The earth's ozone layer, located high above the ground in the stratosphere, filters out harmful burning ultraviolet rays from the sun. For about a billion years, the natural ozone system worked smoothly, allowing life to flourish on earth.

In the 1920's, however, scientists developed a class of chemicals known as chlorofluorocarbons (CFCs) which were most commonly used as aerosol in spray cans and which continue to be used as coolants and insulation in refrigerators and car air conditioners. CFCs are highly stable compounds which drift slowly upwards, carrying millions of tons of extra chlorine into the stratosphere. Many of the CFCs and related HCFCs have atmospheric lifetimes of 50-100 years or longer.

The manufacturers of CFCs and other ozone depleting chemicals include: DuPont, Elf-Atochem, ICI, LaRouche, Akzo Chemie, Rhone Poulenc, Nippon Halon and Allied Signal. The total value of sales of ozone depleting chemicals since 1986 has exceeded $30.6 billion USD with the USA responsible for 30 percent of the total production.

In the 1974, two scientists Sherwood Rowland and Mario Molina, hypothesized that chlorine from CFCs could destroy the earth's ozone layer. According to their predictions, each chlorine atom could destroy 100,000 ozone molecules, meaning that decades of CFC use would cause a substantial decline in the ozone layer. By 1979, the US and some other governments responded by banning the sale of CFC based aerosol cans, this slowed the growth of CFC production. However, worldwide production of the chemicals continued to grow, reaching 3 percent a year growth rate by 1985.

In 1985, many of the world's governments signed the Vienna Convention which called on participants to draw up a plan for action on the issues. As of May 1985, the British Antarctic Survey reported dramatic declines in ozone values over Antarctica each spring- defining the so-called ozone hole.

In September 1987, negotiators from around the world met in Montreal to sign a Treaty setting limits on the use of CFCs and Halons (another class of ozone depleting chemicals). Scientific evidence which emerged throughout the late 1980s prompted further strengthening of the Montreal Protocol, first in London, then in Copenhagen.

Although concentrations of ozone-depleting chemicals may already have peaked, due to the measures taken under the Protocol, destruction of the earth's ozone layer continues at a rapid rate. The 1996 ozone hole over Antarctica exceeded 20 million square kilometers--approximately twice the size of Europe. In April 1997, NASA reported the "lowest ozone values ever measured by the TOMS instruments during late-March and early-April in the Arctic." Ozone levels were 40 percent lower than the average March amounts observed between 1979 and 1982. In fact, ozone depletion over the Arctic has continued to be worse than predicted, observed depletion is about 40% worse than forecasted.

The result of such ozone destruction is an increase in the amount of ultraviolet-B (UV-B) radiation striking the earth's surface. Scientists estimate that, depending upon weather conditions, for every 1 percent of ozone depletion, approximately 2 percent more UV-B radiation strikes the earth's surface. The impacts of increased UV-B radiation exposure includes increased risk of skin cancer and cataracts as well as immune suppression.

Governments still could do a lot to reduce the amount of ozone depleting chemicals in the earth's stratosphere, in particular, strengthening controls on methyl bromide (a toxic pesticide) and HCFCs (a coolant).