Global dimming is a process that reduces the amount of irradiance – also called electromagnetic radiance – present at the Earth’s surface. It is generally speculated that it is caused by an increase in particulates (such as sulfur aerosols) in the atmosphere due to the actions of humans, and is estimated to have resulted in about a 4% reduction in overall irradiance at the planet’s surface between 1960-1990. Global dimming is believed to reduce evaporation (thus affecting the hydrological cycle) and possibly has a cooling effect on the earth as well. However, scientists and the world in general presently focus more of their attention on what is considered to be a much bigger threat to the planet – global warming.