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

Abstract

Two 2 × 10-year climate change experiments made with the Rossby Centre regionalAtmospheric climate model (RCA) are reported. These two experiments are driven by boundarydata from two global climate change simulations, one made with HadCM2 and the other with ECHAM4/OPYC3, in which the global mean warming is virtually the same, 2.6°C. The changesin mean temperature and precipitation show similarities (including broadly the same increasein temperature and in northern Europe a general increase in annual precipitation) as well asdifferences between the two RCA experiments. These changes are strongly governed by thedriving GCM simulations. Even on the RCA grid box scale, the differences in change betweenRCA and the driving GCM are generally smaller than the differences between the two GCMs.Typically about a half of the local differences between the two RCA simulations are attributedto noise generated by internal variability, which also seems to explain a substantial part of theRCA–GCM differences particularly for precipitation change. RCA includes interactive modelcomponents for the Baltic Sea and inland lakes of northern Europe. The simulated changes inthese water bodies are discussed with emphasis on the wintertime ice conditions. Comparisonwith an earlier RCA experiment indicates that a physically consistent treatment of these waterbodies is also of importance for the simulated atmospheric climate change.