Response of a coupled atmosphere-ocean general circulation model to increased carbon dioxide

The response of the IVM RAN coupled atmosphere-ocean model to increased carbon dioxide (CO2) was examined by conducting two 80-year experiments. The CO2 concentration was set equal to its present-day value in the first (control) experiment and was increased by 1% per year from the initially specified present-day value in the second experiment. Global warming at the Earth's surface over the years 61-80 in the latter experiment was found to be about 0.9 K greater than that in the control experiment, and the corresponding increase in precipitation was found to be 0.03 mm day(-1). Warming was maximal in midlatitude Eurasia, where it reached 3-5 K in November-April. About one-third of this warming, most of the precipitation increase over the northern Atlantic and Europe, and most of the precipitation decrease over southern Europe are explained by an increased Arctic Oscillation index. A sensitivity experiment conducted with the atmospheric model having a fixed sea surface temperature (SST) and increased CO2 showed that changes in the atmospheric circulation are similar to those produced by the coupled model, while the global warming of the troposphere and the Earth's surface is several times less than that in the coupled model. The main factor affecting the growth of the global SST and the formation of the spatial pattern of the SST response is a change in the radiation balance of the ocean surface under increased CO2. The response of sea surface salinity is determined primarily by a change in the surface freshwater balance. Moreover, the sea surface salinity decreases in the Pacific and increases in the Atlantic.