American officials have applauded President Xi Jinping ’s commitment to a national market for greenhouse gas quotas as a breakthrough in environmental cooperation. But to work well, Mr. Xi’s pledge, made at the White House on Friday, will demand big changes from a Chinese government accustomed to heavy-handed intervention and skewed statistics. It will take years of effort to build a substantial market that plays a major role in curbing emissions, and even then, it could founder, like similar initiatives elsewhere, experts said. China has had local trials underway since 2013, supported by the liberal doling out of emissions permits or by cajoling companies to take part. Expanding those initial efforts nationwide by 2017, as Mr. Xi pledged to do, will […]