Assessing climate model projections: state of the art and philosophical reflections

A philosophy of science based discussion is presented of the vexing question of how to carry out climate model based assessments of climate model projections. We analyse, from a philosophical perspective, the difficulties that arise in climate model based assessment of climate model projections and outline criteria of adequacy for views about how such assessment should proceed. In addition, a critical overview is offered of the approaches the climate modeling community has actually adopted in assessing climate model projections, including the most recent IPCC approach as well as the Bayesian, Frequentist and Likelihood approaches. Finally, we outline two general philosophy of science based views about how models should be assessed, and critically consider how these philosophical views might be applied to assist in assessing the quality of climate model projections. We find that all available approaches to assessing climate model projections face substantial challenges, with probabilistic approaches such as the Bayesian approach facing particularly serious ones.