WARSAW, POLAND — Rich and poor nations are struggling with a yawning rift at the U.N. climate talks as developing countries look for new ways to make developed countries accept responsibility for global warming — and pay for it.

With two days left, there was commotion in the Warsaw talks Wednesday after negotiators for developing nations said they walked out of a late-night meeting on compensation for the impact of global warming.

“We do not see a clear commitment of developed parties to reach an agreement,” said Rene Orellana, head of Bolivia’s delegation.

U.S. climate envoy Todd Stern downplayed the dispute, saying American negotiators who had attended the meeting were surprised to hear of a walkout. “The meeting ended with everyone leaving,” Stern told reporters.

Contrasting views on what’s been said and done in closed discussions is not unusual in the slow-moving U.N. effort to curb global warming, which has often been held back by mistrust between rich and poor countries. The talks in Warsaw on a new global climate deal in 2015 have been going on since Nov. 11.

The question of who’s to blame for warming is central for developing countries, who say they should receive financial support from rich nations to make their economies greener, adapt to climate shifts and cover the costs of unavoidable damage caused by warming temperatures.

Also, they say the fact that rich nations, historically speaking, have released the biggest amounts of heat-trapping CO2 by burning fossil fuels for more than 200 years means they need to take the lead in reducing emissions. In Warsaw, developing nations are coming up with fresh ways to make their point. Brazil has proposed creating a formula to calculate historical blame.

“They must know how much they are actually responsible ... for the essential problem of climate change,” Brazilian negotiator Raphael Azeredo said.

Developed nations blocked that proposal, however, saying the world should look at current and future emissions when dividing up the responsibility for global warming. China, considered a developing nation at these talks, overtook the U.S. to become the world’s biggest carbon polluter in the last decade, and developing countries as a whole now have higher emissions than the developed world.

To focus only on past emissions “seems to us as very partial and not very accurate,” Stern, the U.S. envoy, said.

The U.S. wants to get rid of the U.N.’s current division between developed and developing nations. Stern noted that a 2007 study showed that by 2020, the all-time emissions of developing countries will exceed those of the developed world, due to emissions growth in large emerging economies like China and India. Those countries are trying to develop in a cleaner way but say it’s unfair to expect them to abstain from the dirty fuels that built Western economies into powerhouses with high living standards.