This claim is actually a come-down from the 1988 claim on the cover of Newsweek that all scientists agree. In either case, the claim is meant to satisfy the non-expert that he or she has no need to understand the science. Mere agreement with the 97% will indicate that one is a supporter of science and superior to anyone denying disaster. This actually satisfies a psychological need for many people. The claim is made by a number of individuals and there are a number of ways in which the claim is presented. A thorough debunking has been given in the Wall Street Journal by Bast and Spencer. One of the dodges is to poll scientists as to whether they agree that CO2 levels in the atmosphere have increased, that the Earth has been warming (albeit only a little) and that man has played some part. This is, indeed, something almost all of us can agree on, but which has no obvious implication of danger. Nonetheless this is portrayed as support for catastrophism. Other dodges involve looking at a large number of abstracts where only a few actually deal with danger. If among these few, 97% support catastrophism, the 97% is presented as pertaining to the much larger totality of abstracts.
Richard Lindzen, Professor of Atmospheric Science, MIT Thoughts on the Public Discourse over Climate Change
The following is a summary of the origins of the very creative “97%” statistic, which is used without embarrassment by the AGW scaremongers, and is an an article written by Ian Tuttle and published in “The Nation” in 2015. It is one of the best summaries I’ve found that explains the bogus mathematics involved in coming up with 97%.
” The “97 percent” statistic first appeared prominently in a 2009 study by University of Illinois master’s student Kendall Zimmerman and her adviser, Peter Doran. Based on a two-question online survey, Zimmerman and Doran concluded that “the debate on the authenticity of global warming and the role played by human activity is largely nonexistent among those who understand the nuances and scientific bases of long-term climate processes” — even though only 5 percent of respondents, or about 160 scientists, were climate scientists. In fact, the “97 percent” statistic was drawn from an even smaller subset: the 79 respondents who were both self-reported climate scientists and had “published more than 50% of their recent peer-reviewed papers on the subject of climate change.” These 77 scientists agreed that global temperatures had generally risen since 1800, and that human activity is a “significant contributing factor.”
A year later, William R. Love Anderegg, a student at Stanford University, used Google Scholar to determine that “97–98% of the climate researchers most actively publishing in the field surveyed here support the tenets of ACC [anthropogenic climate change] outlined by the Intergovernmental Panel on Climate Change.” The sample size did not much improve on Zimmerman and Doran’s: Anderegg surveyed about 200 scientists.
Surely the most suspicious “97 percent” study was conducted in 2013 by Australian scientist John Cook — author of the 2011 book Climate Change Denial: Heads in the Sand and creator of the blog Skeptical Science (subtitle: “Getting skeptical about global warming skepticism.”). In an analysis of 12,000 abstracts, he found “a 97% consensus among papers taking a position on the cause of global warming in the peer-reviewed literature that humans are responsible.” “Among papers taking a position” is a significant qualifier: Only 34 percent of the papers Cook examined expressed any opinion about anthropogenic climate change at all. Since 33 percent appeared to endorse anthropogenic climate change, he divided 33 by 34 and — voilà — 97 percent! When David Legates, a University of Delaware professor who formerly headed the university’s Center for Climatic Research, recreated Cook’s study, he found that “only 41 papers — 0.3 percent of all 11,944 abstracts or 1.0 percent of the 4,014 expressing an opinion, and not 97.1 percent,” endorsed what Cook claimed. Several scientists whose papers were included in Cook’s initial sample also protested that they had been misinterpreted. “Significant questions about anthropogenic influences on climate remain,” Legates concluded
Studies showing a wider range of opinion often go unremarked. A 2008 survey by two German scientists, Dennis Bray and Hans von Storch, found that a significant number of scientists were skeptical of the ability of existing global climate models to accurately predict global temperatures, precipitation, sea-level changes, or extreme weather events even over a decade; they were far more skeptical as the time horizon increased. Most did express concerns about global warming and a desire for “immediate action to mitigate climate change” — but not 97 percent.
A 2012 poll of American Meteorological Society members also reported a diversity of opinion. Of the 1,862 members who responded (a quarter of the organization), 59 percent stated that human activity was the primary cause of global warming, and 11 percent attributed the phenomenon to human activity and natural causes in about equal measure, while just under a quarter (23 percent) said enough is not yet known to make any determination. Seventy-six percent said that warming over the next century would be “very” or “somewhat” harmful, but of those, only 22 percent thought that “all” or a “large” amount of the harm could be prevented “through mitigation and adaptation measures.”
And according to a study of 1,868 scientists working in climate-related fields, conducted just this year by the PBL Netherlands Environment Assessment Agency, three in ten respondents said that less than half of global warming since 1951 could be attributed to human activity, or that they did not know.
Given the politics of modern academia and the scientific community, it’s not unlikely that most scientists involved in climate-related studies believe in anthropogenic global warming, and likely believe, too, that it presents a problem. However, there is no consensus approaching 97 percent. A vigorous, vocal minority exists. The science is far from settled.”
The actual number is 90 to 100%, based on a recently published study: http://iopscience.iop.org/article/10.1088/1748-9326/11/4/048002
This is an open-access article from a peer-reviewed journal, so it should be easy to access. It might be more profitable to interact with these findings rather than blog posts or news magazines.