The Copenhagen summit on climate change taught Europe a hard lesson about its trans-Atlantic partner. Great hope had greeted President Obama when he replaced George W. Bush at the American helm, but a year later Europeans are realizing that Mr. Obama is going to have a very difficult time delivering on his agenda.

During the Copenhagen summit, the American media portrayed President Obama as a global dealmaker, shuttling from leader to leader trying to broker various compromises. What Mr. Obama was really doing was a lot of fence-mending, because the United States was seen as the principal obstacle — and Mr. Obama as the footdragger-in-chief — that prevented any ambitious agreements from being signed.

Certainly the developing countries, led by China and India, were behaving stubbornly, but for good reason. The United States is by far the largest per-capita polluter in the world. Each American generates about 45,000 pounds of carbon dioxide a year, twice as much as the average European or Japanese, and 4 to 10 times more than someone living in China, India or any other developing country. China is close to the U.S. in terms of total carbon emissions — each emits about 25 percent of the world’s total — but it has four times more people.

The U.S. demanded that the developing world join in making drastic cuts, but the poorer countries cried foul. As one Indian official said, “First you do virtually nothing to cut your emissions, and then you threaten us [the developing world] with drowning from global warming sea level rise if we don’t cut ours. It won’t wash.”