23 June 2010

Is There Scientific Consensus on Climate Change?

Research Shows Scientists Agree on Global Warming

Researchers at Stanford and the University of Toronto noted that some people dispute whether there is "scientific consensus" on the reality and causes of climate change. They decided to find out how much consensus there really is.

The Intergovernmental Panel on Climate Change concluded that anthropogenic greenhouse gases have been responsible for "most" of the "unequivocal" warming of the Earth's average global temperature over the second half of the 20th century. But how many scientists who study the subject really believe that? And which scientists disagree?

They tried to "examine a metric of climate-specific expertise and a metric of overall scientific prominence as two dimensions of expert credibility in two groups of researchers", that is, those who agree with the IPCC's conclusion and those who do not.

They "compiled a database of 1,372 climate researchers based on authorship of scientific assessment reports and membership on multisignatory statements about ACC [anthropomorphic climate change]. We tallied the number of climate-relevant publications authored or coauthored by each researcher (defined here as expertise) and counted the number of citations for each of the researcher’s four highest-cited papers (defined here as prominence) using Google Scholar. We then imposed an a priori criterion that a researcher must have authored a minimum of 20 climate publications to be considered a climate researcher, thus reducing the database to 908 researchers."

Of those climate researchers, only a few percent were unconvinced of the IPCC's conclusion. The other 97-98% agreed with the IPCC that climate change is real and is mostly caused by human activities. The study also found that those researchers who published more and were cited more often in the field were more likely to be convinced by the evidence, and that those unconvinced by the evidence were generally those with fewer publications and citations.

"Not all climate researchers are equal"

They concluded that "the expertise and prominence, two integral components of overall expert credibility, of climate researchers convinced by the evidence of ACC vastly overshadows that of the climate change skeptics and contrarians. This divide is even starker when considering the top researchers in each group. Despite media tendencies to present both sides in ACC debates, which can contribute to continued public misunderstanding regarding ACC, not all climate researchers are equal in scientific credibility and expertise in the climate system."

The abstract of the PNAS paper is here, with access to the full paper as PDF. (Bless scientists and their grant providers who pay so that their papers can be open access, not restricted just to the academic community and other professional researchers.)

Dueling Experts

Often debates about climate policy come down to "My experts can beat up your experts". This research shows that there are objective measurements that can reveal which experts are more expert, and therefore should be given more weight in guiding policy. (Not that policy is driven by experts--it's politics.)

Science, after all, is substantially about measuring and quantifying. Even scientific expertise can be measured and quantified. This particular method is not the last word in such analysis. It is true that the lonely dissenter, out of step with the general consensus, who can't get a grant and therefore publishes less, may have a useful contribution to make. In fact she may be right and all the experts may be wrong. But this is not likely. When the skew is 881 to 27, the consensus is clear.

David Wheat's Science In Action site has articles about science and math in the real world, weird science, science news, unexpected connections, and other cool science stuff. There is an index of the articles by topic here.

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