Decision makers in government and business increasingly need to understand the practical implications of deep reductions in global greenhouse gas (GHG) emissions. This report examines the technical and economic feasibility of such a transition in the United States, evaluating the infrastructure and technology changes required to reduce U.S. GHG emissions in the year 2050 by 80% below 1990 levels, consistent with a global emissions trajectory that limits the anthropogenic increase in earth?s mean surface temperature to less than 2°C.