The climate change debate is typically viewed as consisting of two sides: those who accept the consensus ("Accepters") and climate change Skeptics. Actually, that's more the way Accepters characterize the debate. Skeptics tend to make finer distinctions, e.g., there's a whole spectrum of "lukewarmers" I rarely hear about within the Accepter community.
So what does it mean to accept the consensus? We'll start with "consensus".
The idea of a climate change consensus gained considerable traction with a paper by Cook et al (2013). Here is the Abstract:
We analyze the evolution of the scientific consensus on anthropogenic global warming (AGW) in the peer-reviewed scientific literature, examining 11 944 climate abstracts from 1991–2011 matching the topics 'global climate change' or 'global warming'. We find that 66.4% of abstracts expressed no position on AGW, 32.6% endorsed AGW, 0.7% rejected AGW and 0.3% were uncertain about the cause of global warming. Among abstracts expressing a position on AGW, 97.1% endorsed the consensus position that humans are causing global warming. In a second phase of this study, we invited authors to rate their own papers. Compared to abstract ratings, a smaller percentage of self-rated papers expressed no position on AGW (35.5%). Among self-rated papers expressing a position on AGW, 97.2% endorsed the consensus. For both abstract ratings and authors' self-ratings, the percentage of endorsements among papers expressing a position on AGW marginally increased over time. Our analysis indicates that the number of papers rejecting the consensus on AGW is a vanishingly small proportion of the published research.
Ok, so most people I know just say "97% of climate change scientists endorse the consensus". But that's not what Cook et al says. Their initial study was a review of abstracts only, of which two-thirds expressed no opinion on anthropogenic global warming (AGW). Almost all the rest endorsed AGW - but wait! Later in the paper, Cook et al clarify that endorsement could be "implicit" - in other words, inferred by the authors. And in their one example of implicit endorsement, there is no reference to whether climate change is caused by human activity.
In their second study, Cook et al emailed 8547 authors an invitation to rate their own climate-related papers. They received responses on 2142 papers self-rated by 1189 authors. A bit more than a third of the papers were self-rated as having no position on AGW. Of the remaining two-thirds, 97.6% were self-rated as endorsing AGW. But that's not the same thing as saying 97% of the authors endorsed climate change, which is usually how it's represented, as in this quote from the Environmental Defense Fund website:
Ninety-seven percent of climate scientists unequivocally agree that climate change is happening now and that humans are the main cause.
Problem is, only those authors who self-rated their papers as having an opinion on AGW were asked if they personally endorsed AGW themselves. But these authors represented just 62.7% of the whole sample - 746 out of 1189 respondents. The authors who self-rated their papers as having no position on AGW were not asked about their opinion on global warming. They were also climate scientists but for some reason, their opinions didn't count. Why was that?
Next: What does it mean to 'endorse'?
Reference:
Cook J, Nuccitelli D, Green S A, Richardson M, Winkler B, Painting R, Way R, Jacobs P and Skuce A 2013 Quantifying the consensus on anthropogenic global warming in the scientific literature Environ. Res. Lett. 8 024024