Just as weather is what everyone discusses but no one does anything about, global warming has been the issue endlessly negotiated and never acted upon.

Almost ten years ago, the first Earth Summit in Rio de Janeiro highlighted the threat; nearly five years have passed since the first global warming summit in Kyoto, Japan in 1997. Despite annual rounds of talk since, the modest Kyoto goals to curb greenhouse gas emissions have remained just that: goals.

Now, in 2002, a real treaty may actually be ratified. In November 2001, marathon meetings with 161 countries in Marrakech resolved crucial details, and the world's industrial nations are meeting for the second global environmental summit in Johannesburg, South Africa in September. Ten years after Rio, they may adopt the first concerted attempt to slow global warming.

The change won't be dramatic. The watered-down global warming treaty goal is to cut the emission of greenhouse gases such as carbon dioxide to just 2 percent less than was emitted in 1990. That modest target is a retreat from the 5.2 percent cuts tentatively agreed to in Kyoto six years before. Scientists say our civilization will have to reduce polluting gases by at least 50 percent to make a dramatic difference.

Still, as Greenpeace spokesman Bill Hare told reporters in Marrakech, "It's a first step."

Ironically, the United States, which is the world's biggest emitter of greenhouse gases, will watch from the sidelines. President Bush rejected the international proposals in April of 2001, complaining they would harm the U.S. economy and fail to control pollution in developing countries. Bush also contends that global warming science is too uncertain.

Despite this withdrawal, the U.S. may be dragged along by the international consensus. The Bush Administration is reportedly considering forging its own agreement with Canada and Mexico. Bills have been introduced in Congress to track greenhouse gas sources in the U.S. and to research "climate-friendly" technology.

While progress on global warming has been slow, there is a heartening precedent to suggest international action is possible and can make an environmental difference. In 1987 the world's nations adopted the Montreal Protocol to halt release of chemicals that destroy the Earth's protective ozone layer. By 2000, emissions in the U.S., Europe, and Japan had fallen more than 99 percent. As a result, during the last three years, the size of the annual ozone hole over Antarctica has stabilized, and the amount of stratospheric ozone has risen slightly.

It will still take up to 50 years to fully restore the ozone layer.

Nonetheless, that international success encourages nations to try cooperative efforts to control global warming. Even before the breakthrough in Marrakech, Britain had announced a voluntary program to trade carbon credits that could reduce emissions by 2 million tons a year. The European Union had a similar plan that is more compulsory, but it covers only one gas - carbon dioxide.

Such trading addresses the fact that nations are hesitant to put themselves at an economic disadvantage by adopting expensive pollution controls while their neighbors stall. The complex system to "trade" cleanup successes plays off each country's strengths and weaknesses. The idea is to make conservation profitable and marketable, not just a regulatory requirement.

Russia or Chile, for example, may get emission credits simply for growing new forests or for not cutting remaining forests. They could then sell those credits to industries that emit greenhouse gases. Industrialized countries that help developing countries with non-polluting technology can get emission credits to use back home. Nations that meet their emission reduction targets can sell their spare emission rights to other countries.

Global trading of carbon emissions has yet to be tried and may be a turbulent process. Enron, the U.S. energy free-marketer that recently went bankrupt, was planning to be one of the traders, and its demise casts a pall on "carbon trading."

Another plan under debate is to pump excess carbon dioxide or methane into underground storage reservoirs to keep it out of the atmosphere.

One possible solution purposefully left out of the treaty, because of waste and safety issues, is nuclear power. Nations won't get credit for switching from coal and oil-fired plants to nuclear ones, even if the change would reduce greenhouse gases.

All such efforts represent progress, considering that a global warming agreement was declared dead a little more than a year ago after talks broke down in The Hague. National differences seemed too great and compromise too distant.

But as scientific evidence of global warming mounted, the environmental risk of doing nothing began to seem as great as the economic cost of doing something.

Real action is still far from assured. With the U.S. balking at the treaty, virtually every other industrialized country - some 55 nations - must agree in Johannesburg in September to ratify. Even then, the treaty is only a modest step toward what are projected to be far tougher standards in 2012.

The ultimate answer is conservation and technology. Can we find cleaner energy?