The chief U.S. climate negotiator on Monday defended Washington's stand against compulsory caps on global-warming emissions, and said the Bush administration was unlikely to change its policy.

At the opening of a two-week U.N. treaty conference on climate change, Harlan Watson told reporters the United States is doing better at restraining the growth of such gases voluntarily than some countries committed to reductions under the Kyoto Protocol.

"With few exceptions you're seeing those emissions rise again," Watson said of countries bound by Kyoto.

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Developing nations, the European Union, environmentalists and others are urging Washington to sign onto obligatory cuts after 2012 — when Kyoto expires — in emissions of heat-trapping gases blamed by scientists for global warming.

"The international community will need to a take much more ambitious action after 2012," Stavros Dimas, the European Union environment commissioner, said in a statement. What is needed, he said, is "an international consensus," meaning a controls regime that includes the biggest emitter, the United States.

"There is a need for a common commitment," Kenyan Environment Minister Kivutha Kibwana told the conference, which elected him to a one-year presidency of the body governing the 1992 U.N. treaty on climate change.

The 1997 Kyoto accord, an annex to that treaty, requires 35 industrialized countries to reduce greenhouse-gas emissions by 5 percent below 1990 levels by 2012.

Scientists attribute the past century's 1-degree rise in average global temperatures at least in part to the accumulation of carbon dioxide, methane and other greenhouse gases in the atmosphere — byproducts of power plants, automobiles and other fossil fuel-burning sources.

Continued global warming will lead to shifts in climate zones, seas rising from heat expansion and runoff from melted land ice, and more extreme weather, scientists say.

Here in Nairobi, the Kyoto countries will continue talks on what kind of emissions targets and timetables should follow 2012. But many, before committing, are waiting to see whether the United States, accounting for 21 percent of the world's greenhouse gases, will submit to a mandatory regime of cutbacks. Watson's words seemed to rule that out for the next two years.

He was asked at a news conference whether reported pressure from British Prime Minister Tony Blair might have led to a change of attitude in the Bush administration toward Kyoto-style controls.

"I certainly got no indication that there's any change in our position," the U.S. negotiator replied, "nor is there likely to be during this presidency."

Watson cited recent U.N. figures showing that, by one measure, the United States is doing better on greenhouse gases than some countries. "The way the numbers are counted, we're doing very well," he said.

That report showed that growth in U.S. emissions in 2000-2004 was 1.3 percent, compared with 2.4 percent overall for 41 industrialized nations.

When compared with Kyoto's 1990 benchmark, however, the picture is different.

Largely because of the shutdown of many eastern European industries in the 1990s, after the collapse of the Soviet bloc, emissions of all industrialized countries declined by 3.3 percent between 1990 and 2004, while U.S. emissions grew by almost 16 percent.

Among the Kyoto-obligated countries, Germany's emissions dropped 17 percent between 1990 and 2004, Britain's by 14 percent and France's by almost 1 percent.

Japan, Spain and other Kyoto signatories have registered emissions increases since 1990, but U.N. officials say they can meet their Kyoto targets by 2012 via taxes on carbon-based fuels, energy-efficiency regulations and other steps.

The Bush administration objects to Kyoto-style mandates because, it says, they would hamstring U.S. economic growth and because poorer countries are exempted from the controls.

In counterpoint to this, a British government study released last week predicts the damage from unabated climate change will eventually cost between 5 percent and 20 percent of global gross domestic product each year.

That report showed that tackling climate change "is a fundamental economic necessity as well," the Kenyan Kibwana told the conference.

"Climate change threatens development goals for billions of the world's poorest people," he said.