David Hutchinson
Department of Geological Sciences, Stockholm University, Sweden


Time and place
Thursday 3 September 2015, 14.15
Room C609, Arrhenius Labo0ratory, 6th floor

Global warming is occurring at a faster rate in the Northern Hemisphere (NH) than the Southern Hemisphere (SH) and this warming asymmetry is predicted to continue throughout the 21st Century. Several factors contribute to the warming asymmetry, including the greater proportion of land in the NH and the northward transport of heat by the ocean. We examine the role of ocean dynamics in setting the warming asymmetry. First we explore the impact of the Antarctic Circumpolar Current (ACC) on the interhemispheric warming asymmetry, by simulating a global coupled climate model with and without a land barrier across Drake Passage. When the ACC is removed, the asymmetry in sea surface temperature (SST) warming is reduced, due to the presence of a subpolar gyre, and a lower Antarctic sea ice extent. Second we examine the asymmetry of warming when moving from coarse (1°) to eddy-permitting (0.25°) ocean resolution, using a coupled climate model in an Atlantic-like sector domain. A larger high latitude SST asymmetry develops in the 0.25° model than the 1° model, both in control runs and in warming scenarios. The larger warming asymmetry in the 0.25° model is caused by stronger boundary current heat transport and reduced NH sea ice. Finally the impact of realistic bathymetry is explored in the sector climate model. The Atlantic-like sector model is compared with a flat bottom rectangular model. In warming experiments, the rectangular models develop warming and cooling regions in the NH, while the Atlantic models have no significant cooling regions. The Atlantic models also exhibit greater sensitivity of ACC transport to wind forcing, which is likely due to a barotropic free mode mechanism in the presence of realistic bathymetry.