The united front that China and India claim to present on climate change puts the United States in a tough position — but could give President Obama the leverage that he needs to persuade Americans to save energy.

In a calculated move, China, which has just overtaken the US as the world’s largest emitter of greenhouse gases, stole the show at yesterday’s special United Nations summit on climate change with plans to pour billions of dollars into energy-saving technology and nuclear power.

China, which like the US produces about a fifth of global warming gases, made a strong bid to grab the moral high ground and the claim to world leadership — as well as much of the lucrative new market in green technology.

Indian ministers had already jumped the gun with talk of new curbs, although the gesture may be worth more in politics than in science, as analysts are sceptical of their commitment to force through mandatory efficiency standards on vehicles and buildings, renewable energy and stopping deforestation.

The pincer movement by the twin giants of the developing world puts pressure on the US to reverse years of political resistance and set targets for cutting its own emissions. The move by China and India “has a huge political benefit for Obama”, said Paul Bledsoe, of the National Commission on Energy Policy in Washington. “Domestically, one of the biggest obstacles to the President is that large developing countries would not commit” to targets for cutting emissions.

The 1997 Byrd-Hagel resolution (passed by 95-0 in the Senate) said that the US would not accept binding targets on emissions unless developing countries did so too,

and would not in any case if the curbs seriously damaged the economy. “That sentiment still exists in Congress, among Democrats and Republicans,” said Mr Bledsoe, although there have been signs of a shift in the past four years.

In blunt criticism of his predecessor George W. Bush, Mr Obama said: “It is true that mankind has been slow to recognise the threat. It is true of my own country as well. But this is a new era.”

The move by China and India could breathe more life into the struggling Copenhagen summit on climate change in December.

Speaking immediately after Mr Obama yesterday, President Nasheed of the Maldives gave a passionate, desperate speech, saying that if Copenhagen failed, the tiny islands “would no longer exist”.

China, India and other developing countries may account for two thirds of emissions of greenhouse gases within a decade. But they have resisted targets that could impede growth and poverty reduction, saying that the developed world should sort out the problem that it caused. Global recession has helped this year’s grandstanding, of course. US emissions are expected to fall by 6 per cent this year, after a 3.8 per cent fall in 2008, the US Department of Energy has reported.

Global carbon emissions are expected to fall by 2.6 per cent, the biggest drop for 40 years, said the International Energy Agency. The recession has made targets easier to reach and may give the Copenhagen meeting its best chance of recovery.

China — which has already committed a quarter of its $450 billion stimulus package to clean energy — has its eye on the vast emerging market for green technology and nuclear power. Mr Obama is warning Congress that the US will miss out if it holds back.

China’s command of the spotlight yesterday may give him the challenge that he has been seeking.

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