The Response of the Ozone Layer to Quadrupled CO2 Concentrations: Implications for Climate

The quantification of the climate impacts exerted by stratospheric ozone changes in abrupt 4 × CO 2 forcing experiments is an important step in assessing the role of the ozone layer in the climate system. Here, we build on our previous work on the change of the ozone layer under 4 × CO 2 and examine the effects of ozone changes on the climate response to 4 × CO 2 , using the Whole Atmosphere Community Climate Model. We show that the global-mean radiative perturbation induced by the ozone changes under 4 × CO 2 is small, due to nearly total cancellation between high and low latitudes, and between longwave and shortwave fluxes. Consistent with the small global-mean radiative perturbation, the effect of ozone changes on the global-mean surface temperature response to 4 × CO 2 is negligible. However, changes in the ozone layer due to 4 × CO 2 have a considerable impact on the tropospheric circulation. During boreal winter, we find significant ozone-induced tropospheric circulation responses in both hemispheres. In particular, ozone changes cause an equatorward shift of the North Atlantic jet, cooling over Eurasia, and drying over northern Europe. The ozone signals generally oppose the direct effects of increased CO 2 levels and are robust across the range of ozone changes imposed in this study. Our results demonstrate that stratospheric ozone changes play a considerable role in shaping the atmospheric circulation response to CO 2 forcing in both hemispheres and should be accounted for in climate sensitivity studies.