Recent extreme weather in the UK highlights the need to understand the potential for more extreme events in the present-day, and how such events may change with global warming. We present a methodology for more efficiently sampling extremes in future climate projections. As a proof-of-concept, we use the UK’s most recent set of national Climate Projections (UKCP18). UKCP18 includes a 15-member perturbed parameter ensemble (PPE) of coupled global simulations, providing a range of climate projections incorporating uncertainty in both internal variability and forced response. However, this ensemble is too small to adequately sample extremes with return periods over 100 years, which are of interest to policy-makers and adaptation planners. To better understand the statistics of these events, we use distributed computing to run three ~1000-member initial-condition ensembles with the atmosphere-only HadAM4 model at 60km resolution on volunteers’ computers, taking boundary conditions from future extreme winters within the UKCP18 ensemble. This experimental setup allows us to explore the uncertainty surrounding these rare extreme events in UKCP18 more completely, which includes determining whether they were genuinely exceptional events, or if they could have been even greater extremes.
David Sexton is a Science Manager of the Ensemble Climate Projection team at the Met Office Hadley Centre and leads the production and evaluation of the climate simulations used for informing climate adaptation.
Nick Leach is a PhD student on the Environmental Research Doctoral Training Partnership at Oxford University in his fourth and final year. He resides in the Predictability of Weather and Climate research group, supervised by Antje Weisheimer and Myles Allen.