OSLO, Feb 16: A world plan to fight global warming went into force on Wednesday, feted by its backers as a lifeline for the planet amid sniping at the United States for pulling out.

After years of delays, the UN Kyoto Protocol on curbing emissions of heat-trapping gases blamed for disrupting the climate took effect at 0500 GMT with muted celebrations for a deal Washington dismisses as an economic straitjacket.

Green groups marked Kyoto by protesting outside US embassies, by interrupting oil trading on London's International Petroleum Exchange and by carving fast-melting ice sculptures of kangaroos in Australia.

"Climate change is a global problem. It requires a concerted global response," UN Secretary General Kofi Annan said in remarks beamed to the ancient Japanese city of Kyoto where the pact was signed in 1997.

"I call on the world community to be bold, to adhere to the Kyoto Protocol and to act quickly in taking the next steps," he said. "There is no time to lose." Supporters of the 141-nation pact say it is a tiny first step to slow global warming by imposing legally binding caps on greenhouse gas emissions - mainly from burning fossil fuels in power plants, factories and cars - in 35 developed nations.

Many climate experts fear temperature rises will disrupt farming, raise sea levels by melting icecaps, cause more extreme weather like hurricanes or droughts, spread diseases and wipe out thousands of animal and plant species by 2100.

TOO COSTLY: The United States, the world's biggest polluter, pulled out in 2001. President George Bush said Kyoto was too costly, based on unreliable science and unfairly excluded big developing nations like India, China and Brazil which account for a third of the world's population.