Downscaling of greenhouse gas induced climate change in two GCMs with the Rossby Centre regional climate model for northern Europe

Two 2 x 10-year climate change experiments made with the Rossby Centre regi onal Atmospheric climate model(RCA) are reported. These two experiments are driven by boundary data from two global climate change simulations, one ma de with HadCM2 and the other with ECKAM4/OPYC3, in which the global mean wa rming is virtually the same, 2.6 degreesC. The changes in mean temperature and precipitation show similarities (including broadly the same increase in temperature and in northern Europe a general increase in annual precipitat ion) as well as differences between the two RCA experiments. These changes are strongly governed by the driving GCM simulations. Even on the RCA grid box scale, the differences in change between RCA and the driving GCM are ge nerally smaller than the differences between the two GCMs. Typically about a half of the local differences between the two RCA simulations are attribu ted to noise generated by internal variability, which also seems to explain a substantial part of the RCA-GCM differences particularly for precipitati on change. RCA includes interactive model components for the Baltic Sea and inland lakes of northern Europe. The simulated changes in these water bodi es are discussed with emphasis on the wintertime ice conditions. Comparison with an earlier RCA experiment indicates that a physically consistent trea tment of these water bodies is also of importance for the simulated atmosph eric climate change.