英语阅读：Heat Is on These Countries for the Heat大纲

Atmospheric carbon dioxide levels have now touched 400 parts per million—and keep rising. So who's responsible?

Scientists peg the start of this seemingly inexorable rise to about 1750, when people started burning coal to run steam engines. But the CO2 increase also stems from activities like clearing forestlands for farming.

Now a new analysis assigns national blame for CO2 pollution and its ensuing global warming.

The seven biggest contributors—both historically and today—are, in alphabetical order: Brazil, China, Germany, India, Russia, the United Kingdom and the United report is in the journal Environmental Research Letters. [H. Damon Matthews et al., National contributions to observed global warming.

The undisputed champion of greenhouse gas pollution is no surprise: the U.S. Our emissions to date mean we’re responsible for 0.15 degree Celsius of the 0.8 degree Celsius rise in global average temperatures: 19 percent of the total. That’s more than twice as much as the next highest country, China. The worst polluting country per person? The tiny U.K.

Unfortunately, China looks set to pass the U.S., unless their reliance on coal changes in short order. As for us, after several years of our greenhouse gas pollution falling, CO2 emissions rose again in 2013. Here’s one area in which the U.S. shouldn’t want to lead.

—David Biello