Ozone hole impacts on surface temperatures under climate change

Abstract

The Antarctic ozone hole, caused by human releases of chlorofluorocarbons, plays a major role in driving climate change in the southern hemisphere. Atmospheric temperatures and circulation are affected by the severe ozone loss due to a coupling of atmospheric composition, radiation, and dynamics. The ozone hole leads to a springtime stratospheric cooling and a prolonged persistence of the stratospheric polar vortex. Further, it affects surface climate where changes are characterized by a shift of the midlatitude jet towards higher latitudes that is commonly referred to as a shift of the Southern Annular Mode (SAM) towards its positive phase. This shift is associated with warming and cooling patterns in the southern hemisphere, particularly a cooling of large parts of Antarctica and a warming of the Antarctic Peninsula and Patagonia. With stratospheric ozone in the path to recovery, the climate impacts associated with the ozone hole are expected to reverse in the future. The concentration of greenhouse gases will, however, continue to increase. Similarly to the ozone hole, rising greenhouse gas concentrations are associated with a shift of the SAM towards its positive phase. Thus the effects of increased greenhouse gases and ozone recovery are predicted to counteract in the future. For meaningful climate projections, a detailed characterization of ozone hole induced climate change signals is, therefore, essential. However, a precise attribution of climate change signals to the Antarctic ozone hole is complicated due to simultaneous atmospheric composition changes and natural climate variability. In this thesis, idealized timeslice simulations were performed with the ICOsahedral Non-hydrostatic model with Aerosols and Reactive Trace gases (ICON-ART) to investigate ozone hole induced climate change signals isolated from other perturbations of the climate system. Further, the impact of natural climate variability is assessed. Our model results show robust summertime near-surface temperature changes caused by the ozone hole that are characterized by more complex warming and cooling patterns than previous studies suggest. While those studies attributed a large fraction of the detected signal to a shift in the SAM, the ICON-ART results indicate near-surface temperature changes that are not entirely caused by changes of the SAM. The decreased impact of the SAM in the ICON-ART model could result from a weaker, more realistic response of the SAM to external forcing that is commonly overestimated in other chemistry-climate models. Analysis of the SAMs variability shows more persistent SAM anomalies due to the ozone hole and a decreased persistence for future climate. As persistent stratospheric SAM anomalies have a potential impact on tropospheric SAM characteristics and thus near surface meteorology, a prediction metric was calculated to investigate the skill of SAM anomalies at different altitudes in predicting the averaged near-surface SAM one month in advance. Our calculations show that there is a strong decrease in stratospheric predictability for future simulations, regardless of the ozone recovery. The decreased stratospheric influence on the tropospheric SAM will likely affect the quality of extended range weather forecasts in the future.