This story was updated at 6:30 p.m. EST.
UNITED NATIONS, New York—From vanishingly small island states to the world's largest carbon economies, leaders of more than 100 countries pledged their support—at least in principle—to a new treaty addressing the global climate crisis. But many of them didn't weigh themselves down with concrete details.
In the session's signature event, the United States and China said they would do everything in their considerable powers to achieve a binding, universal accord in Paris at the end of next year, but neither President Obama nor Chinese Vice Premier Zhang Gaoli set firm targets beyond the commitments they made after the faltering of treaty talks in Copenhagen five years ago.
The delegates also heard from nations who were making much more ambitious declarations, as well as from some who are in much more dire circumstances.
Sweden said it would eliminate its carbon emissions entirely by 2050. Tuvalu, in danger of elimination itself, called for an end to "pandering to the interests of the fossil fuels industry."
But together, China and America give off half the world's carbon dioxide, and if there is to be a treaty, they will have to reach some kind of detente on its terms.
Obama told the delegates that at a private meeting he had told Zhang "as two of the largest economies and emitters in the world we have a special responsibility to lead. That's what big nations have to do."
It was the only time in his four-minute speech he was interrupted by applause.
Zhang, speaking a few minutes later, promised that "as a responsible major country, a major developing country, China will make an even greater effort to address climate change." He said its carbon dioxide emissions would peak "as soon as possible."
But neither country was ready, yet, to announce any specific commitments except to achieve what they promised to do by 2020 under the voluntary process set up at Copenhagen—to cut U.S. absolute emissions 17 percent and China's emissions intensity, a softer target, by up to 45 percent.
Obama and Zhang also made no mention of carbon pricing, an issue that representatives from dozens of other countries and the private sector identified at the summit as the critical component to reducing global emissions and combating climate change.
"Governments representing 52 percent of the global GDP and 50 percent of the global population agree we need carbon pricing," Dr. Jim Kim, president of the World Bank, told reporters.
The events in and around the landmark UN tower on New York's East Side bore little resemblance to those on the West Side at Sunday's People's Climate March, except that once again the police blocked off surrounding roads, leaving the city with a faint aftertaste of gridlock. This time, it was all pinstripes and black SUV's, not T-shirts and bicycles.
Along with putting a price on carbon, a common theme that ran throughout Tuesday's summit was the need for the developed world to help developing nations—who did little to contribute to climate change—adapt to the challenges of global warming.
Dr. Kim announced that green bonds to support sustainable development have doubled since January, from $10 billion to $25 billion. French President Francois Hollande announced that France, one of the countries leading the climate talks, will contribute $1 billion over three years to a global climate fund aimed at helping developing nations adapt to climate risks. Britain's Prime Minister David Cameron announced that the United Kingdom will allocate another $4 billion to the fund over five years.
"We can't limit ourselves to words, expressions of regrets," Hollande said. "The contributions [to the climate fund] will have to be commensurate with the level of threat."
Cameron said it was "completely unrealistic" to expect the developing world to control its own emissions without substantial financial assistance for green growth.
Not only was it unrealistic, said Gaston Browne, prime minister of Antigua and Barbuda—"the demand is immoral."
"We are the victims of the profligacy of others," he said of the small island states.
Just as at Sunday's climate march, the crowd at the UN on Tuesday was dotted with celebrity faces. Actor Leonardo DiCaprio, a vocal proponent of climate action, told delegates they could "make history or be vilified by it."
And there are some grounds for optimism. "In effect, we are in the process of decarbonizing Europe's economy," observed the president of the European Commission, Jose Manuel Barroso.
But Obama acknowledged that the fossil fuel industries and their allies in governments around the world will fight passage of a strict new treaty.
"Let me be honest—none of this is without controversy," he said. "In each of our countries, there are interests that will be resistant to action. And in each country, there is a suspicion that if we act and other countries don't that we will be at an economic disadvantage."
When Canada and Australia, two nations represented by lower-level officials instead of their prime ministers, took the podium, both speakers studiously avoided their roles as major producers of fossil fuels. Instead, they spoke of their commitments to holding down emissions of greenhouse gases other than carbon dioxide.
Foreign Minister Julie Bishop of Australia, which just became the first industrial country to abolish a tax on carbon, emphasized Australia's support for regional attempts to reverse deforestation. Environment Minister Leona Agluqqak of Canada, which is missing its Copenhagen targets because of burgeoning production of tar sands crude, boasted of its reductions in per capita emissions. Australia called its approach "practical," and Canada used the word "pragmatic."
That some of the biggest players failed to make the kind of "bold" announcements UN Secretary General Ban Ki-moon had hoped for when he called the meeting could deflate the spirits of climate activists who just 48 hours before had thronged 50 blocks of midtown Manhattan in a historic outpouring of public support for fast action.
"If the President really wants collective ambition, he's got to show a little more can do spirit from the world's leading economy," said Bill McKibben, a founder of 350.org, in a statement. "Today's boasts about his climate efforts ring hollow in the face of America passing Saudi Arabia and Russia as the world' s largest oil and gas producer."
Not all environmentalists were such harsh judges, indicating that it's not just the nations, but the climate activists egging them on who are still trying to work out exactly where they stand on how best to move forward.
Jennifer Morgan of the World Resources Institute, which is closely engaged with the UN on the summit, said China's remarks in particular went further than ever before.
"The strong back-to-back statements by the two largest emitters send a clear signal that both countries will work seriously to put in place climate solutions domestically and reach an ambitious international agreement in Paris next year," she said.