She continued, “No agreement will move forward without their participation.”

There remain formidable impediments to reaching a deal in 2015 in Paris, where negotiators will try to fashion a new agreement to replace the moribund Kyoto Protocol. Among them, of course, are the very commitments that countries are willing to make to reduce their greenhouse gas emissions, when they fear that doing so could slow economic growth. Also at issue are questions of so-called climate justice, that is, who should pay for the climate-related damages and how much should be diverted from rich countries to poor ones to protect against the inevitable losses from rising seas and violent storms. These are the fraught subjects under discussion here this week among the 195 members of the United Nations climate treaty meeting to map a path to a new accord.

But it is the confluence of those two issues — emissions reductions and financing for climate adaptation — that has so far frustrated the United States and other developed nations in dealing with China.

Despite China’s being the world’s second-largest economy and the largest greenhouse gas polluter, it is treated under the rules of the United Nations Framework Convention on Climate Change as though it were the relatively poor developing country it was when the treaty was created. China has until now allied itself with the poorest African countries and most vulnerable island states in demanding a set of rules and obligations separate from those that apply to the United States, Japan, Australia, Canada and European nations.

The United States argues that those categories — annexes, in the treaty’s terms — are outmoded in a world in which developing nations will soon surpass the developed world in emissions, and China will soon be the largest emitter in cumulative historical terms.

“They do a lot,” Todd D. Stern, the United States climate envoy, said here this week, describing actions by China to slow its pollution. “I’m not criticizing China. The question is what they’re prepared to agree to.”