Energy Consumption

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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

1 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).

natural gas (Figure 14.1). The transportation sector is 94 percent reliant on petroleum, 56 percent of which is imported (EIA, 2009).

There are important economic and national security issues related to the availability of fossil fuel resources, as well as significant environmental issues associated with their use—including, but not limited to, climate change. For example, the recent report

Biomass 3%

Hydra 2%V ^ TOther Renewables 1%

Nuclear 8%

Nuclear 8%

Fossil Fuels 86%

Fossil Fuels 86%

Total U.S. Consumption = 101.6 Quads

Coal

Nuclear Hydropower Biomass Other Power Renewables

FIGURE 14.1 Energy consumption in the United States in 2007 by fuel source, in quadrillion Btu (bars) and as a percentage of total energy consumption (pie chart). Fossil fuels serve as the primary source of energy. SOURCE: NRC (2009d).

Petroleum Natural Gas

Coal

Nuclear Hydropower Biomass Other Power Renewables

FIGURE 14.1 Energy consumption in the United States in 2007 by fuel source, in quadrillion Btu (bars) and as a percentage of total energy consumption (pie chart). Fossil fuels serve as the primary source of energy. SOURCE: NRC (2009d).

Hidden Costs of Energy: Unpriced Consequences of Energy Production and Use (NRC, 2009f) estimated that the damages associated with energy production and use in the United States totaled at least $120 billion in 2005, mostly through the health impacts of fossil fuel combustion (and not including damages associated with climate change or national security, which are very difficult to quantify in terms of specific monetary damages). While this is undoubtedly a small fraction of the benefits that energy brings, it reinforces the message that there are significant benefits associated with reducing the use of energy from fossil fuels.

As discussed above and in Chapter 6, limiting the magnitude of future climate change will require significant reductions in climate forcing, and GHGs emitted by the energy sector are the single largest contributor. Hence, many strategies to limit climate change typically focus on reducing GHG emissions from the energy sector. These strategies can be grouped into four major categories: (1) reductions in demand, typically through changes in behavior that reduce the demand for energy; (2) efficiency improvements, or reducing the amount of energy needed per unit of goods and services produced (also called energy intensity) through changes in systems, behaviors, or technologies; (3) development and deployment of energy systems that emit few GHGs or other climate forcing agents, or at least emit fewer GHGs per unit energy consumed than traditional fossil fuel-based technologies; and (4) direct capture of CO2 or other GHGs during or after fossil fuel combustion. These general strategies are discussed briefly in subsequent sections.

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