In this file photo taken Saturday, December 12, 2015, visitors to a park gestures at each other near chimneys spewing smoke in Beijing, China. Researchers say Tuesday, April 25, 2017 that China's conversion of coal into natural gas could prevent tens of thousands of premature deaths annually. But there's a catch: It also could undermine efforts to rein in greenhouse gas emissions. (Photo by Ng Han Guan/AP Photo)
