Stefano Castruccio (Newcastle) Global Space-Time Emulators for Ensemble of Opportunities: Assessing Scenario Uncertainty for CMIP5 Hicks J11, 3.30pm
Abstract: Simulating Earth System Models (ESMs) is among the most challenging exercises of contemporary science. ESMs require an extremely high-dimensional input comprising of a value of the forcing scenario for each year, and produce an even higher dimensional output in space, time and variables. Given the considerable computational and logistic challenges of performing even a small set of simulations, an ensemble comprises of a very limited number of runs. In the case of the CMIP5 ensemble, the reference for the latest IPCC assessment report, each modelling group submitted long-term simulations under at most four scenarios, thus providing very limited information for policy making. An emulator in scenario space can be developed to overcome these limitations. However, the modest number of runs, paired with the extremely large dimensionality of the input and output space, poses significant challenges in the development of the statistical methodology. In this talk, I will present a scenario emulator for ESMs that leverages on the temporal structure of the input/output space, on the causality principle and on the gridded geometry of the output. I will present an application to this methodology for temperature and wind data in the case of two ensembles, and I will show how the emulator provides accurate results for a dataset of tens of millions of data points.