National Center for Atmospheric Research
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The Antarctic Ice Sheet and circumpolar Southern Ocean play unique roles in the climate system, strongly regulating the distribution of energy. The Antarctic Ice Sheet surface reflects 80% or more of the solar radiation it receives in the summer, and in winter it emits to space much of the heat received from lower latitudes. The Southern Ocean accounts for an estimated 40% of the global oceanic uptake of anthropogenic carbon, and absorbs excess heat from greenhouse gasses. However, predicting the role and response of Antarctica and the Southern Ocean in global climate change has proven very challenging, due in part to the complex nature of atmosphere-ocean-ice sheet interactions and in part due to sparse observations. For example, there is no agreed-upon explanation for the modest increase in Antarctic sea ice extent since 1979, and differing interpretations on the roles of stratospheric ozone depletion and tropical sea surface temperatures in the strengthening of the westerly winds over the Southern Ocean. Furthermore, our work has shown that sea ice has increased amidst cooling Southern Ocean sea surface temperatures (SSTs) and cooling or unchanging coastal East Antarctic air temperatures. These trends are remarkable against the backdrop of global warming, and this talk will interpret the roles of natural variability as well forcing by ozone depletion and tropical SSTs in driving these trends. We will use traditional climate observations as well as ice core proxies to characterize natural variability, and a series of atmospheric model simulations to investigate the causes of recent trends, with a focus on the wind trends.