Arctic Ozone

The Future of the Arctic Ozone Layer

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The Montreal Protocol of 1987 and later amendments to it were intended to phase out the use of ozone-depleting chemicals for all nonessential purposes and restore the ozone layer to its former healthy state. As a result of these agreements, atmospheric concentrations of some ozone-depleting substances, such as CFC-11, have begun to decline and concentrations of others will follow suit over the next decade (Figure 17).

Because of the time taken for ozone-depleting chemicals to reach the stratosphere and break down, the decline in stratospheric levels of chlorine and bromine will lag any decrease in concentrations of CFCs and other ozone-depleting substances by a few years. It is expected, for example, that the amount of chlorine in the stratosphere, currently at a level of 3.5 parts per billion (ppb), will peak by about 2003 and decrease thereafter. By 2050 it should have fallen to 2.0 ppb, the level at which the Antarctic ozone hole was first detected. One should therefore expect a substantial degree of recovery in ozone values by 2050. These expectations, of course, assume that the gaps in our understanding of ozone-depletion processes turn out not to be important and that present international agreements will be strictly adhered to. If either of these assumptions is incorrect, the time for recovery will be longer.

The recovery of the ozone layer could be delayed further if ozone-depleting substances that are not covered by the present agreements begin to be released into the atmosphere in substantial quantities. This possibility could become a reality by the middle of the twenty-first century as a result of the development of supersonic transport aircraft that would fly in the lower stratosphere. A fleet of 500 to 1000 of these aircraft would release large quantities of nitrogen oxides, water vapour, and sulphates, all of which have the potential to increase ozone depletion. Because these substances contribute to PSC formation as well, their impact on Arctic ozone levels could be particularly harmful.

Ironically, our current efforts to rid the atmosphere of ozone-depleting substances may have a negative impact on climate change and this, in turn, could have consequences for Arctic ozone depletion in the future. Hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs), the most widely used replacements for CFCs, are also greenhouse gases, and some of them are nearly as effective as CFCs as global warming agents. Consequently, their use will contribute to further greenhouse warming and related cooling of the stratosphere. For that reason, the consumption of HCFCs is scheduled to be phased out by 2030 under the Copenhagen Amendments to the Montreal Protocol. The usage of HFCs has been addressed under the 1997 Kyoto Protocol on Climate Change.

In dealing with all of these complex problems, research and monitoring will continue to play an important role. Continuing observations of ozone amounts as well as CFCs, chlorine, bromine, sulphates, nitrates, and other key participants in the ozone depletion process will be necessary to assess progress towards the recovery of the ozone layer. Further studies of atmospheric processes will also be essential if we are to reduce the uncertainties in our current understanding of ozone depletion and improve our capability to predict what is likely to happen to the ozone layer in the future.

The ozone layer will be particularly vulnerable over the next 20 years when atmospheric concentrations of ozone-depleting substances will be at or near their highest levels. The Arctic will be especially vulnerable during this period if continuing increases in greenhouse gases lead to further cooling of the stratosphere and more frequent PSC formation. Natural factors, such as the quasi-biennial oscillation, El Niņos, and the solar cycle will also influence the severity of ozone depletion in any given year, and large volcanic eruptions could lead to particularly serious depletions in some years.

Over the much longer term, the health of the ozone layer will depend primarily on our ability to rid the atmosphere of present ozone-depleting substances and prevent the release of new ones. But it will also depend on our success in controlling greenhouse gases. These issues are linked, as we have seen, through a variety of physical and chemical interactions. They are also linked at the ecosystem level, where plants and wildlife are affected not just by ozone depletion or by climate change independently but by an entire spectrum of human-related stresses on natural systems. That means that we cannot treat any of these issues in isolation. Instead, we must deal with them as interrelated parts of a common strategy for moderating the human impact on the atmosphere.

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