The United States had threatened before the meeting to reject large parts of the German proposal, which reaffirmed the role of the United Nations as the primary forum for negotiating climate agreements.
Now, though, the Bush administration has agreed for the first time to take part in negotiations to develop a new global agreement on climate policy by 2009. Such a pact could form the basis of a successor to the Kyoto Protocol, which has limits on gases that expire in 2012 and was never ratified by the United States.
“One of the features I think we all agreed to is, there needs to be a long-term global goal to substantially reduce emissions,” Stephen J. Hadley, the White House national security adviser, told reporters. “There are obviously a number of ideas as to how that should be done.”
Prime Minister Tony Blair of Britain, who has long prodded Mr. Bush to embrace a stricter climate policy, said the agreement represented “a very substantial coming together” of the world’s leaders. His comments came after he met one-on-one with Mr. Bush for the last time as prime minister.
Environmental groups were more mixed in their reaction, with several noting that the agreement did not alter the Bush administration’s refusal to accept binding targets for emissions reductions.
“He has only agreed to consider the goal,” said Philip E. Clapp, president of the National Environmental Trust, an advocacy group. “This is the kind of language that emerges from a discussion in which people say, ‘We have to have something to take back to our publics.’ ”
Other advocates, though, said it was significant that the Bush administration had agreed to help negotiate a new climate agreement by 2009, within the framework of the United Nations.
As recently as mid-May, climate negotiators for the United States were casting doubt on the need for any fresh treaty commitments.
Mr. Bush’s proposal last week to convene a conference of the largest emitters this fall stoked suspicions among some Europeans that he would pursue climate change on a parallel track with the United Nations.
Fred Krupp, the president of Environmental Defense, a New York-based group, said the spotlight would now shift to Congress, which is drafting legislation that may cap emissions in the United States.
For Europeans, the prospect of a successor to Kyoto is important because it gives the prospect of stability to the market in trading carbon-dioxide credits, which was instituted by Europe as a way to meet its emissions caps under the Kyoto accord.
“The United States is now on a bandwagon they cannot stop,” said Hans Joachim Schellnhuber, Mrs. Merkel’s chief adviser on climate policy. “That is more than I expected. In a way, climate common sense prevailed at the last minute.”
The 11th-hour deal came after weeks of intense diplomacy by Mrs. Merkel — first to marshal support for her plan from other Group of 8 leaders, then to persuade Mr. Bush to edge toward her position.
“Merkel was focused, stubborn, and determined to reach a deal,” said a senior German official who spoke on condition of anonymity, a standard practice in the German government.
The chancellor had the support of Mr. Blair, as well as José Manuel Barroso, the president of the European Commission, with whom she brokered a separate deal to sharply reduce greenhouse gas emissions in Europe. Nicolas Sarkozy, the new French president, also voiced his support.
Then last week, Germany received a crucial endorsement of its plan from Japan’s prime minister, Shinzo Abe, who is scheduled to take over the rotating presidency of the Group of 8 next January.
But the German official said, “It was about winning over Bush to get on board and support the U.N. process on climate change.” Mrs. Merkel telephoned Mr. Bush in recent weeks, and met him for lunch on Wednesday, before the other leaders arrived in Heiligendamm.
Another important step comes Friday, when the Group of 8 confers with officials of five developing countries. If ways cannot be found to foster emissions cuts in fast-growing countries like China and India, any progress in industrialized counties is likely to be swamped by rapidly increasing pollution, particularly in Asia.
Mrs. Merkel, a physicist and former environment minister, staked a lot of prestige on a deal. While playing down hopes of a breakthrough, she instructed her chief negotiator, Bernd Pfaffenbach, to keep pushing for a compromise. Negotiators worked on the text all night Wednesday.
At noon, just before Mrs. Merkel and the other leaders prepared for a forum with young people, she waved a draft of the communiqué before the group. “Any objections?” she asked. There were none.US
A spokesman for Greenpeace, Daniel Mittler, subsequently dismissed the climate agreement, saying the leaders had failed to “live up to their historic responsibility for causing climate change.