The most recent survey of climate scientists said about 57 percent don’t agree with the idea that 95 percent of the change in the climate is caused by CO2.
Republican presidential candidate Rick Santorum sparred with liberal talk show host Bill Maher on a topic near and dear to both men’s hearts for different reasons: climate change. Maher kicked off the debate by naming climate change as one of his main concerns for the 2016 election and challenged Santorum’s skepticism. Santorum, who has repeatedly called climate change "a hoax," shot back by arguing that there really isn’t scientific consensus. "I’m not alone," Santorum said on Maher’s Aug. 28 HBO show. "The most recent survey of climate scientists said about 57 percent don’t agree with the idea that 95 percent of the change in the climate is caused by CO2." Santorum, pressed by an incredulous Maher, repeated the claim: "There was a survey done of 1,800 scientists, and 57 percent said they don’t buy off on the idea that CO2 is the knob that’s turning the climate. There’s hundreds of reasons the climate’s changed." "Rick, I don’t know what ass you’re pulling that out of," Maher retorted. "I’m not! I’ll send you the survey," Santorum promised. Several readers wrote to us asking about Santorum’s numbers, so we asked his campaign to send us the survey as well. They didn’t get back to us, but we did find the figure. In short, Santorum’s claim commits "two orders of mischaracterization," said Anthony Leiserowitz, who studies climate change public opinion at Yale University. He not only uses a flawed statistic, but also misstates what it’s allegedly disapproving. Santorum’s sloppy reading To begin with, Santorum inaccurately describes the "idea" that he says 57 percent of scientists "don’t agree with." What he’s referring to is a finding by the United Nations Intergovernmental Panel on Climate Change in its fifth report. The IPCC has said it is "extremely likely" (meaning a 95 percent confidence level) that humans are causing climate change. The IPCC also said it is "very likely" (meaning a 90 percent confidence level) that greenhouses gases are the driver. Santorum restated IPCC points wrong. They never said 95 percent of the change in the climate is caused by CO2. In fact, no one has ever made that statement, according to Leiserowitz. "There are several other greenhouse gases, including methane, nitrous oxide, and water vapor, as a amplifier. CO2 is the most important of these and others, but no one to my knowledge has ever claimed that CO2 caused 95 percent of the warming," he said. The closest IPCC comes to what Santorum claimed is saying that there’s a 90 percent chance that greenhouse gases are driving climate. That’s a far cry from what Santorum actually said. Even still, the 57 percent figure doesn’t hold up. Fuzzy math The figure likely comes from the blog Fabius Maximus (and repeated by the prominent climate change skeptic Joanne Nova), which re-analyzed the findings of a 2014 survey by the Dutch environmental research agency PBL. According to Fabius Maximus editor Larry Kummer, the survey’s findings disprove the IPCC's confidence level finding. He walked us through how he got the 57 percent: 1. About 65.9 percent of scientists said they agreed that greenhouse gases were the main driver of climate change. 2. Of those scientists, 65.2 percent reported "virtually certain" or it was "extremely likely" that their estimate was correct (corresponding to a 95 percent or higher confidence level). 3. That means, according to Kummer, about 43 percent (65.2 percent of 65.9 percent) were extremely confident that greenhouse gases were the main driver of climate change. In other words, 57 percent weren’t 95 percent confident. We ran Kummer’s analysis by a few experts, including the survey authors themselves, who said his interpretation is flat-out wrong. The survey’s lead author, Bart Verheggen, told us that Kummer — and, by extension, Santorum — made a few mistakes. First, 22 percent of climate scientists surveyed didn’t directly answer a question as to what extent greenhouse gases were causing climate change, says Verheggen. Verheggen said it would be more accurate to consider only those who answered the question. (He goes into more detail in a blog post.) Second, Kummer only counts scientists who were 95 percent or more confident that greenhouse gases drive climate change, when the actual IPCC statement reports a 90 percent certainty, Verheggen pointed out. "Basically, Santorum’s claim is not consistent with the results from our survey," Verheggen concluded. "This is like something out of that book, How to Lie With Statistics," said Stephen Farnsworth, who studies climate change and political communication at the University of Mary Washington. "What we’re talking about here is extraordinary cherry-picking. You’re only counting one question in one survey, and you’re talking about a very high (confidence level). Once you start stacking up numbers like this, you’re really distorting the real finding of this research." What the survey (and others) actually say The real finding of the survey actually backs the idea of scientific consensus on climate change, despite varying levels of confidence, said Verheggen. "It is clear from our survey that a strong majority of scientists agree that greenhouse gases originating from human activity are the dominant cause of recent warming," he said. That’s consistent with most of the literature on scientific opinion about climate change, experts agreed. "You don't get anywhere near 57 percent when surveying the broad earth science community, and you get very close to full consensus when you ask the experts in climate science," said Peter Doran, a professor of earth science at Louisiana State University. National Science Board member James Powell surveyed what’s actually published in scientific journals, finding that the consensus in the literature is about 99.9 percent. And multiple independent studies have "asked scientists directly" and found consensus levels of around 97 percent, said William Anderegg, who studies climate change at Princeton University. "Those studies were rigorously peer-reviewed and thus should be considered more credible than a blog post that misreads an institute report," he said. Our ruling Santorum said, "The most recent survey of climate scientists said about 57 percent don’t agree with the idea that 95 percent of the change in the climate is caused by CO2." He’s not pulling the numbers out of thin air, as Maher suggests more bluntly, but the claim is inaccurate and misleading. Essentially, Santorum garbles a blog’s textbook misinterpretation of a survey. In reality, the survey actually supports the idea of scientific consensus on climate change, the lead author told us. We rate Santorum’s claim False.
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