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Society's Responses to Atmospheric Change

Responses to ozone layer depletion

The concern about the destruction of the ozone layer by chlorofluorocarbons (CFCs) led to the signing of the Vienna Convention for the Protection of the Ozone Layer in 1985 (see Box 5.8). This was an international agreement by nations to take some action to stop atmospheric ozone depletion, but the nature of the action was not spelled out. The Vienna Convention was given teeth with the signing of the Montreal Protocol on Substances that Deplete the Ozone Layer in 1987. The Protocol set timetables for the phase-out of specific chemicals. As increasing numbers of synthetic chemicals have been implicated in ozone depletion, and as the science of the destruction process has become better understood, the Protocol has been amended twice (London in 1990, and Copenhagen in 1992), and adjusted once (Vienna in 1995). These amendments and adjustments have added new chemicals to the list and tightened the phase-out timetables (see Boxes 5.8 and 5.9). (Amendments to the Protocol must be ratified by governments to take effect; adjustments do not require ratification.)

A ban on the production of various CFCs and halons began in January 1996, as required by the Montreal Protocol, and the consumption of CFCs and halons is now dropping globally. There are indications that the ozone-destroying potential of atmospheric chlorine and bromine peaked in the troposphere in 1994.

Provided countries abide by the provisions of the Montreal Protocol, the chlorine/bromine destruction potential should peak in the stratosphere between 1997 and 1999. The ozone layer would then begin to heal slowly, reaching pre-ozone-hole levels by about the year 2050 (Hofmann, 1996) (see Figure 5.18).

Figure 5.25: New Zealand imports of three continuously used ozone-depleting substances, 1986-96