The Senate has taken up a bill that would cut U.S. greenhouse-gas emissions 71% by 2050, partly through a new carbon-allowance market estimated to grow into the trillions of dollars. Floor debate may be fierce, but it’s likely to be a short, early chapter in a legislative story that will certainly stretch into 2009. The bill needs 60 votes to avoid a filibuster and win passage. Even key supporters say that may prove elusive.

Key Provisions in Senate Bill

Gradual cut in greenhouse-gas emissions: 2020 level would be 19% below current mark; 2050 level would be 71% below current.

Sets up new trading market for emissions allowances.

“Transition assistance” totaling $764 billion through 2050 for certain workers, manufacturers, fossil-fuel power generators, petroleum refiners and natural gas processors.

New program to spur energy-efficient buildings, funded at $51 billion. New construction and retrofits eligible.

$150 billion for building owners or operators whose facilities use renewable-energy technology; $51 billion for retailers, distributors of increased sales of energy-efficiency building equipment; $51 billion for manufacturers that show major energy-efficiency improvement.

Source: Senate Environment and Public Works Committee

“The chances of its becoming law this year are pretty darned slim, maybe nothing,” says Andrew Goldberg, American Institute of Architects’ senior director for federal relations. “I think they’re trying to set the stage for next year.” Some think a climate bill will have better prospects under a new administration and Congress.

The White House promised to veto the pending Senate bill, saying its cut in carbon emissions would cost the U.S. economy $6 trillion. But the bill’s sponsor, Environment and Public Works Committee Chair Barbara Boxer (D-Calif.), says allowance trading would raise nearly $1 trillion for the Treasury and $911 billion for utilities to offset consumers’ energy-bill hikes.

The bill requires coal-burning powerplants, refineries and other facilities to reduce carbon emissions starting in 2012, partly through emissions trading. Some allowances would be auctioned, others would be given to certain industries. The allowances and auction proceeds would be worth an estimated $6.7 trillion.

The bill aims to promote energy-efficient buildings, with aid for those undertaking construction and retrofits. Goldberg says a greenhouse-gas bill should have “a significant way to address buildings, because they’re such an important part of the climate-change equation,” accounting for nearly half of greenhouse emissions.

To attract more backing, Boxer made significant changes to a bill that cleared her committee in December. Additions included “transition” assistance for industries and workers. Union leaders, such as Building and Construction Trades Dept. President Mark Ayers, lauded the provisions.

It’s unclear whether the bill would spur more environmental work at powerplants and other facilities. Says Alan Chapple, marketing and communications director for The Shaw Group’s power group, “We’ve got a full plate of air-quality work,” with 14 retrofit jobs under way and a half-dozen new coal-fired powerplants under contract or in construction.