Tropospheric ozone, lightning, and climate change

Tropospheric O 3 is an important greenhouse gas. Lightning is a major source of NO x , and thus of tropospheric O 3 It has recently been suggested that due to an apparent strong correlation between lightning strike rates and surface temperatures, tropospheric O 3 may significantly increase if the climate warms, resulting in a substantial positive climate forcing. This paper attempts to quantify the extent of this forcing and the associated positive climate feedback. Simulations incorporating a tropospheric 03-surface temperature parameterization are performed of the last glacial maximum and of a climate in which greenhouse gas concentrations have been doubled. The O 3 parameterization is based on results from a two-dimensional chemical model. The simulations are obtained using a one-dimensional radiative-convective model, in which CO 2 , CH 4 , tropospheric O 3 , and in the case of the paleoclimate simulation the surface albedo, are varied both independently and in combination. In the paleoclimate case, the tropospheric O 3 feedback has roughly two thirds of the effect on surface temperatures as the change in tropospheric O 3 due to industrialization alone. During climate warming, the effect on surface temperatures is about 60% of that due to a doubling of CH 4 . The results indicate that a surface temperature-lightning-O 3 feedback, currently absent in general circulation models, could significantly affect anthropogenic climate change. Improved modeling and observations are required to confirm this.