COPENHAGEN (Reuters) - U.S. backing for a $100 billion (61.8 billion pounds) climate fund to help poor nations revived hopes for a deal to combat global warming on Thursday as world leaders met on the eve of a U.N. deadline for breaking deadlock.
Many leaders mentioned risks of failure at a two-day summit that started with a gala dinner for about 120 world leaders at Christiansborg Palace, hosted by Denmark's Queen Margrethe.
"Time is against us, let's stop posturing," French President Nicolas Sarkozy said in a speech to leaders. "A failure in Copenhagen would be a catastrophe for each and every one of us."
Environment ministers planned to work late into the night on draft texts outlining curbs on greenhouse gas emissions as part of a 193-nation deal due on Friday to avert more floods, heatwaves, droughts and rising sea levels.
The United States, the number two emitter of greenhouse gases behind China, helped the mood by promising to back a $100 billion a year fund for poor nations from 2020. President Barack Obama will arrive early on Friday.
"The United States is prepared to work with other countries towards a goal of jointly mobilising $100 billion a year by 2020 to address the climate change needs of developing countries," Secretary of State Hillary Clinton told a news conference.
Such funds would be more than all current aid flows to poor nations, a U.N. official said, and in line with demands put forward for African nations. "That's very encouraging," U.N. Secretary-General Ban Ki-moon said of the U.S. pledge.
A U.S. official said Obama was unlikely to be more specific about U.S. commitments to help provide funds for poor countries.
And the U.S. official said he could not predict whether world leaders would reach a deal but said Obama would stay committed to working on the issue if talks were not successful.
A few Greenpeace activists carrying signs saying "Politicians talk, leaders Act" walked straight up the red carpet into Christiansborg Palace after arriving in a motorcade in front of Clinton, Greenpeace said. They were removed by guards.
Accord on finance is one part of a puzzle that also includes a host of other measures, such as saving rainforests, boosting carbon markets and stiffening global carbon emissions curbs.
"If each and everyone does a little bit more than we can do this," German Chancellor Angela Merkel said. She said the European Union was willing to do more but would not act alone.
But any deal will have to be agreed by unanimity. Some small island states and African nations -- most vulnerable to climate change -- insist they will not agree a weak deal.
"We are talking about the survival of our nation," said Prime Minister Apisai Ielemia of the Pacific island state of Tuvalu of the talks that began two years ago in Bali, Indonesia.
The talks, deadlocked for 24 hours, resumed after Danish Prime Minister Lars Lokke Rasmussen dropped plans to present his own compromise texts. His plan had been opposed by poor nations which insisted everyone should be involved.
The draft texts include possible goals such as halving world greenhouse gas emissions by 2050 or obliging developed nations to cut their emissions by between 25 and 40 percent by 2020.
"We are moving out of the valley of death. We are beginning to see the outlines of a compromise, helped by the U.S. offer on finance," said Kim Carstensen, head of the WWF environmental group's global climate initiative.
Earlier on Thursday, prospects for a strong U.N. climate pact seemed remote as nations blamed leading emitters China and the United States for deadlock on carbon cuts. But ministers and leaders urged fresh urgency.
"Copenhagen is too important to fail," China's climate change ambassador Yu Qingtai said, adding that the presence of Premier Wen Jiabao, who arrived in Copenhagen on Wednesday evening, was testament to China's commitment.
India's environment minister Jairam Ramesh accused rich countries of planning a "propaganda campaign" to blame developing nations for any breakdown. Developing economies are expected to add almost all future growth in carbon emissions.
Clinton said a deal would fail unless developing nations, specifically China, committed to transparency on their emissions curbs.