Associated Press: Joining climate change negotiations for the first time, the Obama administration is trying to convince other countries that the U.S. does care about global warming and wants to shape an international accord. After eight years on the sidelines, the U.S. says it is ready for a central role in developing a new agreement to slash greenhouse gases. But whether the U.S, which is the second largest source of heat-trapping pollution, is ready to sign onto a deal by year’s end could depend on …