In an interview with AFP, Yvo de Boer, executive secretary of the UN Framework Convention on Climate Change (UNFCCC), said the global process hinged on a November 29-December 10 meeting in Cancun, Mexico.

After the disappointment of last December's Copenhagen Summit, it was vital for Cancun to yield a "functioning architecture" on big questions, including agreement on how to curb carbon emissions and provide aid for poor countries, said de Boer.

"We reached an agreement in Bali (in 2007) that we would conclude negotiations two years later in Copenhagen, and we didn't," de Boer said.

"The finishing line has now been moved to Cancun, and I wouldn't be surprised if the final finishing line in terms of a legally binding treaty ends up being moved to South Africa," at the end of 2011.

"Copenhagen was the last get-out-of-jail-free card and we cannot afford another failure in Cancun," de Boer said, referring to a card in the board game of Monopoly.

"I think if we see another failure in Cancun, that will cause a serious loss of confidence in the ability of this process to deliver."

Negotiators today headed into the final day of a three-day meeting in Bonn that aimed at picking up the pieces after Copenhagen.

Far from being the glittering triumph envisaged in Bali, Indonesia in 2007, the summit ended rancorously and with a deal lashed by many as lamentably threadbare.

The main achievement was the "Copenhagen Accord," brokered by a couple of dozen countries, which set the goal of limiting warming to two degrees Celsius, earmarked some USD 30 billion in short-term aid and sketched a target of mustering USD 100 billion annually by 2020.

But the agreement, crafted late at night in order to stave off a fiasco, failed to gain the endorsement of a 194-nation plenary.

Some of the fault lines in Copenhagen opened up again in Bonn, notably over how far -- or even whether -- to incorporate the controversial accord in a blueprint for negotiation.