* U.S.-China standoff at heart of talks
* Talks seek successor to 1992 treaty; may be years off
* World may have under-estimated Obama's problems
By Alister Doyle, Environment Correspondent
OSLO, Nov 24 (Reuters) - The world will seek to break a U.S.-China standoff and agree modest steps to rein in global warming at U.N. talks in Mexico next week amid worries that the first climate treaty since 1992 may still be years away.
Most nations have few hopes for the meeting of environment ministers from Nov. 29 to Dec. 10 in the Caribbean resort of Cancun after U.S. President Barack Obama and other world leaders failed to agree a treaty at last year's U.N. Copenhagen summit.
Sights are lower for Cancun, which will test the ability of the United Nations to reconcile the interests of China and the United States, the top greenhouse gas emitters, and those of 192 other nations in a 21st century world order. All have a veto.
"We have to take a few steps forward or there are people who are going to lose faith in the U.N. system," Rajendra Pachauri, head of the U.N. panel of climate scientists.
"I'm a little depressed about Cancun," said Al Gore, the climate campaigner and former U.S. Vice President. "The problem is not going away, it's getting steadily worse."
In new evidence of warming, the World Meteorological Organization said on Wednesday that concentrations of the main greenhouse gases in the atmosphere have reached their highest level since pre-industrial times. [ID:nLDE6AN11Z]
And 2010 is on track to match 1998 or 2005 as the warmest year since records began in the 19th century, leading experts say. [ID:nLDE6AM1OU]
Pachauri's panel says warming will bring more floods, heatwaves, mudslides and rising sea levels. Inaction also raises risks of abrupt changes such as a melt of polar ice or permafrost. <^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ For a TAKE A LOOK on the road to Cancun [ID:nLDE6A915C] Stories on Middle East climate change [ID:nLDE6AB1SN] Stories on politics, economics of climate change [nCLIMATE] For data on carbon markets [nCARBON] Reuters highlights climate change themes for 2011, ranging from renewable energy and forests to why China is crucial, in this PDF: r.reuters.com/mem36q ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^>
The talks will try to agree "building blocks" of a deal such as a green fund to channel aid to poor nations, a mechanism to share new clean energy technologies and a deal to protect tropical forests that soak up greenhouse gases as they grow.
Hopes for a quick binding deal have faded, partly because of a standoff between China and the United States throughout 2010 about new actions and scant prospects that the U.S. Senate would be able to ratify a treaty in coming years.
"There is a total deadlock for the United States, which means China will not be forthcoming," said Johan Rockstrom, head of the Stockholm Environment Institute.
The world agreed the existing U.N. Climate Convention in 1992. In any new deal, China says that Obama must show more leadership than his stalled U.S. plan to curb emissions by 17 percent below 2005 levels by 2020.
Washington says China must toughen a "voluntary" plan to curb the rise of its carbon emissions by between 40 and 45 percent below projected levels by 2020 from 2005. The rivalry overshadows other tensions between rich and poor nations.
Alden Meyer, of the Union of Concerned Scientists, said the world had under-estimated hurdles in the United States, where he said Obama's Democrats risked losing control of the 100-seat Senate in 2012 elections even if Obama is re-elected.
"It's likely to get harder after 2012," he said. Double the number of Democrats face elections in 2012 than Republicans, when a third of the Senate is up for election. The Senate needs 67 votes to ratify an international treaty.
Other countries "have got to figure out, once again, do you try to soldier ahead without the U.S.?" he said.
All industrialised nations except the United States back the U.N.'s Kyoto Protocol, which seeks to cut emissions by 5.2 percent below 1990 levels by 2008-12. They need to decide by the end of 2012 how to extend Kyoto, which underpins carbon prices.
Many other analysts fear the talks may drag on like the 2001 Doha round of trade talks -- which once staged a failed meeting in Cancun. One early chance for a deal may be an Earth Summit in Rio de Janeiro in 2012, Rockstrom said.
Despite pessimism, Andrew Steer, the World Bank's special envoy for climate change, said there had been a "sea change" in developing nations' perceptions of the importance of slowing global warrming by shifting from fossil fuels.
In 1990, just 10 percent of developing nations wanted climate change as a main pillar of development, he said. In the past two years, that figure had risen to 80 percent.
And the WWF environmental group published a report on Wednesday praising emerging economies such as China, India, South Africa and Brazil for work to slow climate change. (With extra reporting by Laura MacInnis in Geneva, Gerard Wynn in London; editing Philippa Fletcher) (For Reuters latest environment blogs, click on: blogs.reuters.com/environment/)