The U.S. must find ways of meeting demands by a suspicious world on reducing greenhouse gas emissions without exceeding what Congress will allow. It must also find the cash in a tight budget.
"The United States is back and President Barack Obama is coming to Copenhagen to put America on the right side of history," said Sen. John Kerry, chairman of the Senate Foreign Relations Committee.
Secretary of State Hillary Rodham Clinton was on her way to Copenhagen as negotiations over a draft agreement effectively came to a halt after an all-night session that broke up at dawn Wednesday with a confused text leaving most issues to be decided by ministers or heads of government. Obama is scheduled to arrive Friday.
Left unresolved are the questions of emissions targets for industrial countries, billions of dollars a year in funding for poor countries to contend with climate change, and verifying the actions of emerging powers like China and India to ensure that promises to reduce emissions are kept.
Denmark, presiding at the conference, said it has drawn up a text that it would present when ministers resume talks, but delegates were undecided on the format to hold the negotiations, whether in a full plenary or in small groups.
Formal discussions were suspended before resuming at 10 p.m. local time, met briefly, then adjourned for the night.
"I still believe it's possible to reach a real success,'' said the U.N.'s top climate official, Yvo de Boer. "The next 24 hours are absolutely crucial and need to be used productively."
The U.S. delegation objected to a proposed text it felt might bind Washington prematurely to reducing greenhouse gas emissions before Congress acts on the required legislation. U.S. envoys insisted, for example, on replacing the word "shall'' with the conditional "should'' throughout the text.
Veterans of these conferences said such stalls were not unusual. "I know that often negotiations reach the halfway point about an hour before an agreement," said Jennifer Haverkamp, a former trade negotiator and a climate analyst for the Environmental Defense Fund.
In one sign of progress, six countries pledged a total of $3.5 billion over three years $1 billion from the U.S. to protect the world's forests. It will be channeled to developing countries that produce plans to slow and eventually reverse deforestation.
But that was just a fraction of a U.N.-proposed three-year package of at least $30 billion for poor countries to prepare defenses against rising seas, drought and other severe effects of global warming, including economic and physical security.
Japan said it would it would contribute half the needed funds, $15 billion, in public and private finance, "on condition that successful political accord is achieved" in Copenhagen.
Dozens of presidents and prime ministers the early arrivals among 115 leaders called for a sweeping agreement to rescue the planet from climate-related devastation. As the conference stretched into the night, the audience dwindled to a handful.
Among Clinton's first scheduled meetings Thursday is a private talk with China, America's protagonist in a dispute over whether developing countries will be required to report and verify their actions to reduce emissions.
"The key is China and the United States," which together emit half the world's greenhouse gases, said Indonesian delegate Emil Salim. "The key question is what the U.S. will do and the U.S. problem is the Senate which hasn't passed a bill that will allow the government to take action."
The U.S. has offered a 17 percent reduction from 2005 emissions levels by 2020. That amounts to a 3 percent to 4 percent cut from 1990 levels the baseline year used by many other countries. China has pledged to cut "carbon intensity'' a measure of carbon dioxide emissions per unit of production by 40 percent to 45 percent by 2020, compared with 2005 levels.
China says it has no obligation to report how it achieves that pledge, while the U.S. says Beijing must allow others to review the report to understand the basis of the carbon calculations.
The U.S. delegation argues that the United States is taking a variety of other actions to control carbon, from requiring more fuel-efficient vehicles by 2016 to promoting clean energy development, to more tree planting and environmentally friendly agricultural practices. These climate friendly activities are reflected in the 17 percent commitment being made in Copenhagen, although Washington argues this will have the effect of producing greater emission reductions in the U.S.
Obama spokesman Robert Gibbs said the White House sees the state of the talks the same way it did several days ago: that "a number of outstanding issues'' have to be worked out. He emphasized the need for a final deal that allowed for transparency so that when countries making pledges, "we know people are living up to those agreements."
Gibbs said the appearance of leaders from around the globe, including Obama, creates the opportunity for a "breakthrough to happen."
Obama, like most world leaders, is constrained by tough politics at home.
"To pass a bill, we must be able to assure a senator from Ohio that steelworkers in his state won't lose their jobs to India and China because those countries are not participating in a way that is measurable, reportable and verifiable," Kerry said. "Every American indeed, I think all citizens need to know that no country will claim an unfair advantage."
Obama can "use the power of the presidency to strengthen the U.S. has on the table," said Annie Petsonk, international counsel for the Environmental Defense Fund.
Administration officials could be looking to see what other ways, not in congressional bills, that Obama could make big decreases in carbon dioxide emissions, including presidential orders that affect big federal government polluters, she said.
He can also bring more money for poor nations by redirecting aid already in the pipeline and can promise to use some of the funds raised from emission credits to help reduce deforestation in developing countries. He can also use the cap-and-trade process to push a certain percentage of caps to be used on reducing deforestation, Petsonk said.
Outside the hall, police fired pepper spray and beat protesters with batons as hundreds of demonstrators sought to disrupt the 193-nation conference, the latest action in days of demonstrations to demand "climate justice" firm steps to combat global warming. Police said 260 protesters were detained.
City roads were chaotic and public transport was disrupted as authorities coped with the unexpected presence of more than 100 leaders who wanted to be part of one of the most complex international deals ever negotiated.