Antarctic Glacial Melt as a Driver of Recent Southern Ocean Climate Trends

Recent trends in Southern Ocean (SO) climate—of surface cooling, freshening, and sea ice expansion—are not captured in historical climate simulations. Here we demonstrate that the addition of a plausible increase in Antarctic meltwater to a coupled climate model can produce a closer match to a wide range of climate trends. We use an ensemble of simulations of the Goddard Institute for Space Studies Earth system model to compute “climate response functions” (CRFs) for the addition of meltwater. These imply a cooling and freshening of the SO, an expansion of sea ice, and an increase in steric height, all consistent with observations since 1992. The CRF framework allows one to compare the efficacy of Antarctic meltwater as a driver of SO climate trends, relative to greenhouse gas and surface wind forcing. The meltwater CRFs presented here strongly suggest that interactive Antarctic ice melt should be included in climate models. Plain Language Summary Climate models do not capture recent Southern Ocean (SO) climate trends of surface cooling, freshening, and sea ice expansion. Here we demonstrate that including a realistic increase in Antarctic meltwater can improve a model's representation of SO trends. We use an ensemble of simulations of the Goddard Institute for Space Studies Earth system model. Model results suggest that Antarctic meltwater drives a cooling and freshening of the SO and an expansion of winter sea ice, all consistent with observations. Results suggest that a better representation of Antarctic ice melt should be included in climate models. Key Points Earth system model projections do not capture recent Southern Ocean climate trends The inclusion of plausible discharges of Antarctic meltwater provides a closer match to observations Results suggest interactive ice sheets should be included in model projections