1. An ozone-friendly future

Full restoration possible by 2050

It might seem odd to describe the state of the ozone layer as a sustainability success story. After all, the thinning of the ozone layer continued throughout the 1990s, with the largest-ever ozone hole recorded over the Antarctic in the spring of 2000. Australia and New Zealand have the world's highest incidence of skin cancer, and UV-B radiation is believed to be the most likely culprit.

Alarming seasonal declines in ozone have been measured over parts of Chile and a drop of up to 10 per cent in ozone levels has been observed over Europe and North America.

However, to regard the ozone problem as just more bad news would be to overlook the substantial progress that has been made in the last decade. Gases like chlorofluorocarbons (CFCs), used as solvents and refrigerants among other applications, will take many years to disappear from the upper atmosphere. After all, it is their high degree of chemical stability that allows them to reach the stratosphere in the first place. Although ozone damage continues, particularly at high latitudes, actual emissions of the main ozone-depleting gases--CFCs, halons, methyl bromide and so on--have fallen sharply.

As a result, the rate at which ozone-destroying gases are building up in the atmosphere is slowing, and the concentration of one of the key agents, CFC-11, has actually begun to fall. If progress is maintained on eliminating ozone-destroying gases, the ozone layer is expected to start recovering in the next few years, and to be fully restored by around 2050.

The Montreal Protocol of 1987 was a turning point in the ozone story, forging a link between science and policy-making. However, the real success story was its subsequent implementation. The Meetings of the Parties, which have taken place annually since 1987, have bolstered several of the key Montreal targets, and provided mechanisms that allowed poorer countries to play a part in the solution.

So is the problem solved? Not yet. For the ozone layer to be restored to its pre-industrial state, it is vital that the momentum of the 1990s be maintained in the decades to come, and that the Montreal Protocol be given the priority it deserves. There are several potential problem areas that could undermine the progress made to date.

In particular, a commitment is needed to phase out the production of hydrochlorofluorocarbons (HCFCs), which were introduced as a less damaging (but still ozone-depleting) alternative to CFCs. The Montreal Protocol requires HCFCs to be phased out by 2030 in developed countries, and by 2040 in developing countries.

Another threat to ozone restoration comes from nitrogen oxide emissions produced by jet aircraft flying in the lower stratosphere. Commercial air traffic continues to grow rapidly, and pressure needs to be kept up on engine manufacturers to design cleaner-burning engines.

Finally, a sustained effort will be needed to prevent illegal smuggling of CFCs. With the supply of these chemicals having almost dried up, the black-market value of second-hand CFC gases has soared, particularly in developing countries.