From the source you linked to: "Cook et al. (2013) stated that abstracts of nearly all papers expressing an opinion on climate change endorsed consensus,which,

From the source you linked to: "Cook et al. (2013) stated that abstracts of nearly all papers expressing an opinion on climate change endorsed consensus,which, however, traditionally has no scientific role; used three imprecise definitions of consensus interchangeably; analyzed abstracts only;excluded 67% expressing no opinion; omitted some key results; misstated others; and thus concluded that 97.1% endorsed the hypothesis as defined in their introduction,namely that the “scientific consensus that human activity is very likely causing most of the current GW (anthropogenic global warming, or AGW)”. The authors’ own data file categorized 64 abstracts, or only 0.5% of the sample, as endorsing the consensus hypothesis as thus defined. Inspection shows only 41 of the 64, or 0.3% of the entire sample, actually endorsed their hypothesis. Criteria for peer review of papers quantifying scientific consensus are discussed." They sampled the data. Just because they didn't review every paper doesn't mean that the papers they didn't review disagree with their assessment. Furthermore, the fact that 67% didn't express an opinion simply shows that they were scientists. One goal of scientific publications is to not editorialize, to not express opinions. However, the results of their research still point to anthropogenic climate change.