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2. Carbon Dioxide Emissions Overview
Total emissions of carbon dioxide in the United States and its territories were 5,795.6 million metric tons in 2002, 47.2 million metric tons (0.8 percent) more than the 2001 total (Tables 4 and 5). The increase in emissions from 2001 to 2002 can be attributed in large part to an increase in overall U.S. economic growth of 2.4 percent in 2002, colder winter weather that increased the demand for heating fuels, and an increase in electricity demand influenced by a hotter summer than the year before. The increase in emissions from 2001 to 2002 follows a decrease of 1.8 percent, or 105.7 million metric tons, from 2000 to 2001 (Figure 1). Since 1990, total U.S. carbon dioxide emissions have increased by an average of about 1.2 percent per year. As discussed below, factors such as a drop in carbon intensity in the electric power sector kept emissions growth in 2002 to less than the average annual growth rate since 1990. In the United States, most carbon dioxide (98 percent) is emitted as the result of the combustion of fossil fuels; consequently, carbon dioxide emissions and energy use are highly correlated. Historically, economic growth, the weather, the carbon and energy intensity of the economy, and movements in energy prices have caused year-to-year fluctuations in energy consumption and resulting carbon dioxide emissions. Annual economic growth in 2002 (2.4 percent) was considerably higher than in 2001 (0.3 percent). In addition, there were both a colder winter and a hotter summer in 2002 than in 2001. The colder winter led to increased demand for heating fuels, such as natural gas and distillate fuel, and the hotter summer led to increased demand for electricity for air conditioning. The increased demand for natural gas as a heating fuel can be seen in the residential and commercial sectors (Tables 6 and 7), where energy consumption is dominated by electricity use for air conditioning during the summer and fuel use for heating during the winter. In the residential sector (Table 6), emissions of carbon dioxide increased by 2.8 percent, from 1,160.8 million metric tons of carbon dioxide in 2001 to 1,193.0 million metric tons in 2002. In the commercial sector (Table 7), carbon dioxide emissions decreased by 0.5 percent (from 1,018.3 million metric tons in 2001 to 1,012.9 million metric tons in 2002). Because commercial sector emissions are dominated by the sector’s share of electricity generation, a decrease in the carbon intensity of electricity generation is the principal reason for the decrease in emissions. Industrial production declined by 0.7 percent in 2002, following a 3.5-percent decline in 2001. Industrial emissions of carbon dioxide also fell by 0.7 percent, from 1,685.3 million metric tons in 2001 to 1,673.7 million metric tons in 2002 (Table 8). Of the six most energy-intensive manufacturing industries, two (primary metals and paper) had declines in output in 2002 compared with 2001 (3.0 percent and 2.3 percent, respectively). Output from the four other energy-intensive industries increased: chemicals by 3.9 percent, nonmetallic minerals by 1.0 percent, and food and petroleum refining both by 0.5 percent. Unlike 2001, when all of the decline in industrial output was attributable to the energy-intensive industries, 2002 saw a 1.5-percent decline in output from computer and electronic products—the first decline in 17 years. Estimates for 2002 indicate that carbon dioxide emissions in the transportation sector (Table 9) increased by 1.2 percent, from 1,827.3 million metric tons in 2001 to 1,849.7 million metric tons in 2002. Net generation of electricity increased by 2.7 percent from 2001 to 2002, and total carbon dioxide emissions from the electric power sector increased by 1.0 percent, from 2,226.6 million metric tons in 2001 to 2,249.0 million metric tons in 2002 (Table 10). Accordingly, the overall carbon intensity of U.S. electricity production dropped by 1.6 percent. In this report, the electric power sector is defined as all utilities, nonutilities, and combined heat and power (CHP) facilities whose primary business is the production of electric power. Carbon dioxide emissions from generators that produce electric power as part of an industrial or commercial operation—that is, businesses that produce electricity primarily for their own use—are not included in the electric power sector total but are assigned to the industrial or commercial sector according to the classification of the business. In addition, the emissions totals reported above for the energy end-use sectors (residential, commercial, industrial, and transportation) include their shares of total electric power sector emissions. Nonfuel uses of fossil fuels, principally petroleum, resulted in carbon sequestration equal to 299.3 million metric tons carbon dioxide equivalent in 2002, an increase of 6.5 million metric tons (2.2 percent) from 2001 (Table 11). The major fossil fuel products that sequester carbon include liquefied petroleum gas (LPG), feedstocks for plastics and other petrochemicals, and asphalt and road oils. It is estimated that, of the amount of carbon dioxide sequestered in the form of plastic, about 19.8 million metric tons was emitted as carbon dioxide from the burning of the plastic components of municipal solid waste as well as other waste burning in 2001. The 2001 estimate of 19.8 million metric tons is used in this report as an estimate for 2002 emissions of carbon dioxide from the burning of wastes. Emissions of carbon dioxide from other sources—including cement production, industrial processes, waste combustion, carbon dioxide in natural gas, and gas flaring—increased by 0.7 percent, from 112.8 million metric tons in 2001 to 113.6 million metric tons in 2002 (Table 4). Energy Consumption
The consumption of energy in the form of fossil fuel combustion is the largest single contributor to greenhouse gas emissions in the United States and the world. Of total 2002 U.S. carbon dioxide emissions (adjusting for U.S. Territories and bunker fuels), 98.0 percent, or 5,682.0 million metric tons of carbon dioxide, resulted from the combustion of fossil fuels. This figure represents an increase of 0.8 percent from 2001 levels. In the short term, year-to-year changes in energy consumption and carbon dioxide emissions tend to be dominated by weather, economic fluctuations, and movements in energy prices. Over longer time spans, changes in energy consumption and emissions are influenced by other factors such as population shifts and energy consumers’ choice of fuels, appliances, and capital equipment (e.g., vehicles, aircraft, and industrial plant and equipment). The energy-consuming capital stock of the United States—cars and trucks, airplanes, heating and cooling plants in homes and businesses, steel mills, aluminum smelters, cement plants, and petroleum refineries—changes slowly from one year to the next, because capital stock usually is retired only when it begins to break down or becomes obsolete. EIA divides energy consumption into four general end-use categories: residential, commercial, industrial, and transportation. Emissions from electricity generators, which provide electricity to the end-use sectors, are allocated in proportion to the electricity consumed in each sector (Table 5). Electricity-related emissions that are allocated across the end-use sectors include emissions from integrated electric utilities and emissions from nonutility power producers (including independent power producers and industrial CHP plants) whose primary business is the production and sale of electricity. Residential Sector At 1,193.0 million metric tons, residential carbon dioxide emissions represented 20.8 percent of U.S. energy-related carbon dioxide emissions in 2002. The residential sector’s pro-rated share of electric power sector emissions accounts for more than two-thirds of that amount (820.7 million metric tons). Petroleum (mainly distillate fuel oil) accounted for 8.7 percent and natural gas 22.4 percent. Since 1990, residential electricity-related emissions have grown by 2.5 percent annually. In contrast, emissions from the direct combustion of fuels, primarily natural gas, in the residential sector have grown by 0.9 percent annually since 1990. Total carbon dioxide emissions from the residential sector increased by 2.8 percent in 2002 (Table 6). Year-to-year, residential sector emissions are strongly influenced by weather. For example, in 1996, a relatively cold year, carbon dioxide emissions from the residential sector grew by 5.8 percent relative to 1995. In 1997, emissions declined by 0.8 percent due to warmer winter weather. The colder winter in 2002, relative to 2001, was a contributor to the 2002 increase in residential sector emissions. Since 1990, the growth in carbon dioxide emissions attributable to the residential sector has averaged 1.9 percent per year. Residential sector emissions in 2002 were 242.2 million metric tons higher than in 1990, representing 32.7 percent of the total increase in U.S. energy-related carbon dioxide emissions since 1990. Long-term trends in residential carbon dioxide emissions are strongly influenced by demographic factors, living space attributes, and building shell and appliance efficiency choices. For example, the movement of population into the Sunbelt tends to increase summer air conditioning consumption and promote the use of electric heat pumps, which increases indirect emissions from electricity use (although the increase could be offset by a reduction in direct emissions from heating fuel combustion). Growth in the number of households, resulting from increasing population and immigration, contributes to more residential energy consumption. Commercial Sector Commercial sector carbon dioxide emissions, at 1,012.9 million metric tons, account for about 17.7 percent of total energy-related carbon dioxide emissions, of which 77.2 percent (781.8 million metric tons) is the sector’s pro-rated share of electricity-related emissions. Petroleum contributes 5.2 percent and natural gas 16.7 percent of the sector’s emissions. Commercial sector emissions largely have their origin in the space heating and cooling requirements of structures such as office buildings. Lighting is a more important component of commercial energy demand than it is in the residential sector. Thus, although commercial sector emissions are strongly affected by the weather, they are affected less than residential sector emissions. In the longer run, because commercial activity is a factor of the larger economy, emissions from the commercial sector are more affected by economic trends and less affected by population growth than are emissions from the residential sector. Emissions attributable to the commercial sector’s pro-rated share of electricity consumption decreased by 1.2 percent in 2002, while emissions from the direct combustion of fuels (dominated by natural gas, as in the residential sector) increased by 1.7 percent. Overall, carbon dioxide emissions related to commercial sector activity decreased by 0.5 percent—from 1,018.3 to 1,012.9 million metric tons—between 2001 and 2002 (Table 7). Since 1990, commercial emissions growth has averaged 2.2 percent per year, the largest growth of any end-use sector. Commercial sector carbon dioxide emissions have risen by 233.4 million metric tons since 1990, accounting for 31.5 percent of the total increase in U.S. energy-related carbon dioxide emissions. Industrial Sector Industrial sector emissions, at 1,673.7 million metric tons of carbon dioxide, accounted for 29.2 percent of total U.S. energy-related carbon dioxide emissions in 2002. In terms of fuel shares, electricity consumption was responsible for 38.4 percent of total industrial sector emissions (643.1 million metric tons), natural gas for 25.9 percent (432.7 million metric tons), petroleum for 24.7 percent (412.8 million metric tons), and coal for 10.7 percent (179.4 million metric tons). Estimated 2002 energy-related carbon dioxide emissions in the industrial sector, at 1,673.7 million metric tons (Table 8), were 0.7 percent lower than the 2001 emissions level of 1,685.3 million metric tons. Carbon dioxide emissions attributable to industrial sector energy consumption have declined by an average of 0.1 percent per year since 1990. As a result, total energy-related industrial emissions in 2002 were 0.9 percent (15.1 million metric tons) lower than in 1990, despite a much larger economy. A contributing factor to the decline in industrial sector carbon dioxide emissions is the erosion of the older energy-intensive (and specifically coal-intensive) industrial base. For example, coke plants consumed 38.9 million short tons of coal in 1990, as compared with 22.5 million short tons in 2002. Other industrial coal consumption declined from 76.3 million short tons in 1990 to 63.1 million short tons in 2002. Energy-intensive industries have been replaced by others that are less energy-intensive, such as computer chip and electronic component manufacturing. Transportation Sector Carbon dioxide emissions from the transportation sector, at 1,849.7 million metric tons, accounted for 32.3 percent of total U.S. energy-related carbon dioxide emissions in 2002. Almost all (97.9 percent) of transportation sector emissions result from the consumption of petroleum products: motor gasoline, at 61.6 percent of total transportation sector emissions; middle distillates (diesel fuel) at 20.5 percent; jet fuel at 12.7 percent of the total; and residual oil (i.e., heavy fuel oil, largely for maritime use) at 2.7 percent of the sector’s total emissions. Motor gasoline is used primarily in automobiles and light trucks, and middle distillates are used in heavy trucks, locomotives, and ships. Emissions attributable to the transportation sector increased by 1.2 percent in 2002, from 1,827.3 to 1,849.7 million metric tons of carbon dioxide (Table 9). The fuel-use patterns and related emissions sources in the transportation sector are different from those in the other end-use sectors. By far the largest single source of emissions, motor gasoline, at 1,138.7 million metric tons of carbon dioxide, grew by 2.5 percent. Since 1990, carbon dioxide emissions related to the transportation sector have increased at an average annual rate of 1.4 percent. The growth since 1990 has meant that transportation emissions have increased by a total of 280.2 million metric tons, representing 37.8 percent of the growth in energy-related carbon dioxide emissions from all sectors. Transportation is the largest contributing end-use sector to total emissions. Electric Power Sector
The data in Table 10 represent estimates of carbon dioxide emissions for the electric power sector. These emissions when taken as a whole account for 39.3 percent of total U.S. energy-related carbon dioxide emissions; electric power sector emissions are distributed to the end-use sectors. The electric power sector includes traditional regulated utilities, as well as independent power producers whose primary business is the generation and sale of electricity. The industrial sector and, to a much lesser extent, the commercial sector also include establishments that generate electricity; however, their primary business is not electricity generation, and so their electricity-related emissions are included in the totals for those sectors, not in the electric power sector. Preliminary estimates indicate that carbon dioxide emissions from the electric power sector increased by 1.0 percent (22.4 million metric tons), from 2,226.6 million metric tons in 2001 to 2,249.0 million metric tons in 2002 (Table 10). Emissions from natural-gas-fired generation increased by 3.4 percent, emissions from coal-fired generation increased by 2.2 percent, and emissions from petroleum-fired generation decreased by 27.5 percent. Carbon dioxide emissions from the electric power sector have grown by 25.3 percent since 1990, while total carbon dioxide emissions have grown by 14.8 percent. Nonfuel Use of Energy Inputs In 2002, carbon sequestration through nonfuel uses of fossil fuels totaled 299.3 million metric tons carbon dioxide equivalent (Table 11). The vast majority was sequestered in petroleum-based products (280.2 million metric tons carbon dioxide equivalent), with smaller amounts in natural-gas-based products (17.3 million metric tons) and coal-based products (1.8 million metric tons). The main products that sequester carbon include feedstocks for plastics and other petrochemicals, asphalt and road oil, liquefied petroleum gas, lubricants, and waxes. The amount sequestered in 2002 was 2.2 percent higher than in 2001, when 292.8 million metric tons carbon dioxide equivalent was sequestered. Since 1990, the annual sequestration of carbon in this manner has increased by 47.4 million metric tons or 18.8 percent. This translates to an average annual growth rate of 1.4 percent. Carbon Dioxide Emissions and Economic Growth
Between 1990 and 2002, U.S. economic growth averaged 2.9 percent per year. Energy-related carbon dioxide emissions, however, grew by an average of 1.2 percent annually. As shown in Figure 2, U.S. energy intensity (energy consumed per dollar of GDP) fell by an average of 1.6 percent per year from 1990 to 2002. The carbon dioxide intensity of energy use (emissions per unit of energy consumed) has remained roughly at the 1990 level. Thus, it is the use of less energy per unit of economic output, not the use of low-carbon fuels, that has kept the growth rate of carbon dioxide emissions equal to about half the growth rate of GDP. The decrease in the energy intensity of the U.S. economy has resulted, in part, from an increase in the non-energy-intensive sectors of the economy relative to the traditional energy-intensive manufacturing industries, as well as energy efficiency improvements. Economic growth does, however, have an indirect effect on emissions, in that consumers with more disposable income use more energy services (such as travel) and tend to live in larger houses. On the other hand, such income effects can be offset somewhat by more energy-efficient vehicles, building shells, appliances, and heating and cooling equipment. It is expected that the trend of increasing energy efficiency will continue in the future, further reducing the carbon intensity of the U.S. economy (carbon dioxide equivalent emissions of greenhouse gases per unit of GDP) at an average rate of 1.5 percent per year from 2001 through 2025. Adjustments to Energy Consumption Total energy consumption and the carbon dioxide emissions upon which they are based correspond to EIA’s coverage of energy consumption, which includes the 50 States and the District of Columbia. Under the United Nations Framework Convention on Climate Change (UNFCCC), however, the United States is also responsible for counting emissions emanating from its territories, and their emissions are added to the U.S. total. Conversely, because the Intergovernmental Panel on Climate Change (IPCC) definition of energy consumption excludes international bunker fuels from the statistics of all countries, emissions from international bunker fuels are subtracted from the U.S. total. Additionally, military bunker fuels are subtracted because they are also excluded by the IPCC from the national total. These sources and subtractions are enumerated and described as “adjustments to energy.” U.S. Territories Energy-related carbon dioxide emissions for the U.S. territories are added as an adjustment in keeping with IPCC guidelines for national emissions inventories. The territories included are Puerto Rico, the U.S. Virgin Islands, American Samoa, Guam, the U.S. Pacific Islands, and Wake Island. Most of these emissions are from petroleum products; however, Puerto Rico and the Virgin Islands consume coal in addition to petroleum products. For 2002, total energy-related carbon dioxide emissions from the U.S. Territories are estimated at 42.9 million metric tons (Table 4). International Bunker Fuels In keeping with the IPCC guidelines for estimating national greenhouse gas emissions, carbon dioxide emissions from international bunker fuels are subtracted from the estimate of total U.S. energy-related emissions of carbon dioxide. The estimate for bunker fuels is based on purchases of distillate and residual fuels by foreign-bound ships at U.S. seaports, as well as jet fuel purchases by international air carriers at U.S. airports. Additionally, U.S. military operations for which fuel was originally purchased in the United States but consumed in international waters or airspace are subtracted from the total, because they are also considered international bunker fuels under this definition. For 2001, the carbon dioxide emissions estimate for military bunker fuels was 8.1 million metric tons. In 2002, approximately 90.2 million metric tons of carbon dioxide was emitted in total from international bunker fuels, including 82.1 million metric tons attributed to civilian consumption of bunker fuels. The total amount is subtracted from the U.S. total in Table 4. Just over half of the carbon dioxide emissions associated with international bunker fuels are from the combustion of jet fuels; residual and distillate fuels account for the other half, with most coming from residual fuel. Other Carbon Dioxide Emissions
Energy Production In addition to emissions resulting from fossil energy consumed, oil and gas production leads to emissions of carbon dioxide from sources other than the combustion of those marketed fossil fuels. The two energy production sources estimated for this report are:
Because many States require flaring of natural gas, EIA assumes that all gas reported under the category “Vented and Flared” is actually flared and therefore should be counted as carbon dioxide emissions rather than methane emissions. In 2002, about 5.1 million metric tons of carbon dioxide was emitted in this way (Table 4). By computing the difference between the estimated carbon dioxide content of raw gas and the carbon dioxide content of pipeline gas, the amount of carbon dioxide that has been removed (scrubbed) in order to improve the heat content and quality of natural gas can be calculated. This amount was about 18.1 million metric tons in 2002 (Table 4). Data on additional energy production sources that are excluded from this report are available in Energy Information Administration, Documentation: Emissions of Greenhouse Gases in the United States 2002 (to be published). Industrial Process Emissions Industrial emissions of carbon dioxide not caused by the combustion of fossil fuels accounted for only 1.2 percent (70.6 million metric tons) of total U.S. carbon dioxide emissions in 2002 (Table 4). Process-related emissions from industrial sources depend largely on the level of activity in the construction industries and on production at oil and gas wells. These sources include limestone and dolomite calcination, soda ash manufacture and consumption, carbon dioxide manufacture, cement manufacture, and aluminum production. Estimated industrial process emissions of carbon dioxide in 2002 were 70.6 million metric tons (17.5 percent) higher than in 1990 and 1.4 million metric tons (2.1 percent) higher than in 2001 (Table 12). Sixty-one percent of the carbon dioxide emissions from industrial processes are from cement manufacture. When calcium carbonate is heated (calcined) in a kiln, it is converted to lime and carbon dioxide. The lime is combined with other materials to produce clinker (an intermediate product from which cement is made), and the carbon dioxide is released to the atmosphere. In 2002, the United States manufactured an estimated 89.0 million metric tons of cement, resulting in the direct release of 43.3 million metric tons of carbon dioxide into the atmosphere. This calculation is independent of the carbon dioxide released by the production of energy consumed in making cement. The estimate for 2002 represents an increase in carbon dioxide emissions of 9.9 million metric tons (29.8 percent) compared with 1990 and an increase of about 1.8 million metric tons (4.4 percent) compared with 2001. There are numerous other industrial processes in which carbonate minerals are used in ways that release carbon dioxide into the atmosphere, including the use of limestone in the production of lime and in flue gas desulfurization and the manufacture and some uses of soda ash. Carbon dioxide is also released during aluminum smelting, when carbon anodes (with the carbon derived from nonfuel use of fossil fuels) are vaporized in the presence of aluminum oxide. Approximately 27.4 million metric tons of carbon dioxide was released in emissions from these other industrial process sources in 2002. Municipal solid waste that is combusted contains, on average, a portion that is composed of plastics, synthetic rubber, synthetic fibers, and carbon black. The carbon in these plastics has normally been accounted for as sequestered carbon, as reported in Table 11. However, according to the IPCC, to properly account for that carbon, emissions from the plastics portion of the municipal solid waste must be counted in total national emissions inventories. These emissions produce about 19.8 million metric tons of carbon dioxide, as calculated by the U.S. EPA, with the most recent estimate being for 2001. The 2001 value has been used as an estimate for 2002. Carbon Dioxide Emissions Tables
Released: October 2003 |
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