Sir, I write to contradict Stephen Foster regarding the greenhouse effect and global warming. It is rather unfortunate that he chose to base his arguments on an extensively criticized paper by Gerlich and Tscheuschner. Not being a physicist myself I do not want to go into the details, but I would advise those who want to delve further into the matter to simply Google ‘Critique of Gerlich and Tscheuschner’. It seems to me from my reading of those critiques that the authors have misunderstood the laws regarding atmospheric physics. I would far prefer to have a debate about global warming with someone who has taken the trouble to familiarize themselves thoroughly with the behaviour of planetary atmospheres – which can be done by reading Professor Raymond. Pierrehumbert’s comprehensive “Principles of Planetary Climate” (Cambridge University Press, 2010).
What I am about to write, by the way, has nothing to do with so-called ‘consensus’ science. It is based on my reading of the available scientific literature.
Dr Foster produces arguments on what the ice cores have to say about the relation between CO2 and temperature. It was indeed thought that CO2 lagged temperature in Antarctic ice cores, but the latest data (Parrenin et al., Science 339, 2013) suggest that it did not. Our understanding of glacial to interglacial warming now is that insolation changes made the ocean warm, which immediately (i.e. at the same time) released CO2 into the atmosphere, which immediately provided a positive feedback to the warming. The two moved in lockstep. This is not surprising if you look at geological history. It is difficult to explain the cooling from the mid Eocene at 50 Ma to the current Ice Age, without calling on changes in CO2 caused by the changing balance between emissions of CO2 from volcanism, and its extraction by weathering and eventual storage in sediment. That has been known as the main mechanism governing climate change since Ebelmen in 1845 and Chamberlin in 1899.
In my view Dr Foster, like many global warming contrarians, makes a mistake in assuming that CO2 and temperature should be tied together tightly over the past 100 years or so if the greenhouse theory of anthropogenic global warming is correct. It is not only CO2 that affects atmospheric temperature. Volcanic dust does too, cooling the atmosphere, as do aerosols emitted from our own industrial processes. It is the emissions of these aerosols, well documented by the Russian climatologist Milkhail Budyko in the 1970s, that would seem to explain at least some of the mismatch between temperature and CO2 in the period 1945-1970.
Equally, it is well known that large El Niño events emit oceanic heat into the atmosphere pushing global temperatures above the climbing temperature trend, while intervening cold La Niña events create a cold Pacific Ocean that cools the atmosphere below the trend. The longer and slower Pacific Decadal Oscillation has the same effect on the 20-year time scale. It likely played a role in the cooling between 1945-1970 and in the present slow down in global warming since the year 2000. So there are good reasons why the CO2 and temperature signals will not be precisely coupled. This is not a single-issue game.
Dr Foster goes on to make several assumptions about how CO2 will interact with infrared radiation in the atmosphere. Unfortunately he does not seem to be aware of classic papers like that of Augustsson and Ramanathan (J. Atmos. Sci. 34, 1977) that explain how absorption works at different concentration levels for both the weak and the strong absorption bands of CO2. While the greenhouse effect due to the 15µm bands does increase logarithmically with respect to CO2, that due to the weak bands increases linearly. Hence “the warming effect of CO2 on the global surface temperature may never saturate out even for large increases in CO2 concentrations”.
Dr Foster mentions Prof R Lindzen of MIT. I heard Dr Lindzen speak not long ago at a meeting in the Houses of Parliament. He was quite clear that CO2 is a greenhouse gas and that it does cause the atmosphere to warm. Where he disagreed with the ‘global warmers’ was that he did not believe that the projected temperature increases would be as large as the IPCC suggests.
Dr Foster then brings in the sun. We have ample information about its behaviour over the past 2000 years from the distribution of cosmic-ray induced 10Be and 14C. These data (Steinhilber et al, PNAS 109, 2012) show that the medieval warm period and other warm intervals within the Little Ice Age correspond with periods of high solar output. One of those solar output events began around 1900 and continued to about 1970, then a decline began that continues to this day (Lockwood, Proc. Ropy. Soc. A, 4676, 2010). Thus solar energy has been going down while global temperature has been going up. Equally, global temperatures were going down or staying flat while solar energy was going up from 1945-70. Ergo, there is no obvious link between the sun and our temperature since about 1940.
The IPCC numerical climate models do, contrary to Dr Foster’s assumptions, take these various sources of information into consideration in their numerical models of the climate system. Those models’ outputs match recent meteorological data well up to the present time, so it cannot be said that anthropogenic global warming has been disproved by the models’ performance. Rather the opposite.
I should close by reiterating an observation from the addendum to the GSL’s climate change statement (2013). Insolation controlled by the Earth’s orbit and axial tilt has been decreasing for the past 10,000 years, driving us into a neoglacial period characterized by the Little Ice Age, which was especially well developed in the northern hemisphere. That insolation is still low. If insolation is not rising, and solar output has been falling since about 1970, what has made global temperatures increase if not greenhouse gases? The answer, I am sure, has nothing to do with politics.
Colin Summerhayes