Depletion of stratospheric ozone


Depletion of stratospheric ozone




Representatives from 24 nations, meeting in Montreal in September 1987, signed the “Montreal Protocol on Substances that Deplete the Ozone Layer,”1 an international agreement designed to reduce the world ­wide production and use of chlorofluorocarbons (CFCs). This protocol is the result of years of negotiation fostered by the United Nations Environment Programme (UNEP) among the major CFC producing countries. Its formulation was a response to a growing international consensus on the need to protect stratospheric ozone from depletion by CFCs. The Montreal Protocol is a landmark agreement in that it is the first international treaty for mitigating a global atmospheric problem before serious environmental impacts have been conclusively detected. As such, the Montreal Protocol has stirred much interest, and both scientists and policymakers have suggested that it can be used as a model for international agreements on other global environmental problems, especially the problem of CO2 and trace-gas induced global warming.

Before such a comparison to other environmental problems can be made, however, it is useful to understand the Montreal Protocol in its historical and political context. Depletion of stratospheric ozone is an example of both the complicated and the global nature of contemporary environmental problems, and the Montreal Protocol shows that innovative approaches to such global environmental problems are possible. During the past two decades concern over stratospheric ozone has evolved from a fringe environmental issue to a major policy issue of national and international importance. An analysis of this evolution is important for understanding both the value of the Montreal Protocol and its implications for other global atmospheric problems.

The evolution of stratospheric ozone policy can be understood as a two-stage process: (1) the development of domestic regulations controlling CFC use in aerosol spray cans in the United States and several other countries in the mid- and late-1970s, and (II) the development of an international policy response to the problem of global stratospheric ozone depletion in the 1980s. These are not separate issues. The development of an international response clearly followed from the concern raised in the United States, Canada, Sweden, and other countries which had taken unilateral action to control CFCs in the 1970s. However, many important differences between stage 1 and II make this distinction a useful tool for analysis. I argue that four key factors are important in understanding the evolution of stratospheric ozone policy: (1) the recognition that ozone depletion is a global problem requiring an international response; (2) the evolving scientific understanding of stratospheric ozone depletion and its influence on policymakers; (3) increasing public concern based on the threat of skin cancer and the perception of the potential for global catas­trophe associated with the discovery of the Antarctic ozone hole; and (4) the availability of acceptable substitutes for CFCs.

This paper analyzes the evolution of stratospheric ozone policy. The first section reviews the science behind the problem of CFC-induced stratospheric ozone depletion. The next two sections discuss the emerg­ence of stratospheric ozone depletion as a national political issue in the United States during stage I, and its evolution to an international political issue during stage II. This is followed by a discussion of how the evolving scientific understanding of the problem, the catastrophic nature of the risks, and the availability of alternatives to CFCs influenced the final negotiations on an international agreement. The last section examines the Montreal Protocol and discusses its prospects for success.


Chlorofluorocarbons are a group of inert, nontoxic, and nonflammable synthetic chemical compounds used as aerosol propellants, in refrigeration and air conditioning, in plastic foams for insulation and packaging, and as solvents for cleaning electrical components. There are many varieties of CFCs; CFC-11 and -12 are the most common compounds and CFC- 113 has important industrial applications as a solvent. Production of CFCs has increased significantly since the 1960s, reaching a peak in 1974 before declining as a result of the decreasing use of CFCs as aerosol propellants. However, non aerosol use continued to increase and by the mid-1980s CFC production again reached mid-1970 levels (see Figure 1). Atmo-


Source: EPA, Assessing the Risks of Trace Gases That Can Modify the Stratosphere, Vol. 2 (1987).

FIGURE 1.Historical Production of CFC-11 and CFC-12 for Countries Re­porting to the Chemical Manufacturers Association.


Cape Grim, Tasmania

1978 1979 1980 1981 1982 1983 1984



Source: UNEP, The Ozone Layer (UNEP/GEMS Environment Library No. 2, 1987).

FIGURE 2. Monthly Measurements of Atmospheric Concentrations of CFC- 11 and CFC-12 at Cape Grim, Tasmania (1978-1984).

spheric concentrations of CFC have also been increasing (see Figure 2). Once in the atmosphere, CFCs have a lifetime of about 100 years. It is this long lifetime that is the root of the problem with CFCs.

Initially, it was believed that these compounds were environmentally safe, but in the early 1970s independent research efforts pointed to a potentially serious problem connecting CFCs with stratospheric ozone depletion. Molina and Rowland first suggested that CFCs might play a role in depleting ozone in the stratosphere, the region of the atmosphere at altitudes from about 12 to 50 km. Ozone (03) in the stratosphere (commonly referred to as the ozone layer) shields the earth from harmful ultraviolet radiation. Molina and Rowland’s theory suggested that CFCs diffuse upward into the stratosphere, where they are broken down by ultraviolet radiation, releasing free chlorine which reacts catalytically with ozone and results in its significant depletion. Recent research continues to point to the role of CFCs in depleting stratospheric ozone. In addition, other synthetic chemicals have been identified as potential stratospheric ozone depleters: most notable are the halons used in fire extinguishers.The stratospheric ozone layer shields the earth from harmful UV-B radiation. An increase in the amount of UV-B radiation reaching the surface of the earth could have significant negative effects on human health, plants, and aquatic ecosystems. The most significant human health effect is an increase in the incidence of skin cancer. The U.S. Environ­mental Protection Agency (EPA) estimates that a one percent decrease in ozone could result in a two percent increase in UV-B, and a one percent increase in UV-B could result in a two to five percent increase in the rate of non-melanoma skin cancers.® In addition, increased UV-B may also result in an increase in the rarer but more deadly malignant melanoma skin cancers. The EPA has estimated that if CFC use continues to grow at 2.5 percent a year until 2050, an additional 150 million skin cancer cases could result, causing more than 3 million deaths in the U.S. pop­ulation born before 2075. Other potential health effects include suppres­sion of the immune system leading to a higher incidence of some infectious diseases, and eye disorders such as cataracts or retinal damage.” Table 1 summarizes the potential human health effects of increased UV-B ra­diation. Research also suggests that increased UV-B radiation could result in decreased crop production, and change in the species composition of natural aquatic ecosystems resulting in more unstable ecosystems.

In addition, CFCs are also an effective greenhouse gas in the lower atmosphere. Recent assessments conclude that, together, greenhouse.



Depletion of stratospheric ozone


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