A Perturbed Parameter Ensemble of HadGEM3-GC3.05 Coupled Model Projections: Global Performance and Future Changes

UKCP (UK Climate Projections) is a multi-organizational, national project to produce several different datasets of future projections to provide support for decision making in a variety of sectors. As part of the most recent UKCP18 climate projections framework, we constructed a 20-member PPE based on the UK Met Office HadGEM3 GC3.05 coupled GCM (similar to the version submitted to CMIP6). The 20 parameter combinations were selected with the aim of being plausible (measured against a wide set of mean climate metrics) and as diverse as possible within the plausible part of parameter space. In the presentation we will evaluate how well the ensemble met those aims. For UKCP18, the final product was a combination of 15 of these members with a set of 13 quality-assured CMIP5 models, to cover a range of plausible outcomes that are wider than the range from either ensemble by itself.