The country’s economic growth – currently at over 10% annually and powered predominantly by coal – is behind the shift, which comes several years earlier than previously predicted.

In 2004 the IEA forecast that China would overtake the US as the world’s biggest polluter, but that the shift would not occur before 2025, while more recently it estimated that China would surpass US levels by 2010.

The IEA now estimates that China, thought to have emitted about 5,600 million tonnes of CO2 last year compared to US levels of 5,900, will in 2007 emit around 6,020 million tonnes compared to around 5,910 from the US.

Many politicians and environmentalists have argued that China’s future emissions (as well as the output from other countries in the so-called developing world) are the key to preventing global warming.

Faith Birol, the IEA’s chief economist, argued yesterday that this growth will eclipse the efforts of the developed world. “There is an order of magnitude of difference,” he said. “If we can’t influence China and India in their coming energy business decisions, we will be locked in, and we will have to live with the consequences for half a century or more.”

But China and other developing nations are opposed to enforced CO2 cuts because of the impact such restrictions will have on economic growth – restrictions, they point out, which were not imposed on developing western nations over the last two centuries.

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