Climate Impacts: Impacts of Ozone on Southern Hemisphere Climate

Abstract

AbstractThis chapter reviews climate response to long-term changes in stratospheric ozone due to human activity. Human-induced stratospheric ozone depletion has occurred most prominently in the springtime Antarctic since the late twentieth century, although signs of its recovery have begun to appear more recently thanks to the implementation of the Montreal Protocol. The ozone depletion has been much appreciated to drive significant changes in the Southern Hemisphere climate system during austral summer, primarily by altering the tropospheric midlatitude jet. Strong cooling of the Antarctic lower stratosphere due to the severe ozone depletion strengthens the stratospheric polar vortex and delays its springtime breakup. This strengthening of the circumpolar westerly flow extends downward through the troposphere to the surface during austral summer. Through this stratosphere-troposphere coupling, the tropospheric midlatitude jet shifts poleward and strengthens. This jet shift is associated with a trend toward the positive phase of the Southern Annular Mode, which is the leading mode of variability of the Southern Hemisphere extratropical circulation. The ozone hole-induced positive trend of the Southern Annular Mode was observed during austral summer in the late twentieth century, accompanied by the surface cooling over East Antarctica and warming over the Antarctic Peninsula and Patagonia. It was also linked to the poleward displacement of the southern mid- to high-latitude precipitation and the poleward shift of the Southern Hemisphere Hadley cell edge. The shift of the Hadley cell edge induced anomalous upward motions and moisture convergence in the subtropical lower troposphere, leading to increases in the subtropical precipitation. Although the direct radiative impact due to the ozone depletion is geographically confined to the region of the Antarctic ozone hole, its climate impacts extend throughout much of the Southern Hemisphere. Several atmospheric reanalyses suggest the positive trend of the Southern Annular Mode paused, or slightly reversed, since around 2000 in response to the ozone recovery.KeywordsOzoneClimate changeSouthern Annular ModeTroposphere-stratosphere couplingOzone hole