period of 1990 to 2010, although at a decreasing rate: Total energy consumption has grown at a slower pace than economic output and population. This slower growth in energy consumption stems from structural changes in the U.S. economy (e.g., the shift to a more service-oriented economy) as well as increasing energy efficiency per unit of economic output. Trends in GHG emissions are closely associated with energy consumption. Figure 2.3 compares growth in GHG emissions with growth in primary energy use, population, and economic output in the United States. Since 1990, the U.S. economy has doubled in size while the population has grown about 20 percent and energy use and GHG emissions have grown 10 to 15 percent (EPA, 2009). Recent government projections out to 2030 are for economic growth to continue along historic rates, outpacing growth in energy use and GHG emissions because of the reduced energy intensity of the economy.