Human Impact on Direct and Diffuse Solar Radiation during the Industrial Era

Abstract In this study the direct and diffuse solar radiation changes are estimated, and they contribute to the understanding of the observed global dimming and the more recent global brightening during the industrial era. Using a multistream radiative transfer model, the authors calculate the impact of changes in ozone, NO2, water vapor, CH4, CO2, direct and indirect aerosol effects, contrails, and aviation-induced cirrus on solar irradiances at the surface. The results show that dimming is most pronounced in central Africa, Southeast Asia, Europe, and northeast America. Human activity during the industrial era is calculated and accounts for a decrease in direct solar radiation at the surface of up to 30 W m−2 (30%–40%) and an increase in diffuse solar radiation of up to 20 W m−2. The physical processes that lead to the changes in direct and diffuse solar radiation are found to be remarkably different and the authors explain which mechanisms are responsible for the observed changes.