President Trump, flanked by company executives and miners, signed a long-promised executive order on Tuesday to nullify President Barack Obama’s climate change efforts and revive the coal industry, effectively ceding American leadership in the international campaign to curb the dangerous heating of the planet.Mr. Trump made clear that the United States had no intention of meeting the commitments that his predecessor had made to curb planet-warming carbon dioxide pollution, turning denials of climate change into national policy.At a ceremony, Mr. Trump directed the Environmental Protection Agency to start the complex and lengthy legal process of withdrawing and rewriting the Obama-era Clean Power Plan, which would have closed hundreds of coal-fired power plants, frozen construction of new plants and replaced them with vast new wind and solar farms...Attorney General Eric T. Schneiderman of New York said he was preparing to challenge any effort to do away with regulations on greenhouse gas emissions. Such a move, he argued, violated the Clean Air Act, as well as established case law.