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Center for Nonlinear Studies |
Despite uncertainties in the projections of future climate change from climate models, quantitative information is required now to set global emission reduction targets and to make plans to adapt some inevitable climate change that will happen over the coming few decades. This talk will describe the production of detailed probabilistic climate predictions for the coming century, conditional upon different emissions scenarios. The projection method is built upon ensembles of the Hadley Centre HadCM3 model with perturbations to key parameters (perturbed physics ensembles) and uses a Bayesian statistical technique. The technique seeks to “emulate” the parameter space of HadCM3 based on some prior assumptions about parameter ranges and then down-weights different model versions based on a comparison of modelled historical mean climate and climate change with observations (taking into account observational uncertainties). The effect of structural uncertainties, not sampled by the perturbed physics approach, are accounted for by incorporating information from the international archive of different models in a term which we call the discrepancy. The method seeks to account for the major uncertainties in feedbacks associated with the atmosphere, surface, ocean, sulphur cycle and terrestrial carbon cycle as well as incorporating uncertainties from the statistical components of the method. The resulting probability distribution functions for future climate change provide a benchmark whereby sensitivities to methodological assumptions may be tested. The method has been implemented, together with a combined dynamical-statistical downscaling approach, to produce probabilistic predictions for the UK at 25km resolution as part of the UK Climate Projections 2009 project (http://ukcp09.defra.gov.uk/)
Host: Ken Cox