Global lightning activity and climate change

The relationship between global lightning frequencies and global climate change is examined in this thesis. In order to study global impacts of climate change, global climate models or General Circulations Models (GCMs) need to be utilized. Since these models have coarse resolutions many atmospheric phenomena that occur at subgrid scales, such as lightning, need to be parameterized whenever possible.; The first chapter introduces a simple parameterization used to simulate total (intracloud and cloud-to-ground) lightning frequencies. The parameterization uses convective cloud top height to approximate lightning frequencies. The second chapter deals with a parameterization for simulating cloud-to-ground (CG) lightning around the globe. This parameterization uses the thickness of the cold cloud sector in thunderstorms (0{dollar}spcirc{dollar}C to cloud top) to calculate the proportion of CG flashes in a particular thunderstorm. The third chapter deals with the modelling of lightning in the Goddard Institute for Space Studies (GISS) GCM. This chapter presents results from the model's control run. The fourth chapter presents two climate change scenarios. One for a climate where the solar constant is reduced by 2% (5.9{dollar}spcirc{dollar}C global cooling), and one for a climate with twice the present concentration of CO{dollar}sb2{dollar} in the atmosphere (4.2{dollar}spcirc{dollar}C global warming). The results imply a 24%/30% decrease/increase in global lightning frequencies for the cooler/warmer climate. The fifth chapter considers the possibility of using the above findings to monitor future global warming. The results show that the earth's ionospheric potential, which is regulated by global thunderstorm activity, could possibly supply valuable information regarding global surface temperature fluctuations. The sixth and final chapter looks at the implications of changes in both lightning frequencies and the hydrological cycle, as a result of global warming, on natural forest fires. In the United States the annual mean number of lightning fires could increase by 40% while the area burned may increase by 65% in a 2{dollar}times{dollar}CO{dollar}sb2{dollar} climate. On a global scale the largest increase in lightning fires can be expected in the tropics where few natural fires occur today.