Ninety Seven Percent
Once again, Cook et al 2013 seems to be generating quite a bit of discussion. According to the abstract, 97% of a selection of scientific papers related to Global Warming “support the consensus” that “humans are causing global warming”, vis:
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.
So far, so good, I don’t have any problem with that. And it’s clear that if 97% of papers agree with something then, by definition, that is a consensus. However, this statement is being interpreted as saying something a bit more: that 97% of those papers support the idea that humans are responsible for more than 50% of the warming seen in the 20th Century. This claim is not supported by the paper’s own data.
The endorsement levels in the supplementary data are:
1 Explicitly endorses and quantifies AGW as 50+%
2 Explicitly endorses but does not quantify or minimise
3 Implicitly endorses AGW without minimising it
4 No Position
5 Implicitly minimizes/rejects AGW
6 Explicitly minimizes/rejects AGW but does not quantify
7 Explicitly minimizes/rejects AGW as less than 50%
Of these, only endorsement level 1, “Explicitly endorses and quantifies AGW as 50+%” matches the claim “Humans responsible for more than 50% of 20th Century warming”.
The distribution of the endorsement level across the examined papers is:
1 Explicitly endorses and quantifies AGW as 50+% 64
2 Explicitly endorses but does not quantify or minimise 922
3 Implicitly endorses AGW without minimising it 2910
4 No Position 7970
5 Implicitly minimizes/rejects AGW 54
6 Explicitly minimizes/rejects AGW but does not quantify 15
7 Explicitly minimizes/rejects AGW as less than 50% 9
So only 64/11944 papers endorse the stronger position of humans having than more than 50% effect on the 20th Century temperature increase. If we exclude from this count the 7970 papers classified as “No Position” (which is what the paper’s authors did) then the figure becomes 64/3974 endorsing the “more than 50%” position. Far from being 97%, this is around 1.6% – a piffling amount. In fact, I would go so far as to say that it is “vanishingly small”.
It seems to me that this paper has discovered that 97% of the papers selected endorse the idea that human activity has caused some degree of warming. This is essentially the position held by the majority of sceptics.
Why all the fuss?