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provides only a brief summary of critical knowledge and research needs in the energy sector.


Globally, total energy consumption grew from 4,675 to 8,286 million tons of oil equivalent between 1973 and 2007 (IEA, 2009). The United States is still the world’s largest consumer of energy, responsible for 20 percent of world primary energy consumption. The next largest user, China, currently accounts for about 15 percent. Energy consumption in the United States has increased by about 1 percent per year since 1970, although there is no longer a direct relationship between energy use and economic growth. Between 1973 and 2008, for example, U.S. energy intensity, measured as the amount of energy used per dollar of gross domestic product (GDP), fell by half, or 2.1 percent per year (EIA, 2009). Despite this trend, the United States still has higher energy use per unit of GDP and per capita than almost all other developed nations. For example, Denmark’s per capita energy use is about half that of the United States (NRC, 2009c).

A nation’s energy intensity reflects population and demographic and environmental factors as well as the efficiency with which goods and services are provided, and consumer preference for these goods and services. Comparison of the energy intensity of the United States with that of other countries indicates that about half of the difference is due to differences in energy efficiency (NRC, 2009c). The differences also reflect structural factors such as the mix of industries (e.g., heavy industry versus light manufacturing1) and patterns of living, working, and traveling, each of which may have developed over decades or even centuries.

Today, about 40 percent of U.S. energy use is in the myriad private, commercial, and institutional activities associated with residential and commercial buildings, while roughly 30 percent is used in industry and the same amount in the transport of goods and passengers (see Chapter 13). Most significantly for GHG emissions, 86 percent of the U.S. energy supply now comes from the combustion of fossil fuels—coal, oil, and


 In accounting for the energy or environmental implications of shifts in the mix of products produced and consumed in the economy, it is important to consider trade flows. For example, if a reduction in domestic production of steel is offset by an increase in steel imports, domestic GHG emissions may appear to decline but there may be no net global reduction in GHG emissions (and emissions may even increase, given the possibility of differences in production-related emissions and the energy expended in transporting the imported product). This concept is an important factor in negotiations over international climate policy (see Chapter 17).

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