Associated Press: Momentum was building Thursday for a novel strategy by the Obama administration to deal in part with global warming: Use the existing U.N. treaty to fix the ozone hole as a way to enact mandatory reductions in a key greenhouse gas — not carbon dioxide but hydrofluorocarbons. The Obama administration, in a major environmental policy shift, is leaning toward asking 195 nations that ratified the U.N. ozone treaty to do just that. Two influential senators on Thursday sent …