In a paper in Geoscience Canada, Veizer (2005) states that ‘the multitude of empirical observations favours celestial phenomena as the most important driver of terrestrial climate on most time scales‘. This paper was cited by a contributor to a debate on the website openDemocracy . In short, the argument is that the cosmic ray flux (CRF, also denoted as ‘GCR’ – galactic cosmic rays – in some papers) is the most important factor affecting our climate. Since this issue is likely to crop up from time to time, it is worth taking a closer look at the Veizer (2005) paper ( Here is a link to short summary, but the actual paper requires subscription). [Update: The actual paper is now available as supplemental material on the Geoscience Canada website.] I will try to show that CRF explanation for the recent global warming is easy to rule out.
One of the main planks of the argument that CRF is responsible for the most recent warming is based on figure 14b in Veizer (2005), where there appears to be a trend in CRF from eg Climax neutron monitor (also, see plots at this URL). This CRF-curve was a surprise to me, and furthermore, it’s at odds with CRF-evolution presented in figure 17 in the very same paper (showing no systematic change) – how can these accounts be so different? The inconsistency becomes even more apparent when it is argued that the ‘balloon and satellite data ([Veizer, 2005] Fig. 17) do not show any clear temperature trend… Instead, their interannual temperature oscillations correlate clearly with … CRF’ (p. 22, 2nd column). Again, no long-term trend in the CRF-data. It has been argued earlier on RealClimate that there is no long-term trend in the modern CRF measurements. The lack of systematic trends in CRF and other solar activity proxies is well-known and published in the scientific literature (eg. Richardson et al, 2002). In fact, the CRF curves presented by some of the key cosmic-ray hypothesis proponents, Marsh & Svensmark, do not exhibit any trend, yet it has been claimed that CRF is responsible for the most recent warming (Marsh & Svensmark say that the wiggles correlate, but don’t discuss the [or lack of] observed trends).
There are other aspects which appear as problematic for the CRF-interpretation for the recent global warming. First of all, according to IPCC (2001) the night-time temperatures have in general increased more than the day-time temperature (the diurnal temperature range, DTR, has decreased in most areas, except over middle Canada, and parts of southern Africa, south-west Asia, Europe, and the western tropical Pacific Islands). Since individual clouds have a life time of hours, and the CRF-interpretation involves changes in the reflected light as well as ionisation, a climatic response from change in CRF is hypothetically almost instantaneous, and it is a challenge to explain why the night side (where there is no sunlight and hence reflection cannot play a role) warms more strongly than the dayside, if the CRF were to drive the recent warming trend. Another equally important challenge is the fact that there are pronounced ~11-year variations in the CRF, but the presence of ~11-year variations in the global mean temperature are much less pronounced than the trend over the 3–4 most recent decades. If the CRF were so important (and the cloud response near-instantaneous) why do we not see more pronounced ~11-year variations in the global mean temperature?
The paper also gives the impression that there is no trend in satellite-based temperatures (MSU), which is wrong. There are various analyses of the satellite trends, all of which indicating a warming trend in the troposphere.
When Veizer summarises in bold type face ‘(above) empirical observations on all time scales point to celestial phenomena as the principal driver of climate’, he neglects to discuss the fact that the stratosphere has been cooling, which at higher levels is consistent with an enhanced greenhouse effect (most of the cooling in the lower stratosphere is related to changes in ozone) but inconsistent with enhanced solar activity and his CRF-hypothesis. Another argument Veizer uses to support his hypothesis is that the correlation between the proxy indicators for CRF is better correlated with ‘climate’ than between CO2 and climate. Yet he does not provide any references or justify his argument. I find this statement rather puzzling, as it seems to me that there is a good correlation between the CO2 and temperature proxies such as can be seen in Veizer’s own figure 7. The same seems to be the case in Fig. 1 below:
Fig.1: A comparison between CO2 and CRF indices with temperature proxy. Superimposed is the Beryllium-10 (blue). All curves are standardised. (paleaoproxy.R).
If we’re looking at the last century, then there is a sulphate aerosol “blip” that worsens the CO2-T correlation. But there are also times when there are distinctive features in the CRF proxies in Veizer (2005) figure 8, when there is no corresponding response in the temperature (figure 7 of Veizer, 2005). Actually, I do not see much resemblance between the CRF-proxies presented in the paper and the temperature proxy, and there is no quantitative statistical analysis of their correspondence. Thus, the above statement appears to be a value judgement, rather than an objective observation. Along the same vein, the paper claims there is a good degree of correspondence between the timing sunspot minima and minima in precipitation curves in Veizer (2005) figure 16. I do not find his (hand waving?) arguments convincing. Note, the paper does not offer any quantitative statistical analysis on the correspondence of these curves. Nor does it discuss how the CRF-proxies may have been affected by past variations geomagnetic field, which clearly would degrade any correlation between CRF and climatic indices. It should be noted that proper attribution studies don’t just do correlations, they are rather more sophisticated. There is the possibility of the presence of a common cause that may have affected the various isotope records (representing both CRF and ‘climate’), and Veizer does not even mention the possibility that the deposition efficiency of these may be affected by climate itself (e.g. circular reasoning).
At other times, the discussion misrepresents the current knowledge when comparing only the clouds’ albedo effect with the CO2 forcing, and not the net effect including the absorption of long-wave radiation (p. 14, 2nd cloumn). The Veizer (2005) paper also tends to make strong statements based on controversial papers (eg. Soon and Baliunas, 2003; p .20, 3rd column – several editors left the journal after it was published because they felt it was flawed). I find Veizer’s reference to other work very selective. The role of CRF as a driver for climate is indeed controversial, and this fact is not acknowledged in the paper.
On a more technical note, an R-script gcr.R is available from this site which helps you retrieve the CRF-data over the Internet and plot the data. Please use it, play around, and see for yourself. Another script, paleaoproxy.R is also available here, and is makes Fig. 1 above.
Richardson et al. (2002), “Long-term trends in interplanetary magnetic field strength and solar wind structure during the twentieth Century”, J. Geophys. Res., Vol 107, A10
Veizer, J. (2005) “Celestial Climate Driver: A Perspective From Four Billion Years Of The Carbon Cycle”, Geoscience Canada, vol 32, no. 1, 13-30.
30 June 2005
Addendum: “Celestial Driver” Part 2
In the above post, time permitted us only to discuss a few of Veizer’s arguments, focussing mainly on the cosmic ray flux. Here we take a look at some of the other arguments presented in his paper.
Solar cycle length
Veizer suggests the recent global warming might be driven by changes in solar activity (his Fig. 14a – dashed line is temperature, solid line with diamonds is solar cycle length). But the figure only shows the temperature record from 1935-1990, even though of course more recent data are available. Veizer must be aware that in view of these more recent data, the scientist who originally proposed this correlation in 1991, Knud Lassen, has concluded in 2000 that solar cycle variations cannot explain the ongoing warming trend .
In the figure below, we have superimposed the standard CRU data set (blue curve) of global mean temperature on Veizers graph.
We see that the graph selectively shows a part of the time series dominated by the well-known temporary “dip” in the global warming trend, reaching a minimum around 1970. The correlation of temperature and solar cycle length applies mainly to this “dip” in the curves. Thus, solar cycle variations may or may not explain this “dip” (one similar-looking dip in two curves is not a significant correlation and could easily be coincidence; there is a better-founded explanation for this “dip” resulting from cooling by aerosol emissions – see the figure from Hansen et al. coming up below).
But there is no indication that solar cycle variations could explain the ongoing warming trend. There is simply no significant trend in this (or any other) solar indicator since 1940. Veizer fails to discuss the key issue (namely, whether the data support the idea that the warming trend, rather than just the temporary dip, could be explained by solar cycle variations). The (often faulty or misleading) use of these solar cycle data by “climate sceptics” has quite a pre-history, see e.g. Damon and Laut (2004). Note that the relative vertical scale of the curves is arbitrary. The article by Damon and Laut (2004) also shows that when solar cycle length is scaled up as much as it is in the above figure in order to match the 1940-1990 temperature record, that this implies a great mismatch for the earlier periods in time. Veizer should be aware of this problem of his proposed match, but he fails to mention it.
As an aside, one of the data points in the above graph is incorrect; the National Geophysical Data Center gives a solar cycle length of 11.8 years for 1963, where Veizer plots 11.0 years.
 P. Thejll and K. Lassen, 2000: Solar forcing of the Northern hemisphere land airtemperature: New data. Journal of Atmospheric and Solar-terrestrial Physics, Vol. 62 (13),1207-1213.
Greenland temperature variations
Veizer’s paper argues that the local preindustrial climate fluctuations over the past millennium in Greenland were not driven by CO2. As a proof, Veizer shows a temperature reconstruction for Greenland together with the CO2 concentration in his Fig. 12. Now, the preindustrial CO2 concentration over this period was constant, and therefore nobody has ever proposed that CO2 could have caused any climate variations during this time. It obviously can’t. Showing this in a plot is thus a completely moot point that is clearly not aimed at any fellow scientist; it is something meant to impress uninformed lay-people. Indeed, the graph is not from a scientific publication, but was reproduced from a popular climate-sceptics book that has been distributed in Germany by the coal-industry lobby.
Using a time period when CO2 did not change at all, to support a general conclusion that “CO2 is not the driver of climate change” and hence is not responsible for the current warming, is hardly logical. It merely highlights the fallacy of looking for one single “driver” that explains climate variations on all time scales. It is well-established in climatology that different causes and mechanisms have caused climate changes in the past (orbital variations, plate tectonics, solar variability, volcanic eruptions, etc.), so that a cause-effect relationship has to be determined for each individual case, rather than looking for one overall “driver”.
(As an inconsequential but telling aside, Veizer wrongly attributes the CO2 curve in Fig. 12 to the Greenland ice core GISP2. It is well-known amongst paleoclimatologists that there are no successful CO2 measurements from Greenland, the record shown is obviously from Antarctica. It is strange how this slipped by the journal’s review.)
A strange temperature graph
Veizer publishes the above graph to suggest that temperature and CO2 concentration do not look alike, hence CO2 has not caused the warming.
First, Veizer’s temperature curve looks unlike anything published in the scientific literature. Temperature in the year 2000 no warmer than 1960? Clearly something is wrong with this – seemingly hand-drawn – graph. It is once again not a scientific diagram but lifted from the german climate sceptics book “Klimafakten” mentioned above. It is remarkable (and perhaps a novelty in the history of science) that the paper takes several graphs straight from climate sceptics PR material produced for lay-people, rather than basing its case on peer-reviewed scientific sources. It is surprising that the faulty temperature graph – which sticks out like a sore thumb to any climatologist – could slip through the review procedure at Geoscience Canada.
Second, this is a very naive argument. CO2 has increased in a smooth trend, hence it can obviously only explain the overall trend in the temperature data, but not any shorter-term variability around this trend. Nobody has ever suggested it should, thus this graph is another moot point clearly not aimed at scientists.
The observed temperature evolution can of course only be the result of all forcing factors combined (including solar variability, volcanic eruptions, and man-made aerosols) – not CO2 alone. If all these forcing factors are taken into account in a recent model simulation, the temperature evolution looks like this:
The black line is the average of five model runs. This is not only in excellent agreement with the observed temperature changes at the surface (blue stars), it also correctly reproduces the observed heat storage in the oceans – a strong indicator that the model’s heat budget is correct. The agreement of this model with observations is particularly good and perhaps partly fortuitous, given that there is still uncertainty both in the climate sensitivity and in the amplitudes of the aerosol and solar forcings. But our main point does not depend on that and is robust: with any model and any reasonable data-derived forcing, the observed 20th Century warming trend can only be explained by anthropogenic greenhouse gases, while other factors can explain the shorter-term variations around this trend. The serious scientific discussion is about the exact contribution of each factor, not about identifying one single “driver”.
Is the CO2 increase anthropogenic?
In this paper (as in the past) Veizer is strangely vague on the question whether the recent CO2 increase in the atmosphere – which is at the very core of global warming concerns – is caused by humans. He claims that the “carbon cycle is piggy-backing on the water cycle”, and he states that “while CO2 may act as an amplifying greenhouse gas, the actual atmospheric CO2 concentrations are controlled in the first instance by the climate, that is by the sun-driven water cycle, and not the other way around.”
Veizer’s alternative hypothesis for 20th century global warming does appear to be: the warming was caused by a “celestial driver” (i.e., a change in solar activity – despite the lack of observed trend), and it is this warming which has increased the CO2 concentration, not the other way round.
If this is Veizer’s hypothesis (and we welcome his clarification if we have misinterpreted it), then this is indeed radical. That humans have caused the increase in CO2 is proven beyond reasonable doubt, and is generally accepted even by “climate sceptics”. We have summarised the evidence here. Not only do we know how much CO2 we emitted (more than is now left in the atmosphere – which means that the natural reservoirs have taken up part of our CO2 emissions, rather than having released CO2 in response to a climate change). That the increasing amounts of CO2 in the atmosphere come from fossil fuels was already demonstrated by isotope analysis in the 1950s. CO2 increases not only in the atmosphere but also in the global oceans – this is documented by 10,000 measurements – and very likely in the biosphere. And it would be difficult to argue that through a natural climate change, CO2 has suddenly increased to values about 30% higher than at any previous time for the past 650,000 years, and that this occurred by chance just at the same time as humans released more than enough CO2 to explain the rise.
In the light of this evidence, it is difficult to believe that Veizer means to suggest the CO2 rise is a response to a natural warming. So perhaps Veizer does agree that the CO2 rise is caused by humans? Then it logically follows that Veizer also agrees there must be anthropogenic warming, since Veizer does agree to that basic fact of physics: that CO2 is a greenhouse gas – see his quote above.
Some final remarks
It is a normal, essential and very valuable part of science to develop and present alternative hypotheses, even if they appear unlikely at first, go against the mainstream, or turn out to be wrong later. Without this process, there would be no progress in science. Hence, any attempt to find an alternative explanation for the ongoing global warming is to be welcomed.
However, to facilitate this process, science has developed a culture with certain rules and standards for scientific discourse. These rules include, for example, that all relevant data are shown: if I want to make a credible case for any hypothesis, I must not hide parts of a data set which do not fit my hypothesis. Rather, I need to discuss them. In a scientific paper, a selective or misleading graph may be of little consequence (except for the author’s reputation), as scientific readers are familiar with the further data and the previous scientific discussions, so they can easily judge the merits of an argument. However, it is in our view more serious and ethically questionable when such selective and misleading use of data is made in a press release: an example from a media release by Veizer / Ruhr University is discussed here.