America has challenged China's view of how to split the burden of curbing carbon emissions, saying the rich-poor divide of previous climate agreements will not work in a future pact.
The US envoy to international climate talks in Qatar, Todd Stern, said that the next climate deal must be based on "real-world" considerations, not "an ideology that says we're going to draw a line down the middle of the world."
Beijing wants to maintain a division between developed and developing nations, setting out softer emissions-cutting requirements for poorer countries. It notes that despite its roaring growth, millions of Chinese still live in poverty, and emission limits would slow the economic expansion that would improve their lot.
The climate pact is one of the key issues under discussion at the United Nations-led talks, which have entered their second week. Last year, governments agreed it should be adopted by 2015 and take effect five years later. The US did not join the only binding emissions agreement to date, the 1997 Kyoto Protocol, because it only covered industrialised nations and not major developing countries like India and China, which is now the world's biggest carbon emitter.
"It's going to be an enormously challenging, and I think enormously important, task to get this agreement right," Mr Stern said.
The dispute will not be resolved in Doha, where negotiators are focusing on side issues including aid to help poor countries shift to renewable energy and protect themselves from rising sea levels and other effects of global warming.
They also plan to extend the Kyoto agreement, which expires this year, until a new treaty is in place. But several nations including Japan and New Zealand do not want to be part of the extension, meaning it will only cover European countries and Australia, which account for less than 15% of global emissions.
Even that has been complicated by disputes over whether emissions allowances granted to Poland and other eastern European countries to offset the early economic fallout after the collapse of communism should carry over into the second phase.
Mr Stern said that president Barack Obama has pushed for reducing fossil fuel subsidies domestically and internationally. "It's difficult in other countries and it's difficult at home to carry it forward because there are a lot of entrenched interests," he said.
While he highlighted US initiatives undertaken during Mr Obama's first term - such as sharply increasing fuel efficiency standards for cars and trucks and investing in green energy - Mr Stern said that more ambitious climate legislation had stalled in Congress and that shifts in the US climate position should not be expected following Mr Obama's re-election.