Impact of Lightning on Air Chemistry and Climate

The study shows that climate change does not necessarily lead to an increase in lightning as proposed by studies linking lightning to convective cloud top heights, but may reduce lightning. The impact of lightning on air chemistry and on climate is studied using simulation results obtained with a coupled ensemble climate-chemistry model from 1960 to 2020. The model simulates lightning and lightning induced nitrogen oxides (NOx) using a parameterisation based on the convective mass flux (updraft velocity). The computed flash frequency distribution over the globe is broadly in agreement with satellite observations, except for some oceanic regions. The results show, different from general expectations, a decrease in lightning activity in a warming climate. The decrease occurs because of less frequent though stronger convective events. Hence lightning decreases in total flash frequency, although individual events produce more lightning. The computed decrease in lightning NOx emissions is overlaid with an increase in sensitivity of ozone production to NOx amounts, which first leads to an increase in lightning ozone until the 1970s and then to a decrease. The sensitivity of climate in terms of radiative forcing to ozone changes is generally decreasing during the simulation