A TROPOSPHERIC OZONE-LIGHTNING CLIMATE FEEDBACK

Tropospheric ozone is an important greenhouse gas. In the upper tropos phere one of the major sources of ozone are the nitrogen oxides produc ed by lightning [IPCC, 1995]. Recently it has been shown that the numb er of lightning flashes may be very sensitive to changes in the surfac e temperature [Williams, 1992]. Here we use a global two-dimensional a tmospheric model and find that for a warmer surface and constant light ning ozone decreases globally except for in the polluted Northern Hemi sphere. However, a warming with increased lightning can more than offs et this decrease. We find that for a 20% increase of lightning the glo bal mean radiative forcing by tropospheric ozone is about +0.1 Wm(-2). There is therefore a possibility of a positive climate feedback mecha nism. The implied sensitivity of ozone to lightning and temperature su ggests a major uncertainty in quantifying anthropogenic perturbations of upper tropospheric ozone.