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Emissions of Greenhouse Gases Report
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Total Emissions | ||||||||||||||||||||||||||||||||||||||||||||
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Greenhouse Gas Intensity | ||||||||||||||||||||||||||||||||||||||||||||
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Greenhouse Gas Emissions in the U.S. Economy | ||||||||||||||||||||||||||||||||||||||||||||
The diagram on the right illustrates the flow of U.S. greenhouse gas emissions in 2007, from their sources to their distribution across the U.S. end-use sectors. The left side shows CO2 by fuel sources and quantities and other gases by quantities; the right side shows their distribution by sector. The center of the diagram indicates the split between CO2 emissions from direct fuel combustion and electricity conversion. Adjustments indicated at the top of the diagram for U.S. territories and international bunker fuels correspond to greenhouse gas reporting requirements developed by the United Nations Framework Convention on Climate Change (UNFCCC). CO2. CO2 emission sources include energy-related emissions (primarily from fossil fuel combustion) and emissions from industrial processes. The energy subtotal (5,991 MMTCO2e) includes petroleum, coal, and natural gas consumption and smaller amounts from renewable sources, including municipal solid waste and geothermal power generation. The energy subtotal also includes emissions from nonfuel uses of fossil fuels, mainly as inputs to other products. Industrial process emissions (105 MMTCO2e) include cement manufacture, limestone and dolomite calcination, soda ash manufacture and consumption, carbon dioxide manufacture, and aluminum production. The sum of the energy subtotal and industrial processes equals unadjusted CO2 emissions (6,096 MMTCO2e). The energy component of unadjusted emissions can be divided into direct fuel use (3,557 MMTCO2e) and fuel converted to electricity (2,433 MMTCO2e). Non-CO2 Gases. Methane (700 MMTCO2e) and nitrous oxide (384 MMTCO2e) sources include emissions related to energy, agriculture, waste management, and industrial processes. Other, high-GWP gases (177 MMTCO2e) include hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6). These gases have a variety of uses in the U.S. economy, including refrigerants, insulators, solvents, and aerosols; as etching, cleaning, and firefighting agents; and as cover gases in various manufacturing processes. Adjustments. In keeping with the UNFCCC, CO2 emissions from U.S. Territories (57 MMTCO2e) are added to the U.S. total, and CO2 emissions from fuels used for international transport (both oceangoing vessels and airplanes) (131 MMTCO2e) are subtracted to derive total U.S. greenhouse gas emissions (7,282 MMTCO2e). Emissions by End-Use Sector. CO2 emissions by end-use sectors are based on EIAs estimates of energy consumption (direct fuel use and purchased electricity) by sector and on the attribution of industrial process emissions by sector. CO2 emissions from purchased electricity are allocated to the end-use sectors based on their shares of total electricity sales. Non-CO2 gases are allocated by direct emissions in those sectors plus emissions in the electric power sector that can be attributed to the end-use sectors based on electricity sales. Residential emissions (1,281 MMTCO2e) include energy-related CO2 emissions (1,261 MMTCO2e); and non-CO2 emissions (20 MMTCO2e). The non-CO2 sources include direct methane and nitrous oxide emissions from direct fuel use. Non-CO2 indirect emissions attributable to purchased electricity, including methane and nitrous oxide emissions from electric power generation and SF6 emissions related to electricity transmission and distribution, are also included. Emissions in the commercial sector (1,355 MMTCO2e) include both energy-related CO2 emissions (1,098 MMTCO2e) and non-CO2 emissions (257 MMTCO2e). The non-CO2 emissions include direct emissions from landfills, wastewater treatment plants, commercial refrigerants, and stationary combustion emissions of methane and nitrous oxide. Non-CO2 indirect emissions attributable to purchased electricity, including methane and nitrous oxide emissions from electric power generation and SF6 emissions related to electricity transmission and distribution, are also included. Industrial emissions (2,610 MMTCO2e) include CO2 emissions (1,760 MMTCO2e)which can be broken down between combustion (1,655 MMTCO2e) and process emissions (105 MMTCO2e)and non-CO2 emissions (850 MMTCO2e). The non-CO2 direct emissions include emissions from agriculture (methane and nitrous oxide), coal mines (methane), petroleum and natural gas pipelines (methane), industrial process emissions (methane, nitrous oxide, HFCs, PFCs and SF6), and direct stationary combustion emissions of methane and nitrous oxide. Non-CO2 indirect emissions attributable to purchased electricity, including methane and nitrous oxide emissions from electric power generation and SF6 emissions related to electricity transmission and distribution, are also included. Transportation emissions (2,036 MMTCO2e) include energy-related CO2 emissions
from mobile source combustion (1,902 MMTCO2e); and non-CO2 emissions (134
MMTCO2e). The non-CO2 emissions include methane and nitrous oxide emissions
from mobile source combustion and HFC emissions from the use of refrigerants
for mobile source air-conditioning units. |
Click Chart to Enlarge |
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U.S. Emissions in a Global Perspective | ||||||||||||||||||||||||||||||||||||||||||||
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Recent U.S. and International Developments in Global Climate Change | ||||||||||||||||||||||||||||||||||||||||||||
United States
International: United Nations Framework Convention on Climate Change and the Kyoto Protocol
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Units for Measuring Greenhouse Gases | ||||||||||||||||||||||||||||||||||||||||||||
Emissions data are reported here in metric units, as favored by the international scientific community. Metric tons are relatively intuitive for users of U.S. measurement units, because 1 metric ton is only about 10 percent heavier than a short ton. Throughout this report, emissions of carbon dioxide and other greenhouse gases are given in carbon dioxide equivalents. In the case of carbon dioxide, emissions denominated in the molecular weight of the gas or in carbon dioxide equivalents are the same. Carbon dioxide equivalent data can be converted to carbon equivalents by multiplying by 12/44. Emissions of other greenhouse gases (such as methane) can also be measured in carbon dioxide equivalent units by multiplying their emissions (in metric tons) by their global warming potentials (GWPs). Carbon dioxide equivalents are the amount of carbon dioxide by weight emitted into the atmosphere that would produce the same estimated radiative forcing as a given weight of another radiatively active gas. Carbon dioxide equivalents are computed by multiplying the weight of the gas being measured (for example, methane) by its estimated GWP (which is 25 for methane). In 2007, the Intergovernmental Panel on Climate Change (IPCC) Working Group I released its Fourth Assessment Report, Climate Change 2007: The Physical Science Basis.2 Among other things, the Fourth Assessment Report updated a number of the GWP estimates that appeared in the IPCC's Third Assessment Report.3 The GWPs published in the Fourth Assessment Report were used for the calculation of carbon dioxide equivalent emissions for this report. Table 4 below summarizes the GWP values from the Second, Third, and fourth Assessment Reports. |
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Methodology Updates for This Report | ||||||||||||||||||||||||||||||||||||||||||||
Carbon Dioxide EIA has begun using a separate carbon coefficient for net imports of metallurgical coke, based on IPCC guidelines. The new coefficient more accurately reflects the carbon content of imported coke. The carbon in coke that is domestically produced, and the carbon dioxide emissions from that coke, are counted in the amount of domestic coking coal consumed. For net coke imports, however, it was decided that the new, higher carbon coefficient should be used. Although the difference between the two coefficients is about 14 percent, the amount of coke imported is relatively small. Thus, the increase in calculated carbon dioxide emissions resulting from the change in coefficients is in the range of 1 to 3 million metric tons for most years over the 1990-2007 period. Estimates of carbon dioxide emissions from natural gas combustion have been adjusted upward, to reflect increasing concentrations of carbon dioxide in the natural gas produced in the United States in recent years. As a result of the change, the estimates of carbon dioxide emissions from natural gas combustion for recent years are about 1 million metric tons higher than those in last years report. Because of a change in methodology, the estimate of carbon dioxide emissions from waste combustion (included in Other Sources) has been adjusted downward, as most of those emissions are accounted for by grid-connected waste-to-energy plants in the electric power sector, which are captured in EIAs surveys. The result of this change is a reduction of 3 to 4 million metric tons per year from 1990 to 2007. An error in the calculation code caused emissions from industrial lubricants to be omitted from total emissions in EIAs emissions inventory reports for 2005 and 2006. Although lubricants are a nonfuel use, there are emissions associated with their use. Emissions from this source are again included in total emissions in this years report. As a result of the correction, the estimates of total U.S. carbon dioxide emissions are higher by about 6 to 7 million metric tons per year from 1990 to 2007 than those in the 2005 and 2006 data reports. Other changes reflect revisions in the underlying activity data. For example, in the 2006 data report, the amount of natural gas consumed in the United States in 2005 was estimated at 22,241 billion cubic feet, whereas in this years report the estimate for 2005 is 22,011 billion cubic feet. As a result, the estimate for carbon dioxide emissions from natural gas combustion in 2005 is about 10 million metric tons lower in this years report than in last years report. Methane In its Fourth Assessment Report (AR4),4 the IPCC developed revised global warming potential factors (GWPs) for selected gases. The GWP for methane was revised from the previously published value of 23 in the IPCCs Third Assessment Report5 to 25 in the Fourth Assessment Report. The revised GWP for methane is used in this report. In addition, this report incorporates an increase in the density of methane from 42.28 to 42.37 pounds per thousand cubic feet, in order to provide consistent temperature and pressure values for methane in all EIA data. Nitrous Oxide The IPCC also updated the GWP for nitrous oxide in its Fourth Assessment Report, to 298, up from 296 in the IPCCs Third Assessment Report. The revised GWP for nitrous oxide is used in this report. High-GWP Gases The IPCC also updated GWPs for most of the high-GWP emissions sources in its Fourth Assessment Report. The revised GWPs are included in Table 4 on page 11, under Units for Measuring Greenhouse Gases. Land Use Forest Land Remaining Forest Land is the major source of change in net carbon dioxide flux resulting from land use. In this report, the addition of newly available forest inventory data, as well as some refinements to previous data, involved the following major changes: incorporating and updating State and sub-State inventory data; and including a portion of Alaskan forest for the first time. In addition, minor refinements to the calculation of flux from harvested wood products included: a shorter half-life for decay in dumps; and separation of decay in dumps from decay in landfills. Overall, these changes, in combination with adjustments in the other sources/sinks within the land-use category, resulted in an average annual increase of 20.1 million metric tons carbon dioxide equivalent (2.5 percent) in net carbon flux to the atmosphere from Land Use, Land-Use Change, and Forestry for the years 1990 through 2005. |
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