Ed Miliband, the British Energy Secretary, has praised the Obama Administration for transforming America’s position on climate change but questioned its ability to overcome powerful opponents.

After three days of talks on global warming in Washington Mr Miliband said: “There is no question about the change of direction and the change in terms of political will. The question is how far can they go — and how quickly?”

The conference was intended to start talks before a meeting in Copenhagen in December at which the international community will discuss a successor to the Kyoto Protocol, which expires in 2012. China and India are unwilling to impose carbon use restrictions unless the developed world, and the US in particular, does more.

Mr Obama pledged to bring US emissions down to 1990 levels by 2020 — a cut of roughly 15 per cent. He said: “Our future on this planet depends on our willingness to address the challenge posed by carbon pollution.”

This is short of the 20 per cent reduction below 1990 levels that the European Union has identified as its minimum target for the next decade.

Congress is considering a Bill that would go further, reducing domestic emissions by perhaps 6 per cent below their 1990 levels through the introduction of a cap-and-trade system.

This is opposed by Senators from rust-belt and coal-mining states and is unlikely to be approved either in its present form or before the Copenhagen conference. Even John Dingell, the Democratic Congressman who was recently ousted from the energy committee chairmanship, has taken to describing the cap-and-trade legislation as “a great big” tax.

Mr Miliband pointed out that six months ago most people expected climate change to drop off the US agenda because of the economy. Instead, he said, “the Administration has decided to make this a political priority”.

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