Delayed Southern Hemisphere climate change induced by stratospheric ozone recovery as seen in the CMIP5 models

Stratospheric ozone is expected to recover over the next century due to the regulation of ozone depleting substances by the Montreal Protocol. Targeted modeling studies suggest that the climate response to ozone recovery will oppose the climate response due to rising GHG emissions, however, to what extent these two forcings will cancel has been difficult to asses. Here, we present results from simulations performed for the IPCC 5th Assessment Report that show ozone recovery largely canceling the influence of GHGs on Southern Hemisphere climate between now and 2045. Specifically, by considering the seasonality of stratospheric ozone and comparing trends across three RCPs, we demonstrate that the position of the jet-stream, width of the subtropical dry-zones, and the seasonality of surface temperature exhibit significantly reduced trends over the first half of the 21st Century due to ozone recovery. After 2045, forcing from GHG emissions dominate the circulation response. Comparing the relative influences of future GHG emissions and historic ozone depletion, we find that the simulated tropospheric circulation changes between 1970-2005 driven by ozone depletion are larger than the projected changes in any RCP over the entire 21st Century. We stress, however, that projected changes due to increases in GHG emissions are no less severe since they will add to those which have already occurred.