Emergence of Southern Hemisphere stratospheric circulation changes in response to ozone recovery

Abstract

Depletion of stratospheric ozone in the Southern Hemisphere (SH) during the late twentieth century cooled local air temperature, which resulted in stronger stratospheric westerly winds near 60° S and altered SH surface climate. However, Antarctic ozone has been recovering since around 2001 thanks to the implementation of the Montreal Protocol, which banned production and consumption of ozone-depleting substances. Here we show that the post-2001 increase in ozone has resulted in significant changes to trends in SH temperature and circulation. The trends are generally of opposite sign to those that resulted from stratospheric ozone losses, including a warming of the SH polar lower stratosphere and a weakening of the SH stratospheric polar vortex. Observed post-2001 trends of temperature and circulation in the stratosphere are about 50–75% smaller in magnitude than the trends during the ozone depletion era. The response is broadly consistent with expectations based on modelled depletion-era trends and variability of both ozone and reactive chlorine. The differences in observed stratospheric trends between the recovery and depletion periods are statistically significant (P < 0.05), providing evidence for the emergence of dynamical impacts of the healing of the Antarctic ozone hole.