BEIJING, CHINA - NOVEMBER 29: A Chinese man wears a mask as he waits to cross the road near the CCTV building during heavy smog on November 29, 2014 in Beijing, China. United States President Barack Obama and China's president Xi Jinping agreed on a plan to limit carbon emissions by their countries, which are the world's two biggest polluters, at a summit in Beijing earlier this month. (Photo by Kevin Frayer/Getty Images)
