Arctic future scenario experiments with a coupled regional climate model

A number of regional Arctic dynamical downscaling scenario experiments are performed with the Rossby Centre Atmosphere Ocean climate model. The simulations are based on IPCC AR4 scenario simulations with the global coupled models BCCR2.0 and ECHAM5/MPI-OM and differ in the surface salinity treatment and lateral boundary conditions. Compared to the global runs, the regional simulations show a warmer Arctic, which agrees better to ERA-40 reanalysis data in the 20th century, and a slightly smaller trend in the 21st century. The ECHAM-forced runs show several periods with rapid summer sea ice reductions and partial recovery thereafter. Summer sea ice disappears for the first time around 2040. The large-scale change patterns of sea level pressure (SLP) and air temperature in the regional simulations are mainly dominated by the forcing of the global models but locally significant modifications occur. Pressure is reduced by 1-3 hPa and air temperature increases by 2-4 K in most Arctic regions and up to 10 K where winter sea ice disappears. The largely reduced Arctic sea ice area leads to increased atmospheric variability and more extremes in winter SLP and summer air temperature.