Senators Barbara Boxer (D-CA) and John Kerry (D-MA) have released their climate bill into the maw of Senate committees. Their Clean Energy Jobs and American Power Act is designed to cut greenhouse gas emissions by 20% from 2005 levels by 2020, with a long-range goal of 80% by 2050.

Sen. Boxer told me in an interview today that five committees have jurisdiction over various pieces of the legislation, which runs about 800 pages at this point (versus 1,400 for the version that narrowly passed the House). She conceded that it’s unlikely to clear the committee gantlet and get to the Senate floor in time for the next major round of U.N. climate talks, set for December 7 in Copenhagen.

Given multiple major distractions such as economic recovery, health care reform, and two ongoing wars, Boxer predicted that it would likely be late December before a version of the climate bill could come to the floor. She said “I have a hunch we’re going to be in until Christmas Eve, frankly.”

Box says she and her colleagues have “broadened the coalition” since a House version of national carbon legislation squeaked through by nine votes over the summer. “We think at the end of the day, they (skeptics) will realize that this is the most flexible way to stand up and fight this challenge called global warming.”

Boxer counterposed this “flexibility” with what some consider the likely alternative; non-legislated regulation of greenhouse gases by the Environmental Protection Agency, under the decades-old Clean Air Act. Coincidentally or not, EPA took a step in that direction today by announcing proposed new requirements for large industrial emitters of carbon dioxide.

EPA’s proposed “tailoring rule” covers six known greenhouse gases produced by power plants, oil & chemical refineries and other large-scale operations. Boxer says she doesn’t see the announcement as competing with Congress. “I think this is a very important signal to my colleagues that the EPA wants to work with us. They’re just going after the biggest polluters and that’s following our lead.”

As for “subnational” initiatives like the Governors’ Climate Summit, going on this week in L.A. (and where EPA chief Lisa Jackson chose to announce the new rules), Boxer said her bill “should encourage the Governors to keep on going. Keep on keepin’ on because the more we all do, the easier it will be in the end.”

Boxer said “We have to step up here or we’re going to see the terrible results of unchecked global warming. This is the moment,” she said. “We’re losing the window.”

Lauren Sommer is covering the L.A. summit for Climate Watch. Watch for her daily posts.