"Deep emissions cuts by industrialised countries are needed," Yvo de Boer, head of the UN Climate Change Secretariat, told the officials at a Bonn hotel. He urged them to take heed of three reports in 2007 by the UN climate panel.

He said poorer nations should get more involved in fighting climate change, especially big emitters, and that developing nations should be provided with incentives to take part.

China is set to overtake the United States as the top emitter of greenhouse gases in coming years. Neither have goals under the Kyoto Protocol, the UN plan by 35 industrial nations to cut emissions by 5 percent below 1990 levels by 2008-12.

"The international community should urgently embark on a transition to low carbon societies," The European Union, a main backer of Kyoto, said in a statement at the start of the talks.

Reports by UN climate scientists this year have blamed mankind for stoking warming, mainly by burning fossil fuels. And they have predicted impacts such as heatwaves, a spread of disease, cuts in crop yields in Africa and melting glaciers.

The third report, issued in Bangkok on Friday, said fighting global warming could brake global economic growth by up to 3 per cent in 2030 and that less stringent curbs on emissions of greenhouse gases could even slightly boost the world economy.

The Bonn talks are preparing the ground for a meeting of environment ministers in Bali, Indonesia, in December. Many nations want to launch formal 2-year negotiations at Bali to agree ways to widen the UN's Kyoto Protocol beyond 2012.

"My sense is of an increasing sense of urgency," De Boer told a news conference, but said many nations were "holding their cards close to their chests" about measures they might take.

President George W. Bush opposes Kyoto-style caps on emissions, reckoning they will cost US jobs and that Kyoto wrongly omits developing nations until 2102.

Some delegates in Bonn want a presentation of the UN climate panel's findings to ministers on the opening day in Bali to put pressure on them to act.

Hans Verolme, climate expert at the WWF environmental group, said ministers had to act in Bali to start formal talks or they would disappoint ordinary citizens increasingly worried by climate change.

"Ministers will have to unclog the traffic jam," he said.

Many developing nations are wary of limiting their emissions, that rising energy use is vital for growth.

The EU said that the UN reports meant the world had to cut emissions of greenhouse gases by 50 percent below 1990 levels by 2050 to limit global warming to a 2 Celsius (3.6 Fahrenheit) rise over pre-industrial times, seen by the EU as a threshold for "dangerous" changes.