OZONE DEPLETION

OZONE DEPLETION became a serious concern in the 1980s and has prompted international agreements and changes in manufacturing processes in an attempt to slow depletion and minimize health and environmental problems. Ozone is a denser form of oxygen that shields the Earth from excessive ultraviolet radiation from the sun; without it, the earth's inhabitants and environment are exposed to damaging UV-B rays. Scientists detected substantial seasonal fluctuations in stratospheric ozone levels over Antarctica as early as the 1950s. In the 1970s the chemists Sherwood Rowland and Mario Molina of the University of California (in findings later confirmed by the National Academy of Sciences) blamed the lower wintertime level of ozone over Antarctica on the rapidly increasing use of chlorofluorocarbons (CFCs) as refrigerants and as propellants in aerosol cans and in the manufacture of plastic foam products. CFC molecules deplete the ozone layer because they migrate to the stratosphere, collect over the Antarctic ice cap during the cold winter months, and become fixed on polar stratospheric clouds, isolated from the normal atmospheric circulation. When sunlight returns to Antarctica in early spring, its ultraviolet rays trigger a chemical reaction that releases a chlorine-oxide free radical, which precipitates another reaction that breaks up the oxygen molecules that form the ozone layer. A world that has been producing and releasing

into the atmosphere 1 million tons of CFCs per year has seen CFC levels in the atmosphere rise from 0.8 parts per billion by volume in 1950 to at least 4 parts per billion at the close of the century.

In 1985 the discovery of an ozone "hole" over wintertime Antarctica prompted international action. In 1987 all major industrial nations signed the Montreal Protocol, agreeing to deadlines for ending the use of CFCs; eighty nations signed amendments calling for the almost total elimination of CFCs, methyl chloroform, and carbon tetrachloride by 1996. By the 1990s, 173 countries, including the United States, had signed.

However, the danger is far from over. Alarm bells rang in October 2000, when for the first time ever, a major ozone hole opened over a populated city: Punta Arenas, Chile. Not all countries and industries are complying with the ban on ozone-depleting substances; for instance, U.S. companies have been fighting efforts to cut use of methyl bromides, claiming that scientists exaggerate their effects on the ozone layer. Furthermore, a black market in CFCs is thriving. Many nations lack the resources to monitor production of ozone-depleting chemicals, and some consumers in more industrialized nations buy smuggled-in compounds to avoid retrofitting the many appliances made before the CFC-phaseout. Without major cuts in CFC and methyl bromide emissions, continuing thinning of the ozone layer may bring quadrupled levels of skin cancer by 2100, increases in cataracts, suppression of the immune system, and increasing rates of non-Hodgkin's lymphoma. Scientific findings in the early 2000s suggest far-reaching ecological disruption may also ensue, including genetic mutations and accelerated species extinctions.

BIBLIOGRAPHY

Cogan, Douglas G. Stones in a Glass House: CFCs and Ozone Depletion. Washington, D.C.: Investor Responsibility Research Center, 1988.

de Gruijl, Frank R., and Jan C. van der Leun. "Environment and Health: 3. Ozone Depletion and Ultraviolet Radiation." Canadian Medical Association Journal 163 (2000): 851–855.

Grundmann, Reiner. Transnational Environmental Policy: The Ozone Layer. New York: Routledge, 2001.

Rowland, F. Sherwood. "Stratospheric Ozone in the Twenty-First Century: The Chlorofluorocarbon Problem." Environmental Science and Technology 25 (1991): 622–628.