An assessment of the foundational assumptions inhigh-resolution climate projections: the case of UKCP09

The United Kingdom Climate Impacts Programme’s UKCP09 project makes highresolution projections of the climate out to 2100 by post-processing the outputs of a large-scale global climate model. The aim of this paper is to describe and analyse the methodology used and then urge some caution. Given the acknowledged systematic, shared shortcomings in all current climate models, treating model outputs as decision relevant projections can be significantly misleading. In extrapolatory situations, such as projections of future climate change impacts, there is little reason to expect that postprocessing of model outputs can correct for the consequences of such errors. This casts doubt on our ability, today, to make trustworthy, high-resolution probabilistic projections out to the end of this century.