George Bush yesterday threw international efforts to control climate change into confusion with a proposal to create a "new global framework" to curb greenhouse gas emissions as an alternative to a planned UN process.

The proposal came less than a week before a G8 summit in Germany and appeared to hit European hopes that the world's industrialised nations would commit to halving their emissions by 2050.

A UN-brokered meeting in Bali in December, at which it had been hoped to agree to keep climate change to a 2C increase in temperature, is supposed to provide a successor to the Kyoto protocol. All that was thrown in doubt by the initiative announced yesterday by President Bush.

"By the end of next year, America and other nations will set a long-term global goal for reducing greenhouse gases. To help develop this goal, the United States would convene a series of meetings of nations that produced most greenhouse gas emissions, including nations with rapidly growing economies like India and China," Mr Bush said.

Under the Bush proposal, the 15 countries responsible for the overwhelming bulk of greenhouse gas emissions would meet in the autumn with the aim of striking a deal by the end of next year. But it was unclear how this new grouping would be able to agree on a scheme so rapidly, when there are such pronounced differences within the smaller G8, largely between the US and its partners.

British and German officials have stressed in recent weeks that a new climate agreement should be based on binding caps on carbon pollution for developed nations, similar to those set up under the UN's Kyoto protocol. President Bush has consistently opposed such restrictions, which he argues would damage the US economy. He prefers voluntary targets and his administration is keen to measure the carbon intensity of polluting activities - a measure of their efficiency - rather than tot up their overall emissions.

Yesterday's announcement contained only a reference to an unspecified long-term goal.

Tony Blair hailed the Bush initiative as an important step forward. "For the first time America's saying it wants to be part of a global deal," the prime minister told Sky News while on a tour of South Africa. "For the first time it's setting its own domestic targets. For the first time it's saying it wants a global target for the reduction of emissions, and therefore for the first time I think [there is] the opportunity for a proper global deal."

Angela Merkel, the German chancellor and host of next week's G8 summit, also welcomed the initiative. "I think it is positive, and the US president's speech makes it clear that no one can avoid the question of global warming any more," Ms Merkel said of the proposal. "This is common ground on which to act."

However, Bernd Pfaffenbach, the chief German negotiator or "sherpa" on climate change was blunter. He told the Suddeutschen Zeitung newspaper that excluding the UN or weakening its role was a "red line" that Ms Merkel "will never cross".

"The leading role of the UN on climate change is non-negotiable," he added. Another German official described the proposal as a "poison pill" aimed at undermining G8 and UN efforts to tackle global warming. "With one stroke you say goodbye to the UN," the official said. "This is a fundamentally different approach, and I'd be very surprised if the other G8 countries abandon the UN course."

Environmentalists were also furious. Daniel Mittler, an analyst at Greenpeace International, said: "It's not even too little too late, but a dangerous diversionary tactic. He doesn't need to start a new process. There already is one. This is meant to slow down the UN process."

The Bush administration moved to dispel the impression that it was an attempt to undermine Europe's position on climate change, or that it represented a transatlantic breach. Jim Connaughton, the former energy lobbyist who heads the Council on Environmental Quality at the White House and is lead negotiator on climate change, claimed that the process the president was advocating was not intended to undercut the influence of the Bali climate conference. "It will run in parallel and reinforce Bali," Mr Connaughton said.

However, he was critical of using emission caps or setting temperature control, the main instruments of Europe's approach, and repeated Washington's opposition to the European goal of limiting climate change to 2C. "We don't think that's a very practical approach," he said. "You can't manage the temperature."

Coming days after the Bush administration's opposition to the 2C goal became public, the new proposal has all but killed off hopes of an agreement on basic principles for combating climate change at the G8 meeting. German officials had hoped the gaps could be narrowed in a meeting between Ms Merkel and Mr Bush on Wednesday but in yesterday's speech the US president appeared to commit himself to an alternative course.

European hopes that the US establishment was now convinced that combating climate change was an urgent global task were also knocked yesterday when the chief of the US space agency said global warming was not an issue of pressing concern. "I have no doubt that a trend of global warming exists," Michael Griffin of Nasa told a radio station. "I am not sure that it is fair to say that it is a problem we must wrestle with."