Large direct and indirect impacts of ozone-depleting substances on past Southern Hemisphere atmosphere-ocean trends

Abstract The indirect impacts of ozone-depleting substances (ODSs) on past Southern Hemisphere (SH) climate change via their impact on the ozone layer have been widely documented, but their direct radiative impacts remain unexplored. Using 20-member ensembles of historical simulations with a state-of-the-art climate model, we quantify this direct impact and compare it with their indirect impact via ozone depletion, as well as with the impacts of tropospheric ozone, CO 2 and aerosols. We find that the radiative impacts of ODSs contributed substantially to annual-mean SH atmosphere and ocean circulation trends between 1955 and 2000, with impacts nearly as large as those of stratospheric ozone, and exceeding those of CO 2 . ODSs also account for 29% of Southern Ocean warming, several times the individual contributions from stratospheric and tropospheric ozone. Our findings highlight the major role of ODSs in SH climate change and underscore the importance of the Montreal Protocol in mitigating climate change.