The problem they are tackling is stark: cars, factories and power plants are pumping so much heat-trapping gas into the air that its changing the worlds climate, causing severe storms and droughts. New weather patterns threaten to wipe out animal species, submerge coastal areas and low islands, and dramatically change peoples way of life.

Despite three years of negotiations on the emissions problem, wide differences remain wide enough to arouse concern that agreements already in place could unravel. On several issues, the United States, the worlds largest polluter, stands apart.

Most scientists agree that humans are already changing climate. The 1990s was the warmest decade in 1,000 years and 1998 the warmest year on record. Researchers say winters in the northern hemisphere are 18 days shorter than those 150 years ago. Glaciers from Montana to the Himalayas are melting. Some animals are migrating uphill to cooler altitudes.

The conference brings together 100 government ministers, bureaucrats, environmentalists, lobbyists, activists and a new breed of businessman pollution traders. Demonstrators also are expected.

The road to The Hague began at the Earth Summit in Rio de Janeiro in 1992 when world leaders, alarmed by predictions of a climate apocalypse, pledged to combat global warming.

Five years later, negotiators meeting in Kyoto, Japan, agreed to cut the amount of greenhouse gases released each year into the atmosphere to 5.2 percent below what it was in 1990. A target date of 2012 was set.

To meet that goal, though, the Kyoto Protocol needs to come into force by 2002. Thats why this is a make-it-or-break-it conference, said Jennifer Morgan, of the World Wildlife Fund for Nature.

The protocol takes effect only when its ratified by 55 nations, including industrialized countries.

The Hague is about making sure the Kyoto agreements are not reopened for debate. Its about putting them into practice, said Jan Pronk, the Dutch environment minister and the conference chairman.

The Kyoto negotiators agreed the European Union would cut greenhouse gas emissions by 8 percent of 1990 levels, the United States by 7 percent and Japan by 6 percent. In all, 38 countries accepted binding commitments, but developing countries with huge economies, like India and China, did not.

Delegates at Kyoto failed to agree on how to meet those reductions, and Pronk said it will require creative diplomacy and political courage to reach an accord. The problem is worsened, he said, because rather than shrinking since 1990, emissions have grown by 20 percent.

Under the Kyoto plan, countries falling short of their targets can strike deals with nations that are able to reduce more than required, trading in credits from the excess. Countries with large emission deficits can sell their shortfall for cash.

Some companies have already started to trade in credits. Last Wednesday, EPCOR Utilities Ltd. of Edmonton, Alberta, announced it had bought 50,000 tons of credits from Fortum Corp., a European power company that cut emissions by converting a fossil fuel plan in Finland to biomass.

The amount of the deal was not announced. But the going rate for a credit for one ton is from dlrs 1.50-3.00 a figure certain to inflate if the protocol takes effect. Natsource, a New York-based company that arranged the EPCOR deal, foresees a market in emissions trading worth dlrs 200 billion a year.

Countries also can earn credits by helping other nations control emissions. For example, the United States could do so by helping India to develop clean energy or to plant forests that soak up carbon dioxide.

Its cheaper to lock up 1,000 tons of carbon dioxide in a forest somewhere than to reduce 1,000 tons of emissions at a coal plant in the United States, said Phil Kosnett of the Global Issues section of the U.S. Embassy in The Hague.

Trading in credits is expected to be one of the hottest issues at The Hague conference.

The European Union, fearing the United States will use the credit loophole to avoid or delay reductions, wants to put a 50 percent ceiling on the tonnage any country can purchase.

The U.S. delegation argues for unrestricted trading. Limiting credits is a wrongheaded idea, the chief U.S. delegate, Frank Loy, told reporters in a video conference from Washington. Its anti-environment.

Among other contentious issues are how to monitor compliance and punish violators.

Australia, for one, objects to a proposed body to police greenhouse gas emissions. Andrew Thomson, head of the Australian parliaments treaty committee, called the idea outrageous and said the Kyoto agreement was so flawed that Australia should simply shelve it for 20 years.