An announcement by Secretary of State Hillary Clinton that the United States would contribute to a climate change fund amounting to $100 billion a year by 2020 was quickly followed by an offer from China to open its books on carbon emissions to international review.
The U.S. delegation did not immediately react to the offer by Vice Foreign Minister He Yafei. But it went a long way toward the U.S. demand that China report on its actions to limit the growth of Beijing's carbon emissions and allow experts to go over its data.
The sudden concessions on the eve of today's final session lifted hopes that the 193-nation conference could reach a framework agreement that could be refined into a legal accord next year on limiting greenhouse gas emissions and fighting climate change.
Mr. Obama and Chinese Premier Wen Jiabao were to join more than 110 world leaders for the last scheduled day of the conference, which for most of its two weeks was embroiled in angry exchanges, a partial boycott by African countries and another entire day wasted in procedural wrangling. It's also possible that once the world leaders depart, the talks could continue at the ministerial level and stretch late into the night and early Saturday.
A pair of Greenpeace activists crashed a Thursday night banquet hosted by Denmark's Queen Margrethe for the world leaders already in town. The couple, dressed in formal wear, unfurled two banners reading "Politicians Talk, Leaders Act" as they walked on the red carpet reception line, and were dragged from the hall by security guards.
The conference seems likely to fall short of the goal set by many developing countries for a deal that would be legally binding on all parties and guarantee the kind of dramatic emissions reductions by the industrial world that threatened nations feel are necessary.
Mrs. Clinton's announcement on funding was widely welcomed. Yoshiko Kijima, a senior Japanese negotiator, said it sent a strong signal by Mr. Obama "that he will persuade his own people that we need to show something to developing countries. ... I really respect that."
Swedish Environment Minister Andreas Carlgren said Mrs. Clinton added "political momentum," and India's Environment Minister Jairam Ramesh called it "a good step forward."
Independent agencies also praised the move. "I think we're closer now than we have been in two years," said Tom Brookes, an analyst for the European Climate Foundation.
"It shows that when the U.S. moves, China moves," said Kim Carstensen, the climate director for the World Wildlife Fund.
The White House was lowering expectations ahead of Mr. Obama's trip.
Neither the U.S. nor China raised its commitment on emissions. Mrs. Clinton repeated the U.S. would cut emissions by 17 percent from 2005 levels by 2020. China announced last month it would cut the amount of emissions in relation to production, by 40 to 45 percent.
An internal calculation by the United Nations, obtained by The Associated Press, said pledges made so far by both industrial and developing countries would mean a 4.8-degree Fahrenheit temperature rise this century, which scientists say could lead to a catastrophic sea level rise threatening islands and coastal cities, kill off many species of animals and plants, and alter the agricultural economies of many countries.
But the U.S.-China moves could prompt the European Union to raise its emissions commitment to a 30 percent reduction by 2020 from 1990 levels, and similarly inspire Japan and Australia to lock into the upper end of their previously announced targets -- 25 percent each.
Mrs. Clinton said the U.S. agreement to the annual transfer of $100 billion to developing countries was contingent on reaching a broader agreement that covers the "transparency" of China's measures to limit heat-trapping gases.