tic product (GDP) has been cut in half since 1973, with about 70 percent of that decline resulting from improvements in energy efficiency (IEA, 2004). Nevertheless, the absolute amount of energy used continues to rise.
Yet the potential for higher energy efficiency is large, as illustrated by two points. First, despite the impressive gains made by the United States over the last 30 years, almost all other developed nations use less energy per capita and less energy per dollar of GDP (see Table 4.1 and Figure 1.5 in Chapter 1). Denmark’s levels of usage, for example, are about half on both measures. While there are structural variations that account for part of this gap, some 50 percent of it results from differences in energy efficiency (Weber, 2009).
The second point is that a greater number of energy-efficient and cost-effective technologies are available today to supply such services as lighting, heating, cooling, refrigeration, transport, and computing—all of which are needed throughout the economy and constitute the underlying driver of the demand for energy. Hundreds of realistic and demonstrated technologies, some already