Tropospheric ozone, lightning, and climate change

Tropospheric O-3 is an important greenhouse gas. Lightning is a major source of NOx, 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 O-3-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 CO2, CH4, 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 CH4. The results indicate that a surface temperature-lightning-O-3 feed-back, currently absent in general circulation models, could significantly affect anthropogenic climate change. Improved modeling and observations are required to confirm this.