PORT-OF-SPAIN - Global climate talks to be held in Copenhagen got a big boost at the weekend when leaders representing a third of the planet's population put their full weight behind sealing a deal.

The heads of government of the 53-nation Commonwealth announced on Saturday that a legally binding climate accord was "essential" and they backed the December 7 to 18 Copenhagen talks to draft a successor treaty to the Kyoto Protocol.

The Commonwealth Climate Change Declaration, issued midway through a three-day summit in Trinidad, also hailed moves promoted by Britain and France to establish a $10billion (R74billion) fund to help offset the cost to poor countries that cut carbon output.

The offer, combined with greenhouse gas emission cuts announced by most of the world's biggest polluting nations, prompted leaders to swap scepticism for optimism.

"I remain fully convinced that it will be possible to reach an agreement in Copenhagen," Danish prime minister Lars Loekke Rasmussen, who will host the talks, said from Trinidad.

UN secretary general Ban Ki-moon said there was momentum for a deal. But he cautioned that it was not yet certain that a treaty would emerge for signing in 2010.

"We are united in purpose, we are not yet united in action," he said, urging world leaders "to stay focused, committed and come to Copenhagen".

So far, 90 leaders have confirmed they will attend the talks in the Danish capital, including US president Barack Obama.

"The Commonwealth, representing one third of the world's population, believe the time for action on climate change has come," Australian prime minister Kevin Rudd said as he unveiled the Commonwealth agreement.

"We believe political goodwill and resolve exist to secure a comprehensive agreement at Copenhagen," he said.

China, the US, the European Union and Brazil have announced greenhouse gas emission reduction targets to contain the level of global warming.

India remains the only big polluter still to declare its target - Sapa-AFP