INCREASED POLAR STRATOSPHERIC OZONE LOSSES AND DELAYED EVENTUAL RECOVERY OWING TO INCREASING GREENHOUSE-GAS CONCENTRATIONS

The chemical reactions responsible for stratospheric ozone depletion a re extremely sensitive to temperature(1). Greenhouse gases warm the Ea rth's surface but cool the stratosphere radiatively(2-5) and therefore affect ozone depletion. Here we investigate the interplay between pro jected future emissions of greenhouse gases and levels of ozone-deplet ing halogen species using a global climate model that incorporates sim plified ozone-depletion chemistry. Temperature and wind changes induce d by the increasing greenhouse-gas concentrations alter planetary-wave propagation in our model, reducing the frequency of sudden stratosphe ric warmings in the Northern Hemisphere(4). This results in a more sta ble Arctic polar vortex, with significantly colder temperatures in the lower stratosphere and concomitantly increased ozone depletion. Incre ased concentrations of greenhouse gases might therefore be at least pa rtly responsible for the very large Arctic ozone losses observed in re cent winters(6-9). Arctic losses reach a maximum in the decade 2010 to 2019 in our model, roughly a decade after the maximum in stratospheri c chlorine abundance. The mean losses are about the same as those over the Antarctic during the early 1990s, with geographically localized l osses of up to two-thirds of the Arctic ozone column in the worst year s. The severity and the duration of the Antarctic ozone hole are also predicted to increase because of greenhouse-gas-induced stratospheric cooling over the coming decades.