A tropospheric ozone‐lightning climate feedback

Tropospheric ozone is an important greenhouse gas. In the upper troposphere one of the major sources of ozone are the nitrogen oxides produced by lightning IPCC, 1995. Recently it has been shown that the number of lightning flashes may be very sensitive to changes in the surface temperature Williams, 1992. Here we use a global two‐dimensional atmospheric model and find that for a warmer surface and constant lightning ozone decreases globally except for in the polluted Northern Hemisphere. However, a warming with increased lightning can more than offset this decrease. We find that for a 20% increase of lightning the global mean radiative forcing by tropospheric ozone is about +0.1 Wm −2 . There is therefore a possibility of a positive climate feedback mechanism. The implied sensitivity of ozone to lightning and temperature suggests a major uncertainty in quantifying anthropogenic perturbations of upper tropospheric ozone.