Climate effect of ozone changes caused by present and future air traffic

The potential of aircraft-induced ozone changes to force a substantial clim ate impact is investigated by means of simulations with an atmospheric gene ral circulation model, coupled to a mixed layer ocean model. We present res ults from several numerical experiments that are based on ozone change patt erns for 1992 aviation and on a future scenario for the year 2015. In both cases, the climate signal is statistically significant. The strength of the ozone impact is of comparable magnitude to that arising from aircraft CO2 emissions, thus meaning a non-negligible contribution to the total climate effect of aviation emissions. There are indications of a characteristic sig nature of the aircraft ozone related temperature response pattern, distinct ly different from that associated with the increase of well-mixed greenhous e gases. Likewise, the climate sensitivity to non-uniform ozone changes inc luding a strong concentration perturbation at the tropopause may be higher than the climate sensitivity to uniform changes of a greenhouse gas. In a h ierarchy of experiments, for which the spatial structure of an aircraft-rel ated ozone perturbation was left fixed, while the amplitude of the perturba tion was artificially increased, the climate signal depends in a non-linear way on the radiative forcing.