Two-decadal aerosol trends as a likely explanation of the global dimming/brightening transition

Global average trends in solar radiation reaching the Earth’s surface show a transition from dimming to brightening that occurred in about 1990. We show that the inter-annual trend in solar radiation between 1980 and 2000 mirrors the trend in primary emissions of SO2 and black carbon, which together contribute about one-third of global average aerosol optical depth. Combined global emissions of these two species peaked in 1988– 1989. The twodecadal rate of decline in aerosol loading resulting from these emission changes, 0.13% yr-1, can be compared with the reported increase in solar radiation of 0.10% yr-1 in 1983 – 2001. Regional patterns of aerosol and radiation changes are also qualitatively consistent. We conclude that changes in the aerosol burden due to changing patterns of anthropogenic emissions are likely contributing to the trends in surface solar radiation.