| Overview | Energy Consumption | Electric Utilities | Industrial Sources | Adjustments to Energy Consumption | Carbon Dioxide Data Tables |
| U.S. Anthropogenic Carbon Dioxide Emissions, 1990-1995 | ||
| Carbon Dioxide | Carbon Equivalent | |
| Estimated 1995 Emissions (Million Metric Tons) | 5,288.5 | 1,442.3 |
| Change Compared to 1994 (Million Metric Tons) | 39.9 | 10.9 |
| Change from 1994 (Percent) | 0.8 | 0.8 |
| Change Compared to 1990 (Million Metric Tons) | 257.9 | 70.3 |
| Change from 1990 (Percent) | 5.1 | 5.1 |
U.S. carbon dioxide emissions are largely caused by the combustion of coal, natural gas, and petroleum [23]. A fraction (less than 2 percent) comes from other sources, including the manufacture of cement and lime. Total estimated emissions increased by 0.8 percent from 1994 to about 1,442 million metric tons of carbon in 1995 (Table 5) [24]. Compared to 1990 emissions levels, the increase is about 70 million metric tons or 5.1 percent [25].
Over the long term, carbon dioxide emissions are related to trends in economic activity and energy consumption, as well as the particulars of fuel choice. In the 1990s the growth in energy consumption lagged behind trends in the economy. For example, in 1995 the economy grew by about 2.1 percent, while energy consumption increased slightly less, by about 1.9 percent (Figure 2). Carbon dioxide emissions rose even less, by a modest 0.8 percent, because of increased nuclear and hydroelectric power production. Between 1994 and 1995 total energy consumption in the United States increased by 1.7 quadrillion Btu. Although low emitting nuclear power and renewable fuels ordinarily provide about 15 percent of the U.S. energy supply, gains from these sources supplied two-thirds of the increase in U.S. energy requirements for 1995, thereby moderating growth in energy-related carbon emissions. The year-to-year increase was only about 11 million metric tons of carbon in 1995, a smaller increase than in the previous year (Figure 3).
| Energy End-Use Sector Sources of Carbon Dioxide Emissions, 1990-1995 | ||||
| Sector | Million Metric Tons Carbon | Percent Change | ||
| 1990 | 1995 | 1990- 1995 | 1994- 1995 | |
| Transportation | 432.1 | 457.2 | 5.8 | 1.5 |
| Industrial | 452.4 | 462.9 | 2.3 | -0.1 |
| Commercial | 206.7 | 218.4 | 5.6 | 2.0 |
| Residential | 253 | 270.9 | 7.1 | 0.9 |
| Note: Electric utility emissions are distributed across sectors. | ||||
EIA energy statistics partition total energy consumption into four end-use sectors: industrial, transportation, residential, and commercial. For all the sectors except transportation, a substantial portion of the energy used is consumed as electricity. In the future most of the growth in energy consumption is expected to be in the transportation sector and in the use of electricity. In this report, emissions for each sector are defined as the sum of emissions resulting from the direct burning of fuels plus emissions associated with producing electric power used in the sector. This approach makes sectoral analysis more meaningful and helps to reveal the full value of conservation when electricity is conserved. Not only is final energy saved but also the substantial amount of energy (and associated emissions) taken as “losses” in electric power generation. More than two-thirds of the carbon dioxide emissions in the residential and commercial sectors are derived from electricity (Figure 4).
About one-third of end-use carbon dioxide emissions are accounted for by the industrial sector (Table 6), which comprises manufacturing industries, the largest part of the sector, along with mining, construction, agriculture, fisheries, and forestry. Energy consumption is dominated by the need for heat and power; however, a large share of industrial energy use involves consumption of raw materials for petrochemical feedstocks. Natural gas and electricity consumption each account for about one-third of the energy consumed in this sector (with losses in electricity generation included).
Although some carbon in the “nonfuel” use of energy is sequestered (Table 7), emissions amounted to nearly 463 million metric tons of carbon in 1995, up 0.5 percent from the previous year (Table 8). Energy efficiency improvements, combined with low growth in energy-intensive industries, have moderated trends in carbon dioxide emissions while total industrial output has expanded. Between 1990 and 1995, emissions for this sector increased by 10.5 million metric tons of carbon.
The transportation sector accounts for about one-third of U.S. carbon dioxide emissions. Growth in this sector is more rapid than in the other end-use sectors. Increases in the driving age population, low energy prices, and stable average fuel efficiency in vehicles all contribute to expanding energy consumption. Motor gasoline accounts for nearly two-thirds of transportation sector energy consumption. Together with emissions from distillate, residual, and jet fuels, total emissions were about 457 million metric tons of carbon for the transportation sector in 1995 (just under the amount emitted by the industrial sector) (Table 9). Transportation sector emissions have accounted for nearly 25 million metric tons, or nearly 40 percent, of the national increase for end-use sectors since 1990. Forecasts of U.S. energy markets imply that emissions from transportation will overtake those from the industrial sector sometime before the year 2000 (Figure 5) [26].
Carbon dioxide emissions from this sector account for less than one-fifth of U.S. emissions (Table 6). Most of these emissions are associated with the use of natural gas and electricity for space heating and air conditioning and thus are subject to the vagaries of the weather. In 1995 residential emissions declined slightly due tomilder weather, which lowered consumption of distillate fuels and natural gas. However, over the 5-year period from 1990, residential emissions have accounted for 18 million metric tons, or about one-third, of the increase in carbon dioxide emissions for all end-use sectors (Table 10).
The commercial sector contributes the smallest share of carbon dioxide emissions, about 15 percent of the total. Since this sector includes all business establishments that are not engaged in transportation or in manufacturing or other types of industrial activity (agriculture, mining, or construction), most of the energy consumed is electricity and natural gas. Commercial sector carbon dioxide emissions increased by 1.6 million metric tons or 0.7 percent to 218.5 million metric tons in 1995 (Table 11). Between 1990 and 1995 the commercial sector accounted for nearly 12 million tons of the total increase in U.S. emissions.
| Electric Utility Carbon Dioxide Emissions
by Fuel Input, 1990 and 1995 | ||||
| Fuel | Million Metric Tons Carbon | Percent Change | ||
| 1990 | 1995 | 1990- 1995 | 1994- 1995 | |
| Petroleum | 26.6 | 14.0 | -47.4 | -32.1 |
| Natural Gas | 41.2 | 47.0 | 14.2 | 7.0 |
| Coal | 409.0 | 432.8 | 5.8 | 0.6 |
| Total | 476.9 | 493.8 | 3.6 | -0.2 |
Although end users create the demand for electricity, the utilities make decisions about how to meet that demand, based on fuel prices and capacity availability. In 1995 demand for power increased by 2.9 percent, but utility carbon emissions declined because nuclear and conventional hydroelectric power generation met a disproportionately large share of the increased demand. Water conditions in the Pacific Northwest were better than normal in 1995, and the average capacity factor for nuclear power was up to 78 percent, following a pattern consistent with a long-term trend in improved availability. Neither of these power sources is associated with any significant carbon dioxide emissions.
Over the longer term, the trend in electric utility emissions has been upward. Although utility efforts to improve efficiency in production and to implement demand-side management programs have kept emissions lower than they otherwise would have been, between 1990 and 1995 emissions from burning fossil fuels to meet end-use demand accounted for an increase of 17 million metric tons of carbon [27]. This was primarily because of increased use of coal, the highest emitting fuel, which currently provides 55 percent of U.S. electric power (Table 12). In the future, expanded use of natural gas may slow further growth in emissions.
| U.S. Carbon Dioxide Emissions from
Industrial Sources, 1990-1995 | |
| Estimated 1995 Emissions (Million Metric Tons Carbon) | 21.3 |
| Change Compared to 1994 (Million Metric Tons Carbon) | 0.3 |
| Change from 1994 (Percent) | 1.4 |
| Change Compared to 1990 (Million Metric Tons Carbon) | 2.4 |
| Change from 1990 (Percent) | 12.8 |
Emissions from industrial sources account for only about 1.5 percent of total U.S. carbon dioxide emissions. This level of emissions fluctuates annually between 20 and 21 million metric tons of carbon, depending largely on the level of activity in the construction industries and production at oil and gas wells. The remaining, relatively minor, sources are limestone and dolomite consumption, soda ash manufacture and consumption, carbon dioxide manufacture, and aluminum production. Most of the change in 1995 resulted from increased cement production and manufacture of lime [28].
When an oil field is developed for petroleum extraction, any natural gas associated with that field may be flared if its use is not economically justifiable. This is typically the case with a remote site or when the gas is of poor quality or minimal volume. In the United States the total amount of natural gas vented or flared has increased in recent years, from about 150 billion cubic feet in 1990 to 228 billion cubic feet in 1994. The portion flared caused nearly 2 million metric tons of carbon emissions in 1995 (Table 13).
Industrial processes account for about 18 to 20 million metric tons of carbon emissions per year (Table 14). Since 1990, emissions from industrial process have increased due to an increase in emissions from cement manufacture and limestone consumption (partially offset by a decrease in emissions from aluminum manufacture). More than one-half of the emissions from industrial process 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), while the carbon dioxide is released to the atmosphere. In 1995, the United States manufactured an estimated 77 million metric tons of cement, or 6 percent of the world’s total. In recent years, this has resulted in emissions of 9 to 10 million metric tons of carbon.
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 flue gas desulfurization and the manufacture and some uses of soda ash. Approximately 5 million metric tons of carbon per year is emitted from these sources. Carbon dioxide is also released during aluminum smelting, when carbon anodes (with the carbon ultimately derived from nonfuel use of fossil fuels) are vaporized in the presence of aluminum oxide.
Adjustments to Energy Consumption
Under the Framework Convention, parties to the agreement committed to providing information on emissions trends, using methods that would facilitate international comparison of emissions estimates. To support such comparisons, a generalized reporting format was adopted. The format differs slightly from that used in the preparation of U.S. national energy statistics, primarily with respect to the definition of “consumption” and the treatment of energy consumption in U.S. territories and consumption of bunker fuels for international transport. EIA’s energy data for the United States cover the 50 States and the District of Columbia but not the U.S. territories. Bunker fuels (fuel consumed by ships and aircraft engaged in international trade) are subsumed in EIA’s transportation sector energy consumption data. By contrast, energy data used by the International Energy Agency for the United States include U.S. territories and excludes bunker fuels. Finally, the generalized format uses a “top-down” approach to estimate “apparent energy consumption” from data on energy production and trade. For most countries around the world this is the best approach, because energy consumption is not always accurately reported. For the United States, however, the EIA provides information (used for estimates in this report) on consumption by end-use sector and fuel type for a wide array of petroleum products, coal, and natural gas.
Collectively, these differences in treatment can produce variations of several percentage points in reported energy consumption, and hence in the estimates of carbon emissions. The methodology for calculating U.S. territories’ emissions and other adjustments, is described in Appendix A.
In this report, emissions from bunker fuels are subsumed in the estimates of carbon emissions from energy consumption [29]. These emissions are also shown separately in Table 15. The estimate is based on purchases of fuel by ocean-going ships in U.S. ports and by international air carriers in U.S. airports. In 1994 bunker fuel emissions amounted to about 21 million metric tons of carbon.
If consumption is estimated as “apparent consumption” using a top-down approach based on production plus imports minus exports plus stock change, then statistical discrepancies will be included in consumption. There are statistical discrepancies between estimated U.S. production and consumption of all fossil fuels. In the case of natural gas, it is probable (though by no means certain) that some portion of the statistical discrepancy is due to unreported natural gas consumption and stock changes. Therefore, this report includes an estimate of emissions from “unaccounted for natural gas” (which is likely to be due to unreported consumption) as an adjustment to the national emissions estimate. This item is also part of the difference between emissions estimates based on “apparent consumption” and estimates based on consumption actually reported. In recent years, the amount of carbon emissions from this source has varied from -1 to 4 million metric tons.
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