Bloomberg: The U.S. said it wants to reach a legally binding climate-change agreement at a summit in Mexico in December, a sign President Barack Obama hasn’t given up the fight for a global accord to limit greenhouse gases. The pact should cover “all major economies,’ and include elements from the non-binding Copenhagen Accord made in December, the State Department said in a letter released today by the UN Framework Convention on Climate Change, or UNFCCC. With China and India resisting …