New paper: Calibrating Climate-Change Time-Slice Projections With Estimates of Seasonal Forecast Reliability

Matsueda, M., Weisheimer, A., Palmer, T. N. (2016) Calibrating Climate-Change Time-Slice Projections With Estimates of Seasonal Forecast Reliability Journal of Climate doi: 10.1175/JCLI-D-15-0087.1

Abstract

In earlier work, it was proposed that the reliability of climate-change projections, particularly of regional rainfall, could be improved if such projections were calibrated using quantitative measures of reliability obtained by running the same model in seasonal forecast mode. This proposal is tested for fast atmospheric processes (such as clouds and convection) by considering output from versions of the same atmospheric general circulation model run at two different resolutions and forced with prescribed sea surface temperatures and sea ice. Here output from the high-resolution version of the model is treated as a proxy for truth. The reason for using this approach is simply that we do not yet know the 21th century climate change signal and hence cannot verify any climate-change projections using observations. Quantitative assessments of reliability of the low-resolution model, run in seasonal hindcast mode, are used to calibrate climate-change time-slice projections made with the same low-resolution model. Results show that the calibrated climate change probabilities are closer to the proxy truth than the uncalibrated probabilities. Given that seasonal forecasts are performed operationally already at several centres around the world, in a seamless forecast system they provide a resource that can be used without cost to help calibrate climate change projections and make them more reliable for users.