With the clock ticking, President Obama will travel to Copenhagen tonight in a last-minute attempt to finalize a global climate change agreement that has become mired in debate in recent days.
After an overnight flight from Washington, Obama will join more than 100 world leaders who are gathered on the last day of the United Nations conference to try and reach a deal .
German Chancellor Angela Merkel and Australian Prime Minister Kevin Rudd have expressed frustration at the lack of progress in Copenhagen, with Rudd admitting that the negotiations were "sticky."
Obama's arrival at the table is seen as a strong signal that a final deal is possible, but negotiators are continuing to hash out details on the eve of his arrival.
The Obama administration dispatched its top diplomat -- Secretary of State Hillary Clinton -- to Copenhagen Wednesday as the prospects of an agreement seemed to diminish in an ongoing dispute between the United States and China on the transparency of emissions reductions.
Clinton landed in the Danish capital today and announced that the United States would contribute an unspecified amount to a $100 billion fund to be established by 2020 to help poorer countries switch to more energy efficient technologies. The news was widely viewed as a shot in the arm for the ongoing discussions.
"We're running out of time," Clinton told reporters at a news conference shortly after arriving. "Without the accord, the opportunity to mobilize significant resources to assist developing countries with mitigation and adaptation will be lost."
Among the roadblocks for a deal is a disagreement with China, one of the world's largest emitters of carbon dioxide, about verification of emissions cuts. A U.S. official is reported as saying China was not willing to sign onto an accord immediately, although Chinese officials have reportedly denied that account.
Clinton met with Chinese Premier Wen Jiao Bao today, but it was unclear whether the discussions were able to break the logjam.
The White House said today that Obama hopes his attendance at the summit with push talks forward. But spokesman Robert Gibbs said the president has never been under any illusion that a deal would be easy.
"We're not going there just to get an agreement for the sake of something that's called an agreement," Gibbs said. "We want something that works for both the international community but also what works for the United States. We think the elements are there to reach that agreement."
The president is facing pressure to return from the conference with tangible results, and his critics have noted that the last time he went to Copenhagen -- to make a last-minute pitch for Chicago's failed Olympic bid -- he came up short.
Gibbs said today that coming back with an empty agreement would be far worse than coming back empty-handed. But if no final climate agreement is reached, Gibbs said, Obama is committed to continuing to work on the issue.
For her part, Clinton tried to play down the notion of a U.S.-China showdown as the clock ticks down on a potential deal.
"We have lost precious time in these past days," Clinton said. "In the time we have left here, it can no longer be about us versus them -- this group of nations pitted against that group. We all face the same challenge together."
Clinton told reporters that verifying emission reductions is key to a successful agreement. She said the U.S. financial contributions, key for the support of poorer nations that fear they would suffer economically if forced to cut emissions, would be in jeopardy "in the absence of transparency from the second biggest emitter -- and now I guess the first, biggest emitter," a reference to China.
A senior administration official said today the "agreement is contingent on a strong overall agreement that includes transparency."
The White House said this morning that the elements of an agreement are in place, and hopes China will get on board but expressed concerns about China's commitment to transparency.
"The elements of getting an agreement are there if countries like China will make some common sense agreements about transparency," Gibbs said. "If the Chinese are unwilling to prove, to be able to prove to the world that they can live up to the agreement that they make, then I think it calls into question whether or not you truly have an agreement."
Obama has laid out a goal of reducing U.S. greenhouse gas emissions 83 percent by 2050, with a benchmark of a 30 percent reduction from 2005 emission levels by 2025.
But Congress is still working out the details on the goals for emissions reduction by 2015. In June, the House passed a bill that mandated a 17 percent cut by 2020, but so far the Senate has not considered the issue.
Clinton also met with leaders from island nations who fear rising ocean levels caused by global warming will sink their countries within the coming decades. Her other meetings today included officials from India, who rebuffed her efforts to secure an agreement on emissions last summer, Brazil, and South Africa.
Sen. John Kerry, D-Mass., chairman of the Senate Foreign Relations Committee, was in Copenhagen this week for the summit and said funding for global climate financing is a "critical component of any agreement" reached there.
"Financing is a major step forward and now we need to reach common ground on decisive national mitigation actions and transparency that provide credibility to the entire process," Kerry said in a statement. "China needs to rejoin the effort and start playing a constructive role."
ABC News' Yunji de Nies and Sunlen Miller contributed to this report.