Delegates at the UN-sponsored meeting lamented the refusal by the United States to ratify the treaty aimed at reducing greenhouse gases.

The Kyoto accord, the world's most ambitious and complex environmental treaty, legally commits 39 industrial nations and territories, including Japan and Europe, to trim their output of six greenhouse gases -- especially carbon dioxide -- by at least 5.2 percent by 2012, compared with 1990 levels.

Russia's ratification last month gave the protocol the final stamp of approval needed to go into force on February 16.

But problems remain, as the United States, the largest producer of global-warming gases, on Monday rejected any change of position. And signatories China and India are producing more greenhouse gases as their economies grow.

Washington's senior climate change negotiator, Harlan Watson, called any talk of a post-2012 regime, when Kyoto runs out, "totally premature."

"Economic development is essential for adopting measures to address climate change," he said.

"For the United States, any future treaty should not hurt the country's economy and should cover every country in the world, including developing nations," he said.

US President George W. Bush's administration has refused to ratify the treaty.

"The EU hopes that longer-term issues can be considered in a manner that will assist parties to develop their understanding for a post-2012 framework," read a statement from the Netherlands, which currently holds the rotating EU presidency.

Environmentalists highlighted the perils of global warming by building an enormous "Noah's Ark" in downtown Buenos Aires.

Under a banner reading "millions at risk," protesters planned to board the vessel to symbolize impending disaster.

"Global warming is here and is having the greatest impact on the poorest countries, where people are most vulnerable," said Juan Carlos Villalonga of Greenpeace Argentina, which sponsored the protest.

At the conference, Argentina's health and environment minister, Gines Gonzalez Garcia, said global warming has already hit Argentina.

"In Argentina, we have been carrying out a systematic study of those adverse effects, and the evidence gathered indicates that the problem is even worse and is speeding up at a faster pace than formerly anticipated," he said.

The South American nation has seen more frequent storms and tornadoes, floods, receding glaciers and a rising sea level, he said, adding that the climate change poses health risks.

He said these weather patterns are "some of the signs confirming in our country that what were identified as possible consequences of global warming are already taking place."

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