"Scientific evidence of the dramatic effects of human-induced climate change is becoming stronger," said Richard Kinley, acting head of the UN Climate Change Secretariat which will host the meeting in a Bonn hotel.

"Governments need to agree on how the world is to reduce emissions within two to three years," he said of a drive to extend the Kyoto pact beyond a first period running to 2012.

Bonn is likely only to be a round of skirmishing on measures to slow warming that could wreak havoc by stoking more droughts, heatwaves, floods, more powerful storms and raise global sea levels by almost a metre by 2100.

"I don't think anyone expects any breakthroughs in Bonn but it will be the start of what could prove to be some very useful discussions," said Elliot Diringer, a director at the Washington-based Pew Center on Climate Change.

STRAITJACKET

President George W. Bush denounces Kyoto as an economic straitjacket that unfairly excludes developing nations from a first round to 2012 even though almost all his industrial allies back the scheme.

Rather than binding caps on emissions, Bush favours big investments in technology such as hydrogen or solar power. Many developing nations say that rich states should take the lead in cuts before asking them to restrain emissions.

"The dialogue will take the form of an open, non-binding exchange of views, information and ideas," the United States said in a note to the Bonn talks of senior officials, reminding them of a limited mandate agreed in Montreal last year.

The meeting will focus on ways to promote economic growth that does not harm the environment, on adapting to climate change, on new technologies and on use of markets to combat warming.

Many scientists fear global warming linked to human burning of fossil fuels could push up temperatures by perhaps 3 Celsius by 2100 after a gain of 0.7 C in the past 100 years.

After the two-day dialogue among all 190 members of the UN Climate Convention, backers of Kyoto will meet from May 17-25 for a round of related talks about how to extend cuts in emissions from power plants, factories and cars beyond 2012.

"It's going to be a long haul, but hopefully won't take more than three years," said Steve Sawyer, a climate policy director at Greenpeace, of a post-2012 Kyoto pact. No experts expect the Bush administration to sign up for a Kyoto successor.

And Kinley said Kyoto backers should reassure investors that markets for trading quotas in heat-trapping carbon dioxide from factories and power plants would continue beyond 2012.

Prices in the European Union carbon market fell to fresh one-year lows on Friday, at 10.5 euros (US$13.52) a tonne on lower than expected emissions from factories and power plants in 2005.

Kyoto obliges rich nations to cut emissions of greenhouse gases by at least 5.2 percent below 1990 levels by 2008-12.

Many participants are way over target, such as Spain, Greece and Canada. Still, high oil prices at US$73 a barrel are spurring interest in non-polluting energies such as wind or solar power.

Canada's green groups this week urged Environment Minister Rona Ambrose, set to lead the Bonn talks, to step down as chair after she said Canada has no chance of meeting Kyoto targets.