Executive Summary ES-1 

Executive Summary 

An emissions inventory that identifies and quantifies a country's primary anthropogenic1 sources and sinks of 

greenhouse gases is essential for addressing climate change. This inventory adheres to both 1) a comprehensive and 

detailed set of methodologies for estimating sources and sinks of anthropogenic greenhouse gases, and 2) a common 

and consistent mechanism that enables Parties to the United Nations Framework Convention on Climate Change 

(UNFCCC) to compare the relative contribution of different emission sources and greenhouse gases to climate 

change. 

In 1992, the United States signed and ratified the UNFCCC. As stated in Article 2 of the UNFCCC, “The ultimate 

objective of this Convention and any related legal instruments that the Conference of the Parties may adopt is to 

achieve, in accordance with the relevant provisions of the Convention, stabilization of greenhouse gas 

concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the 

climate system. Such a level should be achieved within a time-frame sufficient to allow ecosystems to adapt 

naturally to climate change, to ensure that food production is not threatened and to enable economic development to 

proceed in a sustainable manner.”2

Parties to the Convention, by ratifying, “shall develop, periodically update, publish and make available...national 

inventories of anthropogenic emissions by sources and removals by sinks of all greenhouse gases not controlled by 

the Montreal Protocol, using comparable methodologies...”3 The United States views this report as an opportunity 

to fulfill these commitments. 

This chapter summarizes the latest information on U.S. anthropogenic greenhouse gas emission trends from 1990 

through 2008. To ensure that the U.S. emissions inventory is comparable to those of other UNFCCC Parties, the 

estimates presented here were calculated using methodologies consistent with those recommended in the Revised 

1996 IPCC Guidelines for National Greenhouse Gas Inventories (IPCC/UNEP/OECD/IEA 1997), the IPCC Good 

Practice Guidance and Uncertainty Management in National Greenhouse Gas Inventories (IPCC 2000), and the 

IPCC Good Practice Guidance for Land Use, Land-Use Change, and Forestry (IPCC 2003). Additionally, the U.S. 

emission inventory has begun to incorporate new methodologies and data from the 2006 IPCC Guidelines for 

National Greenhouse Gas Inventories (IPCC 2006). The structure of this report is consistent with the UNFCCC 

guidelines for inventory reporting.4 For most source categories, the Intergovernmental Panel on Climate Change 

(IPCC) methodologies were expanded, resulting in a more comprehensive and detailed estimate of emissions. 

[BEGIN BOX] 

Box ES- 1: Recalculations of Inventory Estimates 

Each year, emission and sink estimates are recalculated and revised for all years in the Inventory of U.S. Greenhouse 

Gas Emissions and Sinks, as attempts are made to improve both the analyses themselves, through the use of better 

methods or data, and the overall usefulness of the report. In this effort, the United States follows the IPCC Good 

Practice Guidance (IPCC 2000), which states, regarding recalculations of the time series, "It is good practice to 

recalculate historic emissions when methods are changed or refined, when new source categories are included in the 

national inventory, or when errors in the estimates are identified and corrected." In general, recalculations are made 

to the U.S. greenhouse gas emission estimates either to incorporate new methodologies or, most commonly, to 

update recent historical data. 

 

1 The term “anthropogenic”, in this context, refers to greenhouse gas emissions and removals that are a direct result of human 

activities or are the result of natural processes that have been affected by human activities (IPCC/UNEP/OECD/IEA 1997). 

2 Article 2 of the Framework Convention on Climate Change published by the UNEP/WMO Information Unit on Climate 

Change. See <http://unfccc.int>. 

3 Article 4(1)(a) of the United Nations Framework Convention on Climate Change (also identified in Article 12). Subsequent 

decisions by the Conference of the Parties elaborated the role of Annex I Parties in preparing national inventories. See 

<http://unfccc.int>. 

4 See <http://unfccc.int/resource/docs/cop8/08.pdf>. 
ES-2 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2008 

In each Inventory report, the results of all methodology changes and historical data updates are presented in the 

"Recalculations and Improvements" chapter; detailed descriptions of each recalculation are contained within each 

source's description contained in the report, if applicable. In general, when methodological changes have been 

implemented, the entire time series (in the case of the most recent inventory report, 1990 through 2007) has been 

recalculated to reflect the change, per IPCC Good Practice Guidance. Changes in historical data are generally the 

result of changes in statistical data supplied by other agencies. References for the data are provided for additional 

information. 

[END BOX] 

Background Information 

Naturally occurring greenhouse gases include water vapor, carbon dioxide (CO2), methane (CH4), nitrous oxide 

(N2O), and ozone (O3). Several classes of halogenated substances that contain fluorine, chlorine, or bromine are 

also greenhouse gases, but they are, for the most part, solely a product of industrial activities. Chlorofluorocarbons 

(CFCs) and hydrochlorofluorocarbons (HCFCs) are halocarbons that contain chlorine, while halocarbons that 

contain bromine are referred to as bromofluorocarbons (i.e., halons). As stratospheric ozone depleting substances, 

CFCs, HCFCs, and halons are covered under the Montreal Protocol on Substances that Deplete the Ozone Layer. 

The UNFCCC defers to this earlier international treaty. Consequently, Parties to the UNFCCC are not required to 

include these gases in their national greenhouse gas emission inventories.5 Some other fluorine-containing 

halogenated substances—hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6)—do 

not deplete stratospheric ozone but are potent greenhouse gases. These latter substances are addressed by the 

UNFCCC and accounted for in national greenhouse gas emission inventories. 

There are also several gases that do not have a direct global warming effect but indirectly affect terrestrial and/or 

solar radiation absorption by influencing the formation or destruction of greenhouse gases, including tropospheric 

and stratospheric ozone. These gases include carbon monoxide (CO), oxides of nitrogen (NOx), and non-CH4

volatile organic compounds (NMVOCs). Aerosols, which are extremely small particles or liquid droplets, such as 

those produced by sulfur dioxide (SO2) or elemental carbon emissions, can also affect the absorptive characteristics 

of the atmosphere. 

Although the direct greenhouse gases CO2, CH4, and N2O occur naturally in the atmosphere, human activities have 

changed their atmospheric concentrations. From the pre-industrial era (i.e., ending about 1750) to 2005, 

concentrations of these greenhouse gases have increased globally by 36, 148, and 18 percent, respectively (IPCC 

2007). 

Beginning in the 1950s, the use of CFCs and other stratospheric ozone depleting substances (ODS) increased by 

nearly 10 percent per year until the mid-1980s, when international concern about ozone depletion led to the entry 

into force of the Montreal Protocol. Since then, the production of ODS is being phased out. In recent years, use of 

ODS substitutes such as HFCs and PFCs has grown as they begin to be phased in as replacements for CFCs and 

HCFCs. Accordingly, atmospheric concentrations of these substitutes have been growing (IPCC 2007). 

Global Warming Potentials 

Gases in the atmosphere can contribute to the greenhouse effect both directly and indirectly. Direct effects occur 

when the gas itself absorbs radiation. Indirect radiative forcing occurs when chemical transformations of the 

substance produce other greenhouse gases, when a gas influences the atmospheric lifetimes of other gases, and/or 

when a gas affects atmospheric processes that alter the radiative balance of the earth (e.g., affect cloud formation or 

albedo).6 The IPCC developed the Global Warming Potential (GWP) concept to compare the ability of each 

 

5 Emissions estimates of CFCs, HCFCs, halons and other ozone-depleting substances are included in the annexes of the 

Inventory report for informational purposes. 

6 Albedo is a measure of the Earth’s reflectivity, and is defined as the fraction of the total solar radiation incident on a body that 

is reflected by it. 
Executive Summary ES-3 

greenhouse gas to trap heat in the atmosphere relative to another gas. 

The GWP of a greenhouse gas is defined as the ratio of the time-integrated radiative forcing from the instantaneous 

release of 1 kilogram (kg) of a trace substance relative to that of 1 kg of a reference gas (IPCC 2001). Direct 

radiative effects occur when the gas itself is a greenhouse gas. The reference gas used is CO2, and therefore GWPweighted emissions are measured in teragrams (or million metric tons) of CO2 equivalent (Tg CO2 Eq.)7,8 All gases 

in this Executive Summary are presented in units of Tg CO2 Eq. 

The UNFCCC reporting guidelines for national inventories were updated in 2006,9 but continue to require the use of 

GWPs from the IPCC Second Assessment Report (SAR) (IPCC 1996). This requirement ensures that current 

estimates of aggregate greenhouse gas emissions for 1990 to 2008 are consistent with estimates developed prior to 

the publication of the IPCC Third Assessment Report (TAR) and the IPCC Fourth Assessment Report (AR4). 

Therefore, to comply with international reporting standards under the UNFCCC, official emission estimates are 

reported by the United States using SAR GWP values. All estimates are provided throughout the report in both CO2

equivalents and unweighted units. A comparison of emission values using the SAR GWPs versus the TAR and AR4 

GWPs can be found in Chapter 1 and, in more detail, in Annex 6.1 of this report. The GWP values used in this 

report are listed below in Table ES-1. 

Table ES-1: Global Warming Potentials (100-Year Time Horizon) Used in this Report 

Gas GWP 

CO2 1 

CH4* 21 

N2O 310 

HFC-23 11,700 

HFC-32 650 

HFC-125 2,800 

HFC-134a 1,300 

HFC-143a 3,800 

HFC-152a 140 

HFC-227ea 2,900 

HFC-236fa 6,300 

HFC-4310mee 1,300 

CF4 6,500 

C2F6 9,200 

C4F10 7,000 

C6F14 7,400 

SF6 23,900 

Source: IPCC (1996) 

* The CH4 GWP includes the direct effects and those indirect effects due to the production of tropospheric ozone and 

stratospheric water vapor. The indirect effect due to the production of CO2 is not included. 

Global warming potentials are not provided for CO, NOx, NMVOCs, SO2, and aerosols because there is no agreedupon method to estimate the contribution of gases that are short-lived in the atmosphere, spatially variable, or have 

only indirect effects on radiative forcing (IPCC 1996). 

Recent Trends in U.S. Greenhouse Gas Emissions and Sinks 

In 2008, total U.S. greenhouse gas emissions were 6,956.8 Tg CO2 Eq. Overall, total U.S. emissions have risen by 

approximately 14 percent from 1990 to 2008. Emissions declined from 2007 to 2008, decreasing by 2.9 percent 

(211.3 Tg CO2 Eq.). This decrease is primarily a result of a decrease in demand for transportation fuels associated 

with the record high costs of these fuels that occurred in 2008. Additionally, electricity demand declined in 2008 in 

part due to a significant increase in the cost of fuels used to generate electricity. In 2008, temperatures were cooler 

 

7 Carbon comprises 12/44ths of carbon dioxide by weight. 

8 One teragram is equal to 1012 grams or one million metric tons. 

9 See <http://unfccc.int/resource/docs/2006/sbsta/eng/09.pdf>. 
ES-4 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2008 

in the United States than in 2007, both in the summer and the winter. This lead to an increase in heating related 

energy demand in the winter, however, much of this increase was offset by a decrease in cooling related electricity 

demand in the summer. 

Figure ES-1 through Figure ES-3 illustrate the overall trends in total U.S. emissions by gas, annual changes, and 

absolute change since 1990. Table ES-2 provides a detailed summary of U.S. greenhouse gas emissions and sinks 

for 1990 through 2008. 

Figure ES-1: U.S. Greenhouse Gas Emissions by Gas 

Figure ES-2: Annual Percent Change in U.S. Greenhouse Gas Emissions 

Figure ES-3: Cumulative Change in Annual U.S. Greenhouse Gas Emissions Relative to 1990 

Table ES-2: Recent Trends in U.S. Greenhouse Gas Emissions and Sinks (Tg CO2 Eq. or million metric tons CO2

Eq.) 

Gas/Source 1990 1995 2000 2005 2006 2007 2008

CO2 5,100.8 5,427.3 5,977.2 6,108.4 6,017.2 6,120.2 5,921.2 

Fossil Fuel Combustion 4,735.7 5,029.5 5,593.4 5,753.3 5,652.8 5,757.0 5,572.8 

Electricity Generation 1,820.8 1,947.9 2,296.9 2,402.1 2,346.4 2,412.8 2,363.5 

Transportation 1,485.8 1,608.0 1,809.5 1,895.3 1,876.7 1,893.7 1,785.3 

Industrial 845.4 862.6 852.2 825.6 850.7 842.2 819.3 

Residential 339.1 353.3 371.2 358.4 322.1 341.7 342.7 

Commercial 216.7 223.2 227.7 221.3 206.0 217.4 219.5 

U.S. Territories 27.9 34.5 35.9 50.6 50.9 49.1 42.5 

Non-Energy Use of Fuels 119.6 142.9 146.1 136.5 141.4 135.3 134.2 

Iron and Steel Production & 

Metallurgical Coke 

Production 102.6 95.7 88.1 67.7 70.5 72.8 69.0 

Cement Production 33.3 36.8 41.2 45.9 46.6 45.2 41.1 

Natural Gas Systems 37.3 42.2 29.4 29.5 29.5 30.8 30.0 

Lime Production 11.5 13.3 14.1 14.4 15.1 14.6 14.3 

Incineration of Waste 8.0 11.5 11.3 12.6 12.7 13.3 13.1 

Ammonia Production and Urea 

Consumption 16.8 17.8 16.4 12.8 12.3 14.0 11.8 

Cropland Remaining Cropland 7.1 7.0 7.5 7.9 7.9 8.3 7.6 

Limestone and Dolomite Use 5.1 6.7 5.1 6.8 8.0 7.7 6.6 

Aluminum Production 6.8 5.7 6.1 4.1 3.8 4.3 4.5 

Soda Ash Production and 

Consumption 4.1 4.3 4.2 4.2 4.2 4.1 4.1 

Petrochemical Production 3.3 4.1 4.5 4.2 3.8 3.9 3.4 

Titanium Dioxide Production 1.2 1.5 1.8 1.8 1.8 1.9 1.8 

Carbon Dioxide Consumption 1.4 1.4 1.4 1.3 1.7 1.9 1.8 

Ferroalloy Production 2.2 2.0 1.9 1.4 1.5 1.6 1.6 

Phosphoric Acid Production 1.5 1.5 1.4 1.4 1.2 1.2 1.2 

Wetlands Remaining Wetlands 1.0 1.0 1.2 1.1 0.9 1.0 0.9 

Petroleum Systems 0.6 0.5 0.5 0.5 0.5 0.5 0.5 

Zinc Production 0.9 1.0 1.1 0.5 0.5 0.4 0.4 

Lead Production 0.3 0.3 0.3 0.3 0.3 0.3 0.3 

Silicon Carbide Production and 

Consumption 0.4 0.3 0.2 0.2 0.2 0.2 0.2 

Land Use, Land-Use Change, (909.4) (842.9) (664.2) (950.4) (959.2) (955.4) (940.3)
Executive Summary ES-5 

and Forestry (Sink)a

Biomass - Wood 215.2 229.1 218.1 206.9 207.9 207.4 198.4

International Bunker Fuelsb

 111.8 99.8 98.5 110.5 129.1 127.1 135.2

Biomass - Ethanol 4.2 7.7 9.2 22.6 30.5 38.3 53.3

CH4 613.4 613.2 586.0 553.2 568.2 569.2 567.6 

Enteric Fermentation 132.4 143.7 136.8 136.7 139.0 141.2 140.8 

Landfills 149.3 144.1 120.7 125.6 127.1 126.5 126.3 

Natural Gas Systems 129.5 132.6 130.7 103.6 103.1 99.5 96.4 

Coal Mining 84.1 67.1 60.4 56.9 58.3 58.1 67.6 

Manure Management 29.3 33.9 38.6 42.2 42.3 45.9 45.0 

Petroleum Systems 33.9 32.0 30.2 28.2 28.2 28.8 29.1 

Wastewater Treatment 23.5 24.8 25.2 24.3 24.5 24.4 24.3 

Forest Land Remaining Forest 

Land 3.2 4.3 14.3 9.8 21.6 20.0 11.9 

Rice Cultivation 7.1 7.6 7.5 6.8 5.9 6.2 7.2 

Stationary Combustion 7.4 7.1 6.6 6.6 6.2 6.5 6.7 

Abandoned Underground Coal 

Mines 6.0 8.2 7.4 5.6 5.5 5.7 5.9 

Mobile Combustion 4.7 4.3 3.4 2.5 2.3 2.2 2.0 

Composting 0.3 0.7 1.3 1.6 1.6 1.7 1.7 

Field Burning of Agricultural 

Residues 0.8 0.7 0.9 0.9 0.9 1.0 1.0 

Petrochemical Production 0.9 1.1 1.2 1.1 1.0 1.0 0.9 

Iron and Steel Production & 

Metallurgical Coke 

Production 1.0 1.0 0.9 0.7 0.7 0.7 0.6 

Ferroalloy Production + + + + + + + 

Silicon Carbide Production and 

Consumption + + + + + + + 

Incineration of Waste + + + + + + + 

International Bunker Fuelsb

 0.2 0.1 0.1 0.1 0.2 0.2 0.2 

N2O 322.3 342.5 345.5 328.3 329.5 327.7 318.2 

Agricultural Soil Management 203.5 205.9 210.1 215.8 211.2 211.0 215.9 

Mobile Combustion 43.9 54.0 53.2 36.9 33.6 30.3 26.1 

Nitric Acid Production 18.9 21.0 20.7 17.6 17.2 20.5 19.0 

Manure Management 14.4 15.5 16.7 16.6 17.3 17.3 17.1 

Stationary Combustion 12.8 13.3 14.5 14.7 14.5 14.6 14.2 

Forest Land Remaining Forest 

Land 2.7 3.7 12.1 8.4 18.0 16.7 10.1 

Wastewater Treatment 3.7 4.0 4.5 4.7 4.8 4.9 4.9 

N2O from Product Uses 4.4 4.6 4.9 4.4 4.4 4.4 4.4 

Adipic Acid Production 15.8 17.6 5.5 5.0 4.3 3.7 2.0 

Composting 0.4 0.8 1.4 1.7 1.8 1.8 1.8 

Settlements Remaining 

Settlements 1.0 1.2 1.1 1.5 1.5 1.6 1.6 

Field Burning of Agricultural 

Residues 0.4 0.4 0.5 0.5 0.5 0.5 0.5 

Incineration of Waste 0.5 0.5 0.4 0.4 0.4 0.4 0.4 

Wetlands Remaining Wetlands + + + + + + + 

International Bunker Fuelsb

 1.1 0.9 0.9 1.0 1.2 1.2 1.2 

HFCs 36.9 62.2 103.2 119.3 121.8 127.4 126.9 

Substitution of Ozone 

Depleting Substancesc

 0.3 29.0 74.3 103.2 107.7 110.1 113.0 

HCFC-22 Production 36.4 33.0 28.6 15.8 13.8 17.0 13.6 

Semiconductor Manufacture 0.2 0.3 0.3 0.2 0.3 0.3 0.3 

PFCs 20.8 15.6 13.5 6.2 6.0 7.5 6.7 
ES-6 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2008 

Aluminum Production 18.5 11.8 8.6 3.0 2.5 3.8 2.7 

Semiconductor Manufacture 2.2 3.8 4.9 3.2 3.5 3.6 4.0 

SF6 32.6 27.9 19.1 17.8 17.0 16.1 16.1 

Electrical Transmission and 

Distribution 26.6 21.4 15.0 14.0 13.2 12.7 13.1 

Magnesium Production and 

Processing 5.4 5.6 3.0 2.9 2.9 2.6 2.0 

Semiconductor Manufacture 0.5 0.9 1.1 1.0 1.0 0.8 1.1 

Total 6,126.8 6,488.8 7,044.5 7,133.2 7,059.9 7,168.1 6,956.8 

Net Emissions (Sources and 

Sinks) 5,217.3 5,646.0 6,380.2 6,182.8 6,100.7 6,212.7 6,016.4 

+ Does not exceed 0.05 Tg CO2 Eq. a

 Parentheses indicate negative values or sequestration. The net CO2 flux total includes both emissions and sequestration, and 

constitutes a sink in the United States. Sinks are only included in net emissions total. b

 Emissions from International Bunker Fuels and Biomass Combustion are not included in totals. c

 Small amounts of PFC emissions also result from this source. 

Note: Totals may not sum due to independent rounding. 

Note: One teragram (Tg) equals one million metric tons. 

Figure ES-4 illustrates the relative contribution of the direct greenhouse gases to total U.S. emissions in 2008. The 

primary greenhouse gas emitted by human activities in the United States was CO2, representing approximately 85.1 

percent of total greenhouse gas emissions. The largest source of CO2, and of overall greenhouse gas emissions, was 

fossil fuel combustion. CH4 emissions, which have declined by 5.5 percent since 1990, resulted primarily from 

enteric fermentation associated with domestic livestock, decomposition of wastes in landfills, and natural gas 

systems. Agricultural soil management and mobile source fuel combustion were the major sources of N2O 

emissions. Ozone depleting substance substitute emissions and emissions of HFC-23 during the production of 

HCFC-22 were the primary contributors to aggregate HFC emissions. PFC emissions resulted as a by-product of 

primary aluminum production and from semiconductor manufacturing, while electrical transmission and distribution 

systems accounted for most SF6 emissions. 

Figure ES-4: 2008 Greenhouse Gas Emissions by Gas (percents based on Tg CO2 Eq.) 

Overall, from 1990 to 2008 total emissions of CO2 increased by 820.4 Tg CO2 Eq. (16.1 percent), while CH4 and 

N2O emissions decreased by 45.8 Tg CO2 Eq. (7.5 percent) and 4.1 Tg CO2 Eq. (1.3 percent), respectively. During 

the same period, aggregate weighted emissions of HFCs, PFCs, and SF6 rose by 59.4 Tg CO2 Eq. (65.9 percent). 

From 1990 to 2008, HFCs increased by 90.0 Tg CO2 Eq. (243.7 percent), PFCs decreased by 14.1 Tg CO2 Eq. (67.8 

percent), and SF6 decreased by 16.5 Tg CO2 Eq. (50.5 percent). Despite being emitted in smaller quantities relative 

to the other principal greenhouse gases, emissions of HFCs, PFCs, and SF6 are significant because many of these 

gases have extremely high global warming potentials and, in the cases of PFCs and SF6, long atmospheric lifetimes. 

Conversely, U.S. greenhouse gas emissions were partly offset by carbon sequestration in forests, trees in urban 

areas, agricultural soils, and landfilled yard trimmings and food scraps, which, in aggregate, offset 13.5 percent of 

total emissions in 2008. The following sections describe each gas’ contribution to total U.S. greenhouse gas 

emissions in more detail. 

Carbon Dioxide Emissions 

The global carbon cycle is made up of large carbon flows and reservoirs. Billions of tons of carbon in the form of 

CO2 are absorbed by oceans and living biomass (i.e., sinks) and are emitted to the atmosphere annually through 

natural processes (i.e., sources). When in equilibrium, carbon fluxes among these various reservoirs are roughly 

balanced. Since the Industrial Revolution (i.e., about 1750), global atmospheric concentrations of CO2 have risen 

about 36 percent (IPCC 2007), principally due to the combustion of fossil fuels. Within the United States, fossil fuel 

combustion accounted for 94.1 percent of CO2 emissions in 2008. Globally, approximately 30,377 Tg of CO2 were 
Executive Summary ES-7 

added to the atmosphere through the combustion of fossil fuels in 2008, of which the United States accounted for 

about 19 percent.10 Changes in land use and forestry practices can also emit CO2 (e.g., through conversion of forest 

land to agricultural or urban use) or can act as a sink for CO2 (e.g., through net additions to forest biomass). In 

addition to fossil-fuel combustion, several other sources emit significant quantities of CO2. These sources include, 

but are not limited to non-energy use of fuels, iron and steel production and cement production (Figure ES-5). 

Figure ES- 5: 2008 Sources of CO2 Emissions 

As the largest source of U.S. greenhouse gas emissions, CO2 from fossil fuel combustion has accounted for 

approximately 79 percent of GWP-weighted emissions since 1990, growing slowly from 77 percent of total GWPweighted emissions in 1990 to 80 percent in 2008. Emissions of CO2 from fossil fuel combustion increased at an 

average annual rate of 1 percent from 1990 to 2008. The fundamental factors influencing this trend include (1) a 

generally growing domestic economy over the last 19 years, and (2) significant overall growth in emissions from 

electricity generation and transportation activities. Between 1990 and 2008, CO2 emissions from fossil fuel 

combustion increased from 4,735.7 Tg CO2 Eq. to 5,572.8 Tg CO2 Eq.—an 18 percent total increase over the 

nineteen-year period. From 2007 to 2008, these emissions decreased by 184.2 Tg CO2 Eq. (3.2 percent). 

Historically, changes in emissions from fossil fuel combustion have been the dominant factor affecting U.S. 

emission trends. Changes in CO2 emissions from fossil fuel combustion are influenced by many long-term and 

short-term factors, including population and economic growth, energy price fluctuations, technological changes, and 

seasonal temperatures. On an annual basis, the overall consumption of fossil fuels in the United States generally 

fluctuates in response to changes in general economic conditions, energy prices, weather, and the availability of nonfossil alternatives. For example, in a year with increased consumption of goods and services, low fuel prices, severe 

summer and winter weather conditions, nuclear plant closures, and lower precipitation feeding hydroelectric dams, 

there would likely be proportionally greater fossil fuel consumption than a year with poor economic performance, 

high fuel prices, mild temperatures, and increased output from nuclear and hydroelectric plants. 

Figure ES- 6: 2008 CO2 Emissions from Fossil Fuel Combustion by Sector and Fuel Type 

Figure ES- 7: 2008 End-Use Sector Emissions of CO2, CH4, and N2O from Fossil Fuel Combustion 

The five major fuel consuming sectors contributing to CO2 emissions from fossil fuel combustion are electricity 

generation, transportation, industrial, residential, and commercial. CO2 emissions are produced by the electricity 

generation sector as they consume fossil fuel to provide electricity to one of the other four sectors, or “end-use” 

sectors. For the discussion below, electricity generation emissions have been distributed to each end-use sector on 

the basis of each sector’s share of aggregate electricity consumption. This method of distributing emissions assumes 

that each end-use sector consumes electricity that is generated from the national average mix of fuels according to 

their carbon intensity. Emissions from electricity generation are also addressed separately after the end-use sectors 

have been discussed. 

Note that emissions from U.S. territories are calculated separately due to a lack of specific consumption data for the 

individual end-use sectors. 

Figure ES- 6, Figure ES- 7, and Table ES-3 summarize CO2 emissions from fossil fuel combustion by end-use 

sector. 

Table ES-3: CO2 Emissions from Fossil Fuel Combustion by Fuel Consuming End-Use Sector (Tg CO2 Eq.) 

End-Use Sector 1990 1995 2000 2005 2006 2007 2008 

 

10 Global CO2 emissions from fossil fuel combustion were taken from Energy Information Administration International Energy 

Statistics 2009 < http://tonto.eia.doe.gov/cfapps/ipdbproject/IEDIndex3.cfm> EIA (2009). 
ES-8 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2008 

Transportation 1,488.8 1,611.0 1,813.0 1,900.1 1,881.2 1,898.8 1,789.9 

Combustion 1,485.8 1,608.0 1,809.5 1,895.3 1,876.7 1,893.7 1,785.3 

Electricity 3.0 3.1 3.4 4.7 4.5 5.0 4.7 

Industrial 1,532.2 1,578.8 1,642.0 1,562.5 1,562.8 1,572.2 1,510.9 

Combustion 845.4 862.6 852.2 825.6 850.7 842.2 819.3 

Electricity 686.8 716.2 789.8 737.0 712.0 730.0 691.6 

Residential 932.2 995.1 1,133.6 1,215.1 1,152.9 1,197.9 1,184.5 

Combustion 339.1 353.3 371.2 358.4 322.1 341.7 342.7 

Electricity 593.0 641.8 762.4 856.7 830.8 856.1 841.8 

Commercial 754.6 810.0 968.9 1,025.0 1,005.0 1,039.1 1,044.9 

Combustion 216.7 223.2 227.7 221.3 206.0 217.4 219.5 

Electricity 538.0 586.8 741.3 803.7 799.0 821.7 825.4 

U.S. Territoriesa

 27.9 34.5 35.9 50.6 50.9 49.1 42.5 

Total 4,735.7 5,029.5 5,593.4 5,753.3 5,652.8 5,757.0 5,572.8 

Electricity Generation 1,820.8 1,947.9 2,296.9 2,402.1 2,346.4 2,412.8 2,363.5 

Note: Totals may not sum due to independent rounding. Combustion-related emissions from electricity generation are allocated 

based on aggregate national electricity consumption by each end-use sector. a

 Fuel consumption by U.S. territories (i.e., American Samoa, Guam, Puerto Rico, U.S. Virgin Islands, Wake Island, and other 

U.S. Pacific Islands) is included in this report. 

Transportation End-Use Sector. Transportation activities (excluding international bunker fuels) accounted for 32 

percent of CO2 emissions from fossil fuel combustion in 2008.11 Virtually all of the energy consumed in this enduse sector came from petroleum products. Nearly 53 percent of the emissions resulted from gasoline consumption 

for personal vehicle use. The remaining emissions came from other transportation activities, including the 

combustion of diesel fuel in heavy-duty vehicles and jet fuel in aircraft. 

Industrial End-Use Sector. Industrial CO2 emissions, resulting both directly from the combustion of fossil fuels and 

indirectly from the generation of electricity that is consumed by industry, accounted for 27 percent of CO2 from 

fossil fuel combustion in 2008. Approximately 54 percent of these emissions resulted from direct fossil fuel 

combustion to produce steam and/or heat for industrial processes. The remaining emissions resulted from 

consuming electricity for motors, electric furnaces, ovens, lighting, and other applications. 

Residential and Commercial End-Use Sectors. The residential and commercial end-use sectors accounted for 21 

and 19 percent, respectively, of CO2 emissions from fossil fuel combustion in 2008. Both sectors relied heavily on 

electricity for meeting energy demands, with 71 and 79 percent, respectively, of their emissions attributable to 

electricity consumption for lighting, heating, cooling, and operating appliances. The remaining emissions were due 

to the consumption of natural gas and petroleum for heating and cooking. 

Electricity Generation. The United States relies on electricity to meet a significant portion of its energy demands, 

especially for lighting, electric motors, heating, and air conditioning. Electricity generators consumed 37 percent of 

U.S. energy from fossil fuels and emitted 42 percent of the CO2 from fossil fuel combustion in 2008. The type of 

fuel combusted by electricity generators has a significant effect on their emissions. For example, some electricity is 

generated with low CO2 emitting energy technologies, particularly non-fossil options such as nuclear, hydroelectric, 

or geothermal energy. However, electricity generators rely on coal for over half of their total energy requirements 

and accounted for 95 percent of all coal consumed for energy in the United States in 2008. Consequently, changes 

in electricity demand have a significant impact on coal consumption and associated CO2 emissions. 

Other significant CO2 trends included the following: 

• CO2 emissions from non-energy use of fossil fuels have increased 14.6 Tg CO2 Eq. (12.2 percent) from 

1990 through 2008. Emissions from non-energy uses of fossil fuels were 134.2 Tg CO2 Eq. in 2008, which 

constituted 2.3 percent of total national CO2 emissions, approximately the same proportion as in 1990. 

• CO2 emissions from iron and steel production and metallurgical coke production decreased from 2007 to 

 

11 If emissions from international bunker fuels are included, the transportation end-use sector accounted for 35 percent of U.S. 

emissions from fossil fuel combustion in 2008. 
Executive Summary ES-9 

2008 (3.8 Tg CO2 Eq.), continuing a trend of decreasing emissions from 1990 through 2008 of 33 percent. 

This decline is due to the restructuring of the industry, technological improvements, and increased scrap 

utilization. 

• In 2008, CO2 emissions from cement production decreased by 4.1 Tg CO2 Eq. (9.0 percent) from 2007. 

After decreasing in 1991 by two percent from 1990 levels, cement production emissions grew every year 

through 2006; emissions decreased in the last two years. Overall, from 1990 to 2008, emissions from 

cement production increased by 24 percent, an increase of 7.9 Tg CO2 Eq. 

• Net CO2 flux from Land Use, Land-Use Change, and Forestry increased by 30.9 Tg CO2 Eq. (3 percent) 

from 1990 through 2008. This increase was primarily due to an increase in the rate of net carbon 

accumulation in forest carbon stocks, particularly in aboveground and belowground tree biomass, and 

harvested wood pools. Annual carbon accumulation in landfilled yard trimmings and food scraps slowed 

over this period, while the rate of carbon accumulation in urban trees increased. 

Methane Emissions 

According to the IPCC, CH4 is more than 20 times as effective as CO2 at trapping heat in the atmosphere. Over the 

last two hundred and fifty years, the concentration of CH4 in the atmosphere increased by 148 percent (IPCC 2007). 

Anthropogenic sources of CH4 include landfills, natural gas and petroleum systems, agricultural activities, coal 

mining, wastewater treatment, stationary and mobile combustion, and certain industrial processes (see Figure ES- 8). 

Figure ES- 8: 2008 Sources of CH4 Emissions 

Some significant trends in U.S. emissions of CH4 include the following: 

• Enteric Fermentation is the largest anthropogenic source of CH4 emissions in the United States. In 2008, 

enteric fermentation CH4 emissions were 140.8 Tg CO2 Eq. (25 percent of total CH4 emissions), which 

represents an increase of 8.5 Tg CO2 Eq. (6.4 percent) since 1990. 

• Landfills are the second largest anthropogenic source of CH4 emissions in the United States, accounting for 

22 percent of total CH4 emissions (126.3 Tg CO2 Eq.) in 2008. From 1990 to 2008, net CH4 emissions 

from landfills decreased by 23.0 Tg CO2 Eq. (15 percent), with small increases occurring in some interim 

years. This downward trend in overall emissions is the result of increases in the amount of landfill gas 

collected and combusted,12 which has more than offset the additional CH4 emissions resulting from an 

increase in the amount of municipal solid waste landfilled. 

• CH4 emissions from natural gas systems were 96.4 Tg CO2 Eq. in 2008; emissions have declined by 33.1 

Tg CO2 Eq. (26 percent) since 1990. This decline is due to improvements in technology and management 

practices, as well as some replacement of old equipment. 

• In 2008, CH4 emissions from coal mining were 67.6 Tg CO2 Eq., a 9.6 Tg CO2 Eq. (16 percent) increase 

over 2007 emission levels. The overall decline of 16.4 Tg CO2 Eq. (20 percent) from 1990 results from the 

mining of less gassy coal from underground mines and the increased use of CH4 collected from 

degasification systems. 

• CH4 emissions from manure management increased by 54 percent since 1990, from 29.3 Tg CO2 Eq. in 

1990 to 45.0 Tg CO2 Eq. in 2008. The majority of this increase was from swine and dairy cow manure, 

since the general trend in manure management is one of increasing use of liquid systems, which tends to 

produce greater CH4 emissions. The increase in liquid systems is the combined result of a shift to larger 

facilities, and to facilities in the West and Southwest, all of which tend to use liquid systems. Also, new 

regulations limiting the application of manure nutrients have shifted manure management practices at 

smaller dairies from daily spread to manure managed and stored on site. 

 

12 The CO2 produced from combusted landfill CH4 at landfills is not counted in national inventories as it is considered part of the 

natural C cycle of decomposition. 
ES-10 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2008 

Nitrous Oxide Emissions 

N2O is produced by biological processes that occur in soil and water and by a variety of anthropogenic activities in 

the agricultural, energy-related, industrial, and waste management fields. While total N2O emissions are much 

lower than CO2 emissions, N2O is approximately 300 times more powerful than CO2 at trapping heat in the 

atmosphere. Since 1750, the global atmospheric concentration of N2O has risen by approximately 18 percent (IPCC 

2007). The main anthropogenic activities producing N2O in the United States are agricultural soil management, fuel 

combustion in motor vehicles, nitric acid production, stationary fuel combustion, manure management, and adipic 

acid production (see Figure ES-9). 

Figure ES-9: 2008 Sources of N2O Emissions 

Some significant trends in U.S. emissions of N2O include the following: 

• Agricultural soils accounted for approximately 68 percent of N2O emissions in the United States in 2008. 

Estimated emissions from this source in 2008 were 215.9 Tg CO2 Eq. Annual N2O emissions from 

agricultural soils fluctuated between 1990 and 2008, although overall emissions were 6.1 percent higher in 

2008 than in 1990. N2O emissions from this source have not shown any significant long-term trend, as 

they are highly sensitive to the amount of N applied to soils (which has not changed significantly over the 

time-period), and to weather patterns and crop type. 

• In 2008, N2O emissions from mobile combustion were 26.1 Tg CO2 Eq. (approximately 8 percent of U.S. 

N2O emissions). From 1990 to 2008, N2O emissions from mobile combustion decreased by 40 percent. 

However, from 1990 to 1998 emissions increased by 26 percent, due to control technologies that reduced 

NOx emissions while increasing N2O emissions. Since 1998, newer control technologies have led to a 

steady decline in N2O from this source. 

• N2O emissions from adipic acid production were 2.0 Tg CO2 Eq. in 2008, and have decreased significantly 

since 1996 from the widespread installation of pollution control measures. Emissions from adipic acid 

production have decreased by 87 percent since 1990, and emissions from adipic acid production have 

remained consistently lower than pre-1996 levels since 1998. 

HFC, PFC, and SF6 Emissions 

HFCs and PFCs are families of synthetic chemicals that are used as alternatives to ODS, which are being phased out 

under the Montreal Protocol and Clean Air Act Amendments of 1990. HFCs and PFCs do not deplete the 

stratospheric ozone layer, and are therefore acceptable alternatives under the Montreal Protocol. 

These compounds, however, along with SF6, are potent greenhouse gases. In addition to having high global 

warming potentials, SF6 and PFCs have extremely long atmospheric lifetimes, resulting in their essentially 

irreversible accumulation in the atmosphere once emitted. Sulfur hexafluoride is the most potent greenhouse gas the 

IPCC has evaluated. 

Other emissive sources of these gases include HCFC-22 production, electrical transmission and distribution systems, 

semiconductor manufacturing, aluminum production, and magnesium production and processing (see Figure ES-10). 

Figure ES-10: 2008 Sources of HFCs, PFCs, and SF6 Emissions 

Some significant trends in U.S. HFC, PFC, and SF6 emissions include the following: 

• Emissions resulting from the substitution of ODS (e.g., CFCs) have been consistently increasing, from 

small amounts in 1990 to 113.0 Tg CO2 Eq. in 2008. Emissions from ODS substitutes are both the largest 

and the fastest growing source of HFC, PFC, and SF6 emissions. These emissions have been increasing as 

phase-outs required under the Montreal Protocol come into effect, especially after 1994, when full market 

penetration was made for the first generation of new technologies featuring ODS substitutes. 
Executive Summary ES-11 

• HFC emissions from the production of HCFC-22 decreased by 63 percent (22.8 Tg CO2 Eq.) from 1990 

through 2008, due to a steady decline in the emission rate of HFC-23 (i.e., the amount of HFC-23 emitted 

per kilogram of HCFC-22 manufactured) and the use of thermal oxidation at some plants to reduce HFC-23 

emissions. 

• SF6 emissions from electric power transmission and distribution systems decreased by 51 percent (13.6 Tg 

CO2 Eq.) from 1990 to 2008, primarily because of higher purchase prices for SF6 and efforts by industry to 

reduce emissions. 

• PFC emissions from aluminum production decreased by 85 percent (15.8 Tg CO2 Eq.) from 1990 to 2008, 

due to both industry emission reduction efforts and lower domestic aluminum production. 

Overview of Sector Emissions and Trends 

In accordance with the Revised 1996 IPCC Guidelines for National Greenhouse Gas Inventories 

(IPCC/UNEP/OECD/IEA 1997), and the 2003 UNFCCC Guidelines on Reporting and Review (UNFCCC 2003), 

Figure ES-11 and Table ES-4 aggregate emissions and sinks by these chapters. Emissions of all gases can be 

summed from each source category from Intergovernmental Panel on Climate Change (IPCC) guidance. Over the 

nineteen-year period of 1990 to 2008, total emissions in the Energy, Industrial Processes, and Agriculture sectors 

climbed by 775.0 Tg CO2 Eq. (15 percent), 16.2 Tg CO2 Eq. (5 percent), and 39.7 Tg CO2 Eq. (10 percent), 

respectively. Emissions decreased in the Waste and Solvent and Other Product Use sectors by 18.1 Tg CO2 Eq. (10 

percent) and less than 0.1 Tg CO2 Eq. (0.4 percent), respectively. Over the same period, estimates of net C 

sequestration in the Land Use, Land-Use Change, and Forestry sector (magnitude of emissions plus CO2 flux from 

all LULUCF source categories) increased by 13.7 Tg CO2 Eq. (1.5 percent). 

Figure ES-11: U.S. Greenhouse Gas Emissions and Sinks by Chapter/IPCC Sector 

Table ES-4: Recent Trends in U.S. Greenhouse Gas Emissions and Sinks by Chapter/IPCC Sector (Tg CO2 Eq.) 

Chapter/IPCC Sector 1990 1995 2000 2005 2006 2007 2008

Energy 5,224.1 5,545.8 6,087.5 6,187.9 6,089.1 6,182.9 5,999.0 

Industrial Processes 318.3 339.1 351.9 334.7 339.7 350.9 334.5 

Solvent and Other Product Use 4.4 4.6 4.9 4.4 4.4 4.4 4.4 

Agriculture 387.8 407.7 410.9 419.7 417.2 423.0 427.5 

Land Use, Land-Use Change, and 

Forestry (Emissions) 15.0 17.2 36.3 28.6 49.8 47.6 32.2 

Waste 177.2 174.5 153.0 158.0 159.7 159.3 159.1 

Total Emissions 6,126.8 6,488.8 7,044.5 7,133.2 7,059.9 7,168.1 6,956.8 

Net CO2 Flux from Land Use, LandUse Change, and Forestry (Sinks)* (909.4) (842.9) (664.2) (950.4) (959.2) (955.4) (940.3)

Net Emissions (Sources and Sinks) 5,217.3 5,646.0 6,380.2 6,182.8 6,100.7 6,212.7 6,016.4 

* The net CO2 flux total includes both emissions and sequestration, and constitutes a sink in the United States. Sinks are only 

included in net emissions total. 

Note: Totals may not sum due to independent rounding. Parentheses indicate negative values or sequestration. 

Energy 

The Energy chapter contains emissions of all greenhouse gases resulting from stationary and mobile energy 

activities including fuel combustion and fugitive fuel emissions. Energy-related activities, primarily fossil fuel 

combustion, accounted for the vast majority of U.S. CO2 emissions for the period of 1990 through 2008. In 2008, 

approximately 84 percent of the energy consumed in the United States (on a Btu basis) was produced through the 

combustion of fossil fuels. The remaining 16 percent came from other energy sources such as hydropower, biomass, 

nuclear, wind, and solar energy (see Figure ES-12). Energy-related activities are also responsible for CH4 and N2O 

emissions (37 percent and 13 percent of total U.S. emissions of each gas, respectively). Overall, emission sources in 

the Energy chapter account for a combined 86 percent of total U.S. greenhouse gas emissions in 2008. 
ES-12 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2008 

Figure ES-12: 2008 U.S. Energy Consumption by Energy Source 

Industrial Processes 

The Industrial Processes chapter contains by-product or fugitive emissions of greenhouse gases from industrial 

processes not directly related to energy activities such as fossil fuel combustion. For example, industrial processes 

can chemically transform raw materials, which often release waste gases such as CO2, CH4, and N2O. These 

processes include iron and steel production and metallurgical coke production, cement production, ammonia 

production and urea consumption, lime production, limestone and dolomite use (e.g., flux stone, flue gas 

desulfurization, and glass manufacturing), soda ash production and consumption, titanium dioxide production, 

phosphoric acid production, ferroalloy production, CO2 consumption, silicon carbide production and consumption, 

aluminum production, petrochemical production, nitric acid production, adipic acid production, lead production, and 

zinc production. Additionally, emissions from industrial processes release HFCs, PFCs, and SF6. Overall, emission 

sources in the Industrial Process chapter account for 5 percent of U.S. greenhouse gas emissions in 2008. 

Solvent and Other Product Use 

The Solvent and Other Product Use chapter contains greenhouse gas emissions that are produced as a by-product of 

various solvent and other product uses. In the United States, emissions from N2O from product uses, the only source 

of greenhouse gas emissions from this sector, accounted for about 0.1 percent of total U.S. anthropogenic 

greenhouse gas emissions on a carbon equivalent basis in 2008. 

Agriculture 

The Agricultural chapter contains anthropogenic emissions from agricultural activities (except fuel combustion, 

which is addressed in the Energy chapter, and agricultural CO2 fluxes, which are addressed in the Land Use, LandUse Change, and Forestry Chapter). Agricultural activities contribute directly to emissions of greenhouse gases 

through a variety of processes, including the following source categories: enteric fermentation in domestic livestock, 

livestock manure management, rice cultivation, agricultural soil management, and field burning of agricultural 

residues. CH4 and N2O were the primary greenhouse gases emitted by agricultural activities. CH4 emissions from 

enteric fermentation and manure management represented 25 percent and 8 percent of total CH4 emissions from 

anthropogenic activities, respectively, in 2008. Agricultural soil management activities such as fertilizer application 

and other cropping practices were the largest source of U.S. N2O emissions in 2008, accounting for 68 percent. In 

2008, emission sources accounted for in the Agricultural chapters were responsible for 6.1 percent of total U.S. 

greenhouse gas emissions. 

Land Use, Land-Use Change, and Forestry 

The Land Use, Land-Use Change, and Forestry chapter contains emissions of CH4 and N2O, and emissions and 

removals of CO2 from forest management, other land-use activities, and land-use change. Forest management 

practices, tree planting in urban areas, the management of agricultural soils, and the landfilling of yard trimmings 

and food scraps have resulted in a net uptake (sequestration) of C in the United States. Forests (including 

vegetation, soils, and harvested wood) accounted for 84 percent of total 2008 net CO2 flux, urban trees accounted for 

10 percent, mineral and organic soil carbon stock changes accounted for 5 percent, and landfilled yard trimmings 

and food scraps accounted for 1 percent of the total net flux in 2008. The net forest sequestration is a result of net 

forest growth and increasing forest area, as well as a net accumulation of carbon stocks in harvested wood pools. 

The net sequestration in urban forests is a result of net tree growth in these areas. In agricultural soils, mineral and 

organic soils sequester approximately 5.9 times as much C as is emitted from these soils through liming and urea 

fertilization. The mineral soil C sequestration is largely due to the conversion of cropland to permanent pastures and 

hay production, a reduction in summer fallow areas in semi-arid areas, an increase in the adoption of conservation 

tillage practices, and an increase in the amounts of organic fertilizers (i.e., manure and sewage sludge) applied to 

agriculture lands. The landfilled yard trimmings and food scraps net sequestration is due to the long-term 

accumulation of yard trimming carbon and food scraps in landfills. 
Executive Summary ES-13 

Land use, land-use change, and forestry activities in 2008 resulted in a net C sequestration of 940.3 Tg CO2 Eq. 

(Table ES- 5). This represents an offset of 16 percent of total U.S. CO2 emissions, or 14 percent of total greenhouse 

gas emissions in 2008. Between 1990 and 2008, total land use, land-use change, and forestry net C flux resulted in a 

3.4 percent increase in CO2 sequestration, primarily due to an increase in the rate of net C accumulation in forest C 

stocks, particularly in aboveground and belowground tree biomass, and harvested wood pools. Annual C 

accumulation in landfilled yard trimmings and food scraps slowed over this period, while the rate of annual C 

accumulation increased in urban trees. 

Table ES- 5: Net CO2 Flux from Land Use, Land-Use Change, and Forestry (Tg CO2 Eq.) 

Sink Category 1990 1995 2000 2005 2006 2007 2008

Forest Land Remaining Forest 

Land1

 (729.8) (692.6) (467.7) (806.6) (812.5) (806.9) (791.9)

Cropland Remaining Cropland (29.4) (22.9) (30.2) (18.3) (19.1) (19.7) (18.1)

Land Converted to Cropland 2.2 2.9 2.4 5.9 5.9 5.9 5.9 

Grassland Remaining 

Grassland (52.0) (26.7) (52.6) (9.0) (8.9) (8.8) (8.7)

Land Converted to Grassland (19.8) (22.3) (27.3) (24.6) (24.5) (24.3) (24.2)

Settlements Remaining 

Settlements2

 (57.1) (67.3) (77.5) (87.8) (89.8) (91.9) (93.9)

Other (Landfilled Yard 

Trimmings and Food Scraps) (23.5) (13.9) (11.3) (10.1) (10.3) (9.8) (9.5)

Total (909.4) (842.9) (664.2) (950.4) (959.2) (955.4) (940.3)

Note: Totals may not sum due to independent rounding. Parentheses indicate net sequestration. 

Emissions from Land Use, Land-Use Change, and Forestry are shown in Table ES-6. The application of crushed 

limestone and dolomite to managed land (i.e., liming of agricultural soils) and urea fertilization resulted in CO2

emissions of 7.6 Tg CO2 Eq. in 2008, an increase of 8 percent relative to 1990. The application of synthetic 

fertilizers to forest and settlement soils in 2008 resulted in direct N2O emissions of 1.9 Tg CO2 Eq. Direct N2O 

emissions from fertilizer application to forest soils have increased by 422 percent since 1990, but still account for a 

relatively small portion of overall emissions. Additionally, direct N2O emissions from fertilizer application to 

settlement soils increased of 62 percent since 1990. Non-CO2 emissions from forest fires in 2008 resulted in CH4

emissions of 11.9 Tg CO2 Eq., and in N2O emissions of 9.7 Tg CO2 Eq. CO2 and N2O emissions from peatlands 

totaled 0.9 Tg CO2 Eq. and less than 0.01 Tg CO2 Eq. in 2008, respectively. 

Table ES-6. Emissions from Land Use, Land-Use Change, and Forestry (Tg CO2 Eq.) 

Source Category 1990 1995 2000 2005 2006 2007 2008

CO2 8.1 8.1 8.8 8.9 8.8 9.3 8.6 

Cropland Remaining Cropland: 

Liming of Agricultural Soils 4.7 4.4 4.3 4.3 4.2 4.5 3.8 

Urea Fertilization 2.4 2.7 3.2 3.5 3.7 3.8 3.8 

Wetlands Remaining Wetlands: 

Peatlands Remaining Peatlands 1.0 1.0 1.2 1.1 0.9 1.0 0.9 

CH4 3.2 4.3 14.3 9.8 21.6 20.0 11.9 

Forest Land Remaining Forest 

Land: Forest Fires 3.2 4.3 14.3 9.8 21.6 20.0 11.9 

N2O 3.7 4.9 13.2 9.8 19.5 18.3 11.7 

Forest Land Remaining Forest 

Land: Forest Fires 2.6 3.5 11.7 8.0 17.6 16.3 9.7 

Forest Land Remaining Forest 

Land: Forest Soils 0.1 0.2 0.4 0.4 0.4 0.4 0.4 

Settlements Remaining 

Settlements: Settlement Soils 1.0 1.2 1.1 1.5 1.5 1.6 1.6 

Wetlands Remaining Wetlands: 

Peatlands Remaining Peatlands + + + + + + +

Total 15.0 17.2 36.3 28.6 49.8 47.6 32.2 

+ Less than 0.05 Tg CO2 Eq. 
ES-14 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2008 

Note: Totals may not sum due to independent rounding. 

Waste 

The Waste chapter contains emissions from waste management activities (except incineration of waste, which is 

addressed in the Energy chapter). Landfills were the largest source of anthropogenic greenhouse gas emissions in 

the Waste chapter, accounting for just over 79 percent of this chapter’s emissions, and 22 percent of total U.S. CH4

emissions.13 Additionally, wastewater treatment accounts for 18 percent of Waste emissions, 4 percent of U.S. CH4

emissions, and 2 percent of U.S. N2O emissions. Emissions of CH4 and N2O from composting are also accounted 

for in this chapter; generating emissions of 1.7 Tg CO2 Eq. and 1.8 Tg CO2 Eq., respectively. Overall, emission 

sources accounted for in the Waste chapter generated 2.3 percent of total U.S. greenhouse gas emissions in 2008. 

Other Information 

Emissions by Economic Sector 

Throughout the Inventory of U.S. Greenhouse Gas Emissions and Sinks report, emission estimates are grouped into 

six sectors (i.e., chapters) defined by the IPCC: Energy; Industrial Processes; Solvent Use; Agriculture; Land Use, 

Land-Use Change, and Forestry; and Waste. While it is important to use this characterization for consistency with 

UNFCCC reporting guidelines, it is also useful to allocate emissions into more commonly used sectoral categories. 

This section reports emissions by the following economic sectors: Residential, Commercial, Industry, 

Transportation, Electricity Generation, Agriculture, and U.S. Territories. 

Table ES-7 summarizes emissions from each of these sectors, and Figure ES-13 shows the trend in emissions by 

sector from 1990 to 2008. 

Figure ES-13: Emissions Allocated to Economic Sectors 

Table ES-7: U.S. Greenhouse Gas Emissions Allocated to Economic Sectors (Tg CO2 Eq.) 

Implied Sectors 1990 1995 2000 2005 2006 2007 2008

Electric Power Industry 1,867.2 1,993.7 2,336.8 2,443.5 2,387.5 2,454.0 2,404.2 

Transportation 1,545.0 1,695.2 1,932.3 2,016.1 1,993.0 2,003.5 1,886.1 

Industry 1,506.6 1,531.3 1,469.1 1,350.9 1,380.2 1,374.2 1,342.4 

Agriculture 433.2 460.8 485.3 494.1 515.1 518.0 504.1 

Commercial 395.1 399.6 387.3 399.0 389.2 404.4 410.9 

Residential 345.9 367.6 386.7 370.7 334.9 356.2 359.3 

U.S. Territories 33.7 40.7 46.9 58.9 60.0 57.8 49.9 

Total Emissions 6,126.8 6,488.8 7,044.5 7,133.2 7,059.9 7,168.1 6,956.8 

Land Use, Land-Use Change, and 

Forestry (Sinks) (909.4) (842.9) (664.2) (950.4) (959.2) (955.4) (940.3)

Net Emissions (Sources and 

Sinks) 5,217.3 5,646.0 6,380.2 6,182.8 6,100.7 6,212.7 6,016.4 

Note: Totals may not sum due to independent rounding. Emissions include CO2, CH4, N2O, HFCs, PFCs, and SF6. 

See Table 2-12 for more detailed data. 

Using this categorization, emissions from electricity generation accounted for the largest portion (35 percent) of 

U.S. greenhouse gas emissions in 2008. Transportation activities, in aggregate, accounted for the second largest 

portion (27 percent), while emissions from industry accounted for the third largest portion (19 percent) of U.S. 

greenhouse gas emissions in 2008. In contrast to electricity generation and transportation, emissions from industry 

have in general declined over the past decade. The long-term decline in these emissions has been due to structural 

 

13 Landfills also store carbon, due to incomplete degradation of organic materials such as wood products and yard trimmings, as 

described in the Land-Use, Land-Use Change, and Forestry chapter of the Inventory report. 
Executive Summary ES-15 

changes in the U.S. economy (i.e., shifts from a manufacturing-based to a service-based economy), fuel switching, 

and energy efficiency improvements. The remaining 19 percent of U.S. greenhouse gas emissions were contributed 

by, in order of importance, the agriculture, commercial, and residential sectors, plus emissions from U.S. territories. 

Activities related to agriculture accounted for 7 percent of U.S. emissions; unlike other economic sectors, 

agricultural sector emissions were dominated by N2O emissions from agricultural soil management and CH4

emissions from enteric fermentation. The commercial sector accounted for 6 percent of emissions while the 

residential sector accounted for 5 percent of emissions and U.S. territories accounted for 1 percent of emissions; 

emissions from these sectors primarily consisted of CO2 emissions from fossil fuel combustion. 

CO2 was also emitted and sequestered by a variety of activities related to forest management practices, tree planting 

in urban areas, the management of agricultural soils, and landfilling of yard trimmings. 

Electricity is ultimately consumed in the economic sectors described above. Table ES-8 presents greenhouse gas 

emissions from economic sectors with emissions related to electricity generation distributed into end-use categories 

(i.e., emissions from electricity generation are allocated to the economic sectors in which the electricity is 

consumed). To distribute electricity emissions among end-use sectors, emissions from the source categories 

assigned to electricity generation were allocated to the residential, commercial, industry, transportation, and 

agriculture economic sectors according to retail sales of electricity.14 These source categories include CO2 from 

fossil fuel combustion and the use of limestone and dolomite for flue gas desulfurization, CO2 and N2O from 

incineration of waste, CH4 and N2O from stationary sources, and SF6 from electrical transmission and distribution 

systems. 

When emissions from electricity are distributed among these sectors, industry accounts for the largest share of U.S. 

greenhouse gas emissions (29 percent) in 2008. Emissions from the residential and commercial sectors also increase 

substantially when emissions from electricity are included, due to their relatively large share of electricity 

consumption (e.g., lighting, appliances, etc.). Transportation activities remain the second largest contributor to total 

U.S. emissions (27 percent) despite the considerable decline in emissions from this sector during the past year. In 

all sectors except agriculture, CO2 accounts for more than 80 percent of greenhouse gas emissions, primarily from 

the combustion of fossil fuels. Figure ES-14 shows the trend in these emissions by sector from 1990 to 2008. 

Table ES-8: U.S Greenhouse Gas Emissions by Economic Sector with Electricity-Related Emissions Distributed 

(Tg CO2 Eq.) 

Implied Sectors 1990 1995 2000 2005 2006 2007 2008

Industry 2,179.8 2,228.0 2,239.2 2,071.1 2,077.3 2,084.2 2,018.4 

Transportation 1,548.2 1,698.3 1,935.8 2,020.9 1,997.6 2,008.6 1,890.8 

Commercial 946.8 1,000.2 1,141.5 1,216.5 1,202.2 1,240.1 1,250.6 

Residential 954.0 1,024.5 1,162.4 1,242.2 1,180.3 1,226.9 1,215.6 

Agriculture 464.2 497.1 518.7 523.5 542.5 550.5 531.6 

U.S. Territories 33.7 40.7 46.9 58.9 60.0 57.8 49.9 

Total Emissions 6,126.8 6,488.8 7,044.5 7,133.2 7,059.9 7,168.1 6,956.8 

Land Use, Land-Use Change, 

and Forestry (Sinks) (909.4) (842.9) (664.2) (950.4) (959.2) (955.4) (940.3)

Net Emissions (Sources and 

Sinks) 5,217.3 5,646.0 6,380.2 6,182.8 6,100.7 6,212.7 6,016.4 

See Table 2-14 for more detailed data. 

Figure ES-14: Emissions with Electricity Distributed to Economic Sectors 

[BEGIN BOX] 

 

14 Emissions were not distributed to U.S. territories, since the electricity generation sector only includes emissions related to the 

generation of electricity in the 50 states and the District of Columbia. 
ES-16 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2008 

Box ES-2: Recent Trends in Various U.S. Greenhouse Gas Emissions-Related Data 

Total emissions can be compared to other economic and social indices to highlight changes over time. These 

comparisons include: (1) emissions per unit of aggregate energy consumption, because energy-related activities are 

the largest sources of emissions; (2) emissions per unit of fossil fuel consumption, because almost all energy-related 

emissions involve the combustion of fossil fuels; (3) emissions per unit of electricity consumption, because the 

electric power industry—utilities and nonutilities combined—was the largest source of U.S. greenhouse gas 

emissions in 2008; (4) emissions per unit of total gross domestic product as a measure of national economic activity; 

and (5) emissions per capita. 

Table ES-9 provides data on various statistics related to U.S. greenhouse gas emissions normalized to 1990 as a 

baseline year. Greenhouse gas emissions in the United States have grown at an average annual rate of 0.7 percent 

since 1990. This rate is slightly slower than that for total energy, approximately the same as for fossil fuel 

consumption, and much slower than that for either electricity consumption or overall gross domestic product. Total 

U.S. greenhouse gas emissions have also grown slightly slower than national population since 1990 (see Figure ES15). 

Table ES-9: Recent Trends in Various U.S. Data (Index 1990 = 100) 

Variable 1990 1995 2000 2005 2006 2007 2008

Growth 

Ratea

GDPb 100 113 140 157 162 165 166 2.9%

Electricity Consumptionc 100 112 127 134 135 138 136 1.8%

Fossil Fuel Consumptionc

 100 107 117 119 117 119 115 0.8%

Energy Consumptionc 100 107 116 119 118 120 118 0.9%

Populationd

 100 107 113 118 119 120 121 1.1%

Greenhouse Gas Emissionse

 100 106 115 116 115 117 114 0.7% a

 Average annual growth rate 

b

 Gross Domestic Product in chained 2000 dollars (BEA 2008) 

c

 Energy content-weighted values (EIA 2008a) 

d

 U.S. Census Bureau (2008) 

e

 GWP-weighted values 

Figure ES-15: U.S. Greenhouse Gas Emissions Per Capita and Per Dollar of Gross Domestic Product 

Source: BEA (2008), U.S. Census Bureau (2008), and emission estimates in this report. 

[END BOX] 

Indirect Greenhouse Gases (CO, NOx, NMVOCs, and SO2) 

The reporting requirements of the UNFCCC15 request that information be provided on indirect greenhouse gases, 

which include CO, NOx, NMVOCs, and SO2. These gases do not have a direct global warming effect, but indirectly 

affect terrestrial radiation absorption by influencing the formation and destruction of tropospheric and stratospheric 

ozone, or, in the case of SO2, by affecting the absorptive characteristics of the atmosphere. Additionally, some of 

these gases may react with other chemical compounds in the atmosphere to form compounds that are greenhouse 

gases. 

Since 1970, the United States has published estimates of annual emissions of CO, NOx, NMVOCs, and SO2 (EPA 

 

15 See <http://unfccc.int/resource/docs/cop8/08.pdf>. 
Executive Summary ES-17 

2008),16 which are regulated under the Clean Air Act. Table ES- 10 shows that fuel combustion accounts for the 

majority of emissions of these indirect greenhouse gases. Industrial processes—such as the manufacture of 

chemical and allied products, metals processing, and industrial uses of solvents—are also significant sources of CO, 

NOx, and NMVOCs. 

Table ES- 10: Emissions of NOx, CO, NMVOCs, and SO2 (Gg) 

Gas/Activity 1990 1995 2000 2005 2006 2007 2008

NOx 21,728 21,227 19,145 15,933 15,071 14,410 13,578

Mobile Fossil Fuel Combustion 10,862 10,536 10,199 9,012 8,488 7,965 7,441

Stationary Fossil Fuel Combustion 10,023 9,862 8,053 5,858 5,545 5,432 5,148

Industrial Processes 591 607 626 569 553 537 520

Oil and Gas Activities 139 100 111 321 319 318 318

Incineration of Waste 82 88 114 129 121 114 106

Agricultural Burning 30 30 37 40 40 38 40

Solvent Use 1 3 3 3 4 4 4

Waste 0 1 2 2 2 2 2

CO 130,536 109,114 92,872 71,555 67,909 64,348 60,739

Mobile Fossil Fuel Combustion 119,360 97,630 83,559 62,692 58,972 55,253 51,533

Stationary Fossil Fuel Combustion 5,000 5,383 4,340 4,649 4,695 4,744 4,792

Industrial Processes 4,125 3,959 2,216 1,555 1,597 1,640 1,682

Incineration of Waste 978 1,073 1,670 1,403 1,412 1,421 1,430

Agricultural Burning 766 745 888 930 905 960 970

Oil and Gas Activities 302 316 146 318 319 320 322

Waste 1 2 8 7 7 7 7

Solvent Use 5 5 45 2 2 2 2

NMVOCs 20,930 19,520 15,227 13,761 13,594 13,423 13,254

Mobile Fossil Fuel Combustion 10,932 8,745 7,229 6,330 6,037 5,742 5,447

Solvent Use 5,216 5,609 4,384 3,851 3,846 3,839 3,834

Industrial Processes 2,422 2,642 1,773 1,997 1,933 1,869 1,804

Stationary Fossil Fuel Combustion 912 973 1,077 716 918 1,120 1,321

Oil and Gas Activities 554 582 388 510 510 509 509

Incineration of Waste 222 237 257 241 238 234 230

Waste 673 731 119 114 113 111 109

Agricultural Burning NA NA NA NA NA NA NA

SO2 20,935 16,891 14,830 13,466 12,388 11,799 10,368

Stationary Fossil Fuel Combustion 18,407 14,724 12,849 11,541 10,612 10,172 8,891

Industrial Processes 1,307 1,117 1,031 831 818 807 795

Mobile Fossil Fuel Combustion 793 672 632 889 750 611 472

Oil and Gas Activities 390 335 287 181 182 184 187

Incineration of Waste 38 42 29 24 24 24 23

Waste 0 1 1 1 1 1 1

Solvent Use 0 1 1 0 0 0 0

Agricultural Burning NA NA NA NA NA NA NA

Source: (EPA 2009, disaggregated based on EPA 2003) except for estimates from field burning of agricultural residues. 

NA (Not Available) 

Note: Totals may not sum due to independent rounding. 

Key Categories 

The IPCC’s Good Practice Guidance (IPCC 2000) defines a key category as a “[source or sink category] that is 

prioritized within the national inventory system because its estimate has a significant influence on a country’s total 

 

16 NOx and CO emission estimates from field burning of agricultural residues were estimated separately, and therefore not taken 

from EPA (2008). 
ES-18 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2008 

inventory of direct greenhouse gases in terms of the absolute level of emissions, the trend in emissions, or both.”17 

By definition, key categories are sources or sinks that have the greatest contribution to the absolute overall level of 

national emissions in any of the years covered by the time series. In addition, when an entire time series of emission 

estimates is prepared, a thorough investigation of key categories must also account for the influence of trends of 

individual source and sink categories. Finally, a qualitative evaluation of key categories should be performed, in 

order to capture any key categories that were not identified in either of the quantitative analyses. 

Figure ES-16 presents 2008 emission estimates for the key categories as defined by a level analysis (i.e., the 

contribution of each source or sink category to the total inventory level). The UNFCCC reporting guidelines request 

that key category analyses be reported at an appropriate level of disaggregation, which may lead to source and sink 

category names which differ from those used elsewhere in the inventory report. For more information regarding key 

categories, see section 1.5 and Annex 1 of the inventory report. 

Figure ES-16: 2008 Key Categories 

Quality Assurance and Quality Control (QA/QC) 

The United States seeks to continually improve the quality, transparency, and credibility of the Inventory of U.S. 

Greenhouse Gas Emissions and Sinks. To assist in these efforts, the United States implemented a systematic 

approach to QA/QC. While QA/QC has always been an integral part of the U.S. national system for inventory 

development, the procedures followed for the current inventory have been formalized in accordance with the 

QA/QC plan and the UNFCCC reporting guidelines. 

Uncertainty Analysis of Emission Estimates 

While the current U.S. emissions inventory provides a solid foundation for the development of a more detailed and 

comprehensive national inventory, there are uncertainties associated with the emission estimates. Some of the 

current estimates, such as those for CO2 emissions from energy-related activities and cement processing, are 

considered to have low uncertainties. For some other categories of emissions, however, a lack of data or an 

incomplete understanding of how emissions are generated increases the uncertainty associated with the estimates 

presented. Acquiring a better understanding of the uncertainty associated with inventory estimates is an important 

step in helping to prioritize future work and improve the overall quality of the Inventory. Recognizing the benefit of 

conducting an uncertainty analysis, the UNFCCC reporting guidelines follow the recommendations of the IPCC 

Good Practice Guidance (IPCC 2000) and require that countries provide single estimates of uncertainty for source 

and sink categories. 

Currently, a qualitative discussion of uncertainty is presented for all source and sink categories. Within the 

discussion of each emission source, specific factors affecting the uncertainty surrounding the estimates are 

discussed. Most sources also contain a quantitative uncertainty assessment, in accordance with UNFCCC reporting 

guidelines. 

 

17 See Chapter 7 “Methodological Choice and Recalculation” in IPCC (2000). <http://www.ipccnggip.iges.or.jp/public/gp/gpgaum.htm> 
Figure ES-1: U.S. Greenhouse Gas Emissions by Gas

6,127 6,089 6,192 6,312 6,413 6,489 6,704 6,753 6,795 6,856 7,044 6,924 6,967 6,994 7,095 7,133 7,060 7,168 6,957

0 

1,000 

2,000 

3,000 

4,000 

5,000 

6,000 

7,000 

8,000 

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

Tg CO2 Eq.

HFCs, PFCs, & SF Nitrous Oxide

Methane Carbon Dioxide

6

1.7% 1.9% 1.6%

1.2%

3.3%

0.7% 0.6% 0.9%

2.8%

0.6% 0.4%

1.5%

0.5%

1.5%

0%

1%

2%

3%

4%

Figure ES-2: Annual Percent Change in U.S. Greenhouse Gas Emissions

Figure ES-3: Cumulative Change in Annual U.S. Greenhouse Gas Emissions Relative to 1990

6,127 6,089 6,192 6,312 6,413 6,489 6,704 6,753 6,795 6,856 7,044 6,924 6,967 6,994 7,095 7,133 7,060 7,168 6,957

0 

1,000 

2,000 

3,000 

4,000 

5,000 

6,000 

7,000 

8,000 

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

Tg CO2 Eq.

HFCs, PFCs, & SF Nitrous Oxide

Methane Carbon Dioxide

6

-0.6%

1.7% 1.9% 1.6%

1.2%

3.3%

0.7% 0.6% 0.9%

2.8%

-1.7%

0.6% 0.4%

1.5%

0.5%

-1.0%

1.5%

-2.9%

-4%

-3%

-2%

-1%

0%

1%

2%

3%

4%

1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

-38

65

185

286

362

577 626 669

729

918

797 840 867

969 1,006

933

1,041

830

-100

0

100

200

300

400

500

600

700

800

900

1,000

1,100

1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

Tg CO2 Eq.
Figure ES-4: 2008 Greenhouse Gas Emissions by Gas (percents based on Tg CO2 Eq.)

CO2

85.1%

CH4

8.2%

N2O

4.6%

HFCs, PFCs, 

& SF6 

2.2%

5,637.9

Cropland Remaining Cropland

Ammonia Production and Urea Consumption

Incineration of Waste

Lime Production

Natural Gas Systems

Cement Production

Iron and Steel Production & Metallurgical Coke Production

Non-Energy Use of Fuels

Fossil Fuel Combustion

CO2 as a Portion 

of all Emissions

5,573

Figure ES-5: 2008 Sources of CO2 Emissions

CO2

85.1%

CH4

8.2%

N2O

4.6%

HFCs, PFCs, 

& SF6 

2.2%

5,637.9

0 25 50 75 100 125 150

Silicon Carbide Production and Consumption

Lead Production

Zinc Production

Petroleum Systems

Wetlands Remaining Wetlands

Phosphoric Acid Production

Ferroalloy Production

Carbon Dioxide Consumption

Titanium Dioxide Production

Petrochemical Production

Soda Ash Production and Consumption

Aluminum Production

Limestone and Dolomite Use

Cropland Remaining Cropland

Ammonia Production and Urea Consumption

Incineration of Waste

Lime Production

Natural Gas Systems

Cement Production

Iron and Steel Production & Metallurgical Coke Production

Non-Energy Use of Fuels

Fossil Fuel Combustion

Tg CO2 Eq.

85.1%

CO2 as a Portion 

of all Emissions

5,573

< 0.5

< 0.5

< 0.5

< 0.5
Natural Gas

Petroleum

Coal

Figure ES-6: 2008 CO2 Emissions from Fossil Fuel Combustion by Sector and Fuel Type

Note: Electricity generation also includes emissions of less than 0.5 Tg CO 2 Eq. from geothermal-based electricity generation.

1,050 1,193

1,518

1,818

1,500

2,000

Eq.

From Direct Fossil Fuel Combustion

From Electricity Consumption

43 219

343

819

1,785

2,363

0

500

1,000

1,500

2,000

2,500

U.S. Territories

Commercial

Residential

Industrial

Transportation

Electricity 

Generation

Tg CO2 Eq.

Petroleum

Coal

Natural Gas

Relative Contribution 

by Fuel Type

Figure ES-7: 2008 End-Use Sector Emissions of CO2, CH4, and N2O from Fossil Fuel Combustion

43

1,050 1,193

1,518

1,818

0

500

1,000

1,500

2,000

U.S. Territories

Commercial

Residential

Industrial

Transportation

Tg CO2 Eq.

From Direct Fossil Fuel Combustion

From Electricity Consumption

43 219

343

819

1,785

2,363

0

500

1,000

1,500

2,000

2,500

U.S. Territories

Commercial

Residential

Industrial

Transportation

Electricity 

Generation

Tg CO2 Eq.

Petroleum

Coal

Natural Gas

Relative Contribution 

by Fuel Type
Fi ES 8 2008 S f CH Ei i

0 50 100 150

Incineration of Waste

Silicon Carbide Production and Consumption

Ferroalloy Production

Iron and Steel Production & Metallurgical Coke Production

Petrochemical Production

Field Burning of Agricultural Residues

Composting

Mobile Combustion

Abandoned Underground Coal Mines

Stationary Combustion

Rice Cultivation

Forest Land Remaining Forest Land

Wastewater Treatment

Petroleum Systems

Manure Management

Coal Mining

Natural Gas Systems

Landfills

Enteric Fermentation

Tg CO2 Eq.

8.2%

CH4 as a Portion 

of all Emissions

< 0.5

< 0.5

< 0.5

Figure ES-8: 2008 Sources of CH4 Emissions

Figure ES-9: 2008 Sources of N2O Emissions

0 10 20 30 40

Wetlands Remaining Wetlands

Incineration of Waste

Field Burning of Agricultural Residues

Settlements Remaining Settlements

Composting

Adipic Acid Production

N2O from Product Uses

Wastewater Treatment

Forest Land Remaining Forest Land

Stationary Combustion

Manure Management

Nitric Acid Production

Mobile Combustion

Agricultural Soil Management

Tg CO2 Eq.

216

0 50 100 150

Incineration of Waste

Silicon Carbide Production and Consumption

Ferroalloy Production

Iron and Steel Production & Metallurgical Coke Production

Petrochemical Production

Field Burning of Agricultural Residues

Composting

Mobile Combustion

Abandoned Underground Coal Mines

Stationary Combustion

Rice Cultivation

Forest Land Remaining Forest Land

Wastewater Treatment

Petroleum Systems

Manure Management

Coal Mining

Natural Gas Systems

Landfills

Enteric Fermentation

Tg CO2 Eq.

8.2%

CH4 as a Portion 

of all Emissions

< 0.5

< 0.5

< 0.5

< 0.5

< 0.5

4.6%

N2O as a Portion 

of all Emissions
Figure ES-10: 2008 Sources of HFCs, PFCs, and SF6 Emissions

86.6%

5 000

5,500 

6,000 

6,500 

7,000 

7,500 

Agriculture

Waste Industrial Processes

LULUCF (sources)

0 10 20 30 40 50

Magnesium Production 

and Processing

Aluminum Production

Semiconductor 

Manufacture

Electrical Transmission 

and Distribution

HCFC-22 Production

Substitution of Ozone 

Depleting Substances

Tg CO2 Eq.

113

2.2%

HFCs, PFCs, and SF6 as a Portion 

of all Emissions

Figure ES-11: U.S. Greenhouse Gas Emissions and Sinks by Chapter/IPCC Sector

86.6%

(1,000)

(500)

0 

500 

1,000 

1,500 

2,000 

2,500 

3,000 

3,500 

4,000 

4,500 

5,000 

5,500 

6,000 

6,500 

7,000 

7,500 

1990199119921993199419951996199719981999200020012002200320042005200620072008

Tg CO2 Eq.

Energy

Land Use, Land-Use Change and Forestry (sinks)

Agriculture

Waste Industrial Processes

LULUCF (sources)

Note: Relatively smaller amounts of GWP-weighted emissions are also emitted from the Solvent and Other Product Use 

sectors 

0 10 20 30 40 50

Magnesium Production 

and Processing

Aluminum Production

Semiconductor 

Manufacture

Electrical Transmission 

and Distribution

HCFC-22 Production

Substitution of Ozone 

Depleting Substances

Tg CO2 Eq.

113

2.2%

HFCs, PFCs, and SF6 as a Portion 

of all Emissions
Figure ES-12: 2008 U.S. Energy Consumption by Energy Source

Petroleum

37.4%

Natural Gas

24.0%

Coal

22.6%

Nuclear Electric 

Power

8.5%

Renewable 

Energy

7.4%

1,500

2,000

2,500

O2 Eq.

Electric

Power Industry

Transportation

Industry

Note: Does not include U.S. Territories.

Figure ES-13: Emissions Allocated to Economic Sectors

Petroleum

37.4%

Natural Gas

24.0%

Coal

22.6%

Nuclear Electric 

Power

8.5%

Renewable 

Energy

7.4%

0

500

1,000

1,500

2,000

2,500

1990199119921993199419951996199719981999200020012002200320042005200620072008

Tg CO2 Eq.

Residential

Electric

Power Industry

Transportation

Industry

Agriculture

Commercial
Note: Does not include U.S. Territories.

Figure ES-14: Emissions with Electricity Distributed to Economic Sectors

0

500

1,000

1,500

2,000

2,500

1990199119921993199419951996199719981999200020012002200320042005200620072008

Tg CO2 Eq.

Transportation

Industry

Residential (black)

Agriculture

Commercial (gray)

Real GDP

160 

170 

Figure ES-15: U.S. Greenhouse Gas Emissions Per Capita and Per Dollar of Gross Domestic Product

0

500

1,000

1,500

2,000

2,500

1990199119921993199419951996199719981999200020012002200320042005200620072008

Tg CO2 Eq.

Transportation

Industry

Residential (black)

Agriculture

Commercial (gray)

Emissions 

per $GDP

Emissions 

per capita

Population

Real GDP

60 

70 

80 

90 

100 

110 

120 

130 

140 

150 

160 

170 

1990199119921993199419951996199719981999200020012002200320042005200620072008

Index (1990 = 100)
CH4 Emissions from Manure Management

Indirect N2O Emissions from Applied Nitrogen

Fugitive Emissions from Coal Mining

CO2 Emissions from Iron and Steel Production & Metallurgical 

Coke Production

Fugitive Emissions from Natural Gas Systems

Emissions from Substitutes for Ozone Depleting Substances

CH4 Emissions from Landfills

CO2 Emissions from Non-Energy Use of Fuels

CH4 Emissions from Enteric Fermentation

Mobile Combustion: Aviation

Direct N2O Emissions from Agricultural Soil Management

CO2 Emissions from Stationary Combustion - Oil

CO2 Emissions from Stationary Combustion - Gas

Mobile Combustion: Road & Other

CO2 Emissions from Stationary Combustion - Coal

96%

Key Categories as a Portion of all 

Emissions

Figure ES-16: 2008 Key Categories

Notes: For a complete discussion of the key category analysis, see Annex 1.

 Black bars indicate a Tier 1 level assessment key category.

 Gray bars indicate a Tier 2 level assessment key category.

0 200 400 600 800 1,000 1,200 1,400 1,600 1,800 2,000 2,200

Non-CO2 Emissions from Stationary Combustion

N2O Emissions from Manure Management

Fugitive Emissions from Petroleum Systems

CO2 Emissions from Cement Production

CH4 Emissions from Manure Management

Indirect N2O Emissions from Applied Nitrogen

Fugitive Emissions from Coal Mining

CO2 Emissions from Iron and Steel Production & Metallurgical 

Coke Production

Fugitive Emissions from Natural Gas Systems

Emissions from Substitutes for Ozone Depleting Substances

CH4 Emissions from Landfills

CO2 Emissions from Non-Energy Use of Fuels

CH4 Emissions from Enteric Fermentation

Mobile Combustion: Aviation

Direct N2O Emissions from Agricultural Soil Management

CO2 Emissions from Stationary Combustion - Oil

CO2 Emissions from Stationary Combustion - Gas

Mobile Combustion: Road & Other

CO2 Emissions from Stationary Combustion - Coal

Tg CO2 Eq.

96%

Key Categories as a Portion of all 

Emissions