The much reported paper by John Cook et al finds a very strong consensus about human caused climate change in the scientific literature: Of those abstracts expressing a position on the cause of global warming, 97% (implicitly or explicitly) endorsed human causation of this warming.
Over at Lucia’s, Brandon Shollenberger found a way to search the results of 12,280 out of 12,465 papers. Based on this search method and the SkS paper rating guidelines, Marcel Crok reports the following breakdown of results:
Category 1 (explicit endorsement with quantification): 65
Category 2 (Explicit Endorsement without quantification): 934
Category 3 (Implicit Endorsement): 2933
Category 4 (Neutral): 7930 [the reported number]
Category 5 (Implicit Rejection): 53
Category 6 (Explicit Rejection without quantification): 15
Category 7 (Explicit Rejection with quantification): 10
The 97% is arrived at by adding up categories 1 to 3 and taking that as a percentage of all categories except 4. This percentage is actually 98% using the numbers above, but these are obtained via a shortcut.
Of course, various other fractions could be calculated from this list, each with a slightly different meaning. E.g. of those abstracts making a statement about the quantitative contribution of human activity to the warming, 87% (65/75) endorsed dominant human causation. And of those abstracts expressing an explicit position on the cause of global warming, 97.6% (999/1024) endorsed human causation.
Any way you slice it, a strong consensus it is.
It should not come as a surprise that many papers expressed no position on the causes of global warming: Many papers matching the search terms “global warming” or “global climate change” don’t deal with attribution of the warming, but with impacts (48% of the total) or mitigation (28% of the total) of climate change (e.g. the change in the yield of corn as a function of temperature). Other papers may deal with one specific aspect of climate change (e.g. the influence of organic aerosol on the cloud nucleating ability of CCN). Moreover, as certain aspects of science become widely accepted, new research papers have less and less reason to state the obvious, let alone in their abstracts. This is corroborated by the increasing fraction of “no position” abstracts and the simultaneously decreasing fraction of “endorsement” abstracts over time (fig 1b of the paper).
Including the “no position” category into the denominator (as some people seem to be doing) to arrive at a much smaller percentage endorsement makes about as much sense as including all atmospheric science articles in the denominator too, or even all physics articles: it is to be expected that many papers do not state a position on this particular issue. These should not be included as a reference against which to compare the number of endorsement papers. Another example of an apples to oranges comparison is Brandon Shollenberger comparing the number of explicit and quantified endorsements to the sum of explicit and implicit rejections.
Dana Nuccitelli and John Cook explain that they took a conservative approach in their ratings:
For example, a study which takes it for granted that global warming will continue for the foreseeable future could easily be put into the implicit endorsement category; there is no reason to expect global warming to continue indefinitely unless humans are causing it. However, unless an abstract included (either implicit or explicit) language about the cause of the warming, we categorized it as ‘no position’.
Furthermore, the implicit endorsement category includes e.g. abstracts that
mention increased CO2 leading to higher temperatures without including anthropogenic or reference to human influence/activity
What is slightly surprising to me is the small number of abstracts making a quantitative statement about attribution (75 out of 12,465). There are bound to be many more attribution studies in the sample, but apparently many of these did not provide a quantitative statement on the human contribution in their abstract.