Outgoing Longwave Radiation (OLR) is the energy leaving the earth as infrared radiation at low energy. The OLR is affected by clouds and dust in the atmosphere, which tend to reduce it below clear sky values. Greenhouse gases absorb certain wavelengths of OLR adding heat to the atmosphere, which in turn causes the atmosphere to emit more radiation. Some of this radiation is directed back towards the Earth, increasing the average temperature of the Earth's surface. (OLR - Wikipedia)