13 December 2014 Last updated at 20:41 ET
By Matt McGrath Environment correspondent, BBC News, Lima
Exhausted delegates rest on beanbags during a break at the talks in Lima
The head of the US delegation at UN climate talks has warned of a “major breakdown” in the process if negotiators fail to come to an agreement at a meeting in Lima, Peru.
Talks remain deadlocked by divisions between rich and poor countries over the scale and scope of plans to tackle global warming.
The talks were due to have concluded on Friday but have now overrun.
Disagreements abound over a key building block of a new global treaty.
That element, known as Intended Nationally Determined Contributions (INDCs) in the jargon of the meeting, is seen as a major step as developed nations are due to make pledges on how they will tackle climate change by the end of March next year.
The countries came to Peru to work out the details of what those pledges would entail.
It has not been smooth sailing.
The big emitters like the US and EU want these pledges to be focused mainly on cutting carbon – and they want to include emerging economies such as India and China.
Protesters outside the talks have made clear their frustration
Developing countries object strongly to any attempts to bring them into the fold – and they argue that the pledges of the rich must include substantial finance for the poor.
According to US climate envoy Todd Stern, the deadlock on this and other issues threatens the chances of a new global deal next year.
“Failing to produce the decision before us will be seen as a major breakdown, and will deal a serious blow to the confidence of the parties and others as we approach Paris. And indeed to the hope of a Paris agreement,” he said.