The success of the U.N. climate conference hung in the balance Tuesday as China and the U.S. deadlocked over whether Beijing will allow the world to check its books and verify promised cuts in greenhouse gas emissions.
Princes, presidents and premiers crowded into a vast hall for the formal opening of the largest summit ever held on climate change, but attention was on the leaders of the world's two largest polluters _ President Barack Obama and Prime Minister Wen Jiabao _ who plan to arrive for the final days of talks on a framework to control heat-trapping gases.
Negotiators who have been working for 10 days floated new draft documents on lesser issues. But they left open the vexing questions of emissions targets for industrial countries, billions of dollars a year in funding for poor countries to contend with global warming, and verifying the actions of emerging powers like China to ensure they keep their promises.
"In these very hours, we are balancing between success and failure," said conference president Connie Hedegaard of Denmark. Success is possible, she said, "but I must also warn you: We can fail _ probably without anyone really wanting it so, but because we spent too much time on posturing, on repeating positions, on formalities."
The rest of the 115 leaders were expected to arrive before Friday's summit finale to sign a political outline of a global warming treaty that would set limits on carbon dioxide pollution by the United States, China, India as well as extending emissions targets for the 37 countries regulated under the 1997 Kyoto Protocol.
"There is no understatement that with your signatures you will write our future," Britain's Prince Charles told the conference.
As the conference headed into the final stretch, delegates were disheartened that so many large and small issues remained unresolved, with prospects for a meaningful agreement receding.
Prodipto Ghosh, a member of the Indian delegation, said the negotiations were "not going good" and that fundamental differences between rich and poor nations would be "difficult to bridge" by the end of the week.
Experienced negotiators recall many previous conferences where the deal was done in the final overnight session, against all odds.
Secretary of State Hillary Rodham Clinton was coming Thursday to hold a round of private consultations in preparation for Obama's arrival a day later, said an official in Washington, speaking on condition of anonymity because the trip has not been formally announced.
U.N. Secretary-General Ban Ki-moon said he was positive about a deal but also expressed frustration with the progress to date.
"I'm afraid that negotiations have been too slow," Ban said. "I think all the countries can and must do more."
Delegates were nearing a deal to protect tropical forests, although several substantive issues remained unresolved, including targets for reducing deforestation and money to pay for conservation plans and how that money would be raised, according to the latest draft of a text seen by The Associated Press.
The program called REDD, for Reducing Emissions from Deforestation and Degradation, would be financed either by richer nations' taxpayers or by a carbon-trading mechanism _ a system in which each country would have an emissions ceiling, and those who undershoot it can sell their remainder to over-polluters.
Political and entertainment celebrities crowded onto the Copenhagen stage, followed by a trail of cameras: California Gov. Arnold Schwarzenegger, New York Mayor Michael Bloomberg, former Vice President Al Gore and actor-activist Darryl Hannah. Zimbabwean President Robert Mugabe came, exempted from a European travel ban because he was attending an international conference. British Prime Minister Gordon Brown arrived, saying he could act as a broker in the talks.
Yvo de Boer, the top U.N. climate official who presides over the two-week affair, gave his daily news conference with an orange-and-white life preserver leaning against his podium and joked that he hoped the world wouldn't need it.
The top U.S. and Chinese diplomats at the talks, Todd Stern and Xie Zhenhua, held yet another in a series of private meetings, but neither side indicated any break in the stalemate on the verification issue.
An Asian diplomat who speaks often with both sides said China and the U.S. have made verification a red-line issue and said he feared it could cause a deal to collapse. Neither said has made any serious concessions, the diplomat told the AP on condition of anonymity for fear of compromising his negotiating ability.
China promised last month to slow its carbon emissions, but stressed the move would be voluntary without international assistance or financing _ reflecting its reluctance to commit to internationally verifiable standards.
Washington welcomed Beijing's pledge to nearly halve the ratio of pollution to economic output in the next decade but said China should put that target in an international agreement and open it to fact-checking.
"There ought to be some measure of international consultation or review or dialogue," Stern said. Other countries want to "understand the assumptions behind the numbers."
Yu Qungtain, Xie's deputy at the talks, rebuffed any verification demand that goes beyond previous agreements. "We cannot agree," he said.
The Asian diplomat said China is concerned that verification could lead to penalties for failing to meet its commitments. But he also said the United States was pushing for binding commitments from developing countries that they cannot accept.
"The U.S. is trying all sorts of verbal formulations," said David Doniger of the Natural Resources Defense Council.
China already subjects some data for review under other agreements: it allows the World Bank to check its economic figures and the International Energy Agency to go over its energy output, said Doniger, a former climate negotiator. A new climate agreement might lead to even more intrusive inspections, however.
Doniger saw a possible solution to the dispute in a trade-off in which China would agree to have its figures reviewed in exchange for a firm U.S. offer on financing for developing countries to help them deal with rising seas, drought and other results of global warming. The U.S. has said it cannot put a figure on the table until Congress legislates a climate and energy package, expected in the first half of 2010.
China is grouped with developing nations at the talks, but the U.S. doesn't consider China to be in need of climate-change aid.
The U.S. also has a weapon it has not yet used in the negotiations: the threat to tax Chinese-made goods deemed to be cheaper because they are made with higher carbon emissions than similar U.S. goods _ known as "border adjustments."
Yu said the tactic amounted to trade protectionism using climate change as an excuse, and was unacceptable. On protectionist issues, he said, "no one will benefit. We will all lose."
Associated Press reporters Dina Cappiello in Washington and Cara Anna in Beijing contributed to this report.