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Byline: M. Deque (1), D. P. Rowell (2), D. Luthi (3), F. Giorgi (4), J. H. Christensen (5), B. Rockel (6), D. Jacob (7), E. Kjellstrom (8), M. Castro (9), B. Hurk (10) Abstract: Ten regional climate models (RCM) have been integrated with the standard forcings of the PRUDENCE experiment: IPCC-SRES A2 radiative forcing and Hadley Centre boundary conditions. The response over Europe, calculated as the difference between the 2071--2100 and the 1961--1990 means can be viewed as an expected value about which various uncertainties exist. Uncertainties are measured here by variance in eight sub-European boxes. Four sources of uncertainty can be evaluated with the material provided by the PRUDENCE project. Sampling uncertainty is due to the fact that the model climate is estimated as an average over a finite number of years (30). Model uncertainty is due to the fact that the models use different techniques to discretize the equations and to represent sub-grid effects. Radiative uncertainty is due to the fact that IPCC-SRES A2 is merely one hypothesis. Some RCMs have been run with another scenario of greenhouse gas concentration (IPCC-SRES B2). Boundary uncertainty is due to the fact that the regional models have been run under the constraint of the same global model. Some RCMs have been run with other boundary forcings. The contribution of the different sources varies according to the field, the region and the season, but the role of boundary forcing is generally greater than the role of the RCM, in particular for temperature. Maps of minimum expected 2m temperature and precipitation responses for the IPCC-A2 scenario show that, despite the above mentioned uncertainties, the signal from the PRUDENCE ensemble is significant. Author Affiliation: (1) Meteo-France, Centre National de Recherches Meteorologiques, 42 Avenue Coriolis, 31057, Toulouse Cedex 01, France (2) Met Office, Hadley Centre for Climate Prediction and Research, FitzRoy Road, Exeter, Devon, EX1 3PB, UK (3) Swiss Federal Institute of Technology, Institute for Atmospheric and Climate Science, ETH, Winterthurerstrasse 190, 8057, Zurich, Switzerland (4) Abdus Salam International Centre for Theoretical Physics, Trieste, Italy (5) Danish Meteorological Institute, Lyngbyvej 100, 2100, Copenhagen A, Denmark (6) GKSS Forschungszentrum Geesthacht GmbH, Institute of Coastal Research, Max Planck Strasse, 21502, Geesthacht, Germany (7) Max-Planck-Institut fur Meteorologie, Bundesstrasse 55, 20146, Hamburg, Germany (8) Swedish Meteorological and Hydrological Institute, Folkborgsvagen 1, 60176, Norrkoping, Sweden (9) Dept. de Ciencias Ambientales, Universidad de Castilla La Mancha, Campus Tecnologico, 45071, Toledo, Spain (10) KNMI, Postbus 201, 3730 AE, De Bilt, The Netherlands Article History: Registration Date: 30/11/2006 Received Date: 15/02/2005 Accepted Date: 17/10/2006 Online Date: 20/03/2007