Rather than seeking improved methodologies, difficulty in combining expert opinion should serve as a warning flag that causes us to seek alternative modes of policy analysis. These alternatives are usually more appropriate for the real audience for our analyses.
Policy analysis of climate change is too often framed in terms that amount to preparing the tools with which a benevolent world dictator could do cost-benefit analysis. This tends to overemphasize end-to-end analysis that must rely on the combined opinions of experts. This framing is unrealistic and encourages omission of important aspects of the climate problem such as its heterogeneity. Rejecting this framing in favor of alternate, less all encompassing, forms of policy analysis permits more robust results, and reduces the emphasis on combining expert opinion.
While the opinions expressed here are my own, I thank Hadi Dowlatabadi, M. Granger Morgan, Ted Parson, and James Risbey for their perceptive comments.