UN climate talks are on the brink of unravelling and will collapse within months unless the EU shows global leadership by committing to a second phase of the only legally binding international treaty for cutting carbon emissions, a leading thinktank warned on Thursday.

It came as new analysis from the Stockholm Environment Institute (SEI) showed that developing countries have now pledged to cut more emissions than rich countries and have met all the conditions they signed up to at the Copenhagen and Cancún summits.

"There is still hope [for the talks] if enough developed countries decide they will stay with the Kyoto protocol, starting in 2013," said Martin Khor, the executive director of the Geneva-based South Centre, an intergovernmental thinktank that advises developing countries.

So far, only Norway and Sweden have said they will definitely sign up to a second round of Kyoto, while New Zealand and Australia have indicated they are prepared to sign up. Russia, Canada and Japan have said they will not, and the EU has said it will commit if major economies, such as China, India and the US, take the actions needed to meet targets.

"This is the crunch time. If the EU says, yes, the conditions are fulfilled, then there is some hope. Then Japan, Russia and Canada could be attracted back. But if the EU says no, then the whole thing unravels and the international climate system collapses. It is unthinkable," said Khor.

Khor suggested that the developing countries would see no point in continuing to negotiate without a second Kyoto period. The convention, agreed by all countries in 1997, is the only global agreement that binds rich countries to making emission cuts and is considered politically inviolable by developing countries.

Confirmation that developing countries have met their conditions came today from Sivan Kartha, lead scientist at the SEI.

"The pledges to cut emissions made by developing countries are credible and are more than what major developed countries are doing collectively or individually," he said.