What about Global Dimming?

Global dimming is the gradual reduction in the amount of solar radiation reaching the Earth's surface that was observed for several decades after the start of systematic measurements in 1950s. The effect varies by location, but worldwide it has been estimated to be of the order of a 4% reduction over the three decades from 1960–1990. It is believed to be caused by an increase in particulates such as sulfate aerosols in the atmosphere due to human pollution.