Global dimming can be defined as the reduction of the amount of heat and energy, sent from the sun, that is trapped near the surface of the Earth.  This phenomenon has been observed since the 1950’s and is assumed to occur as a result of pollutants released into the Earth’s atmosphere.  The pollutants alter the state of the Earth’s atmosphere and ultimately cause more heat and energy to be reflected from the Earth into space.  Global dimming creates a cooling effect that is thought to be masking the effects of global warming.