Montreal Protocol on Substances that Deplete the Ozone Layer

The Montreal Protocol on Substances That Deplete the Ozone Layer is an international treaty that was first agreed to in 1987. Signed by just 24 nations in 1987 but subsequently ratified by over 180 governments, the Montreal Protocol is widely considered to be the most successful of the global environmental treaties.


The origins of the Montreal Protocol trace back to a theory, published in 1974 by University of California researchers Sherwood Rowland and Mario Molina, that chlorine atoms released by the breakdown of chlorofluorocarbons (CFCs) in the upper atmosphere could precipitate a chemical chain reaction which would seriously damage the stratospheric ozone layer that protects all life from dangerous ultraviolet radiation (UV-B) emitted by the sun. The theory unleashed a firestorm of controversy, as CFCs, halons, and related chemicals were extremely useful substances—nontoxic, nonflammable, noncorrosive—that were finding continually new applications in thousands of products and processes. From construction, pharmaceuticals, and food processing, to telecommunications, aerospace, and computers, these chemicals seemed virtually synonymous with modern standards of living.

Several nations, including Canada, Denmark, Sweden, and the United States, voluntarily eliminated CFCs in aerosol spray cans in the late 1970s. Although many governments and the major chemical producers and CFC-using industries resisted strong actions, the United Nations Environment Programme organized efforts in 1982 to negotiate an international agreement. The discovery by a British research team in 1983 of an unexpected annual seasonal collapse in ozone concentrations over Antarctica (the “ozone hole”) sparked public interest, but scientists cautioned against basing the CFC negotiations on this phenomenon because there were other plausible causes for this occurrence. Rather, the scientific concern rested on theoretical computer models that predicted more gradual ozone depletion over the mid-latitudes – of which, however, there was no evidence. Indeed, at the time of the negotiations, measurements actually showed declines in UV-B radiation reaching Earth’s surface (a phenomenon that was later understood to be caused by high levels of pollution in the lower atmosphere that filtered out the radiation.)

Vienna Convention

Against this background, three years of difficult negotiations resulted in the 1985 Vienna Convention for the Protection of the Ozone Layer, a treaty that essentially called merely for cooperation in research and did not even mention CFCs in its text. The U.S. National Aeronautics and Space Agency (NASA) and National Oceanic and Atmospheric Administration (NOAA) now spearheaded the most comprehensive international scientific assessment of the stratosphere ever undertaken.

However, when negotiations began in late 1986 on a further treaty to limit CFCs, the case remained theoretical and opposition continued strong in several key producer countries, notably within the European Community (especially France, Italy, Spain and the United Kingdom), the Soviet Union, and Japan. The United States launched a vigorous and multifaceted diplomatic campaign for strong controls, and found important allies in Australia, Austria, Canada, Denmark, Egypt, Finland, Germany, Mexico, Norway, New Zealand, Sweden, and Switzerland. In the end, due largely to unpublicized U.S. bilateral scientific cooperation with Japan and the Soviet Union, these major producers also joined the growing movement for a strong treaty.

Montreal Protocol

In September 1987, the Montreal Protocol was signed, providing for gradual phasedown of CFC production and consumption by industrialized countries to 50 percent of their 1986 levels by 1998-99, with a ten-year grace period for developing nations. Just six months later, scientists confirmed that the Antarctic phenomenon was in fact caused by CFCs, and momentum grew for a total phase-out of ozone-depleting chemicals. The Protocol was amended and substantially strengthened at Conferences of the Parties in London (1990), Copenhagen (1992), and Vienna (1995), and continued to be modified in subsequent years, in a dynamic process informed by periodic scientific, technological, and economic assessments. The number of controlled substances was increased from the original eight to over eighty, and by 1995 most had been eliminated by the industrialized countries and were also on the way to phase out by developing nations.

The Montreal Protocol has been characterized by the heads of the United Nations Environment Programme and the World Meteorological Organization as “one of the great international achievements of the century.” Given the extraordinary nature of the danger to life on the planet and the extent of international cooperation that was mobilized, few observers would consider this statement as hyperbole. It was the first major global environmental treaty to implement the precautionary approach, mandating strong actions even before there was concrete evidence of damage. It was also the first to design mechanisms for financial assistance and technology transfer to enable developing countries to accept difficult commitments. The Protocol stimulated a virtual technological revolution in global industry, leading to development of substitute products and processes more rapidly, and at much lower cost, than originally predicted. For their courageous and pioneering work, scientists Molina and Rowland, together with Paul Crutzen of the Netherlands, received the 1995 Nobel Prize.

Further Reading



Benedick, R. (2007). Montreal Protocol on Substances that Deplete the Ozone Layer. Retrieved from


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