Consensus and Marginal Dissent: A Social Epistemology for the 97%

Around 97% of climate scientists endorse anthropogenic global warming (AGW), the theory that human activities are partly responsible for recent increases in global average temperatures. The fact that so many of the relevant experts endorse AGW is a reason for non-experts to believe in AGW as well. But what is the epistemic significance of the fact that 3% of the experts do not endorse AGW? Put differently, what should we make of the fact that 97% rather than 100% of climate scientists endorse AGW? This paper contrasts unanimity, in which virtually no one disagrees with some theory, with consensus, in which some non-negligible proportion (e.g. 3%) either rejects or is uncertain about the theory. By developing a probabilistic model in which scientists are assumed to be epistemically fallible and socially susceptible, I argue that a consensus is often stronger evidence for a theory’s truth than unanimity. I go on to draw several lessons from this conclusion, e.g. concerning what laypeople should infer from expert pronouncements, how journalists should report on scientific theories, what scientists should communicate to the public, and how philosophers should think about the epistemology of testimony.

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