CO2-induced climate change in northern Europe: CMIP2 versus CMIP3 versus CMIP5

The simulation of near-present-day climate and climate change in northern Europe is compared between the CMIP2, CMIP3 and CMIP5 ensembles of the Coupled Model Intercomparison Project, focusing on an idealized scenario with a doubling of CO2 in 70 years. The control simulations in the three ensembles share similar biases, including generally colder than observed temperatures and an underestimated north-south pressure gradient across northern Europe. The CO2-induced climate changes are also similar, despite a slight increasing (decreasing) trend in the simulated warming (precipitation increase) from the older towards the newer models. About half of the intermodel variance in the simulated annual mean warming in northern Europe is explained by differences in the global mean warming, whereas differences in the regional mean sea level pressure change contribute nearly 40 % of the variance of the annual precipitation change. An energy and water balance analysis for a subset of the models additionally suggests that the spread in the simulated warming is strongly affected by the snow-albedo feedback in spring and changes in cloudiness in summer, while both increased evaporation and changes in atmospheric water vapour convergence are important for precipitation changes. A comparison for the CMIP5 ensemble reveals a close similarity in temperature change in northern Europe between the idealized CO2 simulations and the Representative Concentration Pathways RCP4.5 and RCP8.5 simulations for the twenty-first century, once differences in the rate of the ensemble-averaged global mean warming are accounted for. Precipitation tends to increase slightly more under the RCP scenarios, possibly due to the assumed decrease in anthropogenic aerosols.