Last week, Secretary of State John Kerry warned graduating Boston College students that climate change would have “crippling consequences.” Indeed, he added, “Ninety-seven percent of the world’s scientists tell us this is urgent.”
Where did Mr. Kerry get his 97% figure? Perhaps from his boss, President Obama, who tweeted on May 16 that “Ninety-seven percent of scientists agree: #climate change is real, man-made and dangerous.” Or maybe from NASA, which posted (in more measured language) on its website, “Ninety-seven percent of climate scientists agree that climate-warming trends over the past century are very likely due to human activities.”
In reality, the assertion that 97% of scientists believe that climate change is a man-made, urgent problem is science fiction. The so-called consensus comes from a handful of surveys and exercises in counting abstracts from scientific papers – all of which have been contradicted by more reliable research.
One frequently cited source for the consensus is a 2004 opinion essay published in Science magazine by Naomi Oreskes, a science historian now at Harvard. She claimed to have examined abstracts of 928 articles published in scientific journals between 1993 and 2003, and to have found that 75% supported the view that human activities are responsible for most of the observed warming over the previous 50 years, while none directly dissented.
Ms. Oreskes’s definition of consensus covered “man-made” influences but left out “dangerous” – and excluded scores of articles by prominent scientists such as Richard Lindzen, John Christy, Sherwood Idso, and Patrick Michaels who question the consensus. Her methodology is also flawed. A study published earlier this year in the journal Nature noted that abstracts of academic papers often contain claims that aren’t substantiated in the papers – but she failed to acknowledge or address this.
Another widely cited source for the consensus view is a 2009 article in Eos: Transactions of the American Geophysical Union, by Maggie Kendall Zimmerman–a student at the University of Illinois–and her master’s thesis adviser Peter Doran. It reported the results of a two-question online survey of selected scientists. Mr. Doran and Ms. Zimmerman claimed “97 percent of climate scientists agree” that global temperatures have risen, and that humans are a significant contributing factor.
The survey’s questions don’t reveal much of interest. Most scientists who are skeptical of man-made catastrophic global warming would nevertheless answer “yes” to both questions. However, the survey was silent on whether the human impact – or the rise in temperature – is large enough to constitute a problem. It also failed to include solar scientists, space scientists, cosmologists, physicists, meteorologists, or astronomers, who are the scientists most likely to be aware of natural causes of climate change.
The “97 percent” figure in the Zimmerman/Doran survey represents the views of only 79 respondents who listed climate science as an area of expertise and said they published more than half of their recent peer-reviewed papers on climate change. Seventy-nine scientists out of the 3,146 who responded to the survey – or out of the 10,257 scientists who received it – does not a consensus make.
In 2010, William R. Love Anderegg, then a student at Stanford University, used Google Scholar to identify the views of the most prolific writers on climate change. His findings were published in Proceedings of the National Academies of Sciences. Mr. Love Anderegg found that 97% to 98% of the 200 most prolific writers on climate change believe “anthropogenic greenhouse gases have been responsible for ‘most’ of the ‘unequivocal’ warming.” There was no mention of how dangerous this climate change might be; and, of course, 200 researchers out of the thousands who have contributed to the climate science debate is not evidence of consensus.
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