Of these problems, the only one to have received any substantial public policy action is that centring on the reduction of stratospheric ozone. Ironically, it is perhaps the easiest of the problems to reverse.

The importance of the stratospheric ozone layer in shielding the Earth's surface from the harmful effects of solar ultraviolet radiation has been recognized for several decades. It was not until the early 1970s, however, that scientists began actually to grapple with the fact that even relatively small decreases in the stratospheric ozone concentration can have a serious impact on human health--an increased incidence of skin cancer, particularly among fair-skinned peoples. Plans in the United States, Great Britain, and France to build a commercial fleet of supersonic aircraft triggered much heated discussion over the potential reduction of the ozone layer by the exhaust gases (e.g., nitric oxide) emitted by such high-altitude planes. The debate in turn stimulated intensive scientific research on the stratosphere, which resulted in new findings and new concerns.

By the mid-1970s, various U.S. investigators had determined that chlorofluorocarbons (CFCs), widely employed as propellants in aerosol spray cans, could reduce the amount of stratospheric ozone significantly. A temporary ban was imposed on the use of certain CFCs in the United States, but only after much emotional debate among environmental and industrial scientists, reports by the National Academy of Sciences, and the development by industry of economically viable substitutes for spray-can propellants.