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This picture taken on January 22, 2013 shows a thermal power plant discharging heavy smog into the air in Changchun, northeast China's Jilin province. China has cleaned up its air before but experts say that if it wants to avoid the kind of smog that choked the country this week, it must overhaul an economy fuelled by heavily polluting coal and car use. CHINA OUT AFP PHOTO (Photo credit should read STR/AFP/Getty Images)
This picture taken on January 22, 2013 shows a thermal power plant discharging heavy smog into the air in Changchun, northeast China's Jilin province. China has cleaned up its air before but experts say that if it wants to avoid the kind of smog that choked the country this week, it must overhaul an economy fuelled by heavily polluting coal and car use. CHINA OUT AFP PHOTO (Photo credit should read STR/AFP/Getty Images)

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Greenhouse gas deal faces huge challenges

The new U.S. deal with China on greenhouse gases faces enormous challenges in both countries. Jonathan Mann explains.

Greenhouse gas deal faces huge challenges

The new U.S. deal with China on greenhouse gases faces enormous challenges in both countries. Jonathan Mann explains.