The electric sector is the largest concentrated source of carbon emissions in the United States, accounting for more than one-third of all domestic greenhouse gas (GHG) emissions. Before the United States Environmental Protection Agency (EPA) took steps to regulate GHG emissions under the Clean Air Act, there were no federal limits. In an air pollution seminar at the University of Vermont, Dave Farnsworth explored the implications of Section 111(d) of the Clean Air Act serving as a basis for the EPA’s Clean Power Plan (CPP), the underlying issues driving the structure of the CPP, and the pros and cons of several specific compliance strategies states might consider. Under Section 111(d), the EPA established four building blocks for compliance—energy efficiency, non-emitting generation like renewable and nuclear power, heat rate improvements, and re-dispatch to natural gas—while clearly stating that states may employ other compliance approaches not factored into the state-specific goal. Mr. Farnsworth encourages states to think beyond the four building blocks to consider options such as reducing losses in the transmission and distribution system, fostering new markets for energy efficiency, improving utility resource planning, and adopting cap-and-invest programs such as New England’s Regional Greenhouse Gas Initiative (RGGI) scheme. As energy efficiency can play a major role in drafting an approvable, least-cost compliance plan, Mr. Farnsworth also explains how to quantify avoided emissions from energy efficiency policies and programs.