Ozone is a gas that exists in very small amounts in the atmosphere but is particularly concentrated at high levels, about 30 km (100,000ft) up in the stratosphere. This layer protects the earth from some of the harmful effects of solar radiation in the ultraviolet (UV) wavelengths.

During the 1980s measurement of the ozone concentration in the stratosphere over the Antarctic shoed a rapid decrease in the winter months - the ozone hole. The cause of this decrease is thought to be the release into the atmosphere of chlorofluorocarbons (CFCs). CFC gases are used in the manufacture of some types of plastic foam and are used in refrigerators and as propellants for aerosols.

A reduction or thinning of this high level ozone layer would increase the risk of skin cancers in humans and have harmful effects on some crops, animals and zooplankton, giving higher surface temperatures. Chemical changes in the upper atmosphere as a result of the loss of ozone would also reinforce the greenhouse effect.