CLIMATE CHANGE:

Climate scientists broadly agree that most of the conclusive warming over the last half of the 20th century was caused by human activities. This climate change is having detrimental effects today, and may get worse in the near future.

James Hansen and coworkers recently reported that glaciers on the Tibetan plateau are melting due to black soot, threatening the water supplies of over one billion people. Phillip van Mantgem and coworkers reported that the death of trees in western United States forests is accelerating and widespread, with climate change as the likely culprit. Simon Donner predicts that coral reefs may undergo frequent and damaging bleaching by the end of this century, due to global warming.

While questions remain about some of the scientific details of anthropogenic (human-caused) climate change (e.g. how much has happened and may happen in the future), and while there's much debate on what to do about it (e.g. climate engineering, limiting carbon emissions, trapping it underground, or nothing), there's little debate on its existence. Nevertheless, a vocal minority of scientists and others continue to deny scientific reailty, and claim that large numbers of scientists are on their side.

The crazy guy on the sidewalk screaming of an imminent alien invasion is ordinarily more entertaining than dangerous. Unfortunately, "climate change deniers" have a disproportionate effect on popular opinion and governmental climate change policies, placing the future of the entire planet at risk.

William Anderegg, Stephen Schneider (Stanford University, United States), and coworkers have taken an important step towards removing the scientific veneer of those who deny the existence of anthropogenic climate change. They have demonstrated the enhanced scientific expertise and prominence of climate scientists who accept the scientific reality of anthropogenic climate change.

Defining climate science expertise and prominence.

The scientists compiled a database of nearly 1400 climate researchers. They lumped the researchers into two groups.

One group is convinced of the evidence supporting the reality of anthropogenic climate change, i.e. climate scientists who have signed a statement supporting the primary conclusions of the Intergovernmental Panel for Climate Change (IPCC) Fourth Assessment Report (over 900 researchers). The other is not, i.e. climate scientists who have signed strongly dissenting statements on its conclusions (nearly 500 researchers).

The scientists used Google Scholar to find the total number of climate science technical publications published by these people (by roughly July 2009). This is a measure of scientific expertise.

They also determined how many times each of the top four publications were cited by others. This is a measure of scientific prominence.

The scientists imposed the condition that their analyzed data set was comprised of climate researchers who had contributed to at least 20 publications within this time frame, bringing the total number of analyzed researchers down to a little over 900 (over 800 climate supporters and a little under 100 climate skeptics). Reducing the minimum number of publications to 10, and increasing it to 40, does not qualitatively impact their findings.

They do not claim that their sampling represents the true absolute proportion of climate change supporters and skeptics. The purpose of their procedure was to ensure that all researchers in their data set have demonstrated climate science expertise (i.e. publications).

Age bias and self-citation (disproportionately favoring certain climate scientists over others) is not a major issue when dealing with large datasets over an entire scientific discipline. Furthermore, their dataset from Google Scholar encompasses more technical science publications than would be obtained from other databases, such as Web of Science.

The scientists took great care to neither disproportionately favor nor disproportionately disfavor either the climate change supporters or skeptics. While the best method of evaluating scientific expertise and promince lies in replicating and building upon peer-reviewed research findings over decades, the issue of anthropogenic climate change is so pressing that short-term yet reasonable proxy measures (such as that reported herein) are necessary and valuable.

Evaluation of supporters and deniers.

The scientists found that roughly 97% of the top climate scientists broadly agree with the scientific evidence for anthropogenic climate change. Keeping in mind the scientists' caution that their sampling may not represent the true proportion of climate change supporters and skeptics, this is still a strong indication that climate scientists are largely against the deniers.

Climate scientists who support the broad conclusions of the IPCC contributed a mean of 119 publications, and a median of 84. In contrast, climate scientists who broadly oppose the conclusions of the IPCC contributed a mean of 60 publications, and a median of 34.

Depending on which measure you use (mean or median), this shows that climate change supporters publish twice as much as climate change deniers. Additionally, while only roughly 10% of climate change supporters have published fewer than 20 times, roughly 80% of climate change deniers are within this low publication category.

The climate science expertise of climate change deniers is clearly inferior.

The four most highly cited publications by climate scientists who support the broad conclusions of the IPCC have been cited on average 172 times. In contrast, the top four publications of climate scientists who broadly oppose the conclusions of the IPCC have been cited 105 times.

This shows that climate change deniers are cited only 60% as often as climate change supporters. Taking only the second through fourth most highly cited publications (to eliminate the possible skewing effect of a single highly influential publication) gave nearly the exact same results.

The climate science prominence of climate change deniers is clearly inferior.

Implications.

Not all scientific research is created equal. Most rational people realize that an honest drive for "balance" in the popular media is laudable.

On the other hand, it's important to recognize that climate scientists with the most expertise and prominence largely support the scientific reality of anthropogenic climate change, i.e. that the planet is warming due to human activities. Consequently, presenting "both sides" as "equally valid" is an extreme misrepresentation that does not accurately represent current scientific opinion.

for more information:
Anderegg, W. R. L., Prall, J. W., Harold, J., & Schneider, S. H. (2010). Expert credibility in climate change Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1003187107