To address these concerns, Congress has been debating a range of potential initiatives for reducing atmospheric CO 2 from U.S. sources. Legislative proposals would seek to limit U.S. CO 2 emissions to specific (historical) levels through emissions caps, carbon taxes, or other regulatory mechanisms. In the 110 th Congress, the most prominent CO 2 proposals sought reductions of nationwide CO 2 emissions to 1990 levels or lower by 2030. President-elect Barack Obama has proposed carbon reduction targets as well, intending to cut CO 2 emissions to 1990 levels by 2020, and by an additional 80% by 2050. A fundamental policy question which arises from carbon control proposals is how the CO 2 reduction targets can be achieved. Policy Issues for Congress

Policy research and technical studies show that substantially reducing CO 2 emissions in the U.S. electricity sector over the next few decades likely requires successful deployment of every major carbon mitigation measure at the nation's disposal. However, it is also clear that significant uncertainties cast doubt on the potential of individual measures to achieve their hoped-for carbon impact. For the measures discussed in this report, the key uncertainties can be summarized as follows:
Energy efficiency —Can the United States overcome socioeconomic barriers to achieve four times more potential savings than ever before? Renewable energy —Will there be enough transmission for wind power? Is there enough land to grow the needed biomass? Nuclear power —Could the United States build new plants fast enough to matter? Advanced coal power —Will banks fund them and regulators approve them? Carbon capture and sequestration —Will the technology be commercially deployable in 10 years, 25 years, or never? Plug-in hybrid electric vehicles —How much "low carbon" electricity would be available to charge their batteries? Distributed energy resources —Would carbon costs change distributed energy economics enough to spur deployment? Failure of the CO2 Mitigation Portfolio

Notwithstanding the best efforts of federal policy makers, it is possible that, given the uncertainties they face, that few if any of the major measures proposed to moderate U.S. carbon emissions would achieve their anticipated impacts in a 20-year time frame. As the nation's CO 2 mitigation policies continue to develop, the inherent uncertainty associated with specific carbon measures may be a critical concern. Commitments, either domestic or international, to specific carbon emissions targets over time, or to a specific schedule of carbon costs (whatever form they may take) may be greatly affected by the success of the underlying measures relied upon to achieve them. As Congress considers implementing CO 2 policies, keeping a close eye on the technology and market developments associated with every key measure may be an oversight priority. Balancing responses to energy market volatility and unexpected structural changes against the need for a predictability in R&D and private capital investment may be essential to maintaining the nation on course to meaningful atmospheric CO 2 reduction.
Congress has been debating a range of potential initiatives for reducing atmospheric CO2 from U.S. sources. Legislative proposals would seek to limit U.S. CO2 emissions to historical levels through emissions caps, carbon taxes, or other mechanisms. In the 110th Congress, the most prominent CO2 proposals sought reductions of nationwide CO2 emissions to 1990 levels or lower by 2030. President-elect Barack Obama has proposed cutting carbon CO2 emissions to 1990 levels by 2020, and by an additional 80% by 2050.
A fundamental question arising from carbon control proposals is how the CO2 reduction targets can be achieved in the electricity industry, which is responsible for nearly 40% of U.S. CO2 emissions. It appears from the policy research and technical studies that substantially reducing CO2 emissions in the U.S. electricity sector over the next few decades would likely require every key carbon mitigation measure at the nation's disposal. However, it is also clear that significant uncertainty exists about the potential of individual measures to achieve their hoped-for carbon impact:
Energy efficiency—Can the United States overcome socioeconomic barriers to achieve four times more potential savings than ever before? Renewable energy—Will there be enough transmission for wind power? Is there enough land to grow the needed biomass? Nuclear power—Could the United States build new plants fast enough to matter? Advanced coal power—Will banks fund them and regulators approve them? Carbon capture and sequestration—Will the technology be commercially deployable in 10 years, 25 years, or never? Plug-in hybrid electric vehicles—How much "low carbon" electricity would be available to charge their batteries? Distributed energy resources—Would carbon costs change distributed energy economics enough to spur deployment?
As the nation's CO2 mitigation policies develop, the inherent uncertainty associated with specific carbon measures may be a critical concern. Commitments to specific carbon emissions targets over time, or to a specific schedule of carbon costs (whatever form they may take) may be greatly affected by the success of the underlying measures relied upon to achieve them. Notwithstanding the best efforts of federal policy makers, it is possible that, given the uncertainties each faces, few if any of the major measures proposed to moderate U.S. carbon emissions will achieve their anticipated impacts in a 20-year time frame. As Congress considers implementing CO2 policies, keeping a close eye on the technology and market developments associated with every key measure could be a priority. Balancing responses to energy market volatility and unexpected structural changes against the need for a predictability in R&D and private capital investment may be essential to maintaining the nation on course to meaningful atmospheric CO2 reduction.