On the evening of Sunday, August 10, I asked for citations of research papers in reputable scientific journals that examine the causal link between anthropogenic carbon dioxide and global warming and that quantified the extent of this warming.** In most areas of science, when a clearly articulated theory dominates, a student can nominate several seminal papers that have influenced and directed thinking in that area.
Many people believe increasing concentrations of carbon dioxide lead to increases in temperature. This can be demonstrated in a laboratory, but when you scale up laboratory experiments to the real world, what happens? We know from ice cores that global temperatures have decreased in the past even as carbon dioxide has continued to rise. There are some so-called skeptics who claim that in the real world the radiation forcing of carbon dioxide is overwhelmed by the more powerful constraints of evaporation cooling from the tropical oceans.
I cross-posted my request for papers as a comment on John Quiggin’s blog as I was interested to see what those who follow the issue and generally subscribe to AWG theory would suggest by way of best papers. The next morning my request turned into a bet when Michael Duffy offered to put up $1,000.
By Monday evening the thread at Professor Quiggin’s blog had thrown up three papers that the commentators suggested potentially provided explanation of the causal link and a quantification of the extent of warming. Interestingly one of them was published as long ago as 1938 – perhaps it was a seminal paper.
The papers are:
1. Callendar, G.S., 1938. The artificial production of carbon dioxide and its influence on temperature. Q. J. R. Meteorol. Soc., Vol 64, 223–237.
2. Hofmann, D.J., J. H. Butler, E. J . Dlugokencky, J . W. Elkins, K. Masarie, S. A. Montzka and P. Tans, 2006. The role of carbon dioxide in climate forcing from 1979 to 2004: Introduction of the Annual Greenhouse Gas Index, Tellus B, Vol 58, 614-619.
3. Crowley, T. 2000. Causes of Climate Change Over the Past 1000 Years. Science Vol 289: 270-277.
I have posted comment on two of the papers concluding they do not fit the criteria (part 2 and part 3 of this series of blog posts) and I understand that the author of one of the papers, Thomas Crowley, posted comment at John Quiggins site acknowledging that his paper did not deal with causation.
This is a key point acknowledged by Professor Quiggin in the thread at his blog, though he initially went as far as to claim that there are “hundreds of papers on both the causal link and the question of sensitivity” but could only cite a few papers which he suggested dealt with the issue of sensitivity later in that same thread.
While many scientists would claim you can’t deal with sensitivity if you haven’t established causality, this is attempted in climate science including by correlating output from computer models. Aynsley Kellow has explained this as a technique of post-normal science in his book, Science and Public Policy: The Virtuous Corruption of Virtual Environmental Science (Edward Elgar, 2007).
The 1938 paper by G.S. Callendar is the closest of the three to fitting the criteria in that it attempts to answer the types of questions that a scientist would need to consider if a credible link is to be established between anthropogenic carbon dioxide and warming in the real world. However, it is clear from the discussion section within the paper that Mr Callendar’s findings were not peer reviewed, and furthermore not accepted by his colleagues. Indeed, the following comments are included as part of the discussion within that paper which is presented as ‘a reading’ followed by discussion (pg 237): 1. the numerical results could not be used to give an indication of the order of magnitude of the effect of carbon dioxide, and 2. it is not clear how absorption energy by carbon dioxide is calculated. These are important points that the Callendar paper explains have not been properly examined.
There are of course the voluminous reports from the United Nation’s Intergovernmental Panel on Climate Change, with their findings and theories on popular Anthropogenic Global Warming (AGW) theory. The content of these reports, endorsed by governments around the world, have been repeated over and over, for example, in the recent influential report by economist Ross Garnaut to the Australian government. It is apparent, however, that a body of science published in peer-review journals, establishing a causal link between anthropogenic carbon dioxide and warming and quantifying the extent of this warming, is lacking but would be expected to exist to support popular AGW theory.
** I understand causality to be the relationship between cause and effect. American Environmental Scientists, S Marshall Adams, suggests seven causal criteria for evaluating the relationship between specific environmental stressors and observed effects: strength of association, consistency of association, specificity of association, time order of temporality, biological gradient, experimental evidence, and biological plausibility (Establishing causality between environmental stressors and effects on aquatic ecosystems. Human and ecological risk assessment. Feb 2003, 9, 1, pg. 17-35).