CFCs are the chemicals linked most directly to ozone loss, widely used as aerosol propellants, refrigerants, agents in plastic packaging, and cleaning fluids. Carbon dioxide is also implicated. In 1987 an international treaty called the Montreal Protocol on Substances That Deplete the Ozone Layer mandated a reduction in the use of CFCs. In 1989, 93 nations agreed to phase out CFC production and to aid poorer nations in revising their technologies accordingly, and in 1990 the Montreal Protocol agreement was strengthened to require a phasing out of CFCs by the year 2000. The chemicals thus far devised as replacements are less versatile and more expensive than CFCs.
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