Jeffords' "Global Warming Pollution Reduction Act" is similar to one Rep. Waxman introduced earlier this spring.
Several policy watchers said the recent activity in Congress is a sign that lawmakers are beginning to take global warming more seriously.
"There's definitely an upswing in the tempo," says Alden Meyer, director of strategy and policy at the Union of Concerned Scientists. "You're seeing more and more awareness on Capitol Hill that the problem is real and it's already having impacts. It's getting harder and harder to disagree about it."
But efforts to pass mandatory caps on greenhouse gas emissions have failed before, including 2005 legislation sponsored by Sen. John McCain, R-Ariz., and Sen. Joe Lieberman, D-Conn. After that defeat, New Mexico senators Jeff Bingaman (D) and Pete Domenici (R) successfully passed a resolution that called for mandatory steps to reduce greenhouse gas emissions, but it was non-binding.
Will things be different this year?
"We don't necessarily expect climate change legislation to be voted on this year," says Antonia Herzog with the National Resources Defense Council. "But I would call it the year of ideas."