The claim that 97 percent of scientists believe humans are causing climate change has been debunked by the "head" of the United Nations Intergovernmental Panel on Climate Change. "That number was pulled out of thin air."
Appearing on HBO’s Real Time with Bill Maher, GOP presidential hopeful Rick Santorum doubled down on his skepticism of man-made climate change. Santorum made two claims to back his point. First, in a large survey of climate scientists, "57 percent don’t agree with the idea that 95 percent of the change in the climate is caused by CO2," according to Santorum. (We found that claim False.) Second, Santorum said that a widely cited figure of scientific consensus on climate change — 97 percent — has been debunked by the "head" of the United Nations Intergovernmental Panel on Climate Change, he said. "The 97 percent figure that’s thrown around, the head of the UN IPC (sic) said that number was pulled out of thin air. It was based on a survey of 77 scientists," he said on Aug. 28. "Not even 97 scientists responded to that survey." Several readers asked us to look into Santorum’s claim. His campaign didn’t get back to us, but we found that Santorum misstated both who objected to the figure and what that person objected to. From 2002 until recently, the chairman of the IPCC was climate scientist Rajendra Pachauri, who resigned from his post in February 2015. To our knowledge, neither Pachauri nor current chairman Ismail El Gizouli has criticized the 97 percent figure. Pachauri has, in fact, endorsed the notion of scientific consensus on climate change. "By overwhelming consensus, the scientific community agrees that climate change is real," he said at a press conference in 2010. Santorum is likely referring to Richard Tol, an economist at the University of Sussex who’s been a vocal critic of the 97 percent figure. He is not, as Santorum claims, the "head" of the IPCC, though he was the convening lead author of a chapter of the IPCC’s fifth report. He has since parted ways with the IPCC. Currently, Tol serves as an adviser to the Global Warming Policy Foundation. That group, says Stephan Lewandowsky, a psychologist at the University of Bristol who studies the rejection of climate science, is "the U.K.’s most prominent source of climate change denial." The "thin air" quote Santorum cited is from Tol’s testimony before the U.S. House Committee on Science, Space, and Technology. "I mean it is pretty clear that most of the science agrees that climate change is real and most likely human-made," Tol said on during a 2014 hearing on the IPCC. "But the 97 percent is essentially pulled from thin air. It is not based on any credible research whatsoever." Tol was specifically referring to a 2013 survey by John Cook, who studies climate communication at the University of Queensland. Cook’s study found that among over 4,000 studies that took a position on man-made climate change, 97.1 percent "endorsed the consensus position that humans are causing global phase" and 97.2 of 1,300 authors who responded agreed with the position. Tol takes issue with Cook’s methodology. By his analysis of Cook’s data, the real figure is around 91 percent. (Cook replied critiquing Tol’s methodology and standing by his survey’s original finding of 97 percent.) "There is no doubt in my mind that the literature on climate change overwhelmingly supports the hypothesis that climate change is caused by humans," Tol writes in his analysis. "I have very little reason to doubt that the consensus is indeed correct. Cook et al., however, failed to demonstrate this." So Santorum is talking about the wrong person. And his reference to "a survey of 77 scientists," is talking about something else entirely. The study Santorum is attempting to describe is a 2009 survey by Peter Doran, a professor of earth science at Louisiana State University. About 90 percent of around 3,000 surveyed earth scientists said they think climate change is happening, and about 82 percent said human activity is contributing to it. The 97 percent figure comes from a subsample of climate scientists in Doran’s study, and Santorum correctly describes its small size: 74 out of 77 respondents said they agreed that climate change is man-made. Beyond his and Cook’s study, a 2010 study of over 1,300 climate researchers and their work also showed a 97 to 98 percent consensus. "They keep talking about how ‘the’ 97 percent study is wrong," Doran told PolitiFact in an interview. "Well it turns out, we never know which study they are referring to because there have been three peer-reviewed studies of late that have arrived at this 97 percent number in different ways and by different people." Our ruling Santorum said, "The 97 percent figure that’s thrown around, the head of the UN IPC (sic) said that number was pulled out of thin air. It was based on a survey of 77 scientists." Santorum’s claim confuses several points. First, the critic of the 97 percent he’s referring to isn’t the "head" of the UN’s climate panel, but an economist who has collaborated with but has since left the IPCC. Second, the 97 percent doesn’t come from one specific survey — it appears in at least three. And finally, the study Santorum describes isn’t the one the economist objects to. Moreover, Tol himself doesn’t refute the notion of broad scientific consensus on man-made climate change. Santorum’s claim is inaccurate. We rate it False. Correction, Sept. 3, 2015, 10:45 a.m: Cook's analysis looked at over 4,000 studies that took a position on man-made climate change. An earlier version of this fact-check had a different figure.
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