By Peter Boyle
Following the development last spring of the deepest and widest ozone hole ever recorded over Antarctica, the governments of 93 countries agreed in November to speed up the phasing out of ozone-destroying chemicals. However, after a week of negotiations in Copenhagen, the gathering of environment ministers failed to agree on the immediate curtailment of HCFC (hydrochlorofluorocarbon) production and the phasing out of methyl bromide (which may be responsible for 10% of ozone loss so far).
The ministers agreed to eliminate CFCs (chlorofluorocarbons) and carbon tetrachloride by 1996, instead of 2000. Halons (used in fire extinguishers) will be banned by 1994 instead of 2000, and the elimination of methyl chloroform (a commercial solvent) has been brought forward from 2005 to 1996.
According to New Scientist correspondent Debora MacKenzie, chemical industry representatives argued against stricter limits on HCFCs on the grounds that they are needed as substitutes for CFCs in refrigeration. The conference was persuaded to allow annual HCFC production to increase from 300,000 tonnes to 800,000 tonnes for the immediate future.
It set a long-term target of a 35% reduction in HCFC production by 2004, a 99.5% reduction by 2020, and a total ban from 2030. However, Kevin Gurney of the Washington-based Institute for Energy and Environmental Research estimates that the damage done by HCFCs in this time will simply replace that avoided by the faster CFC phase-out.
Methyl bromide is widely used as a fumigant to kill pests in soil and stored crops, and the opposition to its phase-out came from the European Community and Third World countries heavily dependent on fruit and vegetable exports.
The United States delegation proposed that methyl bromide be phased out by the year 2000. Eventually, the signatories agreed to list methyl bromide as a "controlled substance" and freeze emissions (now growing at 5% annually) at 1991 levels by 1995. Industrialised countries (accounting for 80% of world usage) have said they will introduce stricter controls of their own.
Methyl bromide releases bromine, which destroys up to 60 times as much ozone as the chlorine released by CFCs and other chemicals already controlled by the Montreal Treaty. But it was not until last year that scientists calculated the extent of the threat from methyl bromide, some of which occurs naturally. Production of methyl bromide increased by 50% between 1984 and 1990.
Jan van der Leun, head scientist on the United Nations panel on the effects of ozone depletion, says the new agreement could reduce the number of deaths from non-melanoma skin cancer by 40,000 over the next t 400,000 people will still die in this period because of extra ultraviolet rays getting through the thinning ozone layer in the upper atmosphere.
Meanwhile John Austin of Britain's Meteorological Office has warned that the smaller ozone hole that has developed over the Arctic in recent years could become seriously worse due to an anticipated doubling of carbon dioxide in the atmosphere by the middle of next century.
Greenhouse gases such as carbon dioxide contribute to ozone depletion by trapping heat near the surface of the Earth, making the lower atmosphere warmer and the upper atmosphere (stratosphere) colder. Icy particles form in stratospheric clouds, and chemical reactions on these release chlorine, which attacks ozone.