Anyone in doubt about the pivotal position played by China and India at this month's global climate change talks in Bali should glance through the latest forecasts from the International Energy Agency.

Assuming government policies remain unchanged, Chinese and Indian economic development would be the key drivers in sending annual global energy-related emissions of carbon dioxide - the main greenhouse gas - from 27bn tonnes in 2005 to 42bn by 2030, the IEA said last month.

"China is expected to overtake the US to become the world's biggest emitter in 2007, while India becomes the third biggest emitter by around 2015," the agency said in its World Energy Outlook report.

But while it is clear why China and India are firmly in the Bali spotlight, what role they should play there remains the focus of fierce debate.

Beijing and New Delhi bristle at calls from the developed world that they should accept caps on future greenhouse gas emissions as part of a global deal to replace the Kyoto protocol after it expires in 2012.

Even aUnited Nations Human Development report that suggested developing countries cut emissions by 20 per cent by 2050, while rich nations slash theirs by four-fifths, was enough to infuriate Montek Singh Ahluwalia, the head of India's planning commission.

"Its recommendations look egalitarian but they are not," complains Mr Ahluwalia, arguing that such a target would leave India's per capita emissions capped at less than a third of the average level permitted to the US and EU.

"It cannot be fair that you are projecting a reduction that leaves us on a per capita basis much below the rest of the world," he says.

Mr Ahluwalia's objections go to the heart of the issue: that while the world's two most populous nations are the most important sources of new emissions growth, their citizens individually share little of the blame for global warming.

Not only are Chinese and Indian per capita emissions still small but their past contribution to the crucial "stock" of carbon dioxide in the atmosphere is lower than that of most developed countries.

"These nations accounted for 95 per cent of carbon dioxide emissions worldwide resulting from the use of fossil fuels from the start of the Industrial Revolution in the 18th century to 1950, and for 77 per cent in the 1950-2000 period," China's state Xinhua news agency said of the developed countries in a commentary on Tuesday.

Both Beijing and New Delhi fear that binding emission caps that limit energy use could threaten future economic development - and condemn many of their people to perpetual poverty.

But such a position, however principled, risks making China and India the rock on which dreams of post-Kyoto climate co-operation are broken.

The US and Australia have long used China and, to some extent, India to justify their own refusal to curb emissions.

More willing warriors against climate change fear any global pact will be meaningless if it does not include caps for the two Asian goliaths.

Beijing is seeking to ease such concerns by stressing the action it is already taking to soften its carbon impact. Wen Jiabao, the premier, has made one of the government's top goals reducing China's energy intensity - the amount of energy required to produce each unit of gross domestic product - by 20 per cent between 2006 and 2010.

Some observers say Beijing might be willing to agree to other policy targets instead of binding emission caps, a compromise that might pave the way for a post-Kyoto consensus.

But China is so far failing to hit its energy intensity target and the pressure for caps is sure to grow.

Exempting China and India from binding caps would also be the equivalent of an emissions-free pass for their economic elites, whose luxurious cars, air-conditioned villas and frequent-flyer miles affect global warming as much as those of rich-nation citizens.

Greenpeace, the environmental group, has accused India of "hiding behind its poor", saying the unsustainable carbon footprint of its 150m-strong middle and upper classes is disguised by the tiny emissions produced by their 823m low-income compatriots.

Still, both Beijing and New Delhi are sure to oppose any suggestion that emissions targets be imposed on a sub-national level. Indeed, Chinese officials appear to rule out any acceptance of binding curbs.

India, however, has offered to cap its per capita emissions - currently around 1 tonne of carbon dioxide equivalent a year - below those of the developed world average.

"We have promised our emissions will not move beyond yours," says one Indian negotiator. "Please rise to the challenge. Climate change negotiations cannot be a means of enshrining an economic status quo."