The human health and environmental concerns about ozone layer depletion are different from the risks we face from global warming, but the two phenomena are related in certain ways. Some pollutants contribute to both problems and both alter the global atmosphere. Ozone layer depletion allows more harmful UV radiation to reach our planet's surface. Increased UV radiation can lead to skin cancers, cataracts, and a suppressed immune system in humans, as well as reduced yields for crops.
Ozone is an oxygen molecule that occurs in very small amounts in nature. In the lower atmosphere, ozone occurs as a gas that, in high enough concentrations, can cause irritations to the eyes and mucous membranes. In the upper atmosphere (the stratosphere), ozone absorbs solar UV radiation that otherwise would cause severe damage to all living organisms on the earth's surface. Prior to the industrial revolution, ozone in the lower and upper atmospheres was in equilibrium. Today, excessive ozone in the lower atmosphere contributes to the greenhouse effect and pollutes the air.
Ozone is being destroyed in the upper atmosphere, however, where it has a beneficial effect. This destruction is caused primarily by CFCs. Chlorofluorocarbons don't occur naturally. They are very stable chemicals developed in the 1960s, and they can last up to 50 years. Used primarily for refrigeration and air-conditioning, CFCs have also been used as blowing agents to produce foamed plastics for insulation, upholstery padding, and packaging, and as propellants for fire extinguishers and aerosols. In their gaseous form, they drift into the upper atmosphere and destroy ozone molecules. This allows more UV radiation to reach the surface of the earth, killing or altering complex molecules of living organisms, including DNA. This damage has resulted in an increase in skin cancers, especially in southern latitudes. The Montreal Protocol on Substances that Deplete the Ozone Layer, signed in 1987 by 25 nations (168 nations are now party to the accord), decreed an international stop to the production of CFCs by 2000, but the effects of chemicals already produced will last for many years.
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