Refers to the reduction in concentration of ozone in the Earth's upper atmosphere. This reduction occurs as a consequence of the release of chemicals that rise through the atmosphere and react with ozone when they reach the stratosphere. Depletion of the Earth's protective ozone layer can result in increased incidence of skin cancer and cataracts (a serious condition that damages the lens of the eye), and a range of harmful effects on habitats. These effects are most severe in or near polar regions where ozone depletion is most significant.

Chemicals considered most responsible for ozone depletion include chlorofluorocarbons (CFCs and HCFCs, once commonly used in cooling systems and still extensively used in China and many Third World nations) and halons.

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