A number of commenters seem genuinely confused about what to believe when it comes to climate change, climate science and energy policy. Members of the public seem inclined to believe the scientific consensus and certain commenters on Energy Matters are clearly disturbed by the fact that myself and Roger Andrews should have the audacity to challenge what is presented as settled science that 97% of scientists evidently agree upon.
A number of comments point to John Cook’s blog called Skeptical Science that sets out to straighten the record made crooked by sceptical blogs like WUWT, Roy Spencer, Judy Curry and, I dare say, Energy Matters. It was pointed out that no one has presented a systematic rebuttal to John Cook, and while writing this type of post is not the most favoured use of my time, I think it is potentially useful to try and straighten out some of the issues. At the moment I plan 10 posts to address each of John Cook’s alleged climate myths, but we will see how things go.
The first myth, is attributed to MIT Professor of Meteorology, Richard Linzen. Myth 1: Climate’s changed before:
Climate is always changing. We have had ice ages and warmer periods when alligators were found in Spitzbergen. Ice ages have occurred in a hundred thousand year cycle for the last 700 thousand years, and there have been previous periods that appear to have been warmer than the present despite CO2 levels being lower than they are now. More recently, we have had the medieval warm period and the little ice age. (Richard Lindzen)
Cook does not refute the point that climate has changed before but instead constructs an argument around the pace of climate change, implying that climate today is changing more rapidly than in the past although he presents little hard data to back up this argument. High latitude climate has changed rapidly about 50 times in the last 3 million years associated with the glacial episodes and interglacials of the ice age that we remain in.
He compares today’s burning of fossil fuels to past natural disasters in the form of large scale volcanic eruptions or meteor impacts. And while he recognises that other gasses such as SO2 may also be implicated in extinction events he tends to lay the blame at the door of elevated CO2. This is presented under the banner “what the science really says”.
But all this is moot since Cook misses completely the essence of the sceptic argument bound in Lindzen’s quote. This boils down to attribution of observed temperature changes. The climate science community has tended to attribute all of the temperature rise seen between 1975 and 1998 to human activity, especially rising CO2 (Figure 1). The sceptics say hey wait a minute, Earth’s climate is still seeking equilibrium from the last glaciation and from the Little Ice Age that ended a mere 150 years ago. Warming in the period 1910 to 1945 is attributed to natural warming by most workers. If that warming was natural what evidence is there to suggest that late twentieth century warming was not natural too (Figure 1)?
Figure 1 The HadCRUT4 global temperature reconstruction as graphed by Roger Andrews, my additions in colour. The 20th century has two marked global warming periods, one in the first half and the other in the second half. The warming 1910 to 1945 is attributed by most to natural causes but that from 1970 to 1998 to an increase in atmospheric CO2. How do we know? Note that the gradients of the arrows are identical.
This is important since that late 20th Century warming trend tends to be projected to the year 2100 by many GCMs (climate models) with a rate of 0.6˚C in 40 years = 1.5˚C per century. This underpins many climate models, many of which are now running hot compared to observations. Now, let us imagine that a component of late 20th Century warming is down to natural causes, the climate change that happened before to which Lindzen refers. This significantly deleverages the Human caused component. Introducing a natural warming component to the late 20th century trend provides a way of reducing the CO2 (human) contribution that may be used to bring the hot-running models in line with observations. In essence, the data as it stands seem more consistent with a climate sensitivity in the region 1.5˚C±0.5˚C . The response of society to that outcome should be entirely different to the risks posed by 3˚± 1.5˚C climate sensitivity.
This, in my opinion, lies at the heart of the whole climate debate. How should politicians react to the spread in climate sensitivities to CO2 presented to them by the IPCC in AR5 that have a range form 1.5 to 4.5˚C?
The temperature data in Figure 1 can be placed in an entirely different context using proxy temperatures from the GISP2 (Greenland) ice core that provides a geological record of temperature change in the N Atlantic area that matches what is known from human historical records. That 1˚C of 20th Century warming does not look at all out of place in this context which rather worryingly shows the high latitude N hemisphere continuing to cool. We seem merely to be on the latest warming up leg that may come to an end in about 100 years time.
Figure 2 Proxy temperature reconstruction and forecast from the GISP2 ice core, Greenland. The current temperature rise attributed to the modern warm period does not look out of place set in the context of past climatic fluctuations referred to by Richard Lindzen. We strongly suspect that a component of recent warming is down to CO2 but we do NOT know what that proportion is compared with the natural warming cycle.
The summary rebuttal to John Cook is that Earth’s climate is always changing by natural causes. The glacial – interglacial cycles are subject to large swings in temperature and climate. The climate science community needs to present the evidence for the split between natural and manmade warming for the period 1975 to 1998. Simply attributing it all to CO2 is not scientific.