Less than six months after the world agreed to craft a new climate pact by 2015, negotiations stumbled at a crucial preparatory phase on Friday as rich and poor countries butted heads.
The concluding session of an already troubled 11-day haggle in Bonn ran into delays as countries clashed over who will chair the long negotiations, which aim at a post-2020 deal to roll back greenhouse-gas emissions.
"The window of opportunity is very slowly closing down on us," conference chairwoman Sandea de Wet warned delegates at what was supposed to be a final meeting but was postponed for several hours.
The world is divided between developed and developing nations on apportioning responsibility for curbing global warming.
Fast-growing countries like China insist the West, which has been polluting more for longer, should shoulder more of the mitigation burden.
The latest dispute concerns the leadership of a group known by its initials ADP -- for ad-hoc talks on the so-called Durban Platform.
The ADP will lead the process agreed in South Africa last December to draft a new pact binding all nations, not just rich countries as is the case now.
China and its allies want India to chair the ADP, on the grounds that it is the Asia-Pacific bloc's turn to steer a subsidiary body under the UN Framework Convention for Climate Change (UNFCCC).
The other candidates are Norway and the Caribbean state of Trinidad and Tobago.
"This is a sad state of affairs," South African climate ambassador Nozipho Joyce Mxakato-Diseko told delegates as she announced that for the first time since the UNFCCC was created 20 years ago, a lack of consensus may force an election to be held.
"All parties have confirmed to me they do not want to go this way, it is not in the culture of this structure, consensus is the norm," she said.
An EU delegate informed the gathering that informal corridor talks had flagged a possible settlement, and asked for more time to explore the options.
On Wednesday, Europe warned the process was in danger of floundering, and participants accused China of blocking the ADP negotiating process.
The Asian giant responded Thursday that it was the United States, Europe and other rich states that were applying the brakes, trying to "evade legally binding commitments" by shifting the focus away from already existing emission targets to as yet undefined commitments under the Durban Platform.
Explore further: Block cropping pitted against integration method