Probability of regional climate change based on the Reliability Ensemble Averaging (REA) method

We present an extension of the Reliability Ensemble Averaging, or REA, method [Giorgi and Mearns, 2002] to calculate the probability of regional climate change exceeding given thresholds based on ensembles of different model simulations. The method is applied to a recent set of transient experiments for the A2 and B2 IPCC emission scenarios with 9 different atmosphere-ocean General Circulation Models (AOGCMs). Probabilities of surface air temperature and precipitation change are calculated for 10 regions of subcontinental scale spanning a range of latitudes and climatic settings. The results obtained from the REA method are compared with those obtained with a simpler but conceptually similar approach [Raisanen and Palmer, 2001]. It is shown that the REA method can provide a simple and flexible tool to estimate probabilities of regional climate change from ensembles of model simulations for use in risk and cost assessment studies.