New York Times: Carbon trading put the European Union in the environmental vanguard. Since 2005, the trade bloc has operated the world’s only continentwide system that puts a cap on greenhouse gas emissions and that requires major polluters to hold tradable allowances. But the system has also been the most “costly climate policy program in the world,” according to Jürgen R. Thumann, the president of BusinessEurope, a powerful confederation of industry and employer groups. Mr. Thumann …