Alternatively, it could accept a substantially slower pace of economic growth. But considering that the average Chinese earns about one-fifth as much as the average American, the government in Beijing is unlikely to follow this path.

Can the United States or anybody else do anything to speed China down a low-carbon path?

Heads of state from around the world will be gathering in September on the sidelines of the United Nations General Assembly to start a new international climate agreement, due to be signed at a summit meeting in Paris next year.

They come off a big defeat. In 2009, the Copenhagen conference on climate change broke down to a large extent because big developing countries like China refused to accept legally binding commitments on emission cuts, which might constrain their future development.

Today, the crucial question remains the same: how to meaningfully bring aboard countries like China or India. The debate appears stuck in more or less the same place, with countries arguing over who is responsible for what. How much of the burden should be shouldered by rich countries — which grew rich while spewing carbon into the air in past decades? How much by the fast-growing developing countries — where emissions are growing fastest? Who is to blame for the carbon emitted in making the latest gadget, the developing country that made it or the developed country that bought it?

The latest report from the United Nations Intergovernmental Panel on Climate Change, issued in April, suggested several ways to allot responsibilities. If one starts counting in the 18th century and counts only emissions from industry and energy generation, the United States is responsible for more than a quarter of all greenhouse gases that humanity has put into the air. China, by contrast, is responsible for 10 percent.