- In the GISP2 ice core, Greenland summit, Dansgaard – Oescheger (D-O) warm events 2 to 8  are all associated with low 10Be events most likely caused by active solar magnetic activity. The simplest explanation is that warm D-O events are caused by an active Sun.
- The mechanism by which active solar magnetic activity causes warming remains speculative but could be one of or a combination of the following 1) variable solar magnetic activity is accompanied by variable irradiance; 2) variable solar magnetic activity is accompanied by variable spectral output ; 3) cosmic rays affect global cloud cover ; 4) cosmic rays affect the position and activity of the polar vortex .
- There are at least 20 low 10Be events between 15,000 and 38,000 y before present with an average frequency of 2000 y. Not all low 10Be events are associated with warm D-O events, hence, other variables are also important in determining whether or not high solar magnetic activity results in warming at the Greenland summit.
- Glaciation on Earth is known to be modulated by the 41,000 y obliquity and 100,000 y eccentricity orbital cycles [5, 6]. And yet physical changes to Earth’s orbit are insufficient to create the changes in insolation required to trigger and end glacial periods. It is tentatively suggested that it is orbital cycles of the solar system acting on the Sun that causes solar variability that in turn modulates glaciation.
At the extremes, there are two competing hypotheses to explain climate change on Earth. “Climate Science” led by the International Panel on Climate Change (IPCC) advocates a number of manmade forcings, particularly the accumulation of greenhouse gasses in the atmosphere, that has led to global warming in the last 100 years. “Climate sceptics” are drawn to natural climate variability to explain most of the recent temperature trends where changes to the Sun over time is considered to be the main driver, leading to cyclical warming or cooling.
There are 34 years of satellite observations of the Sun and over this time the Total Solar Irradiance (TSI) changed very little (Figure 1). On this basis the IPCC effectively set the role of the Sun in modulating climate change to zero (Figure 2). This lacks credibility for three reasons 1) assuming that 34 years of observations may be applied to the Sun for “all time” is naive, 2) sceptics do not normally consider TSI to be the key variable (although it could be important) but instead advocate changes to solar magnetic activity and / or changes to the spectrum of energy leaving the Sun to be the key natural drivers of Earth’s climate  and 3) the IPCC approach ignores abundant evidence from geological records that changes in solar activity are linked to past climate change [8, 9, 10, 11].
Figure 1 Total solar irradiance [TSI] as measured by satellites . The cyclical variation in TSI follows the sunspot cycle. Sunspots are dark patches on the face of the Sun and one could reasonably expect that a large number of sunspots mid-cycle could lead to solar dimming. In fact the opposite occurs, when the Sun is active mid cycle, TSI increases. Note that the total variation in TSI is < 2 units (0.15%) which is insufficient to cause significant temperature variance on Earth. While TSI may not have changed much, declining solar activity had seen the pressure of the solar wind drop by 20% by 2008: “This is the weakest it’s been since we began monitoring solar wind almost 50 years ago.” [NASA 13]. Note how in 2009, TSI (and sunspot numbers) reached satellite age minima between cycles 23 and 24. Historically, low solar activity of this sort has been accompanied by occasional extreme cold winters in N America and N Europe.
Figure 2 Summary of climate forcing according to IPCC AR5 . Note that the only natural forcing considered is the Sun which is set to +0.05 Wm-2 (effectively zero). The IPCC have ignored dCloud, dVolcanos, dOcean currents, dSolar wind which are all known to be associated with natural climate variability, their imprint embedded within the historical climate record but ignored in forecasts.
Understanding climate history normally depends upon proxy records, i.e. direct information may not be available but secondary information may be used to estimate the required variable. For example the oxygen isotope (d18O) composition of carbonate fossils can be used to estimate the temperature of the seawater that the creatures lived in. d18O is a proxy for temperature. Cosmogenic isotopes provide a proxy for past solar magnetic activity. The two main cosmogenic isotopes used in climate history studies are 14C and 10Be. Both are made by the action of galactic cosmic rays on Earth’s upper atmosphere. 14C is made by the action of cosmic rays on N. It is naturally radioactive and decays to 14N with a half life of 5730 years.
10Be is made by the spallation of N and O by cosmic rays. It is also radioactive and decays to 10B with a half life of 1.4 million years. The longer half life makes 10Be useful for studying events up to 10 million years ago providing a tool to look back in time on a scale relevant to the ice age that began in the N hemisphere about 2.7 million years ago.
The key variable that controls the production rates of both 14C and 10Be is the intensity of cosmic ray bombardment of Earth and the key variable that controls that are fluctuations in the intensity of the Sun’s magnetic field. Hence the abundance of cosmogenic isotopes in geological layers provide a proxy for investigating past solar magnetic activity.
This post is the first in a mini series on cosmogenic isotopes and climate change and focusses on the extraordinary 10Be record of the GISP2 ice core from the Greenland summit. Hat tip to Mark BLR who posted links to the data in this comment on Tallblokes Talkshop a couple of weeks ago. Some of the questions being asked are:
- What causes glacial periods to end abruptly?
- What causes ice sheets to rebuild so soon after they collapse and melt?
- Why is the pattern of ice sheet collapse and growth correlated with Earth’s orbital cycles?
- What causes transient warm periods recorded in Greenland ice cores? (Dansgaard – Oescheger (D-O events)
- Why are historic climatic phenomena like the Indian ocean monsoon , the flora of North America [10, 11] and drift ice extent of the North Atlantic  all linked to cosmogenic isotope abundances?
The concentration of cosmogenic isotope 10Be in the GISP2 ice core (Greenland summit) shows a very high degree of covariance with temperature at many scales (Figure 3). There are five key variables that controls the concentration of 10Be in ice cores:
- The strength of the Sun’s magnetic field (the Solar wind)
- The strength of Earth’s geomagnetic field
- Variations in the intensity of incoming cosmic rays
- The snow / ice accumulation rate
- The radioactive decay of 10Be
Figure 3 The 10Be data come from NCDC NOAA  and the temperature and accumulation data come from ref . I was surprised to find that the 10Be is not archived in The Greenland ice core gateway . 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.
On the time scale of GISP2 10Be (40,000 years) variations in Earth’s magnetic field are not considered to be significant ; variations in incident cosmic rays upon the solar system are not considered significant ; and variation due to radioactive decay on this time scale is also insignificant. Therefore, the 10Be profile through GISP2 may be interpreted in terms of variations in the strength of the solar wind and in the snow / ice accumulation rate.
The raw 10Be data plotted in Figure 3 presents an over simplified picture since the accumulation rate of ice must be taken into account. I was more than a little surprised to learn that the rate of ice accumulation at the Greenland summit increased by a factor of 5 from the glacial to interglacial Holocene  (Figure 3). This is about as counterintuitive as climate data comes. The story goes that a warmer climate brought more precipitation (snow fall) but also disproportionally larger rate of ice loss around the margin of the ice sheet. The ice accumulation profile can be split into three parts: 1) largely uniform accumulation rate from 40,000 to 15,000 y; 2) large swings and step change up in accumulation rate at the end of the glaciation and associated with the Younger Dryas, 15,000 to 10,000 y and 3) largely uniform accumulation during the Holocene 10,000 to 0 y. The accumulation data are based on counting and measuring layers and then applying an ice flow / de-straining model .
In order to remove the effect of variable accumulation rate the 10Be data have been normalised to a datum of 0.1 m ice / y (Figure 4). In intervals where accumulation rate is uniform, the normalisation does not significantly impact the structure of the data. But in the 15,000 to 10,000 y interval it imparts some irrational structure to the data, for example a spike towards a “quiet Sun” at the end of the last glaciation. And data for the whole of the Holocene are displaced towards higher 10Be which is counterintuitive.
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.
The 10Be story does not support one of the hypotheses I was wanting to test in that there is no evidence for increased solar activity being responsible for the termination of the glacial period (Figure 4). However, I suspect uncertainty in the ice accumulation model may impart spurious structure to the normalised 10Be profile and that hypothesis remains untested. There is variability in 10Be in the 40,000 to 15,000 and 10,000 to 0 y intervals that carry a solar signal . The former is examined in more detail below, while the latter will be the subject of a subsequent post.
The Dansgaard – Oescheger events
The D-O events are pervasive throughout Greenland ice cores and represent transient phases of warming at the summit of about 5˚C (Figure 5). These events are also recognised in Antarctic ice cores but are less obvious on the southern continent.
Figure 5 The temperature record from  and labelled D-O events 2 to 8 in blue from . 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.
D-O events 2 to 8 are labelled on Figure 5 in blue  where it can be seen that each of these events is associated with spikes towards low normalised 10Be concentrations. Low 10Be, normalised for accumulation rate, would equate to an active solar wind shielding Earth from Cosmic rays. Note how prolonged D-O event 8 is associated with a prolonged period of active Sun.
It is difficult to escape the conclusion that warm D-O events are linked to periods of active solar activity and are most likely caused by it. However, there are many more 10Be events in this interval than there are D-O events. I count 20 in all, there could perhaps be a couple more, giving a mean frequency of 2000 y. Notably, there could be some additional “weak” D-O temperature events than counted before  at low 10Be events 7, 10 and 15. Thus it may be concluded that changes in solar magnetic activity on occasions impacted temperature at the Greenland summit and on other occasions did not. It appears that the impact of solar variability has diminished with time post 28,000 y, after D-O event 3. This suggests that solar activity is not the sole variable controlling temperature in Greenland. N hemisphere ice sheet mass and extent, ocean currents, orbital parameters and solar variability may combine to control atmospheric circulation patterns.
While a connection between variable solar magnetic field strength and climate change on Earth has been recognised for a long while understanding the exact mechanism has remained elusive. This to a large extent is down to Satellite Man not having direct observations of the quiet Sun. With the Sun now entering a slumber, both solar and consequential climatic observations are being made for the first time. Europe has been recently exposed to extreme cold winter conditions reminiscent of the Little Ice Age and North America has recently been exposed to extreme cold caused by an expanded, mobile polar vortex. Several, perhaps dependent process, linking solar magnetic activity to climate change are summarised briefly below. They fall into two broad categories: 1) the impact of variable cosmic ray flux on the atmosphere and 2) other changes to the Sun that accompany variable geomagnetic activity.
Cosmic ray flux and cloud formation. Svensmark  has proposed that increased cosmic ray flux may increase the nucleation rate of low clouds leading to a cooling of The Earth. This theory has been tested at CERN but remains largely unproven. We will need to wait and see if increased cosmic ray bombardment that is to be expected with the current solar slumber leads to an increase in cloud cover.
Cosmic ray flux, impact on stratosphere and polar vortex.
It was shown that long-term oscillations of the amplitude and sign of Solar Activity/Galactic Cosmic Rays effects on troposphere pressure at high and middle latitudes are closely related to the state of a cyclonic vortex forming in the polar stratosphere. 
The timing of the pine minima is correlated with a series of quasi-periodic cold intervals documented by various proxies in Greenland, North Atlantic, and Alaskan cores and with solar minima interpreted from cosmogenic isotope records. These events may represent changes in circumpolar vortex size and configuration in response to intervals of decreased solar activity, which altered jet stream patterns to enhance meridional circulation over eastern North America. 
Solar magnetic activity and energy spectrum.
Although sunspots themselves produce only minor effects on solar emissions, the magnetic activity that accompanies the sunspots can produce dramatic changes in the ultraviolet and soft x-ray emission levels. These changes over the solar cycle have important consequences for the Earth’s upper atmosphere. [NASA 13]
SORCE observations made during the decline of solar cycle 23 reveal a remarkably strong decrease in mid-ultraviolet flux, some four to six times greater than previous spectral irradiance reconstructions.
If the updated measurements of solar ultraviolet irradiance are correct, low solar activity, as observed during recent years, drives cold winters in northern Europe and the United States, and mild winters over southern Europe and Canada, with little direct change in globally averaged temperature [2 Met Hadley]
- Warm D-O events at the Greenland summit are associated with low 10Be events most likely caused by high levels of solar magnetic activity. In other words, warm D-O events are linked to an active Sun.
- To explain away the association of 10Be and temperature at the Greenland summit by some other process we would need to invent a new ice accumulation rate model that cancelled out the 10Be concentration profile.
- An active Sun shields Earth from galactic cosmic rays and this can affect Earth’s climate in a number of benevolent ways. Our Sun is now in the process of going very quiet and that benevolence may abandon N Europe and N USA intermittently during winters to come for perhaps another 30 years or more.
- There are two competing theories to explain climate change on Earth. One predicts that Earth will become monotonically warmer with increasing green house gas emissions. The other predicts climatic fluctuations linked to natural variability of the Sun’s activity where low solar activity, like we have now, may cause periodic extreme cold conditions in N America and N Europe.
- Globally averaged lower troposphere temperatures over the last 100 years is not a sound metric for describing climate change on Earth.
I have a PhD in isotope geochemistry, but this does not make me an expert in the interpretation of cosmogenic isotope data from ice cores, although I have extensive experience in the interpretation of isotope geochemical data from bore holes. I have not found any reference linking directly low 10Be to the D-O events. If there are any papers or blog articles out there please let me know and I will ensure credit is given where credit is due.
The original paper by R. C. Finkel and K. Nishiizumi (1997)  does recognise the connection between 10Be and d18O variance but seemed reluctant to draw the conclusion that D-O events are caused by solar variability.
 Richard B. Alley et al (2010) History of the Greenland Ice Sheet: paleoclimatic insights. Quaternary Science Reviews 29 (2010) 1728-1756
 Sarah Ineson et al (2011) Solar forcing of winter climate variability in the Northern Hemisphere Nature Geoscience PUBLISHED ONLINE: 9 OCTOBER 2011 | DOI: 10.1038/NGEO1282
 Svensmark et al (2007) Experimental evidence for the role of ions in particle nucleation under atmospheric conditions Proc. R. Soc. A (2007) 463, 385–396
 S Veretenenko and M Ogurtsov (2013) The stratospheric polar vortex as a cause for the temporal variability of solar activity and galactic cosmic ray effects on the lower atmosphere circulation Journal of Physics: Conference Series 409 (2013) 012238
 Clive Best: Phenomenology of Ice Ages
 Euan Mearns: The Ice Man Cometh
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 NASA The Sunspot Cycle
 IPCC AR5 Summary for policy makers
 NCDC NOAA 10Be concentration (103 atom/g) in GISP2 ice, 719 – 2253 m
 NCDC NOAA GISP2 Ice Core Temperature and Accumulation Data
 NCDC NOAA The Greenland Ice Core gateway
 Finkel, R.C., and K. Nishiizumi. (1997). Beryllium 10 concentrations in the Greenland Ice Sheet Project 2 ice core from 3-40 ka. Journal of Geophysical Research 102:26699-26706.
 Cuffey, K.M., and G.D. Clow (1997), Temperature, accumulation, and ice sheet elevation in central Greenland through the last deglacial transition. Journal of Geophysical Research 102