At a resort complex in sun-drenched Mexico, world governments begin yet another attempt to fight global warming, hoping to overcome the disconnect between rich and poor nations that so divided earlier efforts.

After a disappointing summit last year in Copenhagen, no hope remains of reaching an overarching deal this year to set legal limits on how much carbon dioxide major countries would be allowed to emit. Such an accord was meant to describe a path toward slashing the so-called greenhouse gas emissions by mid-century, when scientists say they should be half of today's levels.

During the upcoming two weeks of talks, the 193-nation U.N. conference hopes to conclude agreements that will clear the way to mobilize billions of dollars for developing countries and give them new, green technologies.

Eighty-five countries have made specific pledges to reduce emissions or constrain their growth, but those promises amount to far less than required to keep temperatures from rising to potentially dangerous levels, some scientists argue. The recriminations that followed the Danish summit raised questions over whether the unwieldy U.N. negotiations, which require at least tacit agreement from every nation, can ever work.

"As is the case with any large puzzle with over 1,000 pieces and over 190 players, one needs to start with the edges and work inwards," Jennifer Morgan, of World Resources Institute, said on Monday.

Christiana Figueres, the top U.N. climate official, said world capitals are aware of both a growing environmental and political urgency. "Governments need to prove that the intergovernmental process can deliver," she said Sunday.

"They know that they can do it. They know that they need to compromise. I'm not saying it's a done deal. It's still going to be a heavy lift," she said.

About 15,000 negotiators, environmental activists, businessmen and journalists are convening at a resort complex under elaborate security precautions, including naval warships a few hundred yards offshore in the Gulf of Mexico.

While delegates haggle over the wording, timing and dollar figures involved in any agreement, scientists and political activists at the conference will be offering the latest indications of the planet's warming. Some 250 presentations are planned on the sidelines of the negotiations.

Meteorologists are likely to report that 2010 will end up tied for the hottest year globally since records began 131 years ago.

The U.N. scientific body that won the 2007 Nobel Peace Prize for its climate change report -- which called global warming "unequivocal" and was the source of tremendous controversy over numerous minor errors -- is expected to tell the conference that its findings and warnings of potential disasters are hopelessly out of date.

Agronomists are due to report on shifting weather patterns that are destabilizing the world's food supply and access to clean water, and that could lead to mass migrations as farmers flee drought or flood-prone regions.
As often happens during the three-year process, attention will focus on the United States and China, two frequently belligerent nations representing the industrialized and developing world.

President Barack Obama has drawn fire for his failure to win passage of domestic climate legislation and what is often described as the feeble U.S. pledge to reduce carbon emissions 17 percent by 2020 from 2005 levels.
The environmental group Greenpeace urged other governments to stop waiting for the Americans.

"It is time for the EU (European Union) to stop hiding behind the U.S.," said Wendell Trio, Greenpeace's climate policy director.

"Equally, China must stop responding to U.S. attempts to goad it into a public fight -- a tactic that is clearly driven by the U.S. administration's need to distract attention from the fact it can bring very little to the table," he said.

The U.S. has insisted it will agree to binding pollution limits only if China also accepts legal limitations. China, now the world's biggest polluter but also the biggest investor in renewable energy, rejects international limits, saying it still needs to overcome widespread poverty and bears no historic responsibility for the problem.

U.S. negotiators may feel further constrained from showing flexibility toward the Chinese after the Republican swing in this month's congressional elections, which brought dozens of new legislators who doubt the seriousness of climate change.

But Figueres, the Costa Rican diplomat who became head of the U.N. climate secretariat in July, said the public argument may appear more bitter than it really is. At the most recent round of talks last October, "they were working very constructively with each other inside the negotiations," she said.

The Associated Press contributed to this report.