ABSTRACT
The earth’s average temperature is governed by the balance between the absorption of shortwave radiation from the sun and the emission of longwave radiation (also referred to as infrared radiation) from the earth. A surplus in the absorption of shortwave radiation over the emission of longwave radiation will cause the climate to become warmer, while an excess of emitted longwave radiation will cause the climate to cool. Longwave radiation is emitted from the earth’s surface and clouds, and to a lesser extent, from the atmosphere itself. The ease with which the earth can emit longwave radiation to space depends on how much of the surface emission can pass through the atmosphere. Certain naturally occurring gases in the atmosphere – water vapour foremost, followed by carbon dioxide (CO2), ozone (O3) and methane (CH4) – absorb some of the longwave radiation emitted from the surface, thereby retaining energy within the atmosphere and making the climate warmer than it would be otherwise. This warming effect is popularly referred to as the ‘greenhouse effect’, and the gases contributing to it are called greenhouse gases (GHGs).
