Global dimming is the slow but sure lessening in the amount of global direct irradiance of the earth’s surface that was observed for several decades after the start of systematic measurement in the 1950. The effect varies by location. However, world wide, it has been estimated to be of the order of a four percent reduction over the tree decades from 1960 to 1990.however, after discounting an anomaly caused by the eruption of Mount Pinatubo in 1991, a very slight reversal in the overall trend has been observed. It is through to have been caused in the atmosphere due to human action .the switch from a global dimming to a brightening trend in 1990 happened just as global aerosol levels started to declaim. Global dimming has interfered with the hydrological cycle by reducing evaporation and may have reduced rainfall in some areas. Deliberate manipulation of this dimming effect is now being considered as a Geo-engineering technique to reduce the impact of global warming.