Andrew C. Revkin & John M. Broder

Copenhagen. After two weeks of delays, theatrics and frantic deal-making, the UN climate-change talks concluded here this past weekend with a grudging agreement by the participants to “take note’’ of a pact shaped by five major nations.

The final accord, a 12-paragraph document, was a statement of intention, not a binding pledge to begin taking action on global warming — a compromise seen to represent a flawed but essential step forward.

But many delegates of the 193 countries that had gathered here left Copenhagen in a sour mood, disappointed that the pact lacked so many elements they considered crucial, including firm targets for mid- or long-term reductions of greenhouse gas emissions and a deadline for concluding a binding treaty next year.

Even President Barack Obama, a principal force behind the final deal, said the accord would take only a modest step toward healing the Earth’s fragile atmosphere.

Participants from a variety of countries also said the chaos and contentiousness of the talks could signal the end of what, for almost two decades, had been viewed as the best approach to tackling the threat of a warming planet: the UN Framework Convention on Climate Change and a series of 15 conventions following a 1992 climate summit meeting in Rio de Janeiro.

The process has become unworkable, many said, because it has proved virtually impossible to forge consensus among the disparate blocs of countries fighting over environmental guilt, future costs and who should referee the results.

“The climate treaty process isn’t going to die, but the real work of coordinating international efforts to reduce emissions will primarily occur elsewhere,’’ said Michael Levi, who has been tracking the diplomatic effort for the Council on Foreign Relations.

That elsewhere will likely be a much smaller group of nations, roughly 30 countries responsible for 90 percent of global warming emissions.

It was these nations that Obama rallied in a series of dramatic encounters on Friday to finally sign a deal that starts a flow of financing for poor countries to adapt to climate change and sets up a system for major economies to monitor and report their greenhouse gas emissions.

This smaller group of nations will meet periodically to tackle a narrower agenda of issues, like technology sharing or the merging of carbon trading markets, without the chaos and posturing of the UN process.

A version of this already exists in the 17-nation Major Economies Forum that has been a model of decorum and progress compared with what the world saw unfold at the climate talks.

With the deal worked out on Friday, a political agreement has been reached among major emitters to curb greenhouse gases, to help developing nations develop clean-energy economies and to cushion the effects of climate change on vulnerable states.

Other countries signaled on Saturday that they would back the accord.

But even if countries live up to their commitments on gas emissions, a stark gap remains — measured in tens of billions of tons of projected flows of carbon dioxide — between the nations’ combined pledges and what would be required to reliably avert the risks of disruptive changes in rainfall and drought, ecosystems and polar ice cover from global warming, scientists say.

The chances of success substantially hinge on whether Obama can fulfill his promises to reduce American greenhouse gas emissions and raise tens of billions of dollars to help other countries deal with global warming.

That in turn depends on whether Congress takes action on a bill that puts a price on carbon and devotes a substantial part of the proceeds to foreign aid.

And that is no sure thing.

Yvo de Boer, the UN official who manages the climate negotiations, said that though the Copenhagen accord was “politically incredibly significant,” it hardly moved the treaty process from where it was in 2007, when the world’s countries pledged to complete a binding agreement here this year.

“We have a lot of work to do on the road to Mexico,” he said, in a reference to the next climate meeting to be held in Mexico City next year.

Even reaching the tenuous accord in Copenhagen was a tortuous path, culminating in an impassioned debate on the floor of the plenary meeting that lasted into the wee hours of Saturday morning.

Speaker after speaker from the developing world denounced the deal as a sham process fashioned behind closed doors by a club of rich countries and large emerging powers.

The debate reached such a pitch that the Sudanese delegate likened the effect of the accord on poor nations to the Holocaust.

That set off a backlash, and many of the smallest and most vulnerable nations, while continuing to express reservations, began falling in line behind the deal.

Ultimately, all but a handful of countries — Venezuela, Cuba, Sudan and Saudi Arabia among them — went along with the decision to accept the document.

Before the parties gathered in Copenhagen, the United States and China had been sniping at each other over various aspects of the proposed agreement, particularly over American demands that Beijing agree to a system of international monitoring, through which its public promise to reduce the carbon intensity of its economy — the rate of emissions per unit of economic activity — could be verified.

But as that friction was growing, there was also significant progress on sharing clean energy technology and even exchanges between American and Chinese environmental officials over ways to accurately measure greenhouse gas emissions.

Obama and Premier Wen Jiabao of China conducted a productive summit meeting in Beijing last month.

On Nov. 26, the Chinese government announced its pollution reduction target and said it would enforce it with domestic law.

US officials privately said the target was too low and raised questions about the reliability of Beijing’s reporting methods, saying that some form of international monitoring would be needed.

China protested and declared that it would not sacrifice its sovereignty to an outside verification scheme.

The friction boiled over on Friday, as Obama arrived at the Copenhagen meeting.

Twice during the day, Wen sent an underling to represent him at the meetings with Obama.

To make things worse, each time it was a lower-level official.

It was bad enough, officials said, describing the atmosphere later, that Vice Foreign Minister He Yafei was sitting at the table with Obama, Chancellor Angela Merkel of Germany and other world leaders.

But Friday afternoon, after what administration officials believed had been a constructive one-on-one meeting between Obama and Wen, the Chinese premier sent his special representative on climate change negotiations, Yu Qingtai, to a meeting of the leaders of major countries, including Obama.

An annoyed White House made a point of noting the snub in a statement to reporters.

Obama, for his part, said to his staff members: “I don’t want to mess around with this anymore.

I want to talk to Wen,” according to an aide.

The White House set up an evening meeting between Obama and Wen.

It also set up a separate meeting with Jacob Zuma, the president of South Africa, President Luiz Inacio Lula da Silva of Brazil and Manmohan Singh, the Indian prime minister, nations whose approval was needed to seal any climate deal.

Shortly before the appointed time of the meeting with Wen, Denis McDonough, the National Security Council chief of staff, and Robert Gibbs, the White House press secretary, arrived and were startled to find the Chinese prime minister already meeting with the leaders of the three other countries.

They alerted Obama, and he rushed down to the site of the meeting.

“Mr. Premier, are you ready to see me?” Obama called from the doorway.

“Are you ready?” Despite its tense start, the meeting led to an accord that settled a number of issues, including a compromise on wording on the issue of monitoring and verification that satisfied Wen.

The New York Times