Popularly, China is a villain in climate change. Many people who attended last year's chaotic U.N. climate-change talks in Copenhagen — especially those who belonged to the U.S. delegation — singled out China as the main reason the summit nearly collapsed. Chinese diplomats fought hard against any form of emissions regulation, even though their country is now the world's No. 1 national carbon emitter, and will emit far more carbon in the future than any other. In Washington, opponents of carbon cap-and-trade also point to China, which is unlikely to take on a carbon cap of its own, and wonder why the U.S. should have to restrain its emissions.

But a new study published in the March 8 edition of Proceedings of the National Academy of Sciences (PNAS) shows that the carbon equation isn't as straightforward as we might think. Scientists at the Carnegie Institution of Washington at Stanford University synthesized carbon emissions and trade patterns and found that more than one-third of CO2 emissions related to the consumption of goods and services in developed countries are actually emitted outside their national borders. Rich nations are essentially outsourcing some of their carbon emissions to developing nations through global trade — by importing goods and services from abroad — thereby shrinking their carbon footprints while inflating those of major exporting nations like China. "It's surprising just how much this effect is driven by the U.S. and China," says Steven Davis, an ecologist at the Carnegie Institution and the lead author of the PNAS paper. "It is significant."

How significant? Davis and his co-author Ken Caldeira estimate that 23% of global CO2 emissions — about 6.2 billion metric tons — are traded internationally, usually going from carbon-intensive developing nations like China to the comparatively less carbon intensive West. In a few rich nations, such as France, Sweden and Britain, more than 30% of consumption-based emissions could be traced to origins abroad; if those emissions were tallied on the other side of the balance sheet, it would add more than four tons of CO2 per person in several European nations.

The effect in the U.S. is less extreme because the country exports more than Western Europe and because the U.S. economy has a higher carbon intensity — but it made a difference. Imports accounted for 10.8% of U.S. carbon emissions, enough to add an additional 2.4 metric tons of CO2 per person. China, of course, fell into the opposite camp: 22.5% of the carbon emitted in China is actually exported to other countries, reducing its per capita carbon footprint from 3.9 tons to 3 tons.

Climate-change critics like Republican Senator James Inhofe may rail against China, but the PNAS paper shows that while Beijing may be leading the world in carbon emissions, that output is in large part due to the fact that it is using energy to make clothes, cars and toys for the rest of us. It also demonstrates that Europe — whose per capita carbon footprint is less than half that of the U.S. — essentially imports some of its green virtue from abroad by outsourcing its carbon emissions. "It does shrink the gap somewhat between the U.S. and Europe," says Davis.

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