1. Ozone Depletion

Doing something about ozone depletion

The sudden and frightening discovery of an enormous ozone hole in 1985 sparked public awareness of the fragile ozone layer. In the meantime, the scientific community had been actively investigating Molina and Rowlandís theory that synthetic chemicals, known as the CFCs, could be destroying the ozone layer. Although global models of the expected ozone depletion initially led to widely varying estimates of the potential threat, affecting the scientistís credibility and dampening public concern, a coordinated international investigation eventually led to a unified assessment of the problem.

A group of approximately 150 scientific experts reported in 1986 that atmospheric accumulations of CFC-11 and CFC-12 had nearly doubled from 1975 to 1985. The continued release of the synthetic chemicals at the 1980 rate could, through the action of their chlorine, they said, reduce the ozone layer by about 9 percent on a global average by the last half of the 21st century, with even greater seasonal and latitudinal differences. As a result, higher levels of dangerous ultraviolet radiation could reach heavily populated regions of the Northern Hemisphere.

Who cares if chemicals are punching a few holes in the sky and letting a little more sunlight reach the ground? The U.S. Environmental Protection Agency, or EPA, cared. In 1986 it published a report of the many serious consequences of ozone depletion. A thinner ozone layer lets more solar ultraviolet radiation through to the ground, where it can produce severe biological harm. The most energetic ultraviolet rays reduce the effectiveness of the human immune system, increasing human vulnerability to infections and cancer.

The EPA estimated that there could be over 150 million new cases of skin cancer in the United States alone among people currently alive or born by the year 2075, resulting in over 3 million deaths. The dangerous ultraviolet would also produce eye cataracts, distorting the vision of about 18 million people in the same population and blinding many of them. Added to this was the potential of widespread genetic damage to crops and forests, if nothing was done to stem the production of ozone-destroying chemicals.
Faced with the evidence of vanishing ozone, the global increase of atmospheric CFCs, and the prospect of widespread skin cancer and eye cataracts, international diplomats forged an accord in 1987 to limit and eventually ban the production of the substances that deplete the ozone layer (Focus OD.1). The treaty, known as the Montreal Protocol, has led to substantial reductions in ozone-destroying chemicals made by humans.

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Focus OD.1. The Montreal Protocol

Growing scientific, political and public awareness of ozone depletion eventually resulted in international negotiations to limit the manufacture and use of chemicals that destroy atmospheric ozone. A scientific consensus in the 1980s indicated that the destruction of the ozone layer by these synthetic chemicals had already begun, and that this would ultimately affect the health of large numbers of people if the production of the chemicals were not curtailed. The press and television also played a vital role in informing the public about the dangers, and the discovery of the ozone hole above Antarctica attracted added attention to the problem.

On 16 September 1987, representatives of 24 nations signed the Montreal Protocol on Substances That Deplete the Ozone Layer, including the United States which was the largest single producer and consumer of the suspect chemicals. The treaty agreed to a 50 percent reduction in important ozone destroyers, such as the chlorofluorocarbons designated as CFC-11 and CFC-12, below 1986 levels by mid-1998.

The ready acceptance of the Montreal Protocol was undoubtedly eased by the development of substitutes for CFCs in refrigerators, air conditioners, foaming, and cleaning solvents. In fact, the biggest producer, Du Pont unilaterally stopped making the chemicals even before the Protocol required it.

The protocol was strengthened in 1990, at a meeting in London, when it was agreed to a complete phase-out of CFC-11 and C FC-12 by the year 2000. The phase-out schedules of other ozone depleting substances were accelerated at another meeting in Copenhagen in 1992, including the halons, which are another type of chlorofluorocarbon. At a meeting in Vienna in 1995 further controls were implemented. A total of 155 countries had ratified the Montreal Protocol by 1996, including the vast majority of both the producers and consumers of the dangerous substances.

The phase-out schedules differed for the rich, industrial countries and the poor, undeveloped ones. The industrial countries had to eliminate halon consumption as of 1 January 1994 and CFC consumption as of 1 January 1996. Developing countries were given a grace period, but had to complete their phase-out by 1 January 2010. Several of these countries will complete their phase-out much before this date. A multilateral fund was also established to assist the developing countries in meeting their goals.

urther amendments were made at meetings in Montreal in 1997 and in Beijing in 1999, all aimed at reducing and eventually eliminating the emissions of all kinds of man-made ozone depleting substances. As an example, a recent amendment, that took effect on 1 January 2001, requires participating countries to freeze the production of hydrochlorofluorocarbons (HCFCs) still used in refrigeration and cooling equipment.

The accord has accomplished far more than halting the production of dangerous synthetic chemicals. The Montreal Protocol was the first international agreement to protect the global environment. The treaty also marked the first time that the governments of the industrial nations agreed to help developing countries with environmentally safe substances and technology. It was further hoped that the precedent would pave the way for international agreement on global warming.

Although production of ozone-destroying substances has been substantially curtailed under international agreement, more than 20 million tons of them have already been dumped into the atmosphere, and this damage cannot be undone. Because of their long lifetime and slow diffusion into the stratosphere, the synthetic chemicals that are already in the air will keep on destroying the ozone layer for about a century.

The springtime hole in the ozone layer above Antarctica has, in fact, shown no signs of closing up, even though many of the chemicals producing them have long been banned. In the year 1990 the ozone hole was about as wide as the North American continent, covering approximately 14 million million (1.4 x 1013) square meters. A decade later, in the year 2000, the ozone hole had grown to its largest size yet, measuring 28 million million (2.8 x 1013) square meters despite the near abolishment of the CFCs.

The chemicals that were already in the air were apparently still wafting upward into the stratosphere. Hopefully their abundance in the ozone layer peaked at the end of the 20th century. After that, ozone loss should be stabilized and the trends reversed as the chemicals are gradually removed by slow washing-out processes.

The ozone layer will not regain full strength until well into the latter half of the 21st century when it should then recover to the natural levels that existed before the ozone hole was discovered. In the meantime, scientists will continue to monitor the ozone layer using a series of NASA satellites, while also keeping a close eye on the Sunís varying ultraviolet output which modulates ozone production by amounts comparable to human destruction of it.

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Copyright 2010, Professor Kenneth R. Lang, Tufts University