WASHINGTON (AP) - It was almost unthinkable. The president of the United States walked into a meeting of fellow world leaders and there wasn't a chair for him, a sure sign he was not expected, maybe not even wanted.
Barack Obama didn't pause, however. "I'm going to sit by my friend Lula," he said, moving toward Brazilian President Luiz Inacio Lula da Silva.
A Brazilian aide gave the U.S. president his chair, and Obama spent the next 80 minutes helping craft new requirements for disclosing efforts to fight global warming. Along with India, South Africa and Brazil, the key member in the room was China, which recently surpassed the U.S. as the world's top emitter of heat-trapping gasses.
At the table this time for China was Premier Wen Jiabao, not an underling as before. Obama was bent on striking a deal before flying home to snowbound Washington.
He would later hail the achievement as a breakthrough. But even Obama said there was much more to do, and climate authorities called Copenhagen's results a modest step in the global bid to curb greenhouse gasses that threaten to melt glaciers and flood coastlines.
Obama's 15-hour, seat-of-the-pants dash through Copenhagen was marked by doggedness, confusion and semi-comedy. Constrained by partisan politics at home, and quarrels between rich and poor nations abroad, he was determined to come home with a victory, no matter how imperfect.
Experts and activists may debate its significance for years. Some, like Jeremy Symons, who watched the talks for the National Wildlife Federation, said it was "high drama and true grit on the part of the president that delivered the deal."
Others were far less kind. The Copenhagen agreements are "merely the repackaging of old and toothless promises," said Asher Miller, executive director of the Post Carbon Institute.
Even though a weary, bleary-eyed Obama had added six hours to his planned nine-hour visit, he was back in Washington by the time delegates at the 193-nation summit approved the U.S.-brokered compromises on Saturday. The agreements will give billions of dollars in climate aid to poor nations, but they do not require the world's major polluters to make deeper cuts in their greenhouse gas emissions.
This account of Obama's hectic day is based on dozens of interviews and statements by key players from numerous countries.
Obama was thrown off schedule almost from the moment he landed Friday morning in Copenhagen, where the summit's final-day talks seemed to be collapsing.
Instead of attending a planned meeting with Denmark's prime minister, he plunged into an emergency session of about 20 nations, big and small, wealthy and poor. Right away there was a troubling sign.
China was the only nation to send a second-tier official: vice foreign minister He Yafei instead of Premier Wen, who was in the building. The snub baffled and annoyed delegates.
For months, Obama had been pressing China to put into writing its promises to reduce greenhouse gas emissions.
Obama later seemed unusually animated when he alluded indirectly to China in a short, late-morning speech to the full conference.
"I don't know how you have an international agreement where we all are not sharing information and ensuring that we are meeting our commitments," he said. "That doesn't make sense."
Things then appeared to turn for the better, as Obama and Wen met privately, as scheduled, for 55 minutes. A U.S. official said they took a step forward as they discussed emissions targets, financing and transparency.
The two leaders directed aides to work on mutual language, and Obama's team proposed specific wording meant to solidify China's promise to be more forthcoming about its anti-pollution efforts.
A short time later, however, the U.S. team was more baffled and irked than before. At a follow-up session of the morning's big meeting, the Chinese sent an even lower-ranking envoy in Wen's place.
An irritated Obama told his staff, "I don't want to mess around with this anymore, I want to just talk with Premier Wen," according to a senior administration official who spoke on background to discuss sensitive diplomatic issues.
By now night had fallen, and it was clear Obama would be late getting home. He kept an appointment to discuss arms control with Russian President Dmitry Medvedev. Meanwhile he asked aides to try to set up a final one-on-one meeting with Wen, and a separate meeting with leaders of India, Brazil and South Africa. He hoped these fast-growing nations, which had been loosely aligned with China on many of the key issues, might influence the Chinese.
Confusion reigned. Chinese officials said Wen was at his hotel and his staff was at the airport. The same was said of top Indian officials, but nothing was clear.
South African President Jacob Zuma agreed to meet with Obama, then canceled when he heard the Indian leader was away, and Brazil would attend only if India did.
The Chinese said Wen could meet with Obama at 6:15 p.m., then changed it to 7 p.m. Obama used the time to talk strategy with the leaders of France, Germany and Great Britain.
Meanwhile, a four-nation negotiating team known as BASIC gathered. The modified acronym reflected its members: Brazil, South Africa, India and China.
Obama was unaware, however, thinking he was going to meet alone with Wen. After some confusion about who had access to the room, White House aides told the president that Wen was inside with the leaders of the three other countries, apparently working on strategy.
"Good," Obama said as he walked through the door. "Mr. Premier, are you ready to see me?" he called out. "Are you ready?"
Inside he found startled leaders and no chair to sit in.
U.S. officials denied that Obama crashed the party, saying he simply showed up for his 7 p.m. meeting with Wen and found the others there.
Whatever the meeting's original purpose, Obama used it to help strike an agreement on ways to verify developing nations' reductions of carbon dioxide and other heat-trapping gases, a good U.S. ending to their talks with the Chinese.
Other agreements that came from Copenhagen were a mixed bag, with some environmentalists keenly disappointed, and probably no nation entirely pleased.
Rich countries vowed to provide $30 billion in emergency climate aid to poor nations in the next three years, and set a goal of eventually channeling $100 billion a year to them by 2020.
The summit's final document said carbon emissions should be reduced enough to keep the increase in average global temperatures below 2 degrees C (3.6 degrees F) since preindustrial times. But average temperatures already have risen 0.7 degrees C (1.3 degrees F) since then.
The nations most vulnerable to climate change, including low-lying islands, say the 2 degree C figure is already too high.
It was just after 1 a.m. EST Saturday when Air Force One landed outside Washington on the flight from Copenhagen. With a steady snow falling, Obama headed for the White House. It would be 3 1/2 more hours before the 193 nations, with a few objections, would agree to the deal brokered by the American president. A short time later the conference adjourned.
Later Saturday, Obama put the best face possible on the results.
"This breakthrough lays the foundation for international action in the years to come," he said from the White House Diplomatic Reception Room.
But he got no plaudits in the Chinese press.
The English-language China Daily newspaper called Obama's Copenhagen speech "grandstanding," and said it left non-governmental organizations at the summit disappointed.
Associated Press writers Seth Borenstein, Michael Casey and Charles Hutzler in Copenhagen; H. Josef Hebert in Washington; and Cara Ana in Beijing contributed to this report.