World leaders from more than 100 countries are in attendance at the U.N. Climate conference in Scotland. But China's Xi Jinping, president of the globe's largest polluter, is absent from the crowd. For any efforts to succeed in fighting climate change, China must be at the forefront. Reducing China's reliance on coal is key. Nick Schifrin and special correspondent Patrick Fok report. PBS NewsHour is supported by - https://www.pbs.org/newshour/about/funders