The impact of stratospheric ozone depletion on the surface energy budget of Antarctica

Abstract:

It is now well established that stratospheric ozone depletion has been one of the dominant drivers of recent climate change in the mid-latitudes of the Southern Hemisphere. However, the effects of ozone depletion on Antarctic climate change during the past several decades are much more uncertain. Here, we examine the impact of ozone depletion on the Antarctic surface energy budget using a suite of simulations from the Community Earth System Model-Whole Atmosphere Community Climate Model (CESM-WACCM). CESM-WACCM is a state-of-the-art atmosphere-ocean general circulation model that includes interactive stratospheric chemistry, as well as a dynamic-thermodynamic sea-ice scheme. We performed two sets of integrations with WACCM for the period 1960-2005, each consisting of 6 ensemble members. In the first set of integrations, the model was driven with all time-varying natural and anthropogenic forcings, most notably the observed increases in ozone-depleting substances (ODSs) and other well-mixed greenhouse gases. The second set of 6 integrations is identical to the first, except that ODSs are kept fixed at 1960 levels, thus preventing the model from developing a springtime Antarctic stratospheric ozone hole. Comparison between these two ensembles of simulations therefore unambiguously quantifies the impact of ozone depletion on the Antarctic surface energy budget. We find that the decrease in stratospheric ozone concentrations in recent decades leads to an increase of 2-3 W/m2 in incident (downward) shortwave radiation at the Antarctic surface during austral spring and summer. However, due to a concomitant increase in surface reflectivity, there is little change in net shortwave radiation in the model simulations. Downward long-wave emission increases as a consequence of greenhouse gases in both ensembles, while latent and sensible heat fluxes do not change significantly. Taken together, these results indicate that ozone depletion alone has a negligible effect on Antarctic surface energy budget. Implications of these results for the interpretation of observed Antarctic surface temperature changes are discussed.