Does the Antarctic climate system response to external forcing depend on the mean state of the model?

Projected changes in Antarctic temperature, sea ice and precipitation differ widely among Earth System Models. Comparisons of results from multi-model ensembles and large, initial condition ensembles suggest that these disparities cannot be fully explained by internal variability. Here, we use the Community Earth System Model (CESM) to assess the implications of reducing absorbed shortwave radiation biases over the Southern Ocean on the response to stratospheric ozone depletion. We conduct a parallel set of two ozone depletion experiments, the first using the original version of CESM that has been used for CMIP5 and numerous other experiments, and the second using a modified version of CESM with reduced cloud radiative forcing biases. The modified version of CESM is considerably cooler and windier at the surface of the Southern Ocean. We will present results showing how these mean state differences affect the response of surface temperature, winds, clouds and radiation to stratospheric ozone depletion, and discuss the implications for understanding the role of structural uncertainty in Antarctic climate change projections.