“Agreement” in the IPCC Confidence measure

- We investigate the IPCC use of “agreement” in the qualitative confidence scale it uses when assessing the uncertainty of its findings.
- IPCC discussions of agreement in confidence assessments display a variety of interpretations, including consensus of the relevant research community.
- IPCC practices of agreement attribution suggest that agreement should be understood in terms of convergence of support.
- These two interpretations suggest different epistemological underpinnings.
- We propose a principle guiding IPCC confidence attributions insofar as they rest on agreement.

The Intergovernmental Panel on Climate Change (IPCC) has, in its most recent Assessment Report (AR5), articulated guidelines for evaluating and communicating uncertainty that include a qualitative scale of confidence. We examine one factor included in that scale: the “degree of agreement.” Some discussions of the degree of agreement in AR5 suggest that the IPCC is employing a consensus-oriented social epistemology. We consider the application of the degree of agreement factor in practice in AR5. Our findings, though based on a limited examination, suggest that agreement attributions do not so much track the overall consensus among investigators as the degree to which relevant research findings substantively converge in offering support for IPCC claims. We articulate a principle guiding confidence attributions in AR5 that centers not on consensus but on the notion of support. In concluding, we tentatively suggest a pluralist approach to the notion of support.