Researchers Report High Level of Agreement Among Leading Experts on Climate Change Basics

While many Americans believe there is substantial disagreement among experts on climate change, researchers today report that in fact 97-98% of leading experts are convinced that climate change is happening and that greenhouse gases from human activities are primarily responsible.  

The findings were described by William R.L. Anderegg , James W. Prall, Jacob Harold and  Stephen H. Schneider in Expert Credibility in Climate Change , published in Proceedings of the National Academy of Sciences (PNAS), 21 June 2010.  The authors summarize their findings:

"We provide the first large-scale quantitative assessment of the relative level of agreement, expertise and prominence in the climate researcher community. We show that the expertise and prominence... 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."

The study assessed 1,372 climate researchers, dividing them into two groups based on their views on anthropogenic climate change (ACC) as reflected in the fundamental conclusions of the Intergovernmental Panel on Climate Change (IPCC):

• Convinced by the Evidence (CE) of ACC.
• Unconvinced by the Evidence (UE) of ACC. 

The analysts used various criteria to measure expertise and prominence and argued that "we have likely compiled the strongest and most credentialed researchers" in both groups and that the "criteria provide conservative, robust, and relevant indicators of relative credibility" of the researchers.

Among the specific findings:

• "The UE group comprises only 2% of the top 50 climate researchers as ranked by expertise (number of climate publications), 3% of researchers of the top 100, and 2.5% of the top 200..."
• "[T]he distribution of expertise of the UE group is far below that of the CE group. Mean expertise of the UE group was around half (60 publications) that of the CE group (119 publications...), as was median expertise (UE=34 publications; CE=84 publications)"
• "[R]esearchers with fewer than twenty climate publications comprise approximately 80% the UE group, as opposed to less than 10% of the CE group. This indicates that the bulk of UE researchers on the most prominent multi-signatory statements about climate change have not published extensively in the peer-reviewed climate literature."
• "While the top-published researchers in the CE group have an average of 408 climate publications (median = 344), the top UE researchers average only 89 publications (median = 68) (Mann-Whitney U test: W=2,455; p<10-15). Thus, this suggests top CE researchers have much stronger expertise in climate science than those in the top UE group."
• "CE researchers top papers were cited an average of 172 times, compared to 105 times for UE researchers."

The authors conclude:

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.  This extensive analysis of the mainstream versus skeptical/contrarian researchers suggests a strong role for considering expert credibility in the relative weight of and attention to these groups of researchers in future discussions in media, policy, and public forums regarding anthropogenic climate change."

The Project on Climate Science notes (in Scientific Consensus of Climate Change Re-affirmed by New Report, 22 June 2010):

"The re-affirmation of the scientific consensus on global warming follows news that the Times of London has retracted its story reporting allegations that the Intergovernmental Panel on Climate Change (IPCC) erred in its account of climate change impacts on the Amazon. The Times retraction follows the withdrawal of a parallel story by the German paper Frankfurter Rundschau that reported charges the IPCC erred in its account of climate change impacts in Africa – charges that have also been proven off-base.

The PNAS study also follows on the heels of several official investigations into allegations of wrongdoing by some scientists, all of which have debunked the purported scandal and upheld the current scientific findings."

Online Resources:

Expert Credibility in Climate Change.  By William R.L. Anderegg , James W. Prall, and Jacob Harold and  Stephen H. Schneider. Published in Proceedings of the National Academy of Sciences (PNAS), 21 June 2010.

New study finds striking level of agreement among climate experts on anthropogenic climate change.  ClimateScienceWatch, June 21, 2010.

New Study Reaffirms Scientific Consensus on Climate Change.  Union of Concerned Scientists, 21 June 2010.

Scientific Consensus of Climate Change Re-affirmed by New Report.  Press release (22 June 2010) from The Project on Climate Science.