Stratospheric ozone depletion

World production of major chlorofluorocarbons (tonnes/year)

World production of the three major CFCs peaked in about 1988 and has since declined to very low values Source: AFEAS 2001

The protection of the Earth's ozone layer has presented one of the major challenges over the past 30 years, spanning the fields of environment, trade, international cooperation and sustainable development. The thinning of the ozone layer threatens human health through diseases such as skin cancer, eye cataracts and immune deficiency, affects flora and fauna, and also influences the planet's climate. Ozone depletion is brought about by a number of chemicals known as ozone-depleting substances (ODS), the most notorious of which are the chlorofluorocarbons (CFCs). In 1974, the results of studies linking stratospheric ozone depletion to the release of chloride ions in the stratosphere from CFCs were made publicly available (Molina and Rowland 1974). ODS are used in refrigerators, air conditioners, aerosol spray, insulating and furniture foams, and firefighting equipment, and their production peaked in the late 1980s as the demand for such goods grew (see graph).

The depletion of the Earth's ozone layer has now reached record levels, especially in the Antarctic and recently also in the Arctic. In September 2000, the Antarctic ozone hole covered more than 28 million square kilometres (WMO 2000, NASA 2001). Current average ozone losses are 6 per cent in the northern mid-latitudes in winter and spring, 5 per cent in southern mid-latitudes all year round, 50 per cent in the Antarctic spring and 15 per cent in the Arctic spring. The resulting increases in harmful ultraviolet irradiation amount to 7 per cent, 6 per cent, 130 per cent and 22 per cent respectively (UNEP 2000a).

However, due to continuous efforts by the international community, the global consumption of ODS has decreased markedly and the ozone layer is predicted to start recovering in the next one or two decades and to return to a pre-1980 level by the middle of the 21st century if all the future control measures of the Montreal Protocol are adhered to by all countries (UNEP 2000a).

International cooperation has been the key to protecting the stratospheric ozone layer. Nations agreed in principle to tackle a global problem before its effects became evident or its existence scientifically proven - probably the first example of acceptance of the precautionary approach (UNEP 2000a).

The Antarctic ozone hole breaks a new record

The ozone hole reached a record size in September 2000 - 28.3 million km2, three times the size of the United States. Dark blue areas denote high levels of ozone depletion Source: NASA 2001 reprinted with permission from Paul A. Newman

International action began in earnest in 1975 when the UNEP Governing Council called for a meeting to coordinate activities on protecting the ozone layer. A Coordinating Committee on the Ozone Layer was established the following year to undertake an annual scientific review. In 1977, the United States banned use of CFCs in non-essential aerosols. Canada, Norway and Sweden soon enacted similar control measures. The European Community (EC) froze production capacity and began to limit use of aerosols. These initiatives, though useful, provided only a temporary respite. After falling for several years, CFC consumption began increasing again in the 1980s, as non-aerosol uses, such as foam blowing, solvents and refrigeration, increased. Stricter control measures were needed and UNEP and several developed countries took the lead, calling for a global treaty on stratospheric ozone layer protection (Benedick 1998).

The Vienna Convention for the Protection of the Ozone Layer was finally agreed by 28 countries in March 1985. It encouraged international cooperation on research, systematic observation of the ozone layer, monitoring of ODS production, and the exchange of information. In September 1987, 46 countries adopted the Montreal Protocol on Substances that Deplete the Ozone Layer (by December 2001, 182 parties had ratified the Vienna Convention and 181 the Montreal Protocol).

The original Protocol required only a 50 per cent cut in consumption of five widely used CFCs by December 1999, and a freeze in the consumption of three halons. Regular scientific assessments were the basis for subsequent amendments and adjustments made to the Protocol in London (1990), Copenhagen (1992), Vienna (1995), Montreal (1997) and Beijing (1999). By the year 2000, 96 chemicals were subject to control (Sabogal 2000).

Most ODS - including all the substances specified in the original Protocol - were phased out in industrialized countries by the end of 1995. The Protocol provides a 10-year grace period for developing countries and the financial mechanism (the Multilateral Fund to the Montreal Protocol) to meet the costs to these countries of phasing out ODS, thus realizing the principle of common but differentiated responsibility. By 2000, the Multilateral Fund had disbursed more than US$1.1 billion for capacity building and projects to phase out ODS in 114 developing countries.

Almost every party to the Montreal Protocol has now taken measures to phase out ODS with the result that, by 2000, the total consumption of ODS had been reduced by 85 per cent (UNEP 2000b).