Greenwire: With global warming legislation sidelined, advocates are bracing for battle over U.S. EPA climate rules, the only game in town for curbing emissions of heat-trapping greenhouse gases. Environmentalists were left reeling this summer when the Senate retreated on climate legislation, and while a few die-hards say a climate bill is still possible this year, most advocates are shifting their focus to upholding EPA’s authority to limit greenhouse gas emissions. "Obviously, the …