New tensions and alignments are emerging at the UN talks here, reflecting subtle but far-reaching changes in the geopolitics of climate change.

Delegates and veteran observers say the shifts challenge the very heart of the nearly two-decade-old climate process, which until now has neatly divided the world into two blocs -- the north and the south, the rich and the poor.

But whether these changes will drive the negotiations towards a potentially catastrophic failure by next Friday's close or whether they will break the deadlock remains unclear, say these sources.

"I've been to 16 of the 17 (annual) meetings since the process started, and this is one of the most unpredictable that has ever been," said Alden Meyer, a policy analyst at the Washington-based Union of Concerned Scientists.

"Everything is fluid, everything is still in play," agreed WWF International's Tasneem Essop, another climate negotiations veteran.

The bedrock for the 194-nation talks is the UN Framework Convention on Climate Change (UNFCCC).

But since that agreement was adopted in 1992 the world has changed dramatically, and some of those changes clash head-on with the document's defining architecture.

Under the terms of the UNFCCC, developed countries acknowledge historical responsibility for global warming and pledge to shoulder most of the burden for fixing it and to help developing countries cope with its impacts.

The convention's landmark achievement, the Kyoto Protocol, adopted in 1997, locked industrialised nations into carbon-cutting commitments that expire next year. The rest of the world pledged to tackle climate change on a voluntary basis.

More than a decade later, however, this vision of the world is, for many, woefully out of date.

"We are not prepared to go forward on the basis of the old-style agreement, which essentially had a firewall between all developed countries and all developing countries," Todd Stern, chief climate negotiator for the United States, said Tuesday in a radio interview.

"China, at this point, is the largest emitter in the world."

When the UNFCCC was crafted, developed countries accounted for two-thirds of greenhouse-gas emissions.

Today, that proportion is fast being reversed.

Developing nations -- led by China, India and Brazil -- emit half, and by 2030 the figure will be 65 percent, according to several estimates.

Indeed, several countries that are still categorised as "developing" economies are now richer per-capita than "developed" nations in eastern and central Europe.

China acknowledges its new status as the world's top carbon polluter, but insists that the current rules should continue to apply, at least until 2020.

But the growing emissions and prosperity of the so-called BASIC nations -- Brazil, South Africa, India and China -- have caused cracks to appear within a once-solid bloc of 132 nations known as the Group of 77 and China.

Poorer countries already struggling to cope with intense droughts, floods and rising seas have gingerly begun to appeal to their developing big brothers to beef up their commitment on climate.

Their concern fanned into alarm when in the opening days of the 12-day parlay in Durban, emerging giants clearly preferred to put off any new pledges on emissions for at least a decade.

"This is extremely worrying for us," said a lead negotiator from one of these most vulnerable nations.

"The science is clear -- if there is no action for another decade, then it means that many of the vulnerable developing countries are doomed."

There has long been simmering tension within the G77 bloc on this issue, he continued, but now it is bubbling to the surface.

At the Durban talks, the European Union (EU) is trying to convince both the United States and BASIC nations to sign on to a "roadmap" leading to a global climate pact in 2015.

So far, the EU proposal has been rejected by both.

For Brice Lalonde, a former French environment minister and co-chair of next year's Rio +20 summit, emerging giants are still on a learning curve.

"They are used to being the spokesman of the poor of the planet. They have not yet had time to make the transition to co-managing the planet," he said before the conference.