But chlorofluorocarbons -- invented in 1928 as refrigerants and as inert carriers for chemical sprays -- upset that balance. Researchers discovered in the 1970s and 1980s that while CFCs are inert at Earth's surface, they are quite reactive in the stratosphere (10 to 50 kilometers altitude, or 6 to 31 miles), where roughly 90 percent of the planet's ozone accumulates. UV radiation causes CFCs and similar bromine compounds in the stratosphere to break up into elemental chlorine and bromine that readily destroy ozone molecules. Worst of all, such ozone depleting substances can reside for several decades in the stratosphere before breaking down.
In the 1980s, ozone-depleting substances opened a wintertime "hole" over Antarctica and opened the eyes of the world to the effects of human activity on the atmosphere. By 1987, the World Meteorological Organization and United Nations Environment Program had brought together scientists, diplomats, environmental advocates, governments, industry representatives, and non-governmental organizations to forge an agreement to phase out the chemicals. In January 1989, the Montreal Protocol went into force, the first-ever international agreement on regulation of chemical pollutants.
"The regulation of ozone depleting substances was based upon the evidence gathered by the science community and the consent of industry and government leaders," Newman noted. "The regulation pre-supposed that a lack of action would lead to severe ozone depletion, with consequent severe increases of solar UV radiation levels at the Earth's surface."
In the new analysis, Newman and colleagues "set out to predict ozone losses as i
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NASA/Goddard Space Flight Center