Montreal Protocol, formally Montreal Protocol on Substances That Deplete the Ozone Layer, international treaty, adopted in Montreal on Sept. 16, 1987, that aimed to regulate the production and use of chemicals that contribute to the depletion of Earth’s ozone layer. Initially signed by 46 countries, the treaty now has nearly 200 signatories.
In the early 1970s, American chemists F. Sherwood Rowland and Mario Molina theorized that chlorofluorocarbon (CFC) compounds combine with solar radiation and decompose in the stratosphere, releasing atoms of chlorine and chlorine monoxide that are individually able to destroy large numbers of ozone molecules. (Along with Dutch chemist Paul Crutzen, Rowland and Molina were awarded the 1995 Nobel Prize for Chemistry for this work.) Their research, first published in the journal Nature in 1974, initiated a federal investigation of the problem in the United States, and the National Academy of Sciences concurred with their findings in 1976. In 1978 CFC-based aerosols were banned in the United States, Norway, Sweden, and Canada.
Further validation of their work came in 1985 with the discovery of a “hole” in the ozone shield over Antarctica by the British Antarctic Survey and the publication of its findings in Nature. Shortly before these findings were to appear, representatives from 28 countries met to discuss the issue at the Vienna Convention for the Protection of the Ozone Layer. The meeting called for international cooperation in research involving ozone-depleting chemicals (ODCs) and empowered the United Nations Environment Programme (UNEP) to lay the groundwork for the Montreal Protocol.
The initial agreement was designed to reduce the production and consumption of several types of CFCs and halons to 80 percent of 1986 levels by 1994 and 50 percent of 1986 levels by 1999. The protocol went into effect on Jan. 1, 1989. Since then the agreement has been amended to further reduce and completely phase out CFCs and halons, as well as the manufacture and use of carbon tetrachloride, trichloroethane, hydrofluorocarbons (HFCs), hydrochlorofluorocarbons (HCFCs), hydrobromofluorocarbons (HBFCs), methyl bromide, and other ODCs. Several subsequent meetings of the signing countries were convened to track overall progress toward this goal and to authorize new changes to the process of phasing out ODCs.