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If federal agencies and states pursue the path of “go getters” and move strongly to achieve the reductions published literature suggests are technically feasible in the sectors analyzed, the U.S. could achieve significant reductions in greenhouse gas emissions, which approach but fall short of President Obama’s Copenhagen pledge to reduce emissions 17 percent below 2005 levels by 2020.

If, however, federal agencies fail to capitalize on available reduction opportunities and states fall short on their announced plans to reduce emissions, middleof- the-road or lackluster reductions will result, falling far short of the 17 percent reduction by 2020 goal.

Longer-term reductions post-2020 are less certain under all analyzed scenarios, primarily due to uncertainty about how quickly aging power plants will be replaced and the transportation sector can be transformed. Regulatory policies can drive technology, but without knowing what technological advances will happen and when, it is difficult to project the tightening of regulatory standards.

All scenarios under current federal authority and announced state plans show the United States far off the pace of reductions the IPCC suggests are necessary by mid-century to prevent average global temperatures from increasing more than 2 degrees Celsius.

While the results of the analysis suggest that existing federal regulatory tools can be used effectively to reduce emissions alongside state actions, it is clear that the federal government and states will need to achieve reductions beyond those identified in even the most ambitious regulatory scenario if the United States is to meet its Copenhagen commitment. Some of these reductions might be found in regulatory policies not analyzed here, such as agricultural and forest lands management (approximately 7 percent of the U.S. inventory) or transportation planning (approximately 27 percent). Implementation of other environmental policies that encourage high-emitting sectors to modernize could also yield more reductions, such as mercury, sulfur dioxide, ozone and ash disposal regulations affecting aging coal plants.

Among the existing federal regulatory tools most useful to achieve reductions are the mobile source and New Source Performance Standard provisions of the Clean Air Act, as well as the existing authority under Title VI of the Act to reduce hydrofluorocarbons. The vehicle fuel efficiency authority of the Department of Transportation is also important. State action that contributes reductions beyond federal regulatory policies will likewise be essential to meeting reduction goals.

The analysis shows that a significant portion of the reductions can be achieved in non-energy emissions. It is expected that these non-energy reductions can be accomplished without energy price increases.

It is likely that the U.S. Congress and states will need to step up to augment existing regulatory tools, especially if the United States is to gear up to reduce emissions by the approximately 80 to 95 percent needed by 2050 to ward off the most deleterious effects of climate change.