WASHINGTON — It wasn’t long ago that Marco Rubio and Tim Pawlenty — two rising Republican stars — supported legislation to limit greenhouse gas emissions. But in recent weeks, both have begun to express doubts about whether cars, factories and power plants have anything to do with global warming. The shift by Rubio and Pawlenty — as well as other prominent Republicans — reflects the rising power of climate change skeptics in the GOP, where global warming is becoming a litmus test for conservatives. Rubio, former speaker of the Florida House of Representatives, is running for the U.S. Senate. Pawlenty, Minnesota’s governor, is eyeing a 2012 presidential bid. For Republicans, ‘the new political expediency is to be a global warming skeptic,’ said Marc Morano, executive editor of the skeptic clearinghouse website ClimateDepot.com and a former aide to outspoken skeptic Sen. James M. Inhofe (R-Okla.). Fuel for the resurgence of attacks on global warming came in December, when leaked e-mails from a British university showed top climate scientists from around the world apparently discussing skirting public information laws and other practices of questionable ethics — an incident that has become known as Climategate. Then came revelations […]