The UN climate chief warned that the success of this year’s global warming negotiations hinged on countries resolving deep differences over the future of the Kyoto Protocol.

Christiana Figueres said breakthroughs made at an annual UN summit in the Mexican resort of Cancun in December allowing other actions to combat climate change could be jeopardised by the stalemate over the protocol.

“The full implementation of the Cancun agreements can only become an important step forward for the climate if there’s a responsible and clear way ahead on the Kyoto Protocol,” Ms Figueres said.

Ms Figueres was speaking at the formal opening of the UN’s first round of climate negotiations for the year in Bangkok.

Signed in 1997, the Kyoto Protocol saw most developed nations agree to legally binding commitments on curbing their greenhouse gas emissions that are blamed for global warming.

Those commitments are due to expire at the end of 2012.

If there is to be a second round of legally binding commitments, those pledges would need to be made at the UN’s next annual climate summit in Durban, South Africa, in November.

But Japan and Russia have firmly opposed extending the protocol because it excludes the world’s two biggest polluters – China and the US – and therefore only covers about 30 per cent of global emissions.

Australia has also said it will only agree to a second round of commitments if all major emitters are part of the process.

Developing countries, including China, did not have to commit to cutting emissions as part of the Kyoto Protocol and most of them maintain this should remain the case.

The US refused to ratify the Kyoto Protocol.

Ms Figueres urged all parties to try and reach a consensus on the issue in time for the Durban summit.

“For Durban to be a success, the unanswered political questions need to be addressed. Most importantly the level of ambition and the legal nature of mitigation (emission reduction) commitments after 2012,” she said.