Met Office Hadley Centre, FitzRoy Road, Exeter, Devon, EX1 3PB, UK

now at: Department of Meteorology, University of Reading, P.O. Box 243, Reading, RG6 6BB, UK

Department of Environmental Sciences and Engineering, The University of North Carolina at Chapel Hill, 146B Rosenau Hall, CB #7431, Chapel Hill, North Carolina 27599, USA

Earth System Science Interdisciplinary Center, University of Maryland, College Park, Maryland, 20740, USA

Earth Science Directorate, NASA Goddard Space Flight Center, Greenbelt, Maryland, 20771, USA

Center for International Climate and Environmental Research – Oslo (CICERO), P.O. Box 1129 Blindern, 0318 Oslo, Norway

NASA Goddard Institute for Space Studies, 2880 Broadway, New York, New York, 10025 USA

Department of Environmental Sciences and Engineering, The University of North Carolina at Chapel Hill, 146B Rosenau Hall, CB #7431, Chapel Hill, North Carolina 27599, USA