The impact of tropical Pacific SST trends on Antarctic Sea Ice in CESM1.1

Abstract:

Coupled atmosphere-ocean models do not capture trends from recent observations in the Antarctic climate. While models forced by natural and anthropogenic forcings show a recent decline in sea ice extent and warming in sea surface temperatures, satellite observations show a puzzling redistribution of Antarctic sea ice and non-uniform surface warming trends. Studies with slab ocean models and observations have shown impacts of tropical teleconnections on variability in the Antarctic climate, but these teleconnections have yet to be thoroughly examined in coupled models. Here we examine the impact of tropical Pacific teleconnections to the Antarctic climate using the Community Earth System Model version 1.1. The 1980-2013 cooling trend in tropical Pacific SST’s is imposed by way of a prescribed heat flux adjustment, and an ensemble of simulations is constructed. The ensemble-averaged response is compared to a 30-member ensemble control run. Both ensembles use the rcp8.5 scenario for greenhouse gas forcing. We find that the response to combined tropical Pacific forcing and greenhouse gas forcing results in a regional expansion of Antarctic sea ice. In the event that the observed cooling trend in the tropical Pacific SST is a result of internal natural variability, our results suggest that natural variability in the tropical Pacific may account for some of the recent changes in Antarctic sea ice extent.