Where does the 97% consensus come from?

Actually, it’s 32% of climate scientists who say that it is likely that humans cause global warming

The climate may be changing but it is debatable (but not on the BBC) whether or not, or by how much, this is as a result of human activity.

John Cook is a research assistant professor at the Center for Climate Change Communication at George Mason University, Virginia, USA. In 2013 he published a paper with others that examined 11,944 abstracts of climate papers published in the peer reviewed scientific literature from 1991 to 2011 in order to determine the level of scientific consensus that “human activity is very likely causing most of the current global warming (anthropogenic global warming, or AGW).”

They found that 66.4% of the abstracts did not directly state a position on AGW. 32.6% endorsed AGW and 1.0% rejected it or were uncertain. Just looking at abstracts that expressed a position on AGW, 97.1% endorsed the consensus position that humans are causing global warming.

Some issues with the reporting of this paper

1. The 97% often quoted actually refers to 97% of the 32.6% of abstracts that stated a position on AGW so surely the headline figure should read “32% of climate scientists surveyed say that humans cause global warming”?

2. Of those that stated a position there are three subdivisions:
Explicit endorsement with quantification. Explicitly states that humans are the primary cause of recent global warming
Explicit endorsement without quantification. Explicitly states humans are causing global warming or refers to anthropogenic global warming/climate change as a known fact
Implicit endorsement. Implies humans are causing global warming without explicitly stating humans are the cause.


I think there are big differences between these categories. They vary from researchers who believe that humans contribute more than 1% of global warming to researchers who believe that humans contribute more than 50% of global warming.

Cook did not give the figures for each subdivision but Mark Bahner, an environmental engineer, has taken the raw data and calculated as follows:

Number of papers that:
a,Explicitly endorses and quantifies AGW as 50+% : 64
b,Explicitly endorses but does not quantify or minimize: 922
c,Implicitly endorses AGW without minimizing it: 2910
d,No Position: 7970
e,Implicitly minimizes/rejects AGW: 54
f,Explicitly minimizes/rejects AGW but does not quantify: 15
g,Explicitly minimizes/rejects AGW as less than 50%: 9

3. The authors did not read the full papers but only reviewed the abstracts of the papers. This could lead to a misunderstanding of the author’s conclusions, especially if the reviewers were not scientists themselves. 8547 authors were emailed for their own self rating but only 14% responded but the outcome was similar.   In fact, the reviewers were volunteers contributing to the Skeptical Science website (www.skepticalscience.com) .

4. Note the consensus is that “human activity is very likely…” i.e. it is not a fact.

(4a) No position Does not address or mention the cause of global warming

(4b) Uncertain Expresses position that human’s role on recent global warming is uncertain/undefined: ‘While the extent of human-induced global warming is inconclusive. . . ’

John Cook et al 2013 Environ. Res. Lett. 8 024024 : Quantifying the consensus on anthropogenic global warming in the scientific literature
Alex Epstein founder of the Center for Industrial Progress and author of The Moral Case for Fossil Fuels writing on Forbes.com. https://www.forbes.com/sites/alexepstein/2015/01/06/97-of-climate-scientists-agree-is-100-wrong/#471b54503f9f
Mark Bahner quoted by David Henderson https://www.econlib.org/archives/2014/03/16_not_97_agree.html