Consistent with previous studies, ozone depletion is the dominant driver of Southern Hemisphere stratosphere climate change. In the austral late spring and summer, the ozone hole causes strong Antarctic lower stratospheric cooling and westerly acceleration, and increases the Brewer-Dobson circulation. The stratospheric trends due to ozone depletion and GHG increases are linearly additive: the sum of the trends from the two single-forcing simulations is similar to that from the control simulation. In the troposphere and surface, however, trends are not linearly additive. Ozone depletion and GHG increases produce comparable trends in the summer surface temperature, precipitation, and the Southern Annular Mode, and the sum of the two single-forcing trends is greater than the control simulation trend. We also assess the roles of the two forcings on Southern Ocean and Antarctic sea ice change. Again we find that the simulated Southern Ocean warming, meridional overturning circulation spin-up, and Antarctic sea ice decrease driven by the two forcings are highly nonadditive.