Global dimming

Global dimming is the gradual reduction in the amount of global direct irradiance at the Earth's surface that was observed for several decades after the start of systematic measurements in 1950s. It is thought to have been caused by an increase in particulates such as black carbon in the atmosphere due to human action. The effect varied by location, but worldwide it was of the order of a 4% reduction over the three decades from 1960–1990. The trend reversed during the past decade. Global dimming has interfered with the hydrological cycle by reducing evaporation and may have caused droughts in some areas. Global dimming also creates a cooling effect that may have partially masked the effect of greenhouse gases on global warming.