Landmark legislation to curb U.S. carbon emissions is set to be introduced in the Senate today, but odds that the Kerry-Lieberman climate bill will pass are less than overwhelming.

Former co-sponsor Sen. Lindsey Graham (R-S.C.) has withdrawn his support because he’s upset with the Senate’s decision to take up immigration reform first. He’s also said he thinks the climate measure needs to be reassessed in light of the catastrophic oil disaster in the Gulf of Mexico.

Nevertheless, Sens. John Kerry (D-Mass.) and Joe Lieberman (I-Conn.) say they will press on because they believe they can win the support needed for passage.

“We are more encouraged today that we can secure the necessary votes to pass this legislation this year in part because the last weeks have given everyone with a stake in this issue a heightened understanding that as a nation, we can no longer wait to solve this problem which threatens our economy, our security and our environment,” according to their joint statement.

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But even if their efforts to craft a federal carbon policy fail, that’s no excuse for the U.S. not to move toward a cleaner energy future, according to a new report.

Commissioned by the nonprofit Civil Society Institute and written by Synapse Energy Economics, “Beyond Business as Usual” [pdf] outlines what it calls a “transition scenario” to step up energy efficiency and the use of renewable energy through currently existing technologies in order to retire all coal-fired power plants and over a quarter of all existing nuclear reactors by 2050.

“What elected officials and other Americans need to understand is that, even if the climate bill falters, we can still make the move to dramatically cleaner and healthier electricity generation,” says CSI President Pam Solo.

The study focuses on what resources would be likely to replace coal and nuclear plants, where those resources are or need to be located, and what the resource mix would cost compared to continuing with business as usual. It finds that making the transition to more efficient use of energy and renewable generation sources would entail modest costs over the short term — but significant savings over the long haul.

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More specifically, the study calculates that while the clean-energy transition scenario would cost about $10 billion more per year in 2020 than keeping the current system, it would save $13 billion annually by 2050. And that’s counting only direct costs and not things like the health impacts of the current power generation system, which the National Academy of Sciences estimates at about $62 billion per year.

The cost savings would come from a reduction in generation over time due to greater efficiency, which costs less than supplying more power. Savings would also come from technology improvements and market maturation cutting the costs of renewable technology, and from reduced use of natural gas, which is assumed to become considerably more expensive in the coming decades.

The study considers the implications for various U.S. regions. Continuing with business as usual (what the report calls the “reference case”), the Southeast — a region that’s heavily dependent on coal, gas and nuclear power — would see generation from dirty sources increase substantially. But in the transition scenario put forth by the study, aggressive efficiency programs would push down demand while solar and wind generation would get a big boost. An added benefit would be a sharp drop in power generation-related pollution, with mercury emissions virtually eliminated. (To see a chart comparing the two scenarios for the Southeast, click here.)

“This is a high-level study, and working out the details of a transition like the one envisioned here would be challenging,” the authors conclude. “However, it would certainly be no more challenging than working out the details of a carbon cap and trade program, a program to retrofit the nation’s coal plants with new emission controls, and a new generation of nuclear power plants.”

(This story originally appeared at Facing South.)