Influence of Continental Ice Retreat on Future Global Climate

Evidence from observations indicates a net loss of global land-based ice and a rise of global sea level. Other than sea level rise, it is not clear how this loss of land-based ice could affect other aspects of global climate in the future. Here, the authors use the Community Climate System Model version 3 (CCSM3) to evaluate the potential influence of shrinking land-based ice on the Atlantic meridional overturning circulation (AMOC) and surface climate in the next two centuries under the Intergovernmental Panel on Climate Change (IPCC) A1B scenario with prescribed rates of melting for the Greenland Ice Sheet, West Antarctic Ice Sheet, and mountain glaciers and ice caps. Results show that the AMOC, in general, is only sensitive to the freshwater discharge directly into the North Atlantic over the next two centuries. If the loss of the West Antarctic Ice Sheet would not significantly increase from its current rate, it would not have much effect on the AMOC. The AMOC slows down further only when the surface freshwater input due to runoff from land-based ice melt becomes large enough to generate a net freshwater gain in the upper North Atlantic. This further-weakened AMOC does not cool the global mean climate, but it does cause less warming, especially in the northern high latitudes and, in particular, in Europe. The projected precipitation increase in North America in the standard run becomes a net reduction in the simulation that includes land ice runoff, but there are precipitation increases in west Australia in the simulations where the AMOC slows down because of the inclusion of land-based ice runoff.