Combined Effects of Global Warming and Ozone Depletion/Recovery on Southern Hemisphere Atmospheric Circulation and Regional Precipitation

Abstract

Ozone depletion led to a positive trend in the summertime Southern Annular Mode (SAM) during the last decades of the 20th century. During the present century, global warming (GW) is expected to contribute to a positive SAM trend while ozone recovery is expected to act in the opposite direction. Here, Southern Hemisphere (SH) circulation and regional precipitation change are studied with a methodology that separates the effects from GW and ozone depletion/recovery. Our results show that a “tug-of-war” between ozone and GW occurs in the summertime stratosphere, propagating to the troposphere where it is manifest in the SAM. However, at the regional scale this “tug-of-war” is not as relevant as the combined effects of other remote drivers of circulation change, which force different kinds of precipitation changes in the SH. For regional precipitation changes, the uncertainty in future circulation change is as important as the uncertainty in the GW level.