Barack Obama ran on a promise to finally do something big on climate change, and when in 2008 he won a wide mandate–and Democrats took broad majorities in both houses of Congress–environmentalists’ hopes soared.

Until they remembered that in the United States, good legislation dies in the Senate.

Under Speaker Nancy Pelosi, Democrats passed a wide-ranging, comprehensive climate and energy bill, the American Clean Energy and Security Act (A.C.E.S), in June 2009. The bill made major concessions to Blue Dog and coal-state Democrats, but nonetheless mandated a 17% reduction of carbon and other greenhouse emissions by 2020 and an 80% reduction by 2050.

It was hailed as a bargaining chip in international climate negotiations and a sign the country had finally gotten serious about dealing with man-made global warming.

Except the U.S. Senate didn’t even bring a climate bill–much less the relatively progressive A.C.E.S.–up for a vote, too distracted by a desperate need to extend the Bush tax cuts for the rich, among other things.

Former Vice President Al Gore, who has mostly held his fire until now, dinged Obama for his inaction in a Rolling Stone article that went online today.

“President Obama has thus far failed to use the bully pulpit to make the case for bold action on climate change,” Gore points out, and having seen the president refer only tangentially to the climate in light of the consensus in the Beltway that the combination of a weak economy and Republican Congress make action impossible, the environmentalist is pushing for activists to pressure their leaders in Washington.

The problem is that even if Democrats have a great 2012 and reelect Obama–and take back the House from climate change-skeptics–it is extremely unlikely they will win the Senate seats needed to overcome an inevitable filibuster of a cap and trade bill (or any other means of dealing with global warming, for that matter). In the meantime, climate activists will have to hope the Environmental Protection Agency uses its powers to their fullest extent under the Clean Air Act to reduce carbon emissions.