AP: China, the world’s biggest carbon emitter, opened a U.N. conference on climate change Monday aimed at narrowing differences before a major year-end meeting in Mexico. Optimism for a binding new treaty on curbing greenhouse gases evaporated after last year’s failed climate summit, and negotiators meeting this week for the last round of talks ahead of Cancun were setting their sights on less-ambitious goals. In her opening speech Monday, the U.N. climate chief Christiana Figueres …