That kind of brinksmanship is typical of the so far unsuccessful diplomatic effort to reduce the heat-trapping carbon emissions that scientists say are warming the planet.
In Warsaw, negotiators were supposed to lay the foundation for a 2015 climate deal in Paris that countries have agreed should apply to them all. But negotiators struggled to agree on texts on emissions targets and climate aid for developing countries as talks continued past their scheduled end Friday.
After all-night wrangling, Chinese negotiator Su Wei requested a reference to an article in the 1992 U.N. convention on climate change that says only developed countries are required to rein in their emissions.
That surprised U.S. climate envoy Todd Stern, who wondered whether that meant that China was no longer ready to put forth commitments for the new deal.
"I hope I'm wrong about what I heard, but it would certainly be disappointing to move backward in time, not forward toward Paris," Stern said.
Countries agreed on the compromise wording, allowing the conference to continue with a final session Saturday.
The U.N. climate talks were launched two decades ago after scientists warned that humans were warming the planet by pumping CO2 and other heat-trapping gases into the atmosphere, primarily through the burning of fossil fuels.
Countries made progress Friday on advancing a program to reduce deforestation in developing countries, an important source of emissions because trees absorb carbon dioxide.
Climate financing proved harder to agree on. Rich countries have promised to help developing nations make their economies greener and to adapt to rising sea levels, desertification and other climate impacts.
They have provided billions of dollars in climate financing in recent years, but have resisted calls to put down firm commitments on how they're going to fulfill a pledge to scale up annual contributions to $100 billion by 2020.
"There is absolutely nothing to write home about at the moment," Fiji delegate Sai Navoti said, speaking on behalf of developing countries.
Pointing to the devastating impact of Typhoon Haiyan in the Philippines, island nations also demanded a new "loss and damage mechanism" to help them deal with weather disasters made worse by climate change. Rich countries were seeking a compromise that would not make them liable for damage caused by extreme weather events.