Simulation of the Meridionally and Seasonally Varying Climate Response Caused by Changes in Ozone Concentration

Abstract

Recent model studies have indicated that observed stratospheric ozone decline can have a cooling effect on climate. This study intends to investigate the climate response due to changes in the radiative fluxes caused by prescribed changes in stratospheric as well as tropospheric ozone. For this purpose the authors use a simplified climate model, basically consisting of an energy balance atmosphere model coupled to an advection?diffusion ocean model. The coupled climate model simulates the latitudinal and seasonal variations in zonal mean surface air temperature and the average lower (12?22 km) and higher (22?100 km) stratospheric temperatures. First, the quasi-equilibrium response of the model to various uniform ozone perturbations is examined. For instance, a uniform 50% reduction in lower stratospheric ozone results in a global average cooling of 3.5°C in the lower stratosphere with maximum values in the Tropics and of 0.46°C at the surface with maximum cooling in the polar winter. The latter is largely due to the albedo?temperature feedback, mainly through increases in sea ice. The albedo?temperature feedback is consistently stronger in the case of tropospheric and lower stratospheric ozone perturbations than in the case of, for instance, CO2 perturbations. This can be attributed mainly to differences in the meridional gradient in tropopause radiative forcing. This study indicates that one must be cautious when using concepts such as global radiative forcing and global climate sensitivity in quantifying climate change. Finally, the transient model response to various ozone trend scenarios indicates that the net effect of tropospheric ozone increases and stratospheric ozone depletions is a slight global average cooling (?0.001 to ?0.003 K yr?1), which offsets by approximately 10% the projected surface warming due to increases in the other greenhouse gases. Results obtained with this climate model provide qualitative insights in the fundamental processes that determine the sensitivity of climate for ozone changes.