ABSTRACT
The sun provides radiant energy to the earth. On the surface this energy is absorbed and re-emitted as longer wavelength infrared radiation. Some of this radiation escapes the atmosphere but the majority is absorbed by molecules of atmospheric gases (particularly carbon dioxide and water vapour) and is re- radiated back towards the earth, warming the surface. These processes, collec- tively known as the ‘greenhouse effect’, are all parts of the natural climatic cycle which maintains the steady state of the global ecosystem. They are also pro- cesses of great importance to life on earth, for if the infrared radiation from the earth were not trapped in the atmosphere in this way the average surface temper- ature of the earth would not be around +15°C but rather around –15°C: a chilly prospect.
