The response of arctic sea ice to global change

The sea ice-covered polar oceans have received wider attention recently for two reasons. Firstly, the global canveyor belt circulation of the ocean is believed to be forced in the North and South Atlantic through deep water f ormation, which to a large degree is controlled by the variations of the se a ice margin and especially by the sea ice export to lower latitudes. Secon dly, CO2 response experiments with coupled climate models show an enhanced warming in polar regions for increased concentrations of atmospheric greenh ouse gases. Whether this large response in high latitudes is due to real ph ysical feedback processes or to unrealistic simplifications of the sea ice model component remains to be determined. Coupled climate models generally use thermodynamic sea ice models or sea ice models with oversimplified dyna mics schemes. Realistic dynamic-thermodynamic sea ice models are presently implemented only at a few modeling centers. Sensitivity experiments with th ermodynamic and dynamic-thermodynamic sea ice models show that the more sop histicated models are less sensitive to perturbations of the atmospheric an d oceanic boundary conditions. Because of the importance of the role of sea ice in mediating between atmosphere and ocean an improved representation o f sea ice in global climate models is required. This paper discusses presen t sea ice modeling as well as the sensitivity of the sea ice cover to chang es in the atmospheric boundary conditions. These numerical experiments indi cate that the sea ice follows a smooth response function: sea ice thickness and export change by 2% of the mean value per 1 Wm(-2) change of the radia tive forcing.