This shows clearly you do not understand the subject. That is why there is no point me reading the references you cite. Instead, I’d urge you to read the references I gave you and the sources linked with in it.

            I hope you recognize that GW is a global phenomenon. Therefore, it is the sum of all local effects, not just cherry picked examples combined with innuendo, that is relevant to the analysis of net benefits of an advocated mitigation policy. We need the sum of benefits and the total costs of the policy for the whole world (and, secondly, for regions). Cherry picked examples are no help at all. They are invariably biased and picked to be scary. The benefits are seldom stated by the alarmists and Dr Colin Summerhayes‘s last comment to me is a good example

            Some of the important inputs that the estimate of net benefits of a policy are most sensitive to are:

            • Damage function
            • Discount rate
            • Climate sensitivity
            • Emissions rate
            • Participation rate

            What do you understand about these?

          • Euan, I don’t meet your “Supplementary Commenting Guidelines,” but several posts have moved into my field, as a (now retired) economic policy adviser with a broad remit of drivers of economic growth. louploup2 refers to AGW/GW as “only one of a few serious problems caused by human failure to behave as if there are limits to growth.” Given that growth is increasingly driven by intellectual property rather than resource use, and that population is expected to stabilize mid-century, I would contend that we do not face limits to growth or serious problems from ignoring such postulated limits. Such arguments have been made regularly for over 200 years, during which time population has increased greatly and well-being has been transformed for billions of people. I support Peter Lang’s earlier comments on AGW-related economics and the extremely excessive policy focus on them to the detriment of far more important factors.

          • Euan Mearns says:

            Genghis, while I want the focus to remain on the climate side of the debate, climate and energy are inextricably linked. There is a strong tendency for those making the case for climate change also making the case for dismantling the energy system founded on FF and nuclear power that has provided ALL our prosperity, defining our civilisation, and replacing this with new renewable devices such as wind and solar, in the belief that this is somehow easy, cheap and beneficial. We can present this group of individuals with mountains of evidence to show how this cannot possibly work, the reasons rooted mainly in thermodynamics, but it makes no difference. It is generally agreed among the regular commenters on this site that we need to wait for blackouts to occur, witness the mayhem and cost this causes, to bring our governments to their senses.

            It should be abundantly clear to those engaged in the broader debate that risks need to be weighed on either side. Dr Summerhayes sees large risks with a high degree of certainty from sea level rise at some distant point in the future. I’m not sure where he stands on energy. I see manageable future risks from climate change but very real and large risks to OECD society today from the dismantling of our energy infrastructure.

            The new energy system is a tax on society for which we get zero benefits. The UK is broke, and it is pertinent to ask the extent to which this invisible tax is to blame.

            But lets try and stay focussed on the climate side for now.

          • Peter Lang says:


            I hope “staying on the climate side” includes discussing the economic costs and benefits of policy to mitigate postulated GW. Assuming I am not breaching your guidelines, and noting that the post’s author, Dr Summerhayes, referred to Sir Nicholas Stern as an authority he trusts, I’d like to link to a critique of the Stern analysis by Faustino (Michael Cunningham). This gives some insight into some of Michael Cunningham’s relevant background and experience. I believe comments by people with a lifetime of experience in policy analysis, including providing policy advice to UK and Australian prime ministers should be welcomed at every opportunity.
            The costs of tackling or not tackling anthropogenic global warming
            By Michael Cunningham (Faustino)

          • louploup2 says:

            Peter Lang tells me apparently haven’t read it or haven’t understood it about his references. Not so; I look at all sites people refer me to, and I have done so with yours. I do not think Cato Institute material is worth the time to address when making arguments grounded on empirical data and peer reviewed analyses. I might as well spend time over at Tony Watt’s site.

            Euan Mearns: Yes, the argument over Malthus’ theory and his/its progeny has raged for close to 2 ¼ centuries now without any definitive conclusion. You project and generalize to state that the economic side of my position includes replacing this [fossil fuels] with new renewable devices such as wind and solar, in the belief that this is somehow easy, cheap and beneficial.

            I never make any such argument, and have a pretty good understanding of the relationship of thermodynamics and economics (Georgescu-Roegen, etc.). I think we’re in for a whole world of hurt; I don’t buy all the dystopian doomer opinions spewed at ourfiniteworld but I believe your former oildrum colleague Gail Tverberg has a much better handle on the economic aspects of our problems than most people.

            In short, I find your belief that when blackouts [and] mayhem occur somehow our governments [will come] to their senses very odd for someone who developed the net energy cliff graphic. I suppose this discussion would be more appropriate at your most recent post (

          • Peter Lang says:


            Peter Lang tells me apparently haven’t read it or haven’t understood it about his references. Not so; I look at all sites people refer me to, and I have done so with yours. I do not think Cato Institute material is worth the time

            Your comment about the Cato article demonstrates demonstrates your ideological bias. It is factual and economically ratiponal – so0mething that apparently doen’t appeal to you. Your comm ent confirms you are clearly an advocate for CAGW and won’t read material that does not support your beliefs. However, why did you comment on that article rather than the article I was clearly discussing – i.e. about the net benefits of mitigation strategies? Clearly it is way beyond anything you know anything about. If you are a scientist you should get back to honest science and stay right out of advocacy especially about fields you know nothing about – e.g., policy analysis, policy advice and costs and benefits of mitigation policies.

          • louploup2 says:

            Your comm ent confirms you are clearly an advocate for CAGW… This is also not true; I think we as a species face some serious problems but AGW is not the only or necessarily the most serious one (the “C” in CAGW). Read my posts. And the fact that you keep projecting your ideation of who I am onto me is a good part of the reason I don’t spend more time responding to your posts.

            Sources have reputations. Cato is not as bad as WUWT, but on science issues I give them the deference that is their due, which in my experience is not a lot.

          • Peter Lang says:


            Your comment is dodging the issue we were discussing – i.e. about the costs and benefits of mitigation policies. You have not commented on the link I gave you on this issue we were discussing so I continue to interpret that to mean you have not read it or not understood it. The Cato article on “Humanity Unbounded: How fossil fuels saved humanity from the environment from the environment from humanity” is an excellent article and you should read it to broaden your perspective but it is not one of the several links I gave in previous comments regarding the net benefits of mitigation policies. That;s what we were debating and what you clearly have no understanding of.

            By the way, all sources have reputations so it is an irrelevant comment (other than it reveals hyour biases). Nature, Science, Bloomberg, The Guardian, Real Climate, SkepticalScience, IPCC, EPA, all have reputations. Do you avoid reading them too because of their advocacy and well known biases? Or do you believe everything you read without question if you it is written in a source you approve of and it supports your beliefs?

          • louploup2 says:

            BTW, Peter Lang, I am an experienced policy analyst (and project manager), and an attorney with 40 years of work with scientists in various fields related to natural resource management: forests, fisheries, geology, and most recently climate change. I do not claim to be a scientist, but I know plenty (and am constantly reading and learning more) and I do know when I don’t know something.

          • Peter Lang says:

            You say:

            and I do know when I don’t know something

            Your responses regarding policy analysis on the net benefits of mitigation policies do not support your claim. Why do you keep dodging that subject? It is the most important of all. That is the basis for a rational analysis of whether or not governments should commit to mitigation policies. You’ve made comments and asked question that clearly show you have negligible understanding of the subject.

          • louploup2 says:

            Look, Peter Lang, your responses to me have become increasingly insulting. Why would I spend the time to dig into your references (some of which you expected me to read I think were in response to others or I overlooked them—and when it’s clear that you never read mine—get to Schramski yet?) when all you do is insult me?

            There are often multiple ways to frame questions, especially with such a complex subject as “mitigation for wildly uncertain impacts of climate change.” Some analysts argue that too much focus on quantification of “net benefits” leads to bad policy results. There’s been much litigation on the demerits of such an approach; it is often and easily gamed and often misses crucial metrics as well as non-quantifiable benefits (and costs). Why should I dig up citations for that proposition when the odds are I’ll just get more insults? I’ve got better things to do.

          • Euan Mearns says:

            I’m drawing a line under this exchange here. Not because it’s offensive or whatever, but simply because it has wandered too far off topic.

            LoupLoup and Peter Lang please try to stick to the subject of the post that is rendered in its title.

          • Peter Lang says:

            Sorry Euan,

            I didn’t see your comments until after I’d posted my two comments. I was replying to them when they arrived by email. The point is made. I’ll make no more.

          • Peter Lang says:


            ‘I didn’t not read your references because from what you said they didn’t not address what we were arguing about and you hadn’t bothered to read the links I cited which explained what is relevant to this most important argument. I also expected from the start you were only interested in restating your beliefs and not interested in challenging them.

            I didn’t ask you to dig up more citations. I suggested you read and digest the citations I’d given (that you said I hadn’t provided) as a first step and discuss that. Although it is about why carbon pricing will not succeed, the same points show why any command any control policy will not succeed.

            Your last paragraph indicates you believe that huge expenditures should be justified on the basis of ideological beliefs rather than sound, rational analysis of the costs and benefits, (including the uncertainties in the analyses). Your comments seem to confirm you have had no real experience in policy analysis.

            Clearly, you don’t like to have your beliefs challenged – especially on the critical issue about whether the advocated GHG mitigation policies are justifiable on a rational basis.

            How about dealing with the issue or admitting you are not interested or not competent to contribute on it.

            A flow chart to help you determine if you we having a rational discussion?

          • Peter Lang says:


            If you want to contribute constructively, discuss this:

            The red line on the chart below shows the net benefit of optimal carbon pricing, with take up at 1/2 the Copenhagen participation rate, negative $33 trillion (in 2010 US$) for this century. However, the most important inputs to the analyses are on the alarmist side of the IPCC central estimates. And it is impossible to achieve the equivalent of the optimum carbon price by any means. Therefore, It is very likely the costs of the abatement policies will be higher and the benefits less than projected. Therefore, the net-benefit of the advocated mitigation policies will worse than negative $33 trillion. No properly informed rational government would implement such mitigation policies, and not properly informed rational negotiator would commit their country to sign onto an internatonal agreement to comply with such policies.

            There is an alternative. It is the economically rational alternative that has been demonstrated to succeed for tens of thousands of years, It is the opposite of the economically-irrational, command and control policies so loved and advocated by those who say they are concerned about GW. These have failed for 30 years and will continue to fail.

        • polarscientist says:

          Being geologically trained I do tend to think long term. Apologies for that – I just can’t help it. But if one takes the long view, as I do, it is plain that the areas worst affected by anticipated sea level rise will be the northeast and northwest coasts of the USA and Canada. And if the geology is correct, and we can expect a rise in sea level of, say, 9 metres for a rise in temperature of a further 2 deg C, then what does that say about the viability of US coastal cities? Your solution seems to be that people will simply migrate. Pardon me for thinking that such a solution is somewhat of an oversimplification of the scale of the potential problem. You also seem to have omitted to consider the possibility that warming may cause an expansion to arid zones, like the middle east and north Africa, from which Europe is already seeing an enormous increase in migration that is putting a strain on various national capabilities. Will the costs of dealing with those two changes truly be insignificant? Could it be that the economists looking at the problem really have no idea of the scale of future change? What happens, for instance, if the northern or southern hemisphere ice sheets start to move faster. The IPCC reports say nothing about that because they had inadequate models of the behaviour of ice sheets. But there is geological evidence that things can move quickly when certain thresholds are passed. Under those circumstances, are you absolutely and completely confident that the economists know what they are on about? My reading, back in the 1970s, of E F Schumacher’s “Small is Beautiful” suggests that a broad swathe of the economics community gave no value to natural resources, something the general public might find odd, but which seems alright in economic models (many of which are quite divorced from reality). Geology tells you something hard and tangible. Economics does not.

          • Peter Lang says:

            Dr Colin Summerhayes

            Many of your comments and replies to me seem as if you are advocating for a cause – a belief in damaging or catastrophic climate change (CAGW) – and straying way from objective research and analysis in your field of expertise. For example:

            it is plain that the areas worst affected by anticipated sea level rise will be ….

            Your comments reveal you have negligible understanding of the damage function, of time and humans ability to adapt, of discount rates, costs and benefits, risk analysis, decision analysis, etc. These are not your fields of expertise, but you continue stating your beliefs about them

        • polarscientist says:


        • polarscientist says:

          Doug Brodie,

          Allow me to comment on your point that it has been suggested that cosmic rays cause an increase in cloud cover that cools the climate. If that hypothesis is correct, then temperatures should have cooled during the Laschamp geomagnetic reversal 41,000 years ago. But Greenland, for example, did not cool during that reversal. Furthermore, a recent review of solar influences on climate a greed that current data do not support the postulated link between cloud cover and cosmic rays (Gray et al, 2010, Reviews of Geophysics 48). That’s why Svensmark is ignored by the iPCC.

          I could not access your graph showing running means. But if you Google Hansen et al 2016 Global Temperatures in 2015 you will see what I mean in their Figure1(b). Equally if you Google Hansen et al 2012, Global temperature in 2011, Trends, and Prospects, you will see what I mean in their Figure 3(b).

          I have provided a lengthy post, not based on the IPCC, and containing numerous references to scholarly works that support my contention that CO2 has played a key role in changing past climate. On what basis do you choose to discard all that non-IPCC evidence? Do you consider my post and all of its supporting references to be evidence in support of your opinion that “the climate establishment is so duplicitous and downright dishonest all the time “. Do you see the authors of those papers to which I refer as merely supporting, as you put it “a politically-motivated theory, with no backing of any empirical evidence”? The papers I refer to in my post contain the evidence. Indeed, the palaeoclimate books that I refer to in paragraph 2 of my post contain thousands more references based on the geological record of change. When John Tyndall first discovered that CO2 was a greenhouse gas he was not developing a politically motivated theory, nor was Arrhenius when he first calculated the effects of CO2 in the atmosphere. My point is that nobody has yet proved them wrong. Indeed, the geological evidence (not at the centre of the IPCC’s deliberations) provides independent support for the probability that adding more greenhouse gases to the atmosphere will increase the greenhouse effect. Common sense, isn’t it, as well as basic physics?

          • Doug Brodie says:

            polarscientist: I have belatedly realised that you are Dr Summerhayes! Your description of yourself as an “informed layman” threw me. As you may have realised from my earlier comments they were made from a beach in the Caribbean and I confess that I didn’t follow the thread comments in detail.

            I note that in your reply to Peter Lang as well as to myself you suggest using a long term moving average on temperature to smooth out short-term “wiggles”. I modified my WFT graph to use a 32-month smoothing as you suggested but the result was very little changed, still showing the same cooling/warming/standstill trends with the same rapid transitions of just a year or so. The same applies with 120-month smoothing.

            What is the point of masking out the reality of the 21st century pause and short-term El Nino peaks and La Nina troughs, if not to obfuscate? Your reference to 2015 being the warmest for centuries, when this is clearly due to natural El Nino warming, is itself a form of obfuscation. It backfires on you because it unwittingly endorses the Bob Tisdale El Nino/La Nina analysis of the warming since 1980 by showing that global warming only happens when natural El Nino warming dominates, as at present.

            I don’t understand why you couldn’t access my WFT graph as the link works OK for me. Here it is again:


            I note that the Hansen smoothed graph you refer to uses GISS which has been particularly heavily adjusted in retrospect to exaggerate global warming, see the following link which includes a revealing quote by Dr Hansen:


            We remain mutually unconvinced. Actually I’m planning to drop out of arguing about climate change for a while as for years I’ve found it impossible to persuade AGW believers that they might be wrong, especially the ones who matter – our politicians. I need to get on with my own life. I’ll probably continue to fund bloggers who fight for climate and energy policy rationality such as Euan Mearns and Paul Homewood. I may return in a couple of years when I expect the data will show that the so-called “pause” has exceeded 20 years (or has even turned into a decline) and our futile decarbonisation plans have continued to go nowhere, achieving next to nothing other than worsening fuel poverty and making businesses uncompetitive. The looming power cuts likely to be caused soon by our futile and unworkable climate change energy policies may bring our politicians to their senses before then.

            You will no doubt also be in disagreement with the contents of the open letter I recently addressed to a leading Scottish MP (who ignored it), see


    • Euan Mearns says:

      Phil, thanks for this thoughtful contribution. It is of course true that many perhaps the vast majority of those engaged in climate research are honest scientists. And I have become frustrated that more do not speak out against the catastrophism hype that is wide spread in our media. But I have been told, for example, the UK Met Office staff are not allowed to speak freely on this.

      I am baffled by the attitude of my government who are dismantling our energy infrastructure at such a rate that we do now face serious risks. It is the voices of extremism that are being heard. And for example, the prior thread to this one reported on UK terrestrial news that claimed global temperatures jumped 1.35˚C in February 2016. The jump was in fact 0.21˚C. The news piece was underpinned by two young climate scientists and I’m unsure if they have set out to deceive or simply don’t understand the data and how it should be presented. Either way, for me it casts the genre of climate science in very poor light.

      The spike in temperatures this year, down to the El Nino, may or may not be cause for concern. If February is the peak, and I use the UAH data then I’m really not that concerned at all. But if temperatures go substantially higher, then a re-evaluation may be in order.

      According to the Encyclopedia of Earth, “Proximate causes of endangerment include loss of habitat, overexploitation, habitat fragmentation, pollution and introduction of alien species. Chief among reasons for habitat loss and fragmentation are conversion of natural habitats to agriculture, with ancillary drivers being deforestation and urbanization. Overexploitation may take the form of overgrazing, overfishing, clear-cutting of forests or hunting fauna to a point near the minimum viable population size in a given region.” Conspicuously missing from this list is any mention of climate change.

      I’m 100% behind you on this. But you can go further to point out how Greenery is actually wrecking habitats. From biofuels, to wind turbines and US biomass replacing coal in UK power stations. And I’m concerned about the well fare of our Ospreys that over winter in N Africa where the construction of solar thermal power plants is underway.

      While I disagree with some of the content of Colin’s article I was happy to publish it because in its entirety I believe our positions are not too far apart. I’ve said many times on this blog that I am cautious on emissions longer term. If it is indeed the case that going from 260 to 400 ppm is causing climate mayhem today then it is already a lost cause – so lets party. If, on the other hand, most of what we see going on today is natural, augmented at the margin by CO2, then there is no urgency. We need to abandon all the short term Scottish, EU, UK and UN targets for CO2 reduction that may well underpin economic malaise throughout the OECD. We need to design an energy infrastructure for the 21st century, and not one based on 18th Century technology.

      • polarscientist says:

        Like Euan, I do not see the change from 280 ppm to 400 ppm CO2 as a causing mayhem – at the moment. But we do have to recognize it is part of a trend, and that there are more or less parallel trends in the emissions of other greenhouse gases, namely methane and nitrous oxide. And, furthermore, in a warming world more water vapour evaporates from the ocean, exacerbating the problem, and more Arctic sea ice melts, changing the heat balance of that region by reducing albedo. You may well say, Aha, but sea ice is growing in the Antarctic, but that would ignore the fact that warm water from the depths is welling up beneath ice shelves, thinning them.

        There is currently no sign that these human-forced trends will cease any time soon – especially as our population grows from 7.5 billion to 10 billion over the next few decades. All those people will want more energy, and its current forms of supply mean yet more emissions. 500 ppm is not far away, which is getting close to what conditions were in the Pliocene 3 million years ago, or the late Eocene 40 million years ago. At those times sea level was markedly higher than it is today, by a minimum of about 10 metres. That, by the way, is a global average. Levels were much higher in some regions (e.g. eastern USA) than others.

        If you are going to argue that most of what we are seeing today is natural, you have to explain what is driving it. There is no evidence for the requisite rise in solar activity. You cannot simply say “it’s natural” and walk away. In the world of science that would amount to abrogating your responsibility. Some thousands of scientists around the world, from many different fields, have examined this question and come down in favour of our emissions being the primary cause. If not that, then what? Tell me, please!

        • Euan Mearns says:

          Colin, first of all thank you for continuing to participate in this mammoth thread. I’m delighted the way the discussion has gone. But with well over 100 comments things now become difficult to manage.

          FF created 7.5 billion souls: heat, light, shelter, health care, food, education, mobility. And you’re right, we are heading for 10 billion on a logistic curve. Population will peak this century.

          So the question is how to care for all these people without FF. But that is not the subject for discussion here.

          Sea level is currently rising at something like 20 cm / century. So the back of my envelope tells me that it will take 50 centuries (5000 years) to reach 10 meters unless something goes seriously non-linear.

          If you are going to argue that most of what we are seeing today is natural, you have to explain what is driving it. There is no evidence for the requisite rise in solar activity. You cannot simply say “it’s natural” and walk away. In the world of science that would amount to abrogating your responsibility. Some thousands of scientists around the world, from many different fields, have examined this question and come down in favour of our emissions being the primary cause. If not that, then what? Tell me, please!

          Well I’ve provided lots of fragments of evidence on this thread. I’ll answer this in either a long comment at the end of this post or in a separate post. But for starters, last time I checked the consensus in climate science was that early 20th century warming was natural and that the current consensus is that at least 50% of warming is down to Man. Stick that into Nic Lewis’ climate sensitivity estimates and the risk level goes away. Comparing that risk level with 10 billion souls that need food (made from FF), heat and shelter. And economic prospects.

        • Euan Mearns says:

          Tell me, please!

          The full response is turning out to take longer to prepare. Note that we have three new posts since this one went up. Its a lot of work keeping on top.

          But the short answer is this. Your view of how climate works is dominated by dInsolation and dRadiative heat loss from the surface. And yet it is convection that is the main mechanism for removing heat from the surface (Houghton) and the 10Be data appear to show clear links to solar activity. And so to your list I add dConvection (ocean and atmosphere) and dSun (spectrum not TSI). And then suddenly you have a much more complex system to understand which is why we are having this debate because despite claims to the contrary, it is not well understood or settled.

          I will assert that it is impossible to understand how the climate works without a 4D picture of temperature and salinity from the oceans. We probably need to wait 30 years before the Argo buoys begin to clarify this moving image.

          I don’t know any sceptics who believe that dTSI drives climate. Though it might if The Sun does things we have yet to observe. The solar argument is based on dMagnetic field which is known to vary a lot and that in turn is correlated with dSpectrum. And yet the IPCC insist upon considering only dTSI. dSpectrum may do many things but mainly where energy is caught – stratosphere versus surface – and ozone production rate.

          Do you accept that dInsolation, dConvection and dSpectrum may combine to cause natural global temperature change. And do you accept that the moment one assumes that a component of the observed dT is down to natural warming that any calculated CS based on observations must fall?

          The MET office rushed out this paper while Europe was freezing to death in 2010:

          Solar forcing of winter climate variability in the Northern Hemisphere
          Sarah Ineson1*, Adam A. Scaife1, Jeff R. Knight1, James C. Manners1, Nick J. Dunstone1, Lesley J. Gray2 and Joanna D. Haigh3

          The cold conditions had nothing to do with GHG or irradiance but a change to the pattern of atmospheric circulation that continues today with a shift from zonal to meridional. The jet stream is never out of the news.

          We got a taste of what the LIA may have been like in 2010. This was during the low point of the last solar minimum that was very low indeed. Lochs and rivers froze that hadn’t frozen for decades. And so there is a test ahead for sceptical opinion. If 2010 turns out to be a one off and The Sun continues to slumber then the sceptic argument about the Sun will be weakened. If on the other hand it repeats and gets worse then the solar argument will be supported.

  9. Euan Mearns says:

    Shaun A. Marcott,1 Jeremy D. Shakun,2 Peter U. Clark,1 Alan C. Mix1 SCIENCE VOL 339 8 MARCH 2013

    • clivebest says:

      I reanalysed all the 73 temperature proxies as used by Marcott, Shakun et al. I was able to reproduce the overall trend but there is no evidence of any recent temperature uptick due to human activity. This is an artifact caused by two effects.

      1) Their interpolation of all proxies to a 20 year time bin when in reality most only have a time resolution of 100y. If instead you bin the data at the recorded times their is no uptick. They also re-dated the carbon dating which then tended to suppress anomalies from 1600-1900 which accentuated their ‘uptick’
      2) Only one proxy contained a significant increase which then biased their result: TN05-17 which is situated in the Southern Ocean (Lat=-50, Lon=6) and this cannot be due to AGW.

      I also studied the proxy time resolution and showed that their result would smear out all short term temperature variations lasting up to 300 years. This is probably the reason why the Roman and middle age warm periods are not apparent.

      • Yes, Marcott et al were criticised for using the uptick of the recent period. But quite independently the 2k group of thePast Global Change programme(PAGES) did a comprehensive analysis of just the past 2000 years and confirmed that it does exist (see references in my post above).

        There is no doubt from ice cores (see the Vostok curves above in Figure 6) that temperatures did decline over the last few thousand years of Holocene time, as shown also by Marcott’s data..

        • clivebest says:

          You’re right! The Pages 2K data has much better definition and coverage, although for shorter time than Marcott and mostly on land. Their results also clearly show the medieval warm period and Little Ice Age, at least in the Northern Hemisphere. I think that even Steve McIntyre accepts there is a rise post 1900, although he did find they had three proxies inverted. So yes human increases in CO2 must change energy balance but the amount is still very uncertain.

          The slow cooling over the last few thousand years is due to the precession of the equinoxes. The earth now reaches its closest distance to the sun during southern summers when the arctic is in darkness. 11,000y ago this was inverted and arctic summers received 20% more solar radiation than now. However, southern oceans currently receive 20% more heat so where is that heat currently going?

          • polarscientist says:

            Actually, Clive, the Earth is closest to the Sun in the northern winter (same as southern summer). What that means is that our northern winters are, relatively speaking warm, with respect to what they were 11,000 years ago when the Earth was closest to the Sun in the northern summer (same as southern winter). The resulting changes in incoming solar radiation are quite small. But they do mean that the Southern Ocean now is very slightly warmer than it would have been 11,000 years ago. The heat is taken down into the ocean interior in the Intermediate Water that sinks on the northern side of the Polar Front. Equally, the current warming of the atmosphere due to our emissions is also being taken into the interior via that route.

      • polarscientist says:

        The best representation of recent temperature change is that from the PAGES 2k group, referred to in my opinion piece. They clearly documented the recent uptick.

  10. Euan Mearns says:

    Note the time scale is 5,000,000 years. You join all this together and you get the chart I posted further up the thread.

    A Pliocene-Pleistocene stack of 57 globally distributed benthic D18O records
    Lorraine E. Lisiecki
    Department of Geological Sciences, Brown University, Providence, Rhode Island, USA
    Maureen E. Raymo
    PALEOCEANOGRAPHY, VOL. 20, PA1003, doi:10.1029/2004PA001071, 2005

  11. Euan Mearns says:

    Insolation peaked around 11,700 years ago, melting the great North American and European ice sheets and parts of West and East Antarctica. Since then, insolation has declined (Berger and Loutre, 2002). As a result, Earth’s climate cooled over the past 10,000 years (Marcott et al., 2013; see also the PAGES 2k Consortium, 2013, for the past 2000 years). The cooling trend culminated in the Little Ice Age of 1350-1850.

    Orbital calculations show that we should remain in this cold condition for the next 5,000 years (Berger and Loutre, 2002). So, why are we not still in the Little Ice Age? Has the sun suddenly gotten hotter? No. The latest data on sunspots (Clette et al, 2014) show that there were about the same peak numbers of sunspots in the 1980s-90s as there were in the 1780s or the 1840s-60s, during the Little Ice Age. Indeed, the number of sunspots has been declining since 1990 (Clette et al, 2014; Lockwood, 2010), so our climate should be cooling from that cause too. Why is it not?

    The chart shows temperature proxies from the LR04 benthic foraminfera stack that geographically covers much of the Atlantic Ocean and Temperatures at Vostok. It is difficult to argue for cooling in the Vostok data and LR04 is clearly warming through the Holocene and the rate of warming appears to be slowing.

    How do we reconcile this with Marcott?

    • A C Osborn says:

      The Marcott paper has been totally deconstructed by Steve McIntyre over at Climate Audit.
      There was Q & A rebuttal by Marcott et al which was answered by Steve here

    • Euan Mearns says:

      The Name is Bond, Gerrard Bond:

      To explain where I’m going with this. This graphic shows Bond’s drift ice cycles in the N Atlantic. Bond et al claim that these correlate with 10Be measurements. I started once to look into this but did not get far. Either Bond et al made this up or the data are real and should not be ignored.

      The relevance here is that I share Peter Lang’s surprise at the notion there was only a single cool period in the Holocene, i.e. the LIA. Bond sees something like 8 cold episodes. One of the things I like about this data is that they align with history. I think climate change probably helped to fell the Roman Empire.

      LIA = Little Ice Age
      MWP = Medieval Warm Period
      DA = Dark Ages
      RWP = Roman Warm period

      These Bond cycles are the Holocene equivalent of D-O cycles that also correlate with 10Be that I will comment on another day. If the Bond data is to be believed then they offer quite strong evidence that SOLAR GEOMAGNETIC ACTIVITY has a strong influence on North Atlantic climate.

      And so while struggling with the concept that Holocene temperatures peaked, declined into the LIA and were then turned around by Man. I’m actually offering this as a bridge to try and close mutual understanding. I will propose that these cycles are linked to substantial changes in the pattern of atmospheric circulation that are caused by changes to The Sun – not TSI but changes in spectral output. This has profound impact on climate in NW Europe and in S California and else where. It is perhaps possible to change climate everywhere without having a substantial change in global average temperature. Europeans fled the Arctic conditions of NW Europe for the glorious S California unaware they were actually fleeing to a desert.

      Persistent Solar Influence on
      North Atlantic Climate During
      the Holocene
      Gerard Bond,1* Bernd Kromer,2 Juerg Beer,3
      Raimund Muscheler,3 Michael N. Evans,4 William Showers,5 Sharon Hoffmann,1 Rusty Lotti-Bond,1 Irka Hajdas,6 Georges Bonani6
      7 DECEMBER 2001 VOL 294 SCIENCE


      Solar forcing of winter climate variability in the Northern Hemisphere
      Sarah Ineson1*, Adam A. Scaife1, Jeff R. Knight1, James C. Manners1, Nick J. Dunstone1, Lesley J. Gray2 and Joanna D. Haigh3

      • Euan Mearns says:

        Putting all these graphics up together I find helpful. I just noticed that the CO2 profile in Taylor Dome is negatively correlated with Marcott. Irrespective of whether CO2 is a cause or consequence of warming this observation quite simply does not fit the Marcott model.

        And while the correlation may not be perfect, it lends substantial support to the picture painted by LR04, which after all lines up pretty well with the ice core records.

        • can you show the respective graphs so we can all see what you are referring to?

        • Euan Mearns says:

          I’m away from home right now otherwise I’d try to make a new chart. But the bottom chart shows, the d18O for benthic forams (I’ve not had time to digest your comment on that yet) the middle shows the warming then cooling of Martcott. The top shows CO2 from Taylor dome, rising from 8000 to 1000 years – not exactly consistent with cooling no matter how you slice and dice it.

          Also just heading out for dinner in an absolutely glorious Perthshire evening.

      • The Bond data show a roughly 1500 year cyclicity, with the cycles shrinking in magnitude considerably in the Holocene (probably because there was a lot less ice around). Nobody haste found a convincing link to solar fluctuations, but there is always the possibility that they are an emergent property of the system, reflecting solar activity indirectly. The last such output of ice rafted debris was in the Little Ice Age.

        Actually, there is evidence in 14C data for centennial fluctuations in solar output through time over the entire Holocene, from people like Stuiver, or Broecker. These would suggest that the 208-year Suess Cycle, and 88-year Gleissberg Cycle in solar output are persistent features that will have caused warming and cooling, which is retrievable from tree ring records. The data of Steinhilber, to which my post refers, show these fluctuations for the past 2000 years. There was a cool period in the dark ages (the Oort solar minimum), which would perhaps link to Bond’s finding. I address this at length in “Earth’s Climate Evolution”.

      • Javier says:


        A careful analysis of Holocene temperature record, solar variability as registered by cosmogenic isotopes, and the 1470 years Dansgaard-Oeschger cycle shows that the Ice rafted debris method of Gerard Bond captures every cold period of the Holocene regardless of its cause, and thus it does not constitute a cycle per se.

        One can clearly see that the period between 12,000 and 7,000 years BP is dominated by a ~1000 years periodicity of probable solar origin as it coincides with the ~1000 years oscillation in solar variability. But cosmogenic isotopes show that the ~1000 years periodicity in solar variability is very much reduced in amplitude between 6,000 and 2,000 years BP, and so the latter part of the record is dominated by an emergent 1500 years oscillation signal previously absent and probably related to the glacial Dansgaard-Oeschger cycles.

        Although labeled as peaks 1-5 by Bond, they are clearly multiple peaks and there is a lot of confusion in the literature as some authors report coincidence of their research with Bond peak 2 when it coincides with Bond peak 2a, or when it coincides with Bond peak 2b, indicating that they are probably of different origin, but originating a lot of confusion. Thus it is no wonder that some authors reject the existence of the Bond cycle when acknowledging the existence of the cold periods including in it.

        So my opinion is that it is not appropriate to talk of a Bond cycle and that trying to look for a common origin for all Bond events is a misguided pursuit.

        The climate during the Holocene shows two very different periods separated by the Mid-Holocene Transition between 6,000 and 5,000 years BP. Several authors support the interpretation that the MHT involved a change of climate regime from solar forcing dominated to oceanic forcing dominated, that is reflected in a lot of evidence, including the clear change in periodicity of the Bond events. See for example:

        Debret M., et al., 2007. The origin of the 1500-year climate cycles in Holocene North-Atlantic records. Clim. Past Discuss., 3, 679–692.

        Debret, M. et al. 2009. Evidence from wavelet analysis for a mid-Holocene transition in global climate forcing. Quat. Sci. Rev., 28, 2675-2688.

        Simonneau, S. et al. 2014. Tracking Holocene glacial and high-altitude alpine environments fluctuations from minerogenic and organic markers in proglacial lake sediments (Lake Blanc Huez, Western French Alps). Quat. Sci. Rev. 89, 27-43.

        • Euan Mearns says:

          The devil is in the detail and I’d agree that Bond cycles are quasi periodic and may be down to the interaction of two or three processes that may have a pseudo common denominator.

          Alastair Dawson is a climate historian whose work I respect and I know him quite well. He is at pains to point the possible role of Icelandic eruptions in the LIA in Europe.

          The Bond theory is that these quasi cycles are linked to the strength and geographic extent of the Gulf Stream that currently runs all the way to the Arctic Ocean but which looks like it may just get chopped any day.

      • Alistair Buckoke says:

        What is interesting about the Bond data is what the cold episodes correspond to, from an archaeological viewpoint. There is a particularly severe cold episode covering the 4th Millennium BC, a time which saw the advent of farming in the UK and the building of large mortuary monuments. The peak of the cold phase tallies well with the main era of monument building.
        Similarly, the next cold episode corresponds to the era of late Neolithic large-scale monument building in the UK, c.2700-2200 BC.
        The cold phase after that occurs around the middle to late Bronze Age in the UK, an era corresponding to the development of more intensive and more rational farming techniques and an abandonment of older patterns of land use and monument focus.

        Could the data suggest cultural change stimulated by environmental adversity, and not by favourable climatic conditions?

        • Javier says:


          It is already known that transitions from Chalcolithic to Early Bronze, from Early to Middle Bronze, and from Late Bronze to Early Iron, occurred during notable arid (and sometimes cold) phases in the Eastern Mediterranean. There is also an hypothesis that the First Kingdom in Egypt initiated after the arrival of climate refugees from the aridification of the Sahara 5.8 kyr BP greatly increased the population of the Nile Valley.

          Roberts et al. (2011) have already proposed that climatic stress could have acted as pacemaker for cultural change. I am sure you would enjoy reading the 50 pages article by Weninger et al. 2009 on the impact of rapid climate change on prehistoric societies.

          Roberts, N. et al. 2011. Climatic, vegetation and cultural change in the eastern Mediterranean during the mid-Holocene environmental transition. The Holocene 21, 147–162.

          Weninger, B. et al. 2009. The impact of rapid climate change on prehistoric societies during the Holocene in the eastern Mediterranean. Documenta Praehistorica 36: 7–59.

          • Alistair Buckoke says:

            Many thanks for the references. My focus is mainly on UK archaeology, so these correspondences particularly struck me.

            Looking at the earlier part of the graph, Peak 10 at c.9300 BC could link with Middle Eastern PPNA sites soon after the end of the Younger Dryas, notably Gobekli Tepe and similar sites. Peak 9 at c.8400 BC corresponds well with a concentration of PPNB starts. Peak 8 at c.7400 BC appears to link with a bunching of PPNC sites and with an expansive impetus which resulted in the first farming in Greece at c.7000 BC, a useful marker. Peak 7 corresponds quite well to a grouping of late PPNC sites (all from Hodder et al. 2010).

            Peak 6 at c.5400 BC corresponds very well to the Linearbandkeramik start in central Europe at c.5500 BC. Peak 5i at c.4750 connects to post LBK groupings, and, perhaps, to new monument building societies in NW Europe from c.4600 BC onwards. Peak 5ii also fits very well with the Michelsberg expansion in NW Europe, which led towards the first arrival of farming in the UK and in Southern Scandinavia.
            As you say, the arrival of Badarian pastoralists in the Nile Valley fits well, and has been confirmed in a recent dating study.

            While would not want to make the thesis too tight, the periodicity is still remarkable, corresponding with many major developments.

            If living got too easy things tended to get boring, so it would seem. Perhaps though there is an underlying dissatisfaction (Cauvin 2000) which surfaced in harder times.

            It looks as though the Bond data is pretty real, occasioning few doubts.

        • Euan Mearns says:

          Alistair, I’m incredibly interested in this! If you were able to flesh this out to 1000 to 2000 word comment it would then become a guest post.

          4th millennium BC is confusing for me – it means 6016 years ago – yes?

          Why do the cold phases tally with monuments? And which monuments?

          One thing that drew me to Bond in the first place was the evidence for MWP, LIA, MWP, DA and RWP that are historically documented. To build on this would be really tremendous.

          I think climate change felled the western Roman Empire – but I don’t have time to look for evidence.

          I’ll mail you a copy of Bond.



          • Alistair Buckoke says:


            I’d be happy to do a piece on this.

            Having just encountered this question, I’m not sure how much has been written on it already, in prehistoric contexts. If anyone has some references that could be followed up it would be very helpful.



          • Euan Mearns says:

            Alistair, I tried to send you the Bond paper but the email bounced.


          • Alistair Buckoke says:

            I’ve checked my email entry and nothing seems wrong here. Do you have any filters or firewalls which could be selecting against certain email addresses? If a second attempt fails I can give you another email address.


          • Alistair Buckoke says:

            Since your automatic notifications via email get to me without difficulty, may I suggest you try just sending an email without an attachment first.

            I have some thoughts on your invitation which might be discussed, though maybe in a less busy moment!


    • Benthic carbonate d18O is a product of ice volume as well as temperature. We have to remember that as the northern hemisphere received more insolation 11,700 years ago, much of the energy went initially to melting the great northern hemisphere ice sheets, so the northern parts of the northern hemisphere stayed cool until the ice sheets were gone. The declining insolation was still enough to warm the world in the Holocene Climatic Optimum following removal of the ice sheets. But continued loss of insolation turned that quickly to cooling into what several have called the Holocene neoglacial, the pinnacle of which was the Little Ice Age. Hence the global temperature curve is much as Marcott et all showed. There is a vast amount of literature on these patterns – for a summary see a basic Paleoclimatology text or “Earth’s Climate Evolution”.

  12. Doug Brodie says:

    I am a simple engineer and I keep asking a simple question which never gets an answer: where is all the man-made global warming, at the predicted warming rate of 0.2degC per decade, that climate scientists and politicians have been going on about for the last 30 years?

    I put up a simple graph of global temperature for the last 70 years overlaid with a plot of atmospheric CO2 levels, see

    The source temperature data for this graph has been adjusted and selected over the years to exaggerate the warming and reduce the cooling but the conclusion is still clear: there has been only about 20 years of sustained global warming in the last 70 years, despite steadily increasing atmospheric CO2 levels.

    To review these 70 years in more detail, first we had global cooling for about 30 years over the period when atmospheric CO2 levels started to increase exponentially, until around 1977. Climate scientists seem unable to give a credible explanation of this anti-correlation. Then we had a sudden, apparently natural switch to global warming for 20 years until about 1998. Then another apparently natural switch occurred and global temperatures flatlined for the next 18 years, acknowledged even by the biassed Met Office in 2013.

    There is good empirical evidence that the global warming of the 80s and 90s was mostly if not entirely natural, caused by a preponderance of sunlight-fuelled El Niños versus cooling La Niñas from cold deep ocean upwelling, see This was probably because solar activity at that time was at a century high with resultant reduced global cloud cover, hence stronger El Niños.

    Since the turn of the century El Niños and La Niñas have been roughly in balance which is consistent with the recent drop in solar activity. The sudden global warming of the last year or so is clearly due to natural El Niño weather rather than man-made CO2. So where is all the man-made global warming in the face of ever-rising atmospheric CO2? It appears to be non-existent.

    To me the really shocking aspect of UN IPCC climate science is that it is only mandated to study alleged man-made causes of climate change, yet they conceal this from the general public and make out that their science is “comprehensive”. This allows them to ignore or downplay natural causes of climate change, to assist the pursuit of their nefarious political agenda, whatever it is – world governance, wealth redistribution, …? Simple textual analysis of their SPM reports shows that since global warming stopped 18 years ago their usage of the term “global warming” has been largely replaced by the obfuscatory term “climate change”. In fact I believe (too difficult to look up from my Caribbean beach) they re-defined “climate change” to mean “man-made climate change”! Why should we believe a word of what they say?

    A good antidote to establishment climate change propaganda is given by the recent interview with independent scientist Dr Piers Corbyn on, of all forums, the biassed BBC. He predicts global cooling over the next 20 years. See

    • I’m afraid that you are incorrect in assuming that there is “good empirical evidence that the global warming of the 80s and 90s was mostly if not entirely natural, caused by a preponderance of sunlight-fuelled El Niños versus cooling La Niñas from cold deep ocean upwelling”. Equally, climate scientists are not “unable to give a credible explanation of [what you refer to as] this anti-correlation” between CO2 and temperature. You are correct that solar input was at a century high late in t he 20th century, but what you need to recognise is that it was no higher than it was in the 1780s or the 1840s-60s, when the climate was significantly colder. There has to be an explanation for why, with the same solar output, it was almost 1 deg C warmer in the late 20th century. The explanation for the cooling steps in the 1945-1979 period is a combination of the cold phase of the Pacific Decadal Oscillation plus massive outputs of aerosols from growing industry that masked the effects of CO2 until nations introduced clean air acts to remove the aerosols. The latest slowdown in warming is likely to be a further negative phase of the PDO combined with the effects of increased aerosols from coal burning in India and China.

      • Doug Brodie says:

        Polarscientist: I’m away from home at present with limited resource access, armed with just an iPad, so my response is less well researched and more tardy than I would like.

        Firstly your point on solar activity. The following link shows a simple graph of solar activity covering much of the Little Ice Age:

        It looks to me from this graph that the late 20th century solar activity was stronger than at the dates you quote. 1780 is reckoned to be the start of the Dalton Minimum and 1850 was the end of the 500-year LIA, so perhaps no surprise that temperatures were lower then than now. Not that the LIA was all cold. As I’m sure you know it was a time of huge climate variation: cold, heat, floods, droughts, storms and “normal”. Another thing I’m not sure of is the strength of the earth’s magnetic field over this period. I have a graph at home which shows that it reached a peak over the second half of the last century, greater than I can’t remember when, which was surely a major influence on global cloud cover.

        I find your argument about aerosols just too pat. I get the impression that aerosols are used like a “joker card” by climate scientists to explain any temperature trend they can’t explain. Are you claiming that the entire world brought in clean air legislation within the couple of years which marked the sudden transition from global cooling to global warming around 1977? I just don’t believe it. Also, if you invoke the PDO cold phase for the global cooling of the period 1944 to 1977, shouldn’t you also concede that the subsequent natural PDO warm phase was partially (wholly?) responsible for the global warming of the 80s and 90s?

        Finally I’d like to go back to my temperature graphs and the global warming of the 80s and 90s. My first HadCET graph looks fairly chaotic at first glance but my second Bob Tisdale graph of Pacific sea surface temperatures shows the origin of that apparent chaos, before it was amplified and diffused into the global surface (land and sea) temperature record. If you accept that the step increases in sst/global surface temperature over the 80s and 90s were due to predominant El Niño events, then where does alleged CO2 warming at a predicted rate of 0.2degC per decade fit in on top of that? It simply doesn’t!

        Thank you for your response but I remain unconvinced. Man-made global warming still looks non-existent to me.

        • Actually, the Wikipedia sunspot graph is now out of date, having been superseded by the Clette graph to which my post refers. Annoying, isn’t it how the science keeps moving the edge of the envelope, making us scurry to keep up! But if you Google Clette et al sunspot graph you will find the complete paper, in which the revised sunspots are given as Fig 28.

          Yes, the PDO warm phase AND the PDO cold phase do affect the global temperature, just as warm El Ninos and cold La Ninas do. To really understand what’s going on you need to do a 16 month running mean, or a 32 month running mean through the data from 1900 onwards. What you will see emerge is the underlying trend that runs through all the wiggles caused by things like El Nino, or occasional volcanic eruptions like Pinatubo. It is THAT underlying trend that we have to compare with the trend for CO2. They match quite well.

          If I may say so, what you are ignoring is the fact that when we burn fossil fuels not only does CO2 go into the atmosphere, but also the atmosphere loses oxygen. Moreover because the fossil fuel is rich in 12C, not 13C, the composition of the CO2 in the atmosphere is changing with time because of our emissions.

          Finally, you have to explain the warming, and we know from many detailed studies of both the ocean and atmosphere (and the Sun) that they are not the cause. The only cause we can find is human emissions of greenhouse gases. It’s not a great surprise, after all, basic physics 101 tells us that this ought to be the case.

          • Euan Mearns says:

            Annoying, isn’t it how the science keeps moving the edge of the envelope, making us scurry to keep up!

            Revising data is not science, revising data is revising data. But you’re right it is hard to keep up so much data revision is going on. And it all seems to be going in one direction and that direction is to support the case you are endeavouring to make. If this goes on we will be left with a situation where we will have no choice other than to conclude that the original archivists of this data were somehow incompetent.

            Data revisions I’m aware of include surface temperature homogenisation, HadCRUT 3 to HadCRUT 4 that got rid of the pause, RSS, Sunspots and Vostok gas ages. I’m sure there are more.

            It’s not a great surprise, after all, basic physics 101 tells us that this ought to be the case.

            Well basic physics 101 was what Svante Arrhenius had, and it turned out to be wrong. Understanding the principles of radiative transfer upwards through the atmosphere is FAR from being basic. And understanding the feedbacks from this are incredibly complex and uncertain.

  13. Roger Andrews says:

    Dr. Summerhayes:

    To get straight to the meat of the issue I present data that cast doubt on the assumption that d18O is a proxy for temperature and challenge you to rebut it.

    Here is a plot of d18O, 10Be, methane K and Ca from the GISP 2 “deep core” in Greenland. The Y scales have been adjusted so that the amplitudes are comparable:

    Note how they all move in lockstep. This can be explained only as a dominant result of changes in precipitation rate, not changes in temperature. Yiou et al. (1997), who reported the results for 10Be, concur:

    Concentrations of the cosmogenic isotope 10Be have been measured in more than 1350 samples from the Greenland Ice Core Project (GRIP) ice core drilled at Summit, Greenland. Although a dust-associated component of 10Be retained by 0.45 micron filters in some of the samples complicates the interpretations, the results confirm that the first-order origin of 10Be concentration variations is changes in precipitation rate associated with different climate regimes. This effect is seen not only between glacial and interglacial periods,but also during the shorter “Dansgaard-Oeschger” interstadials.

    • Euan Mearns says:

      Roger, K, 10Be, CH4 and Ca are all absolute concentrations that need to be corrected for precipitation rate. d18O is a ratio that does not. IMO, what this shows is that precipitation rate is linked to temperature.

      Precipitation rate is a major stumbling block in using the 10Be data. The 10Be data I may show some time soon are corrected for precipitation rate. But your chart gives me an idea. maybe the Ca and K ppms can be used to back out a 10Be residual. Or maybe that’s what the climate scientists have already done?

      • Roger Andrews says:

        To get ice you need sub-freezing temperatures and precipitation. Which is the more important?


        • Euan Mearns says:

          To get ice you need greater winter snow fall than summer melt.

        • Jim Steele says:

          Changes in winter precipitation are more important as witnessed by Kilimanjaro and the retreat of the LIA glaciers.

          If Mann’s hockeystick reconstruction of the Little Ice Age temperatures is correct, the small drop in global temperature during the LIA was not enough to cause the glaciers to advance. Furthermore the rapid retreat of glaciers in the European Alps began in the 1800’s before global temperatures had sufficiently risen. Several researchers call this the Little Ice Age paradox. It appears more likely that rapidly retreating LIA glaciers were driven more by changes in moisture transport.

          Read Vincent C, et al., (2005) Solving the paradox of the end of the Little Ice Age in the Alps. Geophysical Research Letters, vol. 32, L09706, doi:10.1029/2005GL022552

    • donb says:

      Your blanket comment doubting that 18O/16O can be a proxy for temperature ignores the very large literature base using this ratio to determine temperature, ranging from very high temperature mineral formation from magma all the way down to many kinds of chemical equilibria at ambient temperature. If your data interpretation does not seem to agree, one should not question the technique, but look for other interfering factors.

      • Don B:

        I’m sure that if the literature base were printed single-space and laid end- to-end it would stretch from here to Hong Kong. But that isn’t the question.

        The example I presented above shows a close correlation between 18O, 10Be, CH4, K and Ca. This is readily explicable in terms of precipitation changes. It is not readily explicable purely in terms of temperature changes, although I’m not claiming that temperature had nothing to do with it.

  14. clivebest says:

    1. The policy result of the Paris agreement is mainly about good intentions, but little else. They agreed to endorse a new 1.5°C temperature target. But what is not in the agreement is any clue as to how this might be achieved. It is naive to imagine that the world could ‘ban’ fossil fuels without offering any realistic alternative. Sadly the international community has failed to stop Elephant and Rhino poaching, let alone stop anyone digging up and burning abundant coal.

    2. Lindzen & Choi measure climate sensitivity to be 0.7+.5-0.2. The calculated temperature response to CO2 doubling by radiative transfer codes is 1.1C. The actual response depends mostly on feedbacks of the hydrological cycle. These are positive for increased humidity with temperature (H20 GHE), and negative for reduced (moist)lapse rate. However, the largest uncertainty remains increased clouds which may be net positive or even negative. Lindzen’s Iris hypothesis proposed that clouds act like a thermostat in the tropics letting more heat radiate to space if the world gets too hot.

    3. Paleo estimates in AR5 of climate sensitivity are all based on recovery from the LGM but this only works by treating the retreating ice sheets as if they are a forcing. In other words as ice sheets retreat so net solar forcing increases due to the decrease in global albedo. Climate models then apply the ice core CO2 increase to calculate the net temperature response which assumes CO2 is the driver. However since we don’t understand yet how glaciations end, it is most likely that Ice-albedo itself is the main solar albedo feedback and quite why it occurs only after 100,000y is the toughest nut to crack.

    Did this image above load – I wonder? More comments tomorrow. 😉

    • The data being obtained in 2015-6-7 should be very useful. Temperature and water vapor content are very high. The ARGO buoys are taking extensive sea water temperature data. I assume satellites are measuring aerosols and albedo/outgoing long wave radiation. I’m merely an engineer, but I have supervised scientists in my career, and I’m pretty sure the water vapor and cloud feedbacks can be set with a bit more confidence in the near term (thanks to the 2014-15-16 El Niño?).

      This in turn should help narrow the Transient Climate Sensitivity outlook, which will help further ENGINEERING & ECONOMIC studies. These studies should also benefit from a more intelligent look at the world’s potential for CO2 emissions from fossil fuels (which I believe were overstated by the RCP8.5 case and earlier siblings).

      I second Peter’s comments about the IPCC inspired COP21 results. The decision making “apparatus” seems to be dominated by climatologists and a few economists/politicians. In between those two worlds lies the engineering world, which has been largely ignored. The proposed change from fossil fuels to renewables can be considered a “mega project”, and these require much more sophisticated analysis, planning, and evaluation tools. I would caution scientists who aren’t well versed in the projects engineering world to push too hard for action unless much more serious work has been performed.

    • polarscientist says:

      Sorry Clive, but the palaeo estimates of climate sensitivity come from the PALEOSENS paper in Nature (see my reference list). The paper says “Over the past 65 million years, this reveals a climate sensitivity (inKW21m2) of 0.3–1.9 or 0.6–1.3 at 95% or
      68% probability, respectively. The latter implies a warming of 2.2–4.8K per doubling of atmospheric CO2, which agrees with IPCC estimates.” So its 65 million years, not the recovery from the LGM. These PALAEOSENS guys are quite careful you know. They’re not just plucking this stuff out of thin air. They deserve a bit of respect for their hard work.

      • clivebest says:

        I was referring to Chapter 5 in AR5 where the estimates of climate sensitivity are all based on the Last Glacial Maximum. I am sure the PALEOSENS group have done some great work but it doesn’t seem to have made it into AR5, as far as I can see.

        It is also not at all clear to me that ECS is anyway constant in time.

  15. Jim Steele says:

    Dr. Summerhayes has pieced together a narrative supported by limited evidence to suggest CO2 is responsible for the current warmth.

    He suggests current warming is only now equal to the Roman Warm Period, but western Pacific ocean temperatures were “were ~0.9°C warmer during the Medieval Warm period than during the Little Ice Age and ~0.65° warmer than in recent decades.” Read Rosenthal 2013 “Pacific Ocean Heat Content During the Past 10,000 Years”

    Summerhayes cites Miller’s 2013 claim that radio carbon dating of exposed vegetation suggests temperatures are now warmer than the Holocene Optimum. But that claim is contradicted by several Arctic proxies such as Funder 2011 showing Arctic sea ice was far more reduced during that time than now. In Mudie’s 2005 paper “Decadal-scale sea ice changes in the Canadian Arctic and their impacts on humans during the past 4,000 years” they write, ” Our data show that from ~6500 to 2600 BP, there were large oscillations in summer SST from 2–4°C cooler than present to 6°C warmer and SIC ranged from 2 months more sea ice to 4 months more open water… The warming took ~50–100 years and lasted ~300 years before replacement by colder intervals lasting ~200–500 years.”

    Miller’s inference about exposed vegetation and temperature is doubtful for many reasons. Simply consider that most of Beringia was ice free throughout the depths of the last Ice. Vegetation was exposed during the coldest of times. Or consider the fact that glaciers on Kilimanjaro have recently shrunk due to sublimation and below freezing temperature due to changes in moisture trasnport. Vanishing ice due to changes in moisture transport should not be confused with radiative effects.

    Also consider the Dansgaard-Oeschger during which Greenland’s average temperatures dramatically rose on average every 1500 years by 10°C +/- 5°C in a just matter of one or two decades. CO2 concentrations did fluctuate by about 20 ppm during a third of the D-O events, but could contribute directly to no more than 0.4°C to only 30% of the largest warming D-O events. In contrast during 68% of the other D-O events, abrupt warming occurred while CO2 was declining. Thus D-O rapid warming and cooling events seem independent of any CO2 forcing.

    As I wrote in the essay “The Arctic Iris Effect”

    the rapid changes in temperatures are most often due to changes in the transport, storage and ventilation of excess tropical heat in the Arctic.

    Summerhayes also suggested the cooling of the Antarctic and subsequent decline in CO2 concentration is evidence of CO2 as the temperature control knob. But as I discussed in the Antarctic Refrigerator effect (

    the evidence suggests the establishment of the Antarctic Circumpolar Current (ACC) inhibited poleward heat transport, and began a process where the deep oceans began to cool. Outside of the tropics, more heat is radiated away than is absorbed. Polar cooling does not require a driving force. Simply by inhibiting the transport of tropical warmth, Antarctica cooled rapidly whereas the Arctic did not. That suggests cooling was regional not global as would be expected if CO2 was the driving force. Antarctica’s freezing conditions soon produced colder deep water via brine extrusion, and about 30 million years later cooler deep waters began upwelling in the tropics, cooling the atmosphere enough for Arctic ice caps to begin forming.

    Furthermore the intense upwelling associated with the newly formed ACC also shifted the phytoplankton assemblages and promoted the evolution of diatoms (and whales?). The Cretaceous was dominated by chalk forming coccolithophorids that produce CO2 and transport alkalinity to depth when forming their carbonate plates. In contrast larger diatoms began sequestering CO2 and transporting it rapidly to depth. Thus it is highly likely that the formation of the ACC was the driving force that both cooled Antarctica and reduced atmospheric CO2.

    Lastly fishery data also reports that decadal oscillations drive warmer subtropical waters and species into the Arctic on multidecadal time scales. The 1930s witnessed such an event and Arctic summer sea ice melted nearly to the same extent in the 1930s as it has in the most recent decade. The rapid warming of the 30s happened before CO2 concentrations could contribute any theoretically significant warmth. In contrast, the ACC inhibits such warm water intrusions and unlike the Arctic, Antarctic sea ice has expanded. Again regional dynamics better explain observation than does a CO2 driven global change.

    • donb says:

      Jim Steele,
      I found your post “Antarctic-refrigeration-effect” filled with interesting concepts. You make a good case for the importance of oceans and life in determining temperature.

      But a question. The long global cooling over ~60 Myr is much longer than equilibration times of different ocean layers (at different temperatures). Unless the Sun grew dimmer (for which there is no evidence), it would seem that the Earth’s IR emission rate had to increase for the globe to cool this way. I assume here that growth of polar glaciers and increased ice albedo is insufficient to explain the temperature decrease.
      You stress how much heat is transferred from the tropics to the polar regions. And, lower temperatures in the polar areas means IR emission is much less, whereas higher temperatures in the tropics increases IR loss (both by the T^4 relation). This implies that the relative amounts of heat loss between tropics and polar regions depends on the amount of heat transferred, which depends on ocean and atmospheric currents. My question is do you think changes in ocean heat transport over the past ~60 Myr changes the proportion of IR emission tropics-to-poles and importantly changed the total global emission, thus causing Earth to cool?

      • Jim Steele says:

        Dom, You say, “Unless the Sun grew dimmer (for which there is no evidence), it would seem that the Earth’s IR emission rate had to increase for the globe to cool this way.”

        Dom I suspect your estimate of equilibration time is too simplistic.

        First you must distinguish between changes surface advection of heat and vertical storage and ventilation of heat. It is the vertical storage and ventilation I emphasize. The formation of the ACC merely inhibited further poleward transport of tropical heat, allowing Antarctic temperatures to naturally cool to below freezing during the winters. That event had only a small effect regards the global surface temperatures as observed by the simultaneous lack of ice caps in the Arctic. The global temperature is controlled by the stored heat in the oceans, for the same reason we use water baths in the laboratory to control temperatures. Change the ocean’s heat content and its ventilation rates and it changes the global air temperatures.

        The ACC formation triggered a change in how much heat was stored in our “water bath”. Brine extrusion inuring sea ice formation in the Antarctic waters for the first time delivered abundant dense, salty cold waters to the abyss just as it continues to do today. That began cooling the deep oceans, but would not affect IR emissions. Previously the abyss stored heat draining from regions where evaporation exceeded precipitation, such as the pervasive shallow epi-continental seas. Analogous to the Mediterranean water today, these regions warmed the subsurface waters. But as Antarctica’s ice cap grew and the plates shifted, most of the epicontinental seas and the shallow Tethys were greatly reduced or dried up. Thus the cooling of the ocean’s cannot be understood from a simplistic IR emissions formula, restricted ocean surface temperatures. Global temperatures must be seen within a dynamical ocean framework.

        Changes in upwelling altered the rates of heat ventilation and increased the winds. The formation of the ACC itself increased southern hemisphere winds and the upwelling of deep warm waters. Evaporation from strong winds can increase by 10 to 100 fold compared to weak winds, thus geometrically enhancing cooling. The gradual shoaling of the thermocline eventually brought cooler waters to the surface in equatorial and subtropical regions, which not only cooled surface air temperatures but again enhanced the winds. The equatorial cold tongue formed by upwelling of cool waters in the eastern Pacific creates a temperature gradient that enhances the Trade Winds as the Walker Circulation does today. And again enhanced winds enhance heat ventilation.

        There is no need to evoke a dimmer sun or CO2. Both radiative effects could remain constant and the oceans would have still cooled due to the Antarctic Refrigeration Effect.

    • polarscientist says:

      In fact my comments referred to global temperature. It is quite likely that if you take any one region (as you did – western Pacific) you may find warmer (or in some places) colder temperatures. Their existence does not obviate my observation regarding the global trend.

      Miller is not making an inference about Arctic vegetation. He is making an observation. The fact that there may have been vegetation on Beringia, now drowned by the Bering Sea, during the Last Glacial Maximum, is not relevant to what Miller was finding in the Canadian Arctic around Baffin Island recently, not least because Beringia was on the margin of the Pacific, where conditions (e.g. ocean currents, winds) were different from those of the high Canadian Arctic. Miller’s finding tells is that there was vegetation rather than ice growing where now we find ice caps. Those ice caps then grew due to the development of the neoglacial, as temperatures fell from the mid-Holocene Climatic Optimum, driven by falling insolation. Those ice caps are now melting away. And there is no doubt from Arctic records that there has been double the warming in the Arctic as there has across the globe in recent decades, as a function of polar amplification. Kilimanjaro is irrelevant, being in the tropics, under a completely different climatic regime. Let’s compare apples with apples, not with lemons.

      D-O events were indeed likely unrelated to CO2 forcing. They seem to result from natural binge-purge cycles within the ice sheet that may have been exacerbated by short term natural variability within the ocean-atmosphere system.

      As for the Antarctic, there is evidence that gradual cooling caused ice caps to form on Antarctic back in the Eocene, long before there was a gap between Antarctica and the surrounding land masses that would have been large enough to allow formation of an Antarctic Circumpolar Current. That gradual cooling is most likely related to the fall in CO2 from its peak 50 million years ago. Contrary to Mr Steeles’ opinion, polar cooling does require an agent. Antarctic arrived at the South Pole 100 million years ago, but did not develop a major ice sheet until around 34 million years ago. Why not? Because the high CO2 levels kept the globe warm.

      Why did the Arctic not develop an ice sheet at the same time? Because conditions there remained warm, most likely due to northward transport of warm surface water in a proto Gulf Stream. Arctic ice did not begin forming until after the closure of the Panamanian isthmus, which changed the regional oceanography and winds of the North Atlantic and North Pacific (well documented by Michael Sarnthein).

      Arctic warming in the 1930s was on quite a different pattern to what it is today. It occurred in different areas, and was not associated with the same amount of thinning as well as areal extent that we see today.

      Regional dynamics are indeed important. It is most likely the regional shift of winds towards the south in the Southern Ocean that has forced sea ice further north than it used to be. That regional southward shift can be attributed to global warming. Equally, one must not forget that regional upwelling predominates around the continent, bringing warm circumpolar deep water up onto the continental shelf where it gets under ice shelves and thins them, allowing the glaciers behind them to discharge faster into the sea. So while the sea ice may be growing (in winter) the continent is losing ice around its edges from ice shelves being warmed from beneath.

      • A C Osborn says:

        So while the sea ice may be growing (in winter) the continent is losing ice around its edges from ice shelves being warmed from beneath.

        Not losing in overall Ice according to this.

      • Jim Steele says:

        polar scientists says “And there is no doubt from Arctic records that there has been double the warming in the Arctic as there has across the globe in recent decades, as a function of polar amplification. ”

        But polar amplification is highly debatable, As Rigor 2002, 2004 pointed out a change in the wind direction due to the Arctic Oscillation remove thick multi-year ice which allowed greater ventilation of subsurface heat that is stored in the Arctic. The consensus agrees with Rigor’s determination.

        In contrast adherents of CO2-driven change argue the warming in the Arctic is due to reduced albedo and a greater absorption of solar energy. However the most recent estimates of Arctic Ocean heat content by MIT/Harvard oceanographers suggests the upper 700 meters of the Arctic Oceans has lost heat since the 1990s (Heimbach and Wunsch 2014). Their calculations support the notion that Arctic air warming is due to ventilation of heat, not heat accumulation.

        Increased Arctic air temperatures is more likely evidence of a global loss of heat via subsurface ventilation and not evidence of heat accumulation via CO2’s back scattering of infrared,

      • Jim Steele says:

        polarscientist argues “polar cooling does require an agent” but such an empty assertion must be substantiated. ”

        No one, scientist or layperson, will argue that the polar regions do not ventilate more heat than is absorbed. So please polarscientist, justify your argument. The physics clearly suggest any reduction in poleward heat transport will result cooling. Changes in CO2 or another radiative forcing need not be invoked.

      • Jim Steele says:

        polarscientist argues “Antarctic arrived at the South Pole 100 million years ago, but did not develop a major ice sheet until around 34 million years ago. Why not? Because the high CO2 levels kept the globe warm.”

        But that is merely an empty assertion that does not refute changes in heat transport as the major climate driver.

        Modelling studies suggest extremely high CO2 concentrations to maintain the Cretaceous warmth, and those concentrations are not supported by any proxy evidence.

        Furthermore what would cause a drastic drop in CO2 concentrations that allowed the formation of the Antarctic ice caps? The erosion hypothesis has been refuted on several fronts.

        polar scientist argues, “Why did the Arctic not develop an ice sheet at the same time? Because conditions there remained warm, most likely due to northward transport of warm surface water in a proto Gulf Stream. ”

        If a reduced CO2 global blanket allowed Antarctic ice caps to form, but did not allow Arctic glaciers to form for another 30 million years, what is CO2’s role?

        Opportunistically evoking poleward heat transport for the Arctic while denying changes in heat transport to the Antarctic as the driving force defies scientific integrity.

  16. donb says:

    Dr. Summerhayes correctly points out the influence of changing orbital parameters on insolation in INITIATING glacial cycles. However, I think he then ignores the importance of that influence on other parameters effecting the far northern hemisphere (NH), other parameters which really produce the glacial cycles. This omission leads him to oversubscribe to the importance of CO2 changes from ocean degassing in the whole process. (I do not claim that CO2 is not a factor, only that it is a lesser factor.)

    Insolation decreases in the NH are calculated for 65N latitude, and concurrent insolation increases occur in the southern hemisphere (SH). Thus, orbital cycles alone cannot cool the whole Earth. What they do is significantly cool the NH and act as a “COLD TRIGGER” for glacier formation there. This initial cooling via a NH insolation decrease permits winter snow to survive summer melting in the far NH, accumulate over time, and buildup glacial ice. This NH ice then decreases NH albedo and produces some global cooling. However my calculations indicate that, although this higher ice albedo could produce significant global cooling during the last glaciation, the extent and latitude of the ice cannot explain the entire global cooling observed in the data. Some other factor(s) had to be involved.
    I suggest one of those important factors was induced changes in the magnitude and northern penetration of the Atlantic Arctic ocean current (AMO), which today brings considerable heat into the Arctic Ocean. Less heat from the tropics introduced by ocean current, the colder the far NH would get, and the faster glaciers would form. Further, once considerable glacial ice formed, sea level would drop and the Atlantic ocean entry into the Arctic would grow smaller, amplifying the effect. (Most of the Atlantic between Norway and Canada at ~70N latitude is relatively shallow and was exposed at glacial max.) Also, as more former ocean bed was exposed, the albedo of the land (including plant cover) would change. Changes in global cloud cover also may have occurred. We know from ice core data that GL grew much colder. I further suggest such “secondary” drivers of glaciation help explain why ice core data indicate NH temperature often changed considerably over relatively short time scales during the long temperature decrease of the last glaciation, changes that appear correlated with the ~40 kyr orbital cycles but are not explained by the smoothly varying insolation produce by the ~21, ~40, and ~100 kyr orbital cycles. Changes in Atlantic currents bringing heat into the far NH could have been much faster and perhaps rather erratic.
    I suggest that the ocean current and ocean heat play an important role, not only in producing glacial cycles, but possibly also in producing more recent apparent global temperature changes.
    Comments welcome.

    • Peter Lang says:


      I further suggest such “secondary” drivers of glaciation help explain why ice core data indicate NH temperature often changed considerably over relatively short time scales during the long temperature decrease of the last glaciation, changes that appear correlated with the ~40 kyr orbital cycles but are not explained by the smoothly varying insolation produce by the ~21, ~40, and ~100 kyr orbital cycles. Changes in Atlantic currents bringing heat into the far NH could have been much faster and perhaps rather erratic.

      Can you explain what caused the rapid warmings in the North Atlantic regions 14,500 and 11,500 years ago? Coxon and McCarron [1],Figure 15:21 show that the climate warmed from near glacial to near current temperatures in 7 years 14,500 and in 9 years 11,500 years ago, and cooled rapidly in 25 years 12,700 years ago.

      Figure 15.21 The stable isotope record (∂18O) from the GRIP ice core (histogram) compared to the record of N.pachyderma a planktonic foraminiferan whose presence indicates cold sea temperatures) from ocean sediments (dotted line). High concentrations of IRD from the Troll 8903 core are marked with arrows. After Haflidason et al. (1995). The transition times for critical lengths of the core were calculated from the sediment accumulation rates by the authors and these gave the following results: Transition A: 9 years; Transition B: 25 years; and Transition C: 7 years. Such rapid transitions have been corroborated from the recent NGRIP ice core data

      BTW, other figures and text indicate the life thrived during the warming periods.

      [1] Coxon, P. and McCarron, S.G. (2009) Cenozoic: Tertiary and Quaternary (until 11,700 years before 2000). In: Geology of Ireland (2nd ed.)

      • donb says:

        Peter, I agree these other factors are what drove short-term temperature changes, as I tried to imply.
        The warming episodes you refer to may have been caused by pulses of dammed (ice dams such as on Idaho’s Clark Fork River to produce Lake Missoula) glacial melt-water in Canada (McKenzie River?) and elsewhere being suddenly released, thereby changing the nature of Arctic Ocean currents, as has been previously suggested. Also when a glacial mass over a mile thick located over northern Canada significantly shrinks in size, Arctic atmospheric circulation would likely be altered.

      • Javier says:


        The rapid warmings in the North Atlantic regions 14,500 and 11,500 years ago are explained by several authors as constituting Dansgaard-Oeschger events that are even numbered as events number 0 and 1 in Rahmstorf, S. 2003. Timing of abrupt climate change: A precise clock. Geophys. Res. Lett. 30 1510-1514.

        So whether right or not, an explanation for those abrupt events does exist in the literature.

      • polarscientist says:

        The latter part of overall warming out of the Last Glacial Maximum was interrupted by two cold periods. The first at around 14,000 years was Heinrich Event 1, and the second was the Younger Dryas Event at around 12,000 years. Heinrich Events were responses to surges in the Canadian ice sheet. These were in effect extreme examples of the so-called Bond events – cold outbreaks in the North Atlantic, with a cyclicity of around 1450 years reflecting periodicity in North Atlantic circulation that might or might not have a solar trigger. The origin of the Younger Dryas is thought to be the outbreak of a formerly ice-dammed large glacial lake in North America that made its way to the Arctic down the valley of the Mackenzie River and formed a freshwater lid over it and the adjacent North Atlantic, which prevented warm water from the south from warming the Arctic climate. These events did not have anything to do with CO2 as a driver.

        • Peter Lang says:

          polar scientist,

          Thank you for your reply. I know about the Heinrich Events. However your reply does not address my question about the abrupt warming events in Ireland, Iceland and Greenland that raised temperatures from near ice age to near current temperatures in 9 years and 7 years.

          Do you have an explanation fore these abrupt warming events at 14,600 and 11,600 years ago?

          • polarscientist says:

            The warming out of the Last Glacial Maximum towards the Holocene was interrupted by the cold events I mentioned (Younger Dryas and Heinrich Event). The recoveries from these cold events were the rapid warmings seen in Ireland and elsewhere. If we take the Younger Dryas, for example, it represents a time when the North Atlantic thermohaline conveyor bringing heat north was switched off by the cold fresh water lid imposed by the outbreak of Lake Agassiz. Climate was locked in to a new cold state until that freshwater had dissipated, allowing a rapid restart to the conveyor at 11,700 years BP. The earlier cooling, the Heinrich Event, caused by a collapse of the Canadian ice sheet, was equally followed by a rapid return to the ongoing warming trend. In other words if we see the warming as the orbitally driven norm, then that norm was interrupted by two cold events from which recovery was rapid once their effects had dissipated. I hope that answers your question.

          • Peter Lang says:


            Colin thank you for your explanation for the recovery. Can you provide a link to a concise succinct and authoritative explanation of those abrupt warming events?

            However, if true it suggests that the climate would be much more stable without ice sheets at either planet – i.e. the common state fro Earth for at least the past 500 million years. Pu this together with the fact life thrives in warmer climates, ()more food when warmer) and this is another reason why we should not fear warming but certainly should do all we can to avoid cooling,

  17. donb says:

    In my comments above about what drove glaciation, I don’t mean to imply that CO2 uptake by the oceans did not occur. It must have, and It likely contributed to the cooling. (During de-glaciation, CO2 degassing would also have augmented the warming.) However, CO2 was not the major drivers of the process. To assume that CO2 was the main driver would imply CO2 temperature sensitivity greater than even extreme climate models predict.

    As Dr. Summerhayes commented, earlier, some ice core data have been interpreted to mean that warming occurred long before CO2 was released. But later data and interpretations have reduced that time difference. The problem is that CO2 does diffuse from the snow and firn until solid ice forms, and the time required is proportional to the snowfall accumulation rate, as it is the weight of the overbearing snow that helps form ice. Some recent data calculated temperature from isotopic determinations of argon and nitrogen trapped in the ice bubbles along with the CO2. Although with some uncertainty, these types of data yield CO2 levels and temperature at the same point in time.

  18. Javier says:

    Dr. Summerhayes presents in a narrative form the CO2 hypothesis of climate change as if it was already so demonstrated and supported by evidence as to be foolish to think otherwise.

    The CO2 hypothesis, as Dr. Summerhayes has shown, was built from late 19th century to the first half of 20th century, but only became dominant after 1975 when climate change started to agree with it. As any good hypothesis it has to explain all past evidence, so the 1945-1975 cooling that did not fit the hypothesis was explained in terms of human produced aerosols.

    The CO2 hypothesis relies heavily on some crucial assumptions that are not known to be true and that obviously are not part of Dr. Summerhayes narrative. As long as these assumptions are not worked out by science the CO2 hypothesis stands on shaky ground and the correct scientific position is to remain skeptic.
    – The warming is produced by extra CO2 molecules in the atmosphere as both heat and radiation and the CO2 hypothesis assumes that enough radiation ends up in the surface of the Earth to produce all the warming. This has never been measured, only calculated. So the hypothesis assumes the CO2 warming makes it whole to the surface. If the warming has other source, for example less clouds, we would not know.
    – The warming is enhanced by poorly known positive feedback effects. Since CO2 warming is not enough to produce the observed warming these positive feedbacks are crucial to the hypothesis. However scientists know that highly stable systems, like the Earth’s climate, that remains within limits compatible with life unlike the rest of the planets, are characterized by negative feedbacks.

    These and other assumptions that remain unproven after 50 years are summarized in the Equilibrium Climate Sensitivity (ECS) and Transient Climate Response (TCR). The scientists have not been able to constrain the value of the ECS after 35 years of trying. This means without doubt that we do not understand the climate well enough and we do not know how much warming the CO2 produces, which leaves Dr. Summerhayes narrative as a nice story to convince children and people without climate knowledge that we understand climate a lot better than we actually do and that they should not trust competing storytellers.

    The CO2 hypothesis has failed so far to falsify the null hypothesis, that a significant part of the warming is of natural origin. Hypotheses that do not falsify the null hypothesis are usually not even considered hypothesis but assumptions or scenarios. The CO2 hypothesis has failed every prediction that has produced, like the presence of the hotspot (higher tropospheric warming above the tropics), and the continuation of the warming rate in the absence of changes in anthropogenic, solar or volcanic forcings, that produced the failed prediction of +0.2°C/decade, between others. Hypotheses that fail to produce accurate predictions and that explain every change with post hoc arguments, like the hiatus, become unfalsifiable. Unfalsifiable hypotheses stop belonging to the realm of science to enter the realm of beliefs.

    Since Dr. Summerhayes is correct in his summary that CO2 does change temperature, and that temperature does change CO2, it is very difficult to work out their respective roles in paleoclimate history without knowing which one dominates. What if CO2 changes temperature a little, but temperature changes CO2 levels significantly? Then CO2 would be more of a product that a driver. The confidence of Dr. Summerhayes that he has got it right is unwarranted by present knowledge.

    Dr. Summerhayes final argument is that if we don’t know what is responsible for where we are now, then it must be our emissions. This is an unscientific argument as I have ever heard one. He conveniently forgets that present global warming started 350 years ago, and that sea level rise and glacier retreat started 350 years ago, and our emissions cannot be responsible for that.

    In his tale of paleoclimatology Dr. Summerhayes conveniently forgets to mention any bone of contention. For example post-industrial increase in CO2 is already bigger both in amount and proportion to the increase of CO2 produced during the last glacial termination. Even accounting for known changes in solar irradiation from orbital changes, the role of CO2 during glacial termination and during our much more modest present warming is not consistent. Either glacial termination CO2 was a lot more potent warming agent than present CO2, or its role at glacial termination was really minor and most of the warming was done by Sun radiation’s changing angle of incidence.

    Another bone of contention is that the behavior of the CO2 during the Holocene is not consistent with the hypothesis, as in the last 6000 years temperatures have been dropping, yet CO2 has been increasing. Scientists think that they know why CO2 has been on the rise, either naturally (consensus hypothesis) or of human origin (the much contested Ruddiman hypothesis), but what no scientist can explain is why temperatures were dropping when the CO2 hypothesis calls for an increase due to increased CO2. This is called “the Holocene temperature conundrum,” (Liu et al., 2014) and climate models adjusted to reproduce present conditions produce warming instead of cooling for those 6000 years.

    These two significant shortcomings of the CO2 hypothesis point to an overestimation of the CO2 role and probably an underestimation of the Sun role in climate variability by the CO2 hypothesis.

    Finally I don’t know if Dr. Summerhayes ignores or conveniently forgets to mention a more detailed Holocene climate history writing only about the recent MWP. The Holocene is filled with cooling periods followed by warming recoveries, some of which are very significative. Many scientists, starting with J. Bray in 1968 and continuing with S. O’Brien in 1995 and P. Mayewski in 2004, have taken notice of a clear ~2500 years climatic periodicity that produces very profound coolings at its minima, that they assign to solar variability. The LIA is just the last of these coolings that belong to a minimum in the ~2500 year oscillation.

    Previous minima in this periodicity are well known cold periods that profoundly affected both temperature proxies and human history. For example the 2.8 ky BP (2,800 years before present) event took place at the time of the Late Bronze collapse and coincided with the Ancient Greek Dark Ages, and the Third Intermediate Period in Egypt, the worst time in human history.

    The 5.2 ky BP event is another cooling event that is reflected all over the world (Thompson et al., 2006), like South-Cascade Glacier rooted tree-trunk (Washington State); remains and artifacts in the Little Salt Spring (Florida); Quelccaya Glacier ice-buried wetland plant Distichia muscoides (Juncaceae), dated at 5,138 ± 45 yr B.P.; bog pollen records of rapid and drastic vegetation changes in Isla Santa Inés (Chile); dendrochronological records from Irish and Lancashire oaks with some of their most narrow rings during the 3,195 B.C. decade; Ötzi, the ice-man from South-Tyrol; Soreq Cave (Israel) speleothem; Mauritanian coast core 658C; Kilimanjaro ice-core record. The 5.2 ky BP event marks the abrupt onset of a cooling period that culminated with the LIA and that has been termed Neoglacial.

    The 8.2 ky BP event constitutes the largest climatic cooling of the Holocene, and according to Rohling and Pälike (2005) responds to to the temporal coincidence of the three Sahelian solar grand minima with the lakes Agassiz and Ojibway outburst.

    In every case the warming recovery from these four large cooling events took between 200 and 400 years of warming. Present global warming after LIA might be more intense, but given that LIA constituted a more intense cooling, it is not clear how much warming can be attributed to the increase in anthropogenic GHGs.


    This figure (I hope it works) shows the four major coolings during the Holocene according to the combination of proxies by Marcott et al., 2013 but with original published dates and averaged by differencing to prevent excessive effect from proxies ending before the analysis. It has also been rescaled in temperatures to match published research on the Holocene Climate Optimum and Little Ice Age temperatures. It shows that present global warming is in part due to a natural warming and that is the reason it started 350 years ago. Once the natural warming ends we will know for sure how much warming the CO2 is producing, and let’s just hope it is enough to prevent a multicentury cooling trend to take hold, because that is what should be happening starting sometime during the present century according to climate history. The CO2 is up for its biggest challenge during the next decades. I do not think it will survive in the form so surely expressed by Dr. Summerhayes.

    Bray, J.R. 1968. Glaciation and Solar Activity since the Fifth Century BC and the Solar Cycle. Nature 220, 672-674.
    Liu, Z. et al. 2014. The Holocene temperature conundrum. PNAS 111, E3501-E3505.
    Marcott, S.A., et al. 2013. A Reconstruction of Regional and Global Temperature for the Past 11,300 Years. Science Vol. 339, pp. 1198-1201.
    Mayewski, P.A. et al. 2004. Holocene climate variability. Quaternary Research Vol. 62 pp. 243–255.
    O’Brien, S.R. et al. 1995. Complexity of Holocene Climate as Reconstructed from a Greenland Ice Core. Science 270 1962-1964.
    Rohling, E.J. & Pälike, H. 2005. Centennial-scale climate cooling with a sudden cold event around 8,200 years ago. Nature, 434 975-979.
    Thompson, L.G. et al. 2006. Abrupt tropical climate change: Past and present. PNAS 103, 10536–10543.

    • polarscientist says:

      Well, I guess I should not be too surprised to get at least one insulting response, despite my efforts to be matter of fact and to avoid casting slurs on other respondents.

      Mr Javier assumes a little too much, methinks. I have made it plain that evidence for climate sensitivity can be extracted from the geological record of the past 65 million years – note – not from climate models or assumptions. A variety of proxies can be used to determine the likely past levels of CO2. And calculations based on geochemical models of how the carbon cycle works, not on climate models, can be used to estimate past CO2 levels. The convergence between proxy data and geochemical models is quite convincing, though not well known. See papers by Royer, Berner, and PALEOSENS in my reference list. In my view that not very well known but independent geological data confirms that climatological modellers are probably on the right track. Just because you don’t like that argument doesn’t make it a children’s tale. In my view, the null hypothesis that all recent climate change is natural is false because it cannot be demonstrated to be true, whereas providing an additional element to the equation (human emissions of CO2) enables one to match recent change within eminently reasonable limits.

      It is the case that while temperatures have been dropping there has been a very slight increase in CO2 (cf Ruddiman et al, 2015). However, the question should be what is the expected effect of the orbital driver for cooling versus the expected effect of warming from the slight CO2 increase. The answer I am sure is that the cooling effect driven by the Earth’s orbit is in this case the winner.

      My piece at the start of the discussion does talk about the effects of the sun and how it has modulated the effects of the orbitally driven cooling (e.g. with reference to the work of Steinhilber). In a short piece like mine there was no room to cover every single climate driver, so I did not mention the so-called 2300-year long Hallstatt cycle, which caused significant cooling at around 500, 2500, 5500 and 8200 years ago. The cool event at 750BC was one of these (Lamb’s early Iron Age cold epoch). Much work on this and other cold cycles (which were also wet) in Europe has been done by Magny and colleagues (e.g. see Magny, 1993, Quaternary Research 40). This cycle may possible have a solar driver, as did the Medieval Warm Period. My point is that the solar drivers were not large enough globally to overwhelm the driving cooling effects of orbital insolation.

      Sea level rise did not start 350 years ago. Ocean volumes did not start to increase until about 1800 (Jevrejeva et al 2008, Geophysical Research Letters 35). Warming did not start 350 years ago. The PAGES 2k group found that it began at of shortly after 1800, much like the rise in sea level.

      Mr Javier asks why the present rise in CO2 has not led to as much warming as we saw coming out of the last glaciation? But that was when orbital insolation (and warming) was on the rise. Now it is on the decline.

      The data of Steinhilber et al (see my references) show that the solar insolaiton following the latest cool episode of the Little Ice Age had recovered to its warm peak by about 1950. The sunspot data of Clette et al show that the Sun’s energy has been in decline since 1990. Yet most of the years since then have been the warmest in several hundred years. We cannot explain that by calling on natural warming from a Sun who’s activity is declining.

      Finally, a comment on falsification. Geological arguments are not readily falsifiable in the sense of Popper (who was thinking primarily about experimental science), not least because in dealing with understanding of a past world and its climate we are unable to run experiments. In addition, we are dealing with an open system, not a closed laboratory system of the kind Popper envisaged. Contrary to what some people think, Popper does not demand that every scientific statement be tested, merely that it must be capable of being tested. Nor does he say that if any part of a theory or hypothesis (like global warming) is disproved then the whole theory must collapse like a house of cards. What he actually wrote in “The Logic of Scientific Discovery” was that “no conclusive disproof of a theory can ever be produced; for it is always possible to say that the experimental results are not reliable, or that the discrepancies which are asserted to exist between the experimental results and the theory are only apparent and that they will disappear with the advance of our understanding…… If you insist on strict proof (or strict disproof) in the empirical sciences, you will never benefit from experience, and never learn how wrong you are.” So, only if something is blatantly daft or evidently subjective rather than objective will scientists reject it, rather than seeking instead to fill or repair gaps in their knowledge. In the case of the global warming hypothesis some of what appeared in the past to be ‘show stoppers’ turned out to be correctable – for example where there was a discrepancy between satellite and surface temperature data careful inspection found that the satellite’s position had drifted, enabling the satellite data to be subsequently corrected – confirming the wisdom of Popper’s advice. Incidentally the footnote to that Popper quote states that “I have been consistently misinterpreted as upholding a criterion …. based upon a doctrine of ‘complete’ or ‘conclusive’ falsifiability”. Clearly, one should beware of misinterpreting Popper.

      • Euan Mearns says:

        Dear Colin, I accept that part of Dr Javier’s response crossed the line. Thank you for shrugging that off.

        But his comment at 1571 words must have taken 2 to 3 hours to write and is laden with information that is referenced. Some of that information I know about and agree with, much of it is new to me and I will try to find time to cross reference many historic claims.

        Your reply here is robust on the philosophy of science, but I’m not sure you answer the many technical points raised by Javier. As this debate has gone on I find myself becoming more entrenched in my views that I hope are based on the data before me rather than on the opinion of others.

        But ironically at the same time I believe our fundamental positions are not that far apart, so this is a little confusing. We certainly appear to have different ways of looking at data and drawing conclusions from it.

        A variety of proxies can be used to determine the likely past levels of CO2. And calculations based on geochemical models of how the carbon cycle works, not on climate models, can be used to estimate past CO2 levels. The convergence between proxy data and geochemical models is quite convincing, though not well known.

        And still not known to the readers of this blog. You are welcome to submit a second article providing the details of this geological evidence. From what I can surmise, observations are made from geological records on changes in CO2 and T from which estimates of climate sensitivity are derived?

        I will posit that it is almost impossible to use proxies to achieve this for the last 2000 years. And so equally impossible for geologic time. One may observe geologic changes in CO2 and temperature (with large uncertainty). But how do you overcome the uncertainty of deciding if CO2 causes T to change or vv. And then you need to include land surface, photosynthesis, atmospheric and ocean circulation, orbit and Sun – for the whole planet for an instant in time. We can’t calculate this today so how is it done in the past? Please send me copies of the 2 or 3 most important seminal papers / reports.

        Most of what I write about is based upon my own first order observations from data.

        Best E

      • Javier says:

        I am sorry that you took it personally, Dr. Summerhayes. I was attacking your arguments, and the way you presented them, not you. I am sorry you felt insulted.

        But your response again misses the mark. The CO2 hypothesis is very clearly established by its guardian body, the IPCC, as anthropogenic forcings being fully responsible for all observed warming between 1951 and 2010. I encourage you to look at figure SPM3, pg. 6 of the Summary for Policymakers
        “The best estimate of the human-induced contribution to warming is similar to the observed warming over this period.”

        The IPCC believes that Greenhouse gases (green bar) have contributed more than 100% to the observed warming (black bar) between 1951 and 2010. They believe that natural variability contributed zero.

        So you are mistaken about the null hypothesis. The null hypothesis is the opposite of the hypothesis and it is not that all warming is natural, that would be absurd as we know that CO2 does produce some warming. The null hypothesis is that an important part of the observed warming between 1951 and 2010 is due to natural causes. Obviously the null hypothesis has not been falsified to any significant degree, and thus the CO2 hypothesis remains unproven. It is clear that if 50% of the warming was due to natural causes then we could forget about any dangerous effect from our emissions and no action would be required.

        You also say:
        “In my view, the null hypothesis … is false because it cannot be demonstrated to be true.”
        Here you are inverting the burden of proof. The null hypothesis in good scientific practice is assumed to be true until falsified. To be acceptable as part of a theory, any hypothesis has to pass three very stringent requirements:
        – It has to explain all available evidence.
        – It has to demonstrate that the null hypothesis is >95% unlikely.
        – It has to predict future events or discoveries.
        The CO2 hypothesis in its present form has failed all three. It is so far a nice explanation likely to be wrong.

        You also say about the Holocene temperature conundrum:
        “It is the case that while temperatures have been dropping there has been a very slight increase in CO2.”
        What you call a very slight increase in CO2 is about a third of the increase that took place at glacial termination:
        – Glacial CO2 termination values according to Shakun et al. 2012:
        190-265 ppm. Increase +75 ppm
        – Holocene CO2 changes between 6800 and 600 yr BP according to Monnin et al. 2004:
        258-283 ppm. Increase +25 ppm
        In the first case temperatures raised about 5°C, in the second they dropped about 1°C. No wonder that climate models choke on the data and are unable to reproduce temperature changes.

        And yes, I agree with you that solar forcing is the winner. It is clearly much stronger than CO2 forcing and the models are probably incorrectly accounting for this.

        Regarding the start of the global warming and global sea level rise, most reconstructions put the coldest period of the Little Ice Age within the 17th century, that would constitute the bottom of the LIA. For example: Moberg et al., 2005; Loehle & McCulloch, 2008; Wanner et al., 2008; Ljungqvist, 2010; Christiansen & Ljungqvist, 2011; Marcott et al., 2013.
        Also the oldest temperature registry, Central England Temperature, recorded since 1659 shows its coolest period between 1659 and 1700.

        So the warming clearly started between 1600 and 1700.

        Regarding sea levels we probably have the same picture as they seem to follow temperatures. At least this is the opinion expressed in:
        Grinsted et al. (2009), Reconstructing sea level from paleo and projected temperatures 200 to 2100AD. Clim. Dyn. (, of which Svetlana Jevrejeva is the last author.
        The figure of their reconstruction shows a lower minimum sea level for the late 17th to early 18th century:

        So yes, we are dealing with a three century plus warming trend of which our CO2 emissions can only be responsible for the last 65 years, less than 1/5 of the time. Did the natural warming conveniently stop when our emissions started? That is what the IPCC proposes but does not prove.

        Finally we can go to the incongruity that the Eemian interglacial 125,000 years ago had peak CO2 levels at 287 ppm according to Vostok ice core measurements, yet it was a lot warmer than present interglacial where we have already 400 ppm CO2, judging by the 6 m of sea level above current levels and by temperature proxies. We know Greenland almost completely melted because ice cores from there rarely go past the Eemian. It is evident that CO2 is not the main driver of temperatures in this planet. Insolation levels and distribution are the main temperature driver, and CO2 role is probably overstated.

        Given the high political stakes, and the level of compromise of the most influential climatologists with the CO2 hypothesis, it is probably going to take decades to finally have enough data and knowledge to determine the correct role of CO2 in climate change (the climate sensitivity). The current trend is for that role to be reduced as ECS estimates continue to go down. In the end we will learn what we have always known. The only dangerous climate change is the one that produces cooling.

        • polarscientist says:

          As I pointed out in my post there are times in the geological past when CO2 was a significant driver of climate change, ultimately driven itself by plate tectonic processes involving the changing balance between volcanism driven by sea floor spreading rates, and chemical weathering during periods of rising mountains.

          Equally, as I also pointed out in my post, there are times when insolation was much more important and temperature leads CO2. That is particularly true of Pleistocene times – the Ice Age. Even so, the warmings in temperature caused by orbital insolation during the ice Age led to the emission of CO2 from the ocean that then fed back to enhance ongoing warming. That’s what got us out of glacials and into interglacials. I don’t think anyone is seriously arguing against either of these main points.

          As to what happened to climate during the Holocene, we have a growing array of information indicating that at least in the northern hemisphere the main insolation driver first melted the northern ice sheets (a process that kept the climate cool), then led to the mid Holocene climatic optimum, which was followed by cooling (e.g. papers by Moburg, and by Vinther). The rise in CO2 during this cooling period did not warm the climate, but quite possibly prevented the cooling from being more than it would have been had the CO2 not been there (cf Ruddiman et al).

          The peak cold of the Little Ice Age was in the Maunder Minimum around 1690, but there were also cold periods caused by solar minima in 1830 (Dalton) and 1890 (Gleissberg). The sea level evidence from Church’s 2010 book strongly suggests that the rise in sea level driven by warming and ice melt did not begin until around 1900. Clearly the period from 1900 to 1950 involved increasing solar input from the peak low of the Gleissberg Minimum. The key question is what happened after 1950, as CO2 really took off, and as solar output flattened off and started to decline? My interpretation is that CO2 played an increasing role in warming the climate, as the Sun declined. The actual relationship between CO2 and temperature was then modulated by natural fluctuations like El Ninos and the PDO as well as by aerosol outputs, giving us what we have now. The question for the future is – where next. That will depend on the balance between solar output, CO2, aerosols, and natural oscillations (El Ninos and the PDO).

  19. Bartemis says:

    The actual correlation is between the rate of change of CO2 and temperature anomaly.

  20. Dr. Summerhayes didn’t respond to my earlier comment pointing out some of the obvious difficulties with accepting d18O as a temperature proxy in the GISP2 core, but undeterred I will try again.

    Here’s an XY plot of CO2 versus temperature (deuterium) in the Vostok record. The R squared value for the trend line is 0.8, implying that changes in CO2 explain 80% of the changes in temperature ….

    ….. with the corollary implication being that Milankovitch cycles, changes in albedo, changes in atmospheric and oceanic circulation patterns,changes in vegetation cover, ice sheet dynamics and all the other changes that accompany Ice Ages and interglacials explain the remaining 20%.

    Does anyone else have trouble with the concept that temperature changes during Ice Ages and interglacials are controlled almost entirely by variations of 0.01% in the chemical composition of the Earth’s atmosphere and essentially nothing else?

    • Euan Mearns says:

      Roger, one of the more important points not yet made is that at a termination, CO2 is at a minimum and albedo at a maximum. What happens next? The N hemisphere ice sheets melt and temperatures rise several degrees. CO2 rises sharply to inter-glacial high. And what happens next? The whole thing freezes up again and CO2 follows the way down several thousand years later.

      It is abundantly clear that CO2 has no control over the terminations and inception phases and that like methane it is simply following the leader. The leader is most likely orbit and insolation.

      • polarscientist says:

        And I already explained in one of my posts why CO2 does not follow temperature closely during the cooling after the termination.

    • Euan Mearns says:

      Roger, I’ve worked it out. But can YOU tell us what climate sensitivity to CO2 this graph implies.

      • Roger Andrews says:

        Climate sensitivity is defined as the increase in the Earth’s surface temperature caused by a doubling of atmospheric CO2. Measure it anywhere along the trend line and you get about 18C. This is of course an estimate specific to Vostok. I don’t know what it might mean in terms of a “global” CS, if anything.

        • A C Osborn says:

          Which is patently not the case, otherwise we would already be seeing around 7 degrees C rise in temperature since 1770.
          It really does make you wonder about the validity of past Temps and CO2 “Estimations” doesn’t it.

    • polarscientist says:

      My understanding is that Milankovitch cycles control heating, which controls CO2, which provides a feedback to temperature. Hence, during the Ice Age (as we see in ice cores) CO2 was a supplementary driver, not the main driven. But because it is driven out of the ocean by heating, it must follow temperature closely, which it does, as your graph shows.

  21. E.J. Mohr says:

    I’m with you Roger. The simplest explanation to me is that [CO2] is dependent on ocean temperature and this would explain most of the ice core data. It would also explain why [CO2] has been much higher in the past without a runaway greenhouse.

    What Dr. Summerhayes describes is the earth climate system with [CO2] as the temperature control.

    I once subscribed to that theory, but what had me lying awake at night was the problem of how, if [CO2] is a key driver, did the mostly warm Paleozoic and Mesozoic ever come to an end? I don’t buy the idea of rock weathering being a key sink for CO2, and so the end of the Palaeozoic and Mesozoic hot house climate(s) is not well explained.

    Nevertheless, and closer in time, is the question of how Ice Ages can be initiated and terminated if the orbital perturbations are not really that big and they aren’t really otherwise I’d expect they would show up in the distant geologic record. The fact that the ice cores show dT changing before d[Co2] makes everything fall into place for me since it shows that [CO2] cannot be a major player and is controlled by dT. The fact that the Holocene Climate Optimum, when orbital forcing was greater than today but [CO2} was lower, had tree lines far north of where they are today, and vegetation as indicated by palynology that was characteristic of warmer drier climate here in Southern British Columbia tells me that [CO2] cannot have the powers ascribed to it.

    Of much greater interest are the possible Bond Cycles that may show in the Holocene and the D-O and Heinrich cycles of the Ice Ages where amazing temperature changes occurred without any change in [CO2]. These are the things that now keep me awake since these types of changes need explanation.

    • E.J. Mohr:

      A dependence of CO2 on temperature is clearly the more plausible explanation.

      Note also that the gradient of the trend line indicates a climate sensitivity of about 18C.

    • polarscientist says:

      Dear Mr Mohr,

      I do indeed ascribe much of Earth’s history to control by CO2, but not all of it. Read my post carefully again and you will see that I say there are times when CO2 was in the driving seat and changing temperatures, but there were other times when temperature was in the driving seat and changing CO2.

      The Paleozoic was warm until the Carboniferous glaciation. The world then warmed into the Mesozoic, which was brought to an abrupt end by a meteorite impact. However the general cooling trend from peak warmth in the mid Cretaceous continued into mid Eocene times before formation of the Antarctic ice sheet. So the boundaries of Paleozoic and Mesozoic time are not defined by Earth’s temperature curves. We do have good explanations – see the three paleoclimate texts referred to at the beginning of my post.

      Orbital perturbations on Milankovitch frequencies do permeate the geological record. They are less visible before the Pleistocene because that’s when Earth became really cold, so those cycles became exaggerated.

      You have not read my post clearly or you would have picked up on t he fact that recent work (Parrenin et al) shows that careful re-examination of the data shows that CO2 does not follow temperature in ice cores, it moves in concert with it at terminations, as expected from basic physics (you warm water and CO2 emerges). So, insolation controls temperature, which controls CO2, which feeds back to temperature. CO2 is an assistant, not the main driver AT THESE TIMES.

      The tree line moved north in the mid Holocene because once the ice had gone there was a lot of orbital insolation (and CO2) about (though less CO2 than today). Insolation was the main driver. But in pre-ice age times, like the Cretaceous, CO2 was the main driver.

      There are good explanations for Bond Events and Heinrich Events and D-O Cycles. See the three paleoclimatology texts at the beginning of my post.

      • E.J. Mohr says:

        Dr. Summerhayes, with all due respect, I don’t think our positions are that far apart.

        I formerly thought [CO2] was a matter of concern, but since the effect is logarithmic I don’t see great harm in the present levels, nor do I worry about the increase, especially in light of the fact that it has been much higher in the distant past. I could be wrong, but I would expect that we should soon see evidence if [CO2] has a stronger effect than I think it does.

        I find myself wondering why the Eemian was warmer than now despite lower [CO2]. To me this indicates CO2 is a bit player on the climate stage, but not the lead actor.

        As another example, if we look back into the last Ice Age, when [CO2] was much lower than now, we have the conundrum of the interstadials where climate abruptly warmed, and of course Heinrich style abrupt cooling. The degree and suddenness of warming and cooling is extraordinary compared to the Holocene and takes place in what seems to be very low and constant [CO2].

        “Marine Isotope stage 5a) “Pronounced interstadial [85-80kyBP] return of cool mixed forest to parts of northern Europe..”

        Marine isotope stage 5b) 85-94kyBP “Northern Europe descends into taiga and tundra…”

        Marine isotope stage 5c) “Pronounced Interstadial [105-94kyBP] forests return to northern Europe.

        Marine isotope stage 5d) 107-117kyBP “Onset of glacial climate with northern Europe shifting from temperate forest to taiga…”

        This data is excerpted from Table 4.2 of Climate Change, A Multidisciplinary Approach, by William James Burroughs. To me this provides food for thought since the record is complicated to say the least and the D-O and H events all in a low CO2 world indicate, to me at least, that CO2 has a minor role.

        • polarscientist says:

          The higher warmth of the Eemian is attributed to its orbital insolation. As I have said many times, during the Ice Age orbital insolation drove warming, which drove CO2, which fed back to warming, but the main driver was insolation, not CO2.

          The various warmings and coolings within any one given Ice Age cold period, were likely driven by internal fluctuations within the ocean atmosphere system, leading to what is called the bipolar see-saw, where (i) warming in Antarctica rises, (ii) the heat is then transferred through the ocean to the northern hemisphere, which (iii) warms abruptly as Antarctica cools. The northern warming is followed by (iv) northern cooling, during which (v) the Southern Ocean starts warming again, etc etc. These warmings and coolings may possibly have had some solar component. In any case they did not much change the CO2, which was not in the driving seat. This helps to underscore my point that to understand the climate at any one time in the past you have to disaggregate the signal to tease our how much was due to each of several possible forcings.

  22. E.J. Mohr says:

    Roger I completely agree that CO2 is dependent on temperature – to me the geological record is very clear on this. Perhaps by mentioning ocean temperature I made this less clear since I was thinking of CO2 solubility and how it increases in colder water, but your graph and all other data that I am aware of shows clearly that CO2 is temperature dependant.

    Now as far as the 18C climate sensitivity, while that may hold true for Vostok, and your graph shows this clearly I don’t think we can extrapolate that to other locations, but more importantly if [CO2] is the dependent variable then we’d be putting the cart before the horse if we expected [CO2] to have that kind of effect on temperature. That is of course what the AGW crowd would have us believe:)

    Meanwhile, if Be-10 can give us solar magnetic field and activity data and if it can be teased out of precipitation data, then we may have an avenue to solar activity far into the past. I’d be very interested in seeing if Euan or you can shed more light on this.

    • donb says:

      To Roger, E.J., and Euan,
      That ice core data that attempts to more accurately correlate data on temperature and CO2 retention times (e.g. diffusion modeling of isotopic fractionation) places times of ICE formation and CO2 retention as quite similar, but still having an overall uncertainty of perhaps a few hundred years.
      However, most paleo-climatologists do not claim that increasing CO2 caused increasing temperature, but that other factors, likely orbital effects on insolation, was the prime driver. These climatologists DO maintain that once warming began, ocean-degassed CO2 augmented that warming. The glacial cycles are not good analogs for recent warming.

    • polarscientist says:

      Read Steinhilber et al – see my post for reference

  23. Judith Curry’s “testimony” is slanted to agree with her biases. It cannot be used as a neutral, unbiased description of anthropogenic climate change.

  24. Jonathan Madden says:

    Thank you Dr. Sumerhayes and all contributors for this fascinating discussion.

    Thinking back to a popular book I enjoyed thirty years ago, Ice, by Fred Hoyle, it speculates that meteorites alternate in something like a five to one Stony/Iron ratio, contributing to ice ages and warmings respectively. He concludes that a prolonged ice age is almost inevitable following a future chondritic meteorite impact, and that cold ocean water should be mass-circulated from depth to build up a thermal reservoir to resist the cooling effects of reflective dust!

    The K-Pg extinction around 65MYA event has been put down to one or both of the Chicxulub meteorite and the Deccan Traps, which were curiously quite close to each other in time. The extensive layer corresponding to the Gubbio Clay, which contains an anomalously high Iridium content, is associated with this meteorite and might therefore have been an Iron rich sideritic rather than a stony chondritic impact. Hoyle’s view is that dispersion of nano-Iron particles into the atmosphere would cause a warming event.

    I take it that large meteorites are not thought to act as climate switches, at least on a time scale beyond that of the complete settling of atmospheric dust, say a few tens of thousands of years. That a temporarily adjusted global temperature would revert to where it would have been some time later.

    Lastly I have had a quick look at low temperature records on Wikipaedia. Although measurements only go back a century or so, there are a reasonable number that are recent. Surprisingly Italy manages almost -50C, admittedly on top of a 10,000 ft mountain in the Dolomites, in 2013! I am just vaguely wondering if the Antarctic records that go below -80C suggest any deposition of solid CO2 snow? In any case warming the next summer would sublimate it away. But if there was a meteorite event that caused exceedingly low polar temperatures for an extended period perhaps CO2 could accumulate and thereby diffuse concentration away from the lower latitude atmosphere and extending global cooling.


    • polarscientist says:

      Since Fred Hoyle’s day there has been an explosion of knowledge about the Earth’s major biological extinctions. So far only one is definitively associated with a meteorite impact – at the K-T boundary. Even there we have the added complication that this was also the time when the Deccan Traps in India spilled thousands of square kilometres of lava onto a surface area of about one third the size of the subcontinent. Such eruptions would have been associated with the emission of various gases including CO2, nnd probably contributed to the demise of the dinosaurs. Most of the major biological extinctions in the geological record are related in time to these kinds of eruptions (see papers by Courtillot). Fortunately they do not occur often, and between them climate behaves much as I describe in my post.

  25. E.J. Mohr says:

    Another topic that comes to mind is the fact that the Miocene and Pliocene periods that predate the Pleistocene had similar [CO2] to today, but were much warmer. The Pliocene is thought to have similar Milankovitch Forcing to today, so the warmth is sometimes referred to as the Pliocene Paradox. The closing of the Panama seaway is invoked as a possible explanation for what seems like anomalous warmth compared to the Pleistocene. Once we get to the Pleistocene we have further mysteries.

    Why, during the Pleistocene, did the ice ages change from a 41y cycle to a 100 ky cycle? This is even more baffling in light of the fact that the 100 ky Milankovitch forcing is the weaker of the cycles. Another matter of interest is how long the ground was buried under ice during the last few 100,000 year long ice ages. Here in western Canada the ice may have advanced in pulses, possible during Heinrich Events and the ground may not have been entombed for the whole time.

    Then there is the matter of climate south of the known ice front. A very interesting bit of data came from Oregon just last fall that I recommend anyone who is interested read. The link is right here:

    • Javier says:


      During the entire period that you mention the planet was cooling at a rate of 1°C/million years, as determined by Uk’37 alkenones and d18O isotope (see figure 1 in Lawrence et al., 2006). The cause is unknown, but seems to be the cause of the Quaternary Ice Age.

      There is an hypothesis that says that the glacial-interglacial cycle is and has always been determined by the 41 Kyr obliquity cycle, not by the 65°N summer insolation. This hypothesis has no problem explaining the cycles of the Lower Pleistocene, and at the Mid Pleistocene Transition proposes that the planet finally got so cold that obliquity cycles were no longer capable of getting the planet out of glacial conditions and started to skip one (82 kyr) or two (123 kyr) obliquity cycles giving rise to an average of 100 kyr average distance. For example last interglacial took place 125 kyr ago, not 100.

      This hypothesis has been defended by authors like Peter Huybers and Zhonghui Liu, that for example has the following to say:

      However, our examination of the development of ∼100-kyr cycles favors an obliquity bundling mechanism to form late Pleistocene 100-kyr cycles.

      Huybers, P. 2007. Glacial variability over the last two million years: An extended depth-derived agemodel, continuous obliquity pacing, and the Pleistocene progression. Quat. Sci. Rev. 26 37-55.

      Huybers, P. and Wunsch, C. 2005. Obliquity pacing of the late Pleistocene glacial terminations. Nature 434 491-494.

      Lawrence, K.T., Liu, Z., and Herbert, T.D. 2006. Evolution of the Eastern Tropical Pacific Through Plio-Pleistocene Glaciation. Science 312 79-83.

      Liu, Z., Cleaveland, L. C. and Herbert, T. D. 2008. Early onset and origin of 100-kyr cycles in Pleistocene tropical SST records. Earth Planet. Sci. Lett. 265 703-715.

      • Euan Mearns says:

        Earlier this year I was invited to write an article on the disappearing Alpine glaciers for The Alpine Journal. My starting point was to explain that we are in an inter-glacial and that ice is supposed to melt in interglacials. I spent a long time looking at the LR04 stack (click to get a big picture) and concluded that the pattern was dominated by the 41,000 year cycle or multiples thereof. I wasn’t aware that this observation had already been made by others.

        You get different results if you count between the glacial troughs and the interglacial peaks. And another problem arises from the fact that glaciation is sometimes in phase with obliquity and sometimes in anti-phase. I conclude that there is a lot we still do not know even about the basics of how glaciations begin and end.

        I am also of the opinion that glaciation is always dynamic, never static. Hence the choice we have is melting ice OR glacier advance. Which is better for humanity?

        • Javier says:


          I also wrote an article about glacial cycles last fall and reached the same conclusion. Then I reviewed the literature and found that several people have already published defending an obliquity paced glacial cycle. I finally published the article on February in my blog.

          Huybers & Wunch 2005 (referenced above), has this figure where they have multiple runs of their model plotted and looks very much like your second figure:

          It predicts that with enough oscillations of the cycle we will eventually see a 164 Kyr glacial period.

          Meanwhile some researchers are predicting an end to glacial periods due to favorable 65°N summer insolation precession cycle and elevated CO2 levels for the next 50-100,000 years.

          I find it really surprising that almost the entire scientific community including almost all experts gets fixated on 65°N summer insolation when the evidence so clearly supports obliquity that even outsiders can immediately see it. I think it is the same problem with the CO2 hypothesis. It doesn’t speak well of the group thinking mentality from scientists. They get trapped inside a paradigm and simply reject any contradictory evidence no matter how strong. It requires either a big shake out or a long slow erosion of that paradigm to get them out, and then they will happily look for another group paradigm to get inside.

          According to my calculations and understanding of the Bray 2500 years cycle during the Holocene, I think the next glacial inception could take place as soon as 1500-2000 years from now. For the good of future humanity I hope I am wrong and the alarmists are right in that CO2 is really a very powerful warming agent with a really very long decay time.

          • polarscientist says:

            I would rather rely on the astronomically based calculations of Andre Berger, which keep us in Llittle Ice Age conditions, but not full glacial conditions, for at least the next 5000 years and probably 30-50,000 years into the future.

      • E.J. Mohr says:

        Javier and Euan thanks, you are both fountains of information. You might find the link I posted above to be of interest since it describes the climate of Oregon, an area that was far south of continental glaciation, 50,000 years ago. It’s a real surprise to find that the temperatures for that area are thought to be 18F colder than today. The idea that an open spruce alpine fir parkland would exist there is amazing, at least to me. It tells me that Ice Age climate was much different than expected even in areas far from the ice sheets.

    • clivebest says:

      “Modern-day erosion and landscape change is slow compared to what it was during cold, dry climate intervals when there were no Douglas firs around and the hills were covered by grassy meadows,”

      During the Pleistocene the climate cooled so much that life itself began to be threatened. The switch from 41k to 100k glacial cycles is because obliquity changes in insolation at the poles became no longer sufficient to melt back the ever larger polar ice sheets. Life is the thermostat that now regulates temperature and drags us out of an ice age.

      As oceans cool CO2 levels drop dangerously below 200 ppm and simultaneously precipitation also diminishes. Type3 photosynthesis starts to shut down and boreal forests die off across northern continents. Erosion and low snowfall covers the ice sheets in thick dust layers which finally breaks the ice-albedo negative feedback cycle. The next Northern maximum summer insolation is enough to break the cycle and rapidly melt back the ice sheets. An interglacial begins. CO2 levels rise with temperature, precipitation returns and life flourishes again.

      On the big scale of things it is low concentrations of CO2 that threaten life.

      • E.J. Mohr says:

        Clive I am glad you checked the article I linked upthread. I agree glacial climate is so cold and inhospitable to life that it’s hard to imagine. Where I reside in southern British Columbia at 51 degrees north you would have to move at least 5000 feet higher in elevation to get the Ice Age climate of Oregon at 44 degrees north. To me that is astounding to say the least.

        The fact that TSI is thought not to vary a great deal seems logical based on our measurements, but I can’t help but wonder if the sun has other modes. It would be very interesting if Euan is able to work the Be-10 data to give us an inkling of what may have happened back then. I know we can use palynology and other data to go back into the Holocene, but it would be great to have a better handle on the Ice Ages.

        Here in southern BC we know Holocene climate has slowly been cooling for the 1000’s of years. We also know that the Holocene Climate optimum was much warmer, at least in summer, than today. Forests grew where now there is alpine tundra, and lake sediments in southern BC show evidence of frequent forest fires. The forests of southern BC have in the last few 1000 years evolved in a way the shows species indicative of cooler wetter conditions. To me this says that we know so little, and nature is telling us something, if only we could decipher everything.

        • Euan Mearns says:

          The fact that TSI is thought not to vary a great deal seems logical based on our measurements, but I can’t help but wonder if the sun has other modes. It would be very interesting if Euan is able to work the Be-10 data to give us an inkling of what may have happened back then.

          Big post on 10Be at bottom. I too have wondered about different modes of The Sun. Its a big angry beast after all. Not sure my posting answers this, need to have a think about it. Uncertainty in snow deposition rate gets in the way of detailed scrutiny of 10Be.

    • polarscientist says:

      During the mid Miocene there was a warm event (Mid-Miocene Climatic Optimum) that was associated with CO2 levels of around 400-500 ppm. The warming coincided with the eruption of the Columbia River Plateau Basalts, but it would be fair to say that we do not fully understand the origins of this warming event. Various papers suggest that the event was a response to the development of tropical sources of warm ocean water, and that the subsequent cooling reflected continued growth of the Antarctic ice sheet. The closing of a deep water connection between the Pacific and Indian Oceans by t he northward movement of New Guinea may have played a role in these changes. The process of warming of Mid Miocene seas, possibly aided by orbital change plus movements in ocean currents, would have released CO2 to the atmosphere. However, there is not enough data to provide a definitive answer.

      There was a similar warm event in the Pliocene, also associated with similarly high levels of CO2. There the association with plate tectonics is clearer, as the warming followed deflection of a formerly east-west directed equatorial current towards the north and south in the Atlantic when the current’s path to the Pacific was blocked by the emergence of the Panamanian isthmus (cf Sarnthein et al). This led to warming of the Arctic, and emission of CO2 from warm surface water over a wider area of the globe than formerly, which one would expect to exacerbate warming. The tropics do not seem to have warmed. As in the Miocene there was also association between orbital change and the emission of CO2. Interestingly we note that the relatively small increase in CO2 was associated with quite a substantial warming, suggesting that the Climate Sensitivity to a doubling of CO2 was higher than the IPCC had calculated (Pagani et al, Nature Geoscience 3, 2010; Lunt et al., Nature Geoscience 3, 2010 ).

  26. Graeme No.3 says:

    Is everyone certain that the CO2 concentrations in the ice cores are accurate reflections of the whole world? What of the plant stomata work which suggests higher CO2 levels in warmer times?
    And below:

    Also, can anyone direct me to actual measurements of atmospheric heating due to CO2? Surely this would have been measured in the laboratory.

    • Javier says:


      I think the situation is clearly described by Margret Steinthorsdottir:

      “The ice core records offer continuous windows into the past, going back as far as 800 000 years, but might not be accurate chroniclers of rapid, transient changes of pCO2. Stomatal proxy records on the other hand face limitation in terms of accurately quantifying the plants’ physiological signals, and typically offer continuous records of a few thousand years at most during the Late glacial, but may potentially accurately record year-to-year relative changes in pCO2. The stomatal based pCO2 records across the Younger Dryas onset together point to much more dynamic Late glacial CO2 behaviour than do the ice core records.”

      The ice core record essentially provides a low band pass filter of past CO2 levels that eliminates any short term variation and averages values so peaks and valleys in CO2 levels disappear. The stomata data is very complex to properly calibrate and very discontinuous, so it has limited usefulness to paleoclimatologists. On the very long term everybody uses Geocarb III, a model that appears to give very good results.

      Steinthorsdottir, M. et al., 2014. Synchronous records of pCO2 and D14C suggest rapid, ocean-derived pCO2 fluctuations at the onset of Younger Dryas. Quaternary Science Reviews 99 84-96.

    • donb says:

      Graeme No.3. Whereas plant stomata are sensitive to temperature, they are also sensitive to precipitation and to some other environmental factors, which require somewhat uncertain corrections. But then most climate data require some type of correction.

    • polarscientist says:

      Yes, it was measured by John Tyndall in the early 1860s. See my post.

  27. Marcel Crok says:

    Thanks Euan for facilitating this interesting exchange;
    Colin Summerhayes already had an exchange in the past with Carter and Courtillot that is relevant for the discussion here:

  28. Graeme No.3 says:

    I would agree that the ice core results are not the absolute accuracy of CO2 levels which some claim. Whether a rise in CO2 causes a rise in temperature. and how much is, to some anyway, debatable. There is no direct correlation that I am aware of for the last 2-300 years, let alone with the ice cores. Yes, stromata figures are also likely to be in error, but should not be rejected just because they
    More importantly if a rise in CO2 causes a rise in temperature, why is an indisputable rise in temperature not associated with higher CO2? (Eemian with associated lion, elephant, giraffe and hippo fossils in the Thames Valley, Tassili frescoes in Holocene Optimum Sahara).

    And why haven’t “the world’s best scientists” or possibly “the world’s best funded scientists” in the last 43 years been able to measure the warming effect in the laboratory? I am aware that Knut Ångström tried this in 1900, mainly as a generally accepted rebuttal to Arrhenius, but surely more modern equipment would have put the case beyond doubt? Such measurements would settle amy argument and it is surprising that no-one seems to have attempted them.

    • A C Osborn says:

      Graeme, what could a Laboratory test possibly tell you about the how the Earth’s Climate reacts to CO2 unless it can reproduce the Earth’s total conditions of Solar/Cosmic/Atmosphere/Oceans etc

    • Javier says:


      I cannot tell you anything about the physics of CO2 in the atmosphere except for the most basic facts, as I am not well versed in that. I would say that the warming is due to higher energy molecules of CO2 that can either transmit the heat to other molecules or emit long wave radiation. Both temperature and radiation are easily measured both in the laboratory and at the troposphere, in the latter case on a daily basis.

      Regarding stomata data on CO2, I think it is valuable data with a much higher capability to resolve temporal changes, as plants adapt to increased CO2 levels probably within one season or to the next season, as the change in stomata index does not require genetic changes. The only limit to the temporal resolution of that technique is the dating of the leave. In fact, the recent increase in CO2 is reflected in the decrease of stomata from the leaves of the same oak collected repeatedly for herbaria since 1840:

      Beerling, David J., and William G. Chaloner. “The impact of atmospheric CO2 and temperature changes on stomatal density: observation from Quercus robur lammas leaves.” Annals of Botany 71.3 (1993): 231-235.

      Regarding the Eemian I don’t think we can know with certainty maximum levels of CO2. Levels from ice cores are probably a low average. In any case our present CO2 levels are probably much higher given our great recent increase, that is quite higher than anything measured during the Holocene whether from ice cores or stomata.

      • A C Osborn says:

        One thing I can tell you about CO2 Down Welling Long Wave Radiation is that not all Radiation Energy is the same.
        Solar Radiation according the Climate Science Energy Budget is around 342 W per metre squared.
        It can do lots of work warming things up like Solar Heated Water, including being “focused” as in Solar Stills and the Ivanpah solar facility.

        CO2 generated Back Radiation according the Energy Budget is around 324 W per metre squared.
        However it can do no work warming things up, in fact if you use a solar still on a clear night when there is only back radiation it actually cools things down from ambient.

        So not all radiation is generated equally.

        Ask any Climate Change buff why this is and they will tell you it can only do “work” when the object it strikes is at a Cooler temperature than the temperature from whence the Back radiation came from, ie the Troposphere.

        There is plenty of literature on both versions that I describe, what do YOU think it tells us about CO2 Global Warming?

        • Javier says:

          A C,

          Thank you for your informed opinion. I do not think the CO2 hypothesis has sufficient explanatory power for the great majority of present global warming.

          However the theory predicts that CO2 warming should be biggest when the air is very dry (i.e. very cold), and the effect should then be most noticeable in rising winter minimal temperatures and increased warming over glaciers and polar regions. I think it is indisputable that this has been taking place. Global glacier retreat is clearly outside long term trend, and has reached levels not seen in about 5000 years. There is multiple evidence of this, and it is clear that Ötzi would have not been found if it wasn’t for this unusual melting.

          Present global warming has been taking place for 350 years, but it has been enhanced by the increase in GHGs. We just don’t know how much it has been enhanced. In any case, alarmism about CO2 levels or global warming is unjustified, in my opinion.

          • A C Osborn says:

            “Global glacier retreat is clearly outside long term trend, and has reached levels not seen in about 5000 years”

            Are you absolutely sure about that?
            The Hymalayan Glaciers are not retreating at the moment.

            I thought that most of the World’s Glaciers were retreating faster in the early 1900s than they are now.

          • Javier says:

            A C,

            Yes, I am convinced that increased GHGs have caused glacier melting beyond what should be expected if the warming was just natural. The evidence is quite strong that that is the case.

            Relevant bibliography

            1. J. Oerlemans. Holocene glacier fluctuations: is the current rate of retreat exceptional? Annals of Glaciology, Volume 31, Number 1, January 2000, pp. 39-44(6)
            “Integrations for a 10 000 year period, driven by random forcing of a realistic strength, show that the current retreat cannot be explained from natural variability in glacier length and must be due to external forcing.

            2. Johannes Koch, John J Clague and Gerald Osborn: Alpine glaciers and permanent ice and snow patches in western Canada approach their smallest sizes since the mid-Holocene, consistent with global trends. The Holocene 2014 24: 1639
            “Glacier retreat in western Canada and other regions is exposing subfossil tree stumps, soils and plant detritus that, until recently, were beneath tens to hundreds of metres of ice. In addition, human artefacts and caribou dung are emerging from permanent snow patches many thousands of years after they were entombed. Dating of these materials indicates that many of these glaciers and snow patches are smaller today than at any time in the past several thousand years.”

            “The global scope and magnitude of glacier retreat likely exceed the natural variability of the climate system and cannot be explained by natural forcing alone. This departure is best explained by the ascendancy of another forcing factor – the increase in carbon dioxide and other greenhouse gases in the atmosphere.”

            3. Goehring, B. M. et al. 2012. Holocene dynamics of the Rhone Glacier, Switzerland, deduced from ice flow models and cosmogenic nuclides. Earth and Planetary Science Letters 351–352, 27–35.

            “After 5 ka, the Rhone Glacier was larger than today, but smaller than its LIA maximum extent. The present extent of the Rhone Glacier therefore likely represents its smallest since the middle Holocene and potential climate warming will lead to further rapid retreat of the Rhone Glacier.”

            4. B. K. Reichert, L. Bengtsson and J. Oerlemans: Recent Glacier Retreat Exceeds Internal Variability. Journal of Climate 15 (2002) 3069.

            “Preindustrial fluctuations of the glaciers as far as observed or reconstructed, including their advance during the Little Ice Age, can be explained by internal variability in the climate system as represented by a GCM. However, fluctuations comparable to the present-day glacier retreat exceed any variation simulated by the GCM control experiments and must be caused by external forcing, with anthropogenic forcing being a likely candidate.”

            5. O. Solomina, W. Haeberli, C. Kull, G. Wiles Historical and Holocene glacier–climate variations: General concepts and overview. Global and Planetary Change 60 (2008) 1–9

            “The finding of the Oetztal ice man in the uppermost part of a small glacier in the Austrian Alps clearly illustrates that Alpine glacier volumes (not lengths!) have become smaller now than during at least the past about 5000 years.”

            6. Bakke, J., Lie, Ø., Dahl, S.O., Nesje, A., Bjune, A.E., 2008. Strength and spatial patterns of the Holocene wintertime westerlies in the NE Atlantic region. Global and Planetary Change 60, 28–41

            “The retreat of maritime glaciers along western Scandinavia over the last century is unprecedented in the entire Neoglacial period spanning the last 5200 yrs.”



            A) Koch & Clague 2006 meta-study of global glacier extent showing that current retreat exceeds the global range and minimum extent trend since mid-Holocene (Trend lines added). Notice how it shows glaciers now shorter than Medieval Warm Period and Roman Warm Period.

            Koch, J., & Clague, J.J. 2006. Are insolation and sunspot activity the primary drivers of Holocene glacier fluctuations? PAGES News, Vol. 14 No 3 pp 20-21.

            B) Thompson et al., 1995 study of the Huascarán glacier. Ice-core of the glacier with the temperature proxy showing that current glacier temperature is unprecedented for thousands of years and anomalous within trend.

            Thompson, L.G. et al. 1995. Late Glacial Stage and Holocene Tropical Ice Core Records from Huascaran, Peru. Science vol. 269, 46-50.


            Organic remains entombed in ice at mid-Holocene and freed by present global warming.


            It is clear that small glaciers and permanent snow patches are very sensitive indicators that show that the level of global glacier retreat is near Mid-Holocene levels. In a cooling planet a natural warming period should not have taken glacier melting that far.

            But let me be clear that this is the most sensitive test of the effects of GHGs-enhanced warming. As CO2 has a disproportionate effect on very dry air, that global glaciers have retreated to a point about 5000 years ago, does not mean that global temperatures have increased that far back. As the effect is enhanced over glaciers, indeed that could be used as an argument that present temperatures are still well below Holocene Climate Optimum average temperatures. It just cannot be otherwise.

      • clivebest says:

        Back radiation is a red herring.

        The temperature at a given height up to about 10,000 m is determined by thermodynamics – the adiabatic (moist) lapse rate and not by radiation. This scale is set by the surface temperature. The air thins out with height until IR photons emitted by H2O, CO2 or O3 can escape to space. This cools off the top of the troposphere and sets the scale. The earth remains approximately in energy balance so that the energy lost to space equals the absorbed incoming solar radiation. This effectively determines the temperature of the ‘top of the troposphere/atmosphere’ and equals 255K. The surface temperature approximately is then determined by the lapse rate.

        The transient energy in-balance at the top of the atmosphere caused by a sudden increase in CO2 is called ‘radiative forcing’. Once energy balance has been restored by a small rise in surface temperature, the radiative forcing returns to zero

        If CO2 rises from 400ppm to 600ppm then the increase in radiative forcing would be about 2 W/m2. That is about the same as the energy density removed from the atmosphere by a wind farm. So as a percentage it is far smaller than 1% and could be offset by a tiny increase in cloud cover. In that respect it is noticeable how the the largest cloud cover is over found over the warmest tropical oceans during summer months.

  29. niclewis says:

    Dr Summerhayes,

    Thank you for contributing this article. I accept much of what you say in it. But I would like to take you up on two points in your reply at 4.33 pm on 19 March to peter lang that concern my work (I am assuming you are “polarscientist”).

    You wrote:

    “You can if you wish stick with Nic Lewis’s estimate of climate sensitivity, but what I am pointing out is that estimates like his are well outside the mainstream.”

    That isn’t true, in respect of either ECS or TCR, for estimates published during the last four or five years that are based on observations during the instrumental period. Other such studies that give median ECS estimates in the 1.5–2°C range include Aldrin et al (2012), Ring et al (2012), Otto et al (2013), Masters (2014), Skeie et al (2014), as well as Lewis (2013) and Lewis (2016).

    The 1.5–2°C range is within the IPCC AR5 ‘likely’ range for ECS of 1.5–4.5°C, so can hardly be said to be “well outside the mainstream” – not that, if it were, that would imply that it was wrong.

    A study could hardly be more mainstream than Otto et al (2013): its authors include fourteen lead authors of AR5 WG1 chapters relevant to estimation of ECS and TCR.

    For those estimates for which their sensitivity to inclusion of the post early 2000s hiatus period was tested, it was found to be minor.

    ECS estimates based on instrumental observations necessarily actually estimate ‘effective’ climate sensitivity, corresponding to feedbacks operating over the 100+ year period concerned. In many but not all current generation (CMIP5) coupled atmosphere-ocean models (AOGCMs), equilibrium climate sensitivity (ECS) is higher than effective climate sensitivity. However, the difference is under 10%, averaged over CMIP5 models. It is not known whether ECS exceeds effective climate sensitivity in the real climate system.

    As I expect you know, the definition of ECS allows for the deep ocean to reach equilibrium, but not for slow feedbacks such as in ice sheets. Earth system sensitivity (ESS), which does allow for slow feedbacks, may well be higher than ECS, but is mainly relevant over multimillenial timescales. In many cases, geological evidence is more suited to estimating ESS than ECS.

    You also wrote, regarding Judith Curry, that:

    “Her and Lewis’s estimate of climate sensitivity did not take into consideration the geological evidence as far as I am aware.”

    That is correct; it was based on observed warming over the last 150 or so years. However, it is worth noting that IPCC AR5 WG1 concluded (12.5.3) that estimates of ECS based on past climate states very different from today may differ from the climate sensitivity based on the climate feedbacks of the Earth system today, and (Section, penultimate sentence) that true uncertainties for palaeoclimate ECS estimates are likely greater than those for multidecadal instrumental-observation estimates.

    IMO it is, however, worth considering ECS estimates based on the transition from the last glacial maximum to the Holocene (LGM studies). AR5 appears to take the same view, concluding that estimates of ECS from more distant palaeoclimate periods are difficult to directly compare with ECS in today’s climate state. The LGM transition has been much studied; all but one of the palaeo ECS estimates shown in AR5 are based on it.

    Simple calculations in which the global temperature anomaly at the LGM is divided by the total estimated forcing relative to the preindustrial state have long been used to generate estimates of the equilibrium climate sensitivity (Annan and Hargreaves,, 2015). Although ECS estimates from earlier LGM studies that did so were typically around 3°C, current best estimates of GMST (4°C below preindustrial: Annan and Hargreaves, 2013) and of relevant forcings (8–11 Wm−2 below preindustrial: Annan and Hargreaves, 2006) at the LGM imply an ECS estimate of approximately 1.75 °C, very close to the Lewis and Curry 2015 estimate.
    Aldrin M, Holden M, Guttorp P, Skeie RB, Myhre G, Berntsen TK (2012) Bayesian estimation of climate sensitivity based on a simple climate model fitted to observations of hemispheric temperatures and global ocean heat content. Environmetrics 23:253-271
    Annan, J.D., Hargreaves, J.C., 2006. Using multiple observationally-based constraints to estimate climate sensitivity. Geophys. Res. Lett. 33, L06704.
    Annan, J.D., Hargreaves, J.C., 2013. A new global reconstruction of temperature changes at the Last Glacial maximum. Clim. Past 9 (1), 367-376.
    Annan, J and Hargreaves, J., 2015. A perspective on model-data surface temperature comparison at the Last Glacial Maximum. Quaternary Science Reviews 107 1-10
    Lewis N (2013) An objective Bayesian improved approach for applying optimal fingerprint techniques to estimate climate sensitivity. J. Climate, 26, 7414-7429.
    Lewis N (2016) Implications of recent multimodel attribution studies for climate sensitivity. Climate Dynamics, 46(5), 1387-1396
    Lewis N, Curry JA (2015) The implications for climate sensitivity of AR5 forcing and heat uptake estimates. Clim. Dyn. 45, 3, 1009-1023
    Masters T (2014) Observational estimate of climate sensitivity from changes in the rate of ocean heat uptake and comparison to CMIP5 models. Clim Dyn 42:2173-2181 DOI 101007/s00382-013-1770-4
    Otto A, Otto FEL, Boucher O, Church J, Hegerl G, Forster PM, Gillett NP, Gregory J, Johnson GC, Knutti R, Lewis N, Lohmann U, Marotzke J, Myhre G, Shindell D, Stevens B, Allen MR (2013) Energy budget constraints on climate response. Nature Geosci 6:415–416
    Ring MJ, Lindner D, Cross EF, Schlesinger ME (2012) Causes of the global warming observed since the 19th century. Atmos Clim Sci 2:401–415
    Skeie RB, Berntsen T, Aldrin M, Holden M, Myhre G (2014) A lower and more constrained estimate of climate sensitivity using updated observations and detailed radiative forcing time series. Earth Syst Dynam 5:139–175

    • Euan Mearns says:

      Thanks for this Nic, for those who want to read Lewis and Curry:

      Volcanic eruptions are of course meant to affect climate. Laki certainly was bad news for Europe during the LIA. But I’ve never been convinced that I can see a volcanic signal in the T record.

      May I ask if you assume all warming from the thermometer record is down to CO2 and Man?

      One thing that may separate you from Otto et al, is that they made clear that we still needed to phase out FF.

      • niclewis says:


        All my climate sensitivity studies are based on the usual assumption that all warming is forced, with unforced variability contributing to uncertainty but not the central sensitivity estimate. Natural forcing changes were small over the analysis periods that I used, so this implies that essentially all the warming is down to man.

        However, although CO2 is the largest single anthropogenic forcing there are various others, both positive (CH4, N2O, CFCs, ozone, black carbon on snow, etc.) and negative (aerosols, maybe land use change). However, CO2 is unusual in that a non-negligible fraction of emissions are thought to have a very long (>1000) lifetime, so part of the initial warming from CO2 emissions is persistent.

        My papers are scientific studies of climate sensitivity. A statement that man needs to phase out FF is a policy statement, which I don’t think really belongs in a scientific study of climate sensitivity.

        • A C Osborn says:

          I assume that when you say “Natural forcing changes were small over the analysis periods” you mean TSI or Sun Spot Activity?

          • niclewis says:

            TSI for solar, and forcing derived from AOD for volcanism. I have an open mind about the possibility that solar variability, e.g in UV radiation or magnetic field/ solar wind, may mean it has considerably more effect on GMST than suggested by variations in TSI. However, the current evidence does not seem clear-cut to me.

          • A C Osborn says:


        • Javier says:


          I have long suspected that we are not getting the nature of natural forcing changes correctly.

          The largest effect on temperatures comes from cooling due to very low solar activity (grand solar minima) that consistently coincides with cold periods of the past. The effect could be thought as reducing the fire under a pot so the content starts cooling and stops boiling. Even though solar variability is small, a continue small change can have a much larger effect than a short term large change if the system has a built in delay and perhaps amplification mechanism.

          Once the grand solar minimum ends, the Sun returns to normal activity very quickly and this can be equated to rising back the fire under the pot. Now for a period of equilibration due to the built in delays, you can see the content of the pot increasing progressively its temperature even if the fire is now constant. You could think that it is not the fire that is increasing the temperature if you erroneously assume that the system was in equilibrium instead of moving towards a new one. So the answer “it is not the fire because it is not changing” is unsatisfactory and you can start to blame the atmosphere in the kitchen that is becoming warmer for warming the food in the pot.

          By looking at past cooling periods during the Holocene, the recovery time afterwards went from 200 to 400 years, and we have been warming for 350 years.

          So yes, a great part of present warming could still be the Sun, and climate sensitivity to CO2 could be really, really low. We will know when the planet reaches the new equilibrium and the warming from the Sun stops. And this could be as early as the next few decades to the mid 21st century if past is prologue. The lower Sun activity of cycles 24 and 25 is going to constitute a good test of this hypothesis.

      • Javier says:


        The volcanic signal on the temperature record depends proportionally on the amount of SO2 produced by the volcano, and the location of the volcano with respect to the equator, as tropical volcanoes affect both hemispheres unlike higher latitude volcanoes.

        Usually volcanoes only have a multiyear effect, but larger eruptions can have a decadal effect and huge eruptions or groupings of large eruptions can have a multi-decadal effect.

        The effect of this huge eruptions on the temperature record manifests therefore as a period of several very cold years with summer temperatures specially depressed, followed by a recovery period with warmer than average temperatures. It is clearly seen during the Little Ice Age:

        So even though volcanic eruptions did not cause the Little Ice Age, they contributed to make people’s lives more miserable during that period.

        For scientific support for the decadal effects of big volcanic eruptions you can see:
        Sigl et al. 2015. Timing and climate forcing of volcanic eruptions for the past 2,500 years. Nature 523, 543–549

    • niclewis says:

      Correction: There was a typo in “(8–11 Wm−2 below preindustrial: Annan and Hargreaves, 2006)”. It should read 6–11 Wm−2 below preindustrial. The implied ECS estimate of 1.75°C used the correct median value of 8.5 Wm−2 below preindustrial. The 8.5 Wm−2 value is also indicated by Figure 6.5 of the IPCC AR4 WG1 report.

  30. There are also problems concerning the accuracy of paleotemperature reconstructions, take for instance the PETM 55 million years ago, about which we still do not know what it was and what caused it. However the CO2 levels jumped and so did the sea surfaces temperatures, right?

    Maybe not. One of the references Sluijs et al 2006 propose a Sea Surface Temperature jump from 18C to 23C. That’s a very nice pool temperature, but in the Arctic Ocean?

    However this is based on the TEX86 method, which is challenged here for instance
    (first and second abstract, also: .)

  31. Euan Mearns says:

    This is Marcott 2013 compared with CO2. I’ll add GISP 2 later. Something is wrong!

    • Javier says:


      As I already said in my post above:

      “Another bone of contention is that the behavior of the CO2 during the Holocene is not consistent with the [CO2] hypothesis, as in the last 6000 years temperatures have been dropping, yet CO2 has been increasing. Scientists think that they know why CO2 has been on the rise, either naturally (consensus hypothesis) or of human origin (the much contested Ruddiman hypothesis), but what no scientist can explain is why temperatures were dropping when the CO2 hypothesis calls for an increase due to increased CO2. This is called “the Holocene temperature conundrum,” (Liu et al., 2014) and climate models adjusted to reproduce present conditions produce warming instead of cooling for those 6000 years.”

      Liu, Z. et al. 2014. The Holocene temperature conundrum. PNAS 111, E3501-E3505.

      Look at their figure 1. This problem is known, but rarely discussed.

      • Euan Mearns says:

        Javier, many thanks for this. I had read your earlier comment but read through what you said about the Holocene temperature conundrum. Kind of a cognitive block when someone says CO2 rising and T falling.

        I would say it is unwise to use the Marcott proxies as data to support the CO2 hypothesis when Marcott totally contradicts it.

        Trying to reconstruct global temperature history over thousands of years from proxies is never going to work. You need long records for each proxy from all over the globe. I would argue the LR04 stack is perhaps as close as you get. But even there the temperature recorded will be dependent upon the depth the beasties lived in. LRO4 I seem to recall is dominated by a single foram.

        CO2 in ice cores is perhaps the best global proxy for temperature. We know that it co-varies with temperature proxies give or take a few hundred years with the exception of glacial inceptions. It is a record of mean ocean temperature ± dPhotosynthesis.

        It’s kind of interesting that Mann’s original hokey stick wrote the LIA out of history. But now its back and being used to support the warmist argument. It is hard to keep up.

        I am of the view that the Bond / D-O cycles likely have a small imprint on global average temperature. They are caused by changes to ocean and atmosphere circulation patterns. This is something that could bite us hard in Europe. Climate may change everywhere, some places get warmer and some colder.

        • Javier says:


          Marcott’s proxies reconstruction contains some difficult to justify decisions, like changing the original dates of some proxies, an incorrect method of averaging, that produces artefacts at end points of proxies (like the infamous stick), and the Montecarlo running that eliminates all detail losing a huge amount of information.

          However when those defects are corrected like Tamino did here:

          (see black curve in previous to last figure, Published ages with Differencing method)
          the resulting reconstruction, even if probably it still contains quite a few errors, and needs to be rescaled for temperatures to agree with other research, reproduces a lot of climatic characteristics that we know by other means, and so it is valuable. At least until we have a better global reconstruction.

          I have studied the level of agreement between this reconstruction and many climatic features, for example in the following figure I compare it with obliquity changes, global glacier advances and Bond events, and found it useful. It contains a lot of information.

          It would be long to explain, but the main conclusion is that the temperature reduction during the Holocene is driven by the reduction in obliquity. This slow temperature decrease is interrupted by the cooling effect of three cycles. Two of them of solar origin, one of a ~2500 years associated to the Hallstatt cycle that produces a cluster of grand solar minima at its lows, and the other a millennial solar cycle that changes in intensity during the Holocene and also produces grand solar minima at its lows. The third one is a cooling 1500 years cycle that appears in the latter part of the Holocene. I believe is the same cycle that produces warming during the glacial period during D-O events. The best explanation that I can come with is that it is a cycle caused by lunisolar tides that produce the warm interstadial during the glacial period by vertical mixing of warm stratified subsurface water under the sea ice in the Norwegian sea, but that during interglacials produces cooling by the same mechanism of vertical mixing of colder deeper water.

          There are also climatic events not explained by these three cycles, like the 4.2 kyr event that caused extreme aridity for about 100 years, and marked the end of the Egyptian Old Kingdom, the collapse of the Akkadian Empire in Mesopotamia, and initiated the dispersion of the urban Harrapan civilization in the Indus Valley. Also the precession cycle has had a lot of climatic efects, mainly through the displacement of the Inter Tropical Convergence Zone that ended the African Humid Period.

          Finally, the Little Ice Age was so cold because there was a near coincidence in the lows of the three cycles plus increased volcanic activity. This coincidence of the three cycle lows is rare. As it is so close to us, only ~500 years ago, the next low is from the solar millennial cycle and should not take place for at least 400 years.

          Decreasing obliquity will continue driving temperatures lower once present global warming ends, which should happen within 21st century, but a major cooling that could start the next glacial period should not take place for 1500-2000 years until the next low in the Hallstatt cycle.

          • clivebest says:

            Changes to the earth’s obliquity does not change the total solar radiation flux. It just changes its distribution with latitude and season. As obliquity increases so climate zones likewise increase in size which thereby accentuate the seasons.

            If the earth had a circular orbit then the 23K precession term would have no effect. It only comes into play because eccentricity is non-zero. Eccentricity amplifies the effect of precession. It works as follows.

            Once every 23,000 years the Northern hemisphere summer coincides with perihelion (closest distance of approach) of the earth-sun orbit. Solar radiation increases can increase by 20%. This reaches maximum effect when eccentricity is at a maximum. All these conditions occurred at the LGM, but even this was not enough to trigger an interglacial because eccentricity was at a minimum of the 400,000 year super-cycle. The earth needed some help extra from life. Die back of forests and soil erosion caused by low CO2 levels, dumped huge quantities of dust over the ice sheets. This eventually reduced albedo enough to melt back the ice sheets.

            The last glaciation had a classic saw-tooth shape which is only apparent when eccentricity is small. A nearly exact example can be found 400,000y ago. When eccentricity is high the glacial cycle reverts nearly to a 41,000y cycle such as the last but one glaciation.


            The modulation effect of eccentricity on the precession term can be see well here:


            The idea of dust due to vegetation die-back at low CO2 levels is due to Ellis.

          • Euan Mearns says:

            Clive, as I said by email yesterday, dust, cations and 10Be all need to be corrected for deposition rate. Given constant dust deposition, if the snow deposition rate goes down, then the dust concentration goes up. A deposition rate correction is required. The dD and d18O ratios are not affected directly by this, although a change in d18O may accompany a change in precipitation rate. CO2 and CH4 in gas bubbles are also not affected directly since this is concentration in air, not snow. But very slow deposition rate at Vostok means that air may be mobile in firn for about 1000 years before bubble closure. Vostok provides a 1000 year running mean of atmospheric change.

          • Javier says:


            The consensus Milankovitch hypothesis that you have explained has very important problems. Let’s review some of them.

            Eccentricity, despite being the only orbital change that alters the amount of solar radiation received by the Earth, has a small direct effect because those changes are very small as the Earth’s orbit has always a very low eccentricity. So it is postulated that changes in eccentricity act indirectly through changes in precession. The major eccentricity cycle is a 400 kyr cycle, with the 100 kyr cycle being a minor one. The signal from the 400 kyr cycle is completely absent from temperature records, which is conveniently forgotten from defenders of the consensus theory. How can the minor oscillation dominate when the major oscillation is nowhere to be seen?

            Precession is a combination of orbital precession and axial wobble precession, and although it produces the biggest changes in solar radiation distribution, those changes are averaged over the entire year, so what is given to one season is taken from the previous and the annual total insolation at any latitude does not change. Precession has an important effect on climate as it determines the position of the ITCZ (Inter Tropical Convergence Zone) that controls the monsoons and produces the African Humid Periods with a 23 kyr oscillation.

            Obliquity is second to precession in the distribution of solar radiation through latitudes and seasons, but it has a crucial difference. Obliquity alters the annual total insolation at any latitude so a small change in insolation accumulates year after year, increasing its effect every year, for 20,000 years before it reverses. And this is a such a huge amount of time that that small change (not so small at the poles) has a huge difference.

            A known problem of the consensus theory is the Stage 5, Termination II problem, also known as the causality problem. Data from crystals at the Devils Hole cave in Nevada (Winograd et al., 1992; Ludwig et al., 1992), sea level changes from coral reefs in Bahamas (Gallup et al. 2002), Barbados, and Papua, and speleothems from an Italian cave (Drysdale et al. 2009), all indicate that termination II was essentially completed 135 kyr BP, a time when 65°N summer solar insolation levels where still very low, lower than 70% of the previous 100 kyr. So the effect precedes the cause, and termination II could not have been driven by changes in 65°N summer insolation changes.

            Another problem that is obviated is that the precession cycle is asymmetrical, producing warming in one hemisphere while cooling in the other. We do know that glacial terminations are symmetrical phenomena. The obliquity cycle is symmetrical and produces warming or cooling simultaneously at both poles.

            There is an important disconnect between 65°N insolation and the temperature record that proponents of the consensus theory do not meditate. It can be illustrated by the following figure from J. Imbrie et al. 1993. Paleoceanography Vol. 8 no. 6 pp. 699-735:
            Part A of the figure (Top) is an analysis of the calculated 105 W/m2 variation at 65°N divided in the contribution by the precession, obliquity and eccentricity bands.
            Part B of the figure (Bottom) is an analysis of the temperature proxy decomposed in its 23 kyr, 41 kyr and 100 kyr frequency contributions.
            That illustrates very well the problem. The only cycle that is contributing what it should is the 41 kyr obliquity cycle. Precession changes have very little effect on temperatures and eccentricity changes have huge effect on temperatures despite their tiny contribution to insolation changes.

            A similar analysis has been done by John Baez using a Gabor transform modulus, which essentially is a windowed Fourier transform. The results speak for themselves:
            Of the 65°N july insolation bands (Left Panel), the biggest one, 23 kyr, is barely detectable in the temperature data (Right Panel), while the 41 kyr band has essentially the same intensity in the temperature data, and two new bands appear that are not predicted by the insolation theory, an 83 kyr band and a 100 kyr band, indicating an aggregation effect of the 41 kyr band.

            The conclusion is inescapable. The obliquity cycle is the master of temperature changes on Earth, and the consensus theory is wrong.

            Another illustration explains how obliquity achieves its effect. This one is a modification of a figure from Steve Carson, of Science of Doom. The background color represents the annual insolation anomaly. Precession does not contribute because it does not change annual insolation, just redistributes it within a year. Over that I have overlaid Epica Dome C temperature proxy.
            Highs in the obliquity cycle are characterized by a blue band in central latitudes and show periods of warming, while lows in the obliquity cycle are characterized by a yellow band in central latitudes and show periods of cooling. For the next 20,000 years we will be getting another yellow period.

            As you can clearly see in that figure, precession modifies the effect of obliquity, determining how high the peaks are, their position, and how long the interglacials last. A rising precession can reduce cooling from a falling obliquity, but due to current low eccentricity, current precession is low, so it will not be able to stop the cooling much.

            The increase of dust during glaciations is not new. It has been long known that during glacial periods the Earth becomes very unproductive. Not only large parts of the Northern Hemisphere are buried in ice, but elsewhere deserts expand due to low precipitations. The increase in dust from these expanded arid regions causes a fertilization effect on the oceans, so what the land loses on productivity it is gained by the oceans. The oceans are a lot more productive during glacial periods and a lot less productive during interglacials.

            What is new from Ralph Ellis is the proposal that dust cycles drive the glacial-interglacial cycles, but he is probably wrong. He is confusing cause and effect. What drives interglacials in the Late Pleistocene is a spring mechanism that allows enough melting of the ice mass to overcome its negative feedback in the short period of less than 20,000 years that obliquity has to get out of the glacial conditions. It is important that precession is not working against obliquity, otherwise it fails, and that rules out some cycles. See previous figure, cycles where the maximum in obliquity coincides with a minimum in precession fail to produce an interglacial. The other factor is sea level. The lower the sea level, the stronger the spring mechanism, because water is very effective at melting ice and as the sea level rises, it melts a lot of low lying ice creating a powerful positive feedback that gives the extra push that obliquity needs to get the planet out of glacial conditions before its time runs up.

            In my opinion dust is not an important factor because it goes to basal levels as soon as the obliquity cycle starts rising, and gets buried under meters of snow and ice while the obliquity cycle is working its way up, so it probably has no effect at the crucial period when rising obliquity, rising sea levels, and hopefully rising precession are doing the time-constrained heavy melting required to get the planet out of glacial conditions.

          • clivebest says:


            Given constant dust deposition, if the snow deposition rate goes down, then the dust concentration goes up. A deposition rate correction is required.

            I know what you are saying and agree that such a correction is needed if we are to measure the amount of dust in the atmosphere. However all that is really needed to reduce the ice-albedo effect is ‘dirty snow’ and that is what the ice-core data are showing.

            There are thick layers of dust left in small layers of ice. This only occurs when CO2 falls below 220ppm (or low temperatures)

          • Euan Mearns says:

            Agreed. But this links back to understanding process. If it gets so cold that precipitation falls to zero then we get dust accumulation instead.

          • A C Osborn says:

            With so much dust in the Atmosphere shouldn’t that also reduce the amount of Insolation reaching the surface?
            ie like the supposed cooling after a major eruption.

      • polarscientist says:

        The Liu et al paper omitted to mention that the temperatures on Greenland show much the same sort of curve as Marcott does for the Holocene of the northern hemisphere (see Bo Vinther et al, 2009, Nature 461, Holocene thinning of the Greenland ice sheet) – i.e. an initial rise (when the ice sheets were melting), followed by a significant cooling that followed the trend of decaying orbital insolation. Now, Liu et al (2014) argue that Marcott’s northern hemisphere data for the early Holocene were biased by alkenone derived sea surface temperatures that represented summer conditions. But since the data WITH those alkenones is much the same as Vinther has for Greenland, it seems quite likely that Liu et al were wrong in their assumption about the alkenone-based SSTs.

        • Javier says:

          In this I agree with you Dr. Sumerhayes. Liu et al., 2014 give two possible reasons to explain the disparity between temperatures and CO2 levels during the second half of the Holocene.

          The first one is that the temperature reconstruction is wrong and temperatures did not decrease during the second half of the Holocene. But I agree with you that this is highly unlikely, as Marcott’s reconstruction agrees well with what we know from numerous sources.

          The second one is that the climate models are wrong, and they either give too little weight to changes in insolation, or too much weight to changes in CO2, or both. To me this is the most likely explanation.

    • Euan Mearns says:

      Here’s a chart from Clive Best that shows maximum summer insolation at the N pole. Declining ever so slightly from 11,000 to about 7000 y ago and then turning to rise ever so slightly.

      • clivebest says:

        Note how every time CO2 levels fall below ~220ppm there is a rapid increase in dust as measured by Antarctic ice cores. The large increase in polar insolation 87,000y ago increased temperatures but had little effect on total ice volume. If eccentricity had been higher, then the increase in insolation would have been sufficient to curtail the glaciation at the 41K obliquity maximum, as occurred 200,000y ago.

        • Peter Lang says:

          Clive Best,

          Thank you. I’ve often pointed this out and made the point that the planet was much drier, windier and less vegetated during cold times. Hard times!!

          Do you happen to know of an authoritative references that shows the relations hip between mass of C tied up in the biosphere versus global mean surface temperature?

      • clivebest says:

        @Javier says: March 22, 2016 at 12:45 pm

        I don’t think mine is at all the consensus Milankovitch hypothesis. That states that northern summer insolation at 65N is the driver. However this clearly doesn’t work since the largest value during the last glaciation occurred 85Ky ago and had little effect. For this reason and others what really ends glaciations is still a mystery. Various proposals have been made:

        – 100,000y variation in the inclination of the earth-sun orbit causing the earth to pass through interstelar dust clouds – Muller et al.
        – Ruddimen argued that CO2 changes induced by Ocean temperatures should be seen as a feedback on Ice Volume rather than a cause direct cause. He argues that the current saw tooth oscillations are caused by non-linear CO2 feedbacks.
        – Extreme lunar tides coincident with maximum eccentricity and low sea levels may help break up ice sheets.
        – Ralf Ellis proposal

        You say there is no signal at 400,000y but that is also not true. The primary benthic foram d13C varies primarily with a period of 400,000y for over 20M years persisting even into the early Pleistocene. Some years ago I did this fit.

        I agree that the primary variance in total annual insolation at high latitudes is surely obliquity. This regular increase was evidently sufficient to end all glacial cycles from 5My ago to ~1My ago. There was then a transitionary period when glaciations lasted 2 or 3 obliquity cycles. But since 800ky ago the overall glacial cycle has switched to ~100ky always coincident with maximum eccentricity.

        Interestingly something similar occurred during the Middle Miocene cooling. Before 13.8 My ago Benthic d18O/d13C followed a 41,000y cycle. Afterwards the cooling this switched to a 100ky cycle (Holbourn et al 2005). There must be a similar reason. At high eccentricity summers which coincide with minimum earth-summer distance are much warmer. Precession and eccentricity work together to boost obliquity alone.

        • Euan Mearns says:

          So you don’t believe my analysis of LR04 that suggests the 100,000 y cycle is a myth?

          • clivebest says:

            I think we are both right. The basic metronome is the 41k cycle, but it now needs a helping hand from maximum maximum eccentricity.

        • Javier says:


          The 400 kyr signal that you show in the figure is a lot smaller than the 41 kyr signal, and it is supposed to be a lot stronger than the 100 kyr signal. I don’t think that argument plays in favor of the importance of the 100 kyr eccentricity cycle. Also that during the Miocene something similar happened speaks of it probably having the same cause, but it does not say what was the cause.

          Evidence shows that when obliquity is not enough alone, it simply starts skipping oscillations. How are those oscillations to be skipped selected? Obviously the chances of an obliquity oscillation being skipped increase if it has an unfavorable precession and/or eccentricity configuration, and the chances of an obliquity oscillation being selected for interglacial increase if it has also a favorable precession and/or eccentricity. This creates an apparent 100 kyr cycle when in reality the heavy lifting in temperatures is always done by the obliquity cycle.

          But since 800ky ago the overall glacial cycle has switched to ~100ky always coincident with maximum eccentricity.

          Well, not really. Last interglacial was 123 kyr before this one, as the obliquity pacing predicts. Euan’s figure is proof that the 100 kyr spacing is just a mathematical average, not a physical cycle.

          I don’t see the interest in looking for mysterious causes (dust, CO2, etc)when what we know about orbital changes already explains what we see. Ockam’s razor indicates that if obliquity fully explained glaciations before the mid-Pleistocene transition, and it fully explains glaciations afterwards simply by skipping one or two oscillations, there is no need to invoke mysterious causes. The planet is just too damn cold for obliquity to produce an interglacial at every oscillation, but we are getting worried that it could become too warm. Homo stupidus I would say.

  32. Euan Mearns says:

    Solar influence on glaciation in Greenland

    10Be is a cosmogenic isotope made by interaction of galactic cosmic rays with O and N in Earth’s atmosphere (I don’t understand how – Clive? Javier?). Assuming a uniform background flux of cosmic rays, the main variables to control 10Be formation are the Sun’s and the Earth’s magnetic fields that shield us from cosmic rays. Active Sun, more shielding, less 10Be and vv.

    Gaseous O and N get turned into Be that precipitates out of the atmosphere quickly in rain and snow. The snow deposition rate affects the 10Be concentration in ice and a correction is required.

    Figure 3 The 10Be data come from NCDC NOAA [15] and the temperature and accumulation data come from ref [16]. I was surprised to find that the 10Be is not archived in The Greenland ice core gateway [17]. Note the high degree of correspondence between 10Be and temperature. However, the raw 10Be data plotted here cannot be used since it must be corrected for the rate of ice accumulation (left hand panel) as plotted in Figure 4.

    Figure 3 is uncorrected. Note how T and snow PPT rate both rise in Holocene. The big drop in 10Be at 15,000y is down to this.

    Figure 4 10Be normalised to an ice accumulation rate of 0.1 m / y. The large variations in accumulation rate in the time interval 15,000 to 10,000 y and their attendant uncertainties has likely given rise to spurious 10Be structure in this part of the sequence and above.

    Making the correction (Figure 4), the big jump disappears. It is probably slightly over-corrected. But there is residual structure left in the 10Be signal. Let’s see if this tells anything.

    Figure 5  The temperature record from [16] and labelled D-O events 2 to 8 in blue from [1]. Low 10Be events 1 to 20 labelled in red. These low 10Be events would equate to an active solar magnetic field, shielding Earth from Galactic cosmic rays. It is possible that another 3 weak D-O events are present at 10Be events 7, 10 and 15. A quirk of XL means that it is only possible to plot 2 variables against time by placing time on the x-axis with the present day to the left. On this chart 10Be is normalised to the mean value for the interval = 0.23 m / y.

    We see that each D-O event is aligned with a 10Be anomaly. But there are many more 10Be anomalies than D-O events. I never got around to looking at the Holocene part of the section.

    Conclusion: The large temperature swings seen in Antarctic ice cores and LR04 benthic foram stack align with the 41,000 y obliquity cycle and multiples thereof. Small scale T fluctuations in Greenland correlate with changes to Sun+Earth magnetic field. Bond speculated that these T variations were down to truncation of Gulf Stream by Labrador current. The expression of these cycles may not be large on global average temperatures, but when N hemisphere atmosphere circulation goes into reverse, Europe freezes.

    I count 20 10Be cycles in 23,000 years. Mean cycle length = 11500 years.

    • donb says:

      The ~100, ~41, and ~21 kyr orbital cycles are ALL real and play a role. Being of different time phase, they add and subtract to get the total insolation changes over time. When they are all additive, versus subtractive, one gets up to ~90 watts/m^2 insolation change at 65N.
      Earth is currently at a low change point in the 100 kyr cycle and is approaching the low-point of a combined cycle. Note that calculated orbital changes show only relatively small changes in insolation over the next 50 kyr plus. There will not be anew ice age soon.

      Also note that max and min. insolation alternate between hemispheres, so the whole Earth receives about constant insolation. What initiates glaciation is when the NH gets colder (and the SH warmer) and initiates higher ice albedo and changes Atlantic circulation, both chilling further.

      • Javier says:


        “Note that calculated orbital changes show only relatively small changes in insolation over the next 50 kyr plus. There will not be anew ice age soon.”

        You did not read my comments above about obliquity driving the glacial-interglacial cycles.

        The closest astronomical analog to the Holocene was MIS19, 777,000 years ago. Please take a look at the following figure:

        In red is the Holocene, and in black is MIS19. The vertical dotted line at zero is where we are now. Look at NH June insolation (e, continuous). The black (MIS19) curve rises more over the next 10,000 years. Now look at obliquity (f, continuous). The black (MIS19) curve drops less over the next 10,000 years.

        Despite these advantages you can see that temperatures for MIS19 (b) started to fall faster at about the equivalent time to where we are now, due to glacial inception.

        Our only chance to avoid a glacial inception in about the next 2000 years is that alarmists are right that CO2 is such a powerful warming agent and we can continue producing enough of it for thousands of years.

  33. E.J. Mohr says:

    So just eyeing the graph it seems, figure 3 shows there may be a step change in Be-10 from Ice Age conditions into the Holocene.

    With the normalized data there still is a step change, but the Holocene in figure 4 shows a less active sun. Since Be-10 production is inversely associated with a more active sun is it possible the normalization over corrected? By this I mean that the precipitation normalized Holocene has higher Be-10 production than the Ice Age indicating that solar magnetic fields and activity are lower in the Holocene. The uncorrected data show the opposite which seems intuitively correct to me. Nevertheless the normalized Ice Age data show D-O events coinciding with lower Be-10 as expected. Then at around 40 ky the Be-10 rises sharply – clearly that would be the Laschamp Event?

    Meanwhile it does appear that Gerard Bond did the Be-10 for the Holocene, as you’ve mentioned, and came to the same conclusion. It’s too bad we don’t have Bond’s data. According to Fred Singers book Bond radio-dated the Holocene ocean sediments for accuracy and used a ratio of C-14 and Be-10 to deduce solar activity.

  34. Peter Lang says:

    Can anyone tell me the mass of carbon tied up in biota during the Mesosoic and Cenozoic eras and the Holocene?

  35. Euan Mearns says:

    After a week and 217 comments the thread has become unwieldy and so comments are now closed (Friday 25th March). I’d like to thank Dr Summerhayes and all commenters for the lengthy and thoughtful contributions. There will be opportunities to continue the discussion in weeks ahead since I will have a couple of follow up posts.

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