In recent papers and now in an interview with Reuters, Hu said global climate talks culminating in Copenhagen late next year could be a final opportunity for the planet to avoid calamitous damage from more extreme storms, droughts and floods.

"I think the Copenhagen summit is a last chance not only for China but also for the world," Hu said of the talks aiming to settle on a successor to the Kyoto Protocol climate change treaty from 2013.

China should act even if rich nations drag their feet, because its geography leaves it especially vulnerable to drought, rising seas and other ravages of a changing climate, he said.

"Don't think that if China does not participate and assume obligations then it can avoid disaster," he said during Reuters Global Environment Summit.

Hu, 55, has long helped shape Chinese development policy, submitting advice to top leaders from his book-lined office in the capital's university district.

But his advocacy of steep, mandatory cuts to its emissions by as soon as 2010 puts him at odds with his government's insistence that poorer countries should not take on such caps any time soon.

China has insisted that, as a developing country with relatively low average greenhouse gas output per person, it must grow first and not accept any caps until it becomes wealthier.

China's emissions of carbon dioxide, the main greenhouse gas pollutant from burning fossil fuels, was an average 4.1 tonnes per person in 2005, according to the International Energy Agency. The United States' per-capita average was 20.1 tonnes.

Beijing also points out that rich countries, during their industrial growth, created most of the accumulated greenhouse gas pollution now threatening to dangerously disrupt the climate.

Under the Kyoto Protocol, only 37 developed nations have obligations to curb emissions until 2012, when the pact's first phase expires.

But many rich nations are failing to meet their reduction targets, and the United States refused to ratify the Protocol, arguing it was unfair to leave China and other big polluters untethered.

"NOT A DEVELOPING COUNTRY IN THE USUAL SENSE"

In a torrent of Chinese and English, Hu laid out his argument for a radically different strategy for Beijing.

China is fast emerging from the ranks of other Third World countries, and the sheer size of its emissions places special obligations on it, he said. Many experts believe China's carbon dioxide emissions already rival the United States'.

"China is not a developing country in the usual sense. It's a constantly advancing country," he said.

"When China becomes the top polluter, it must also shoulder its responsibility to reduce emissions....China must assume its due obligations, even though the current leaders haven't grasped this."

Hu's proposed scheme for determining emission reduction burdens places countries in four tiers using the UN Development Programme's human development index.

China, he said, was climbing from the second tier into the first. And as it and other countries rise up the ladder, they should come under tightening obligations to cut greenhouse gas pollution, he said.

"If China does not actively cooperate ..., not only China but also globally we will suffer from this disaster," he said. "Now it's already too late, but any later and there's nothing we can do."

Hu also said his country, often regarded with suspicion by the West, could win international acclaim and a technological and economic headstart by transforming itself into a "green" power.

But the chances of such a sea change happening before Copenhagen were slim, Hu said.

"Copenhagen is more likely to fail than succeed," he said. "We just want to use the Copenhagen green summit to make Chinese people and leaders understand that China has a responsibility to the world." (For summit blog: http://summitnotebook.reuters.com/) (Additional reporting by Emma Graham-Harrison; Editing by David Fogarty)