SIMULATION OF THE MERIDIONALLY AND SEASONALLY VARYING CLIMATE RESPONSE CAUSED BY CHANGES IN OZONE CONCENTRATION

Recent model studies have indicated that observed stratospheric ozone decline can have a cooling effect on climate. This study intends to in vestigate 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, ba sically 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 temp erature and the average lower (12-22 km) and higher (22-100 km) strato spheric temperatures. First, the quasi-equilibrium response of the mod el to various uniform ozone perturbations is examined. For instance, a uniform 50% reduction in lower stratospheric ozone results in a globa l average cooling of 3.5 degrees C in the lower stratosphere with maxi mum values in the Tropics and of 0.46 degrees C at the surface with ma ximum cooling in the polar winter. The latter is largely due to the al bedo-temperature feedback, mainly through increases in sea ice. The al bedo-temperature feedback is consistently stronger in the case of trop ospheric 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 s uch as global radiative forcing and global climate sensitivity in quan tifying climate change. Finally, the transient model response to vario us 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 approxi mately 10% the projected surface warming due to increases in the other greenhouse gases. Results obtained with this climate model provide qu alitative insights in the fundamental processes that determine the sen sitivity of climate for ozone changes.