On the face of things, Democratic presidential candidates Barack Obama and Hillary Clinton have identical plans to curb greenhouse gas emissions: a cap and trade system to lower CO2 emissions to 80 percent of 1990 levels by the year 2050. Every carbon credit would be auctioned to the highest bidders, and some of the proceeds would be used to invest in clean energy and energy-efficiency programs.

Yet both candidates are co-sponsors of a bill that comes up short of their stated reduction goals, known as the Climate Stewardship and Innovation Act of 2007. The bill was introduced by Senator Joseph Lieberman (I-CT) in January of 2007, and prescribes a cap and trade program to lower CO2 emissions 66 percent by 2050 from year 2000 levels. Senator John McCain is also a co-sponsor of the bill, saying “America can and must assume its proper leadership role in addressing the preeminent environmental issue of our time.”

The bill has driven a wedge in the environmental community because it gives away carbon allowances rather than auctioning them, and it lets industries earn carbon credits if they can facilitate “offsets” in developing countries, something that has drawn sharp criticism from groups like the California Environmental Justice Movement and Climate Justice Chicago. The bill is supported by Environmental Defense, the Natural Resources Defense Council and National Wildlife Federation, but opposed by Friends of the Earth, U.S. PIRG and Clean Air Watch.

Here’s a press release from the group Friends of the Earth, which says the legislation “could provide giveaways worth hundreds of billions or even trillions of dollars to polluting industries.”

If the bill ever makes it onto the Senate floor for a vote, it is likely to create quite a stir. It raises the issue of whether some action is better than no action. Scientist say the window of time remaining to begin radically reducing our carbon emissions is closing fast, and some say it is already shut.