The lessons of Montreal.

This September, diplomats will gather in Montreal to mark the tenth anniversary of a landmark in international environmental diplomacy: the Montreal Protocol on Substances That Deplete the Ozone Layer. The event will provide a much-needed reminder that some of the daunting environmental problems confronting humanity can be solved. And it will offer some important lessons about how to cope successfully with those global problems that still loom.

The Montreal Protocol stands out as the one global environmental accord so far to produce clear results: production of chlorofluorocarbons (CFCs), the most voluminous ozone-depleting substances, has plunged by more than three-quarters from its peak in 1988. If all countries meet their commitments under the treaty, scientists estimate the ozone shield will gradually begin to heal within the next few years, with a full recovery expected by about 2050. Millions of skin cancer cases will have been prevented as a result, as well as untold agricultural losses and ecological damage.

Coincidentally, this year the world also passed another important milestone - the fifth anniversary of the Rio Earth Summit. This occasion was marked by much hand wringing about the fact that most global environmental trends continue to run rapidly in the wrong direction. Yet "Earth Summit II" produced discouragingly little in the way of concrete action.

In December, diplomats plan to complete negotiations on the Kyoto Protocol to the climate change convention. It is urgent that Kyoto follow the lead of Montreal, and not the disappointing example of Rio. We need, now, to accomplish for global warming what we have begun to accomplish for ozone depletion.

What can we learn from Montreal's relative success? One lesson is the importance of the precautionary principle. The decision to take action in Montreal before there was complete proof of the link between CFCs and ozone depletion was an act of foresight that must be replicated with the problems of climate change, species loss, and the proliferation of health-threatening toxic chemicals, among others.

Secondly, the Montreal Protocol demonstrated the pivotal role of industry. As public and scientific concern over ozone depletion mounted, the business community decided to give up on blocking the accord and instead put its energies into taking advantage of the new business opportunities opened up by the shift to substitutes for CFCs. Many businesses then became advocates for further progress, rather than obstacles to it.

Finally, the experience with ozone depletion proves that North-South environmental partnerships can work. Industrial countries have largely honored their promises of financial and technological support to help developing countries make the transition to ozone-benign technologies. Most developing countries, in turn, have become strong participants, with many of them ahead of schedule in phasing out CFCs.

At a time when global environmental trends are so daunting, it is reassuring that the international community has responded cooperatively to the challenge of rescuing the ozone layer. We now need to devote similar energy to tackling the other pressing environmental challenges that cry out for attention. If this happens, by the tenth anniversary of the Rio conference there will be some real progress to report.