Washington Post: President Obama’s chief climate-change negotiator said Sunday that the United States would be “powerfully, fervently engaged” in global talks to reduce carbon emissions but warned that a difficult path lay ahead. Todd Stern, a Washington lawyer and former Clinton White House official, said at a U.N. conference in Bonn, Germany, that despite high expectations, Obama did not have a magic solution for fashioning a global climate-change treaty by the end of the year. “We all have …