The UN just issued a sobering report on climate change that brings China and the US, the world's two biggest carbon emitters to attention. --Washington has bailed on the Paris agreement on fighting climate change, while China met the 2030 emission's goal this year, 12 years early. Are the ongoing China-US trade tensions complicating things? CGTN's Xia Cheng sat down to discuss the issue with John Holdren, former senior advisor to President Barack Obama on science and technology.