"If 98% of doctors said you needed urgent surgery, wouldn't you have it?!" "If 98% of aeronautical engineers told you that your next flight is unsafe and likely to crash, would you listen to them or to the 2% who say otherwise?" John Kerry, US Secretary of State, claimed in May this year that the consequences of climate change could be "crippling" and that "97% of the world's scientists tell us this is urgent". Last year, a tweet in President Barack Obama's name asserted that "Ninety-seven percent of scientists agree: climate change is real, man-made and dangerous." Note: "dangerous". Obama cited a study of climate science consensus led by University of Queensland academic, John Cook. (About which, more later).
I have heard these analogies and claims repeated in various forms by politicians and 'climate activists' through the media for a few years now. They certainly have a great run in the mainstream but they rarely cite a source for the 97%-98% figure. So, I decided to do a bit of investigating for myself.
Surveys of what the climate experts' think take two methodological approaches: reviews of peer-reviewed literature and polls. Doran, Kendall and Zimmerman polled 10,257 Earth scientists in 2009 while Anderegg, Prall, Harold and Schneider reviewed 1,372 abstracts and citation data in the climate change/global warming field in 2010. Last year, John Cook et al examined nearly 12,000 abstracts from the peer-reviewed scientific literature.
Doran et al (2009)
Doran is interesting because it used a polling methodology and a seemingly big sample of more than 10,000 Earth scientists. However, on closer inspection, they point out that only 3,146 of the scientists responded. Still, that's not a bad figure. But the 98% figure is derived not from those 3,000-plus but from those deemed to have special expertise in climate change, that is, those who had published at least 50% of their peer-reviewed papers in that area. The actual numerical basis for the 98% figure on this occasion is from 77 out of 79 in the study. Seventy-nine agreed with the proposition that global mean temperature has risen since the late nineteenth century and 77 agreed that human activity is a significant factor. The Doran study is called 'Examining the scientific consensus on climate change' published in the American Geophysical Union journal. http://onlinelibrary.wiley.com/doi/10.1029/2009EO030002/abstract So, when John Kerry refers to "the world's scientists", one can only hope he has some other evidence in mind.
Anderegg et al (2010)
The Anderegg survey in 2010 was published in the Proceedings of the US National Academy of Sciences. Anderegg et al reviewed abstracts and citation data of 1,372 climate researchers (they use the term 'researchers', though presumably most are scientists) and drew conclusions from 908 of them. Leaving aside that publication does not necessarily equate to expertise, Anderegg et al measured the climate researchers' positions regarding the same two basic questions: Has the planet warmed and has human activity been a significant factor? They found that 97% to 98% of the 908 abstracts and citations agreed with both propositions. The Anderegg report is called 'Expert credibility in climate change'. http://www.pnas.org/content/107/27/12107.full.pdf+html
Cook et al (2013)
The 2013 work by Cook et al received international attention. It reviewed 11,944 abstracts from peer-reviewed climate-related scientific literature and the authors concluded that 97% of those who took a position supported the consensus that warming has happened and that human activity is responsible for at least half the warming since 1950. However, 66% of the abstracts reached no conclusion or took no position on the topic and so were not included. Thus, the figure of 97% refers to 97% of those with a position: approx. 4,000 out of about 12,000 abstracts. Leaving aside for a moment the question as to how the 8,000 with 'no opinion' might have been better dealt with, the Cook et al review found essentially what Anderegg and Doran had found: 97% consensus. Cook et al's study is called 'Quantifying the consensus on anthropological global warming in the scientific literature' in Environmental Research Letters. http://iopscience.iop.org/1748-9326/8/2/024024/article
Questioning and scepticism
In each case, the objective was to find out what climate experts felt about the question of whether the planet has warmed and whether human activity plays a significant part. None of the studies – and none that I know of – have sought to ascertain what the climate experts think about the likelihood of "crippling consequences", to quote John Kerry, or the likelihood of crisis or catastrophe. Nor do the studies seek to ascertain expert opinion on whether warming may be good or bad on balance.
So, how do the words of John Kerry and other alarmists measure up against these studies of expert opinion? Do 97% to 98% of experts believe the situation is "urgent" and will have "crippling consequences"? The answer is no. There is no evidence for such a consensual view.
Discuss in our Forums
See what other readers are saying about this article!
Click here to read & post comments.
71 posts so far.