Associated Press: The top U.S. negotiator on climate change said Tuesday that he is slightly more optimistic about striking a new international agreement to curb global warming after a two-day meeting with the world’s largest emitters of greenhouse gases. Todd Stern, the U.S. special envoy for climate change, told reporters at a briefing Tuesday that he is “a bit more optimistic” that the U.S. will be able to broker a new deal in Copenhagen in December. But he warned that it is not going to be …