Figure 23.3U.S. energy consumption, shown here for the period 1775–2011, has successively been dominated by the burning of wood, coal, and oil. In just the past few years (magnified in the inset), the energy from petroleum and coal has dropped while that from natural gas and renewable sources such as solar and wind has increased. Here and elsewhere in this chapter, the energy units are quads (1 quad = 1015 Btu).