COPENHAGEN (AFP) - Marathon UN climate change talks open on Monday facing grim warnings that a hothouse planet looms if world leaders fail to hammer out an ambitious pact to tackle global warming.

As delegates gathered in the Danish capital, newspapers from 45 countries argued in an unprecedented joint appeal that leaders have two weeks to save the world from being ravaged by climate change.

The summit is aimed at forging a new pact to tackle greenhouse gas emissions after the Kyoto Protocol's requirements expire in 2012, and will be attended by US President Barack Obama among other world leaders.

Delegates have to craft a blueprint for tackling manmade "greenhouse" gases blamed for trapping solar heat and disrupting Earth's climate system.

They must also put together a funding mechanism for helping poor nations most exposed to the potential catastrophic effects of climate change, from drought to floods, vicious storms to rising seas.

Negotiators from 192 countries were to embark Monday on a gruelling round of talks under the aegis of the UN Framework Convention on Climate Change (UNFCCC) before around 100 leaders attend a summit on December 18.

"Negotiators now have the clearest signal ever from world leaders to craft solid proposals to implement rapid action," said Yvo de Boer, the UNFCCC's executive secretary.

"Never in 17 years of climate negotiations have so many different nations made so many firm pledges together.

"So whilst there will be more steps on the road to a safe climate future, Copenhagen is already a turning point in the international response to climate change."

Further negotiations are expected to take place in 2010 to fill in the details of whatever is agreed at Copenhagen. If all goes well, a legally binding treaty would take effect from the end of 2012.

Analysts, though, stress the deep gap between the demands of developing countries and the willingness of rich countries to dig both into their pockets and into their carbon emissions.