Chlorofluorocarbon gases (CFCs) became widely utilized in the mid-1960s—as refrigerants such as Freon, as fire retardants such as Halon, as spray-can propellants, as solvents, and as foam-blowing agents. CFCs were far more stable, far more chemically inert than alternatives and were, therefore, much safer to use. Unfortunately, they are so stable that they are likely to last in the atmosphere for more than 100 years.
Within three to five years, the time we now know it takes for CFCs to reach the stratosphere, annual average global temperatures began rising. By 1973, James Lovelock, using his new electron capture detector, found significant amounts of CFC-11 in all 50 air samples collected pole to pole. Stimulated by Lovelock’s work, Mario Molina and Sherwood Rowland discovered in 1974 that when CFCs reach the stratosphere, they can be broken down by solar ultraviolet radiation ultimately freeing atoms of chlorine. One atom of chlorine can destroy 100,000 molecules of ozone by catalytic processes that are particularly effective in polar stratospheric clouds.