Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2009 1 

n emissions inventory that identifies and quantifies a country's primary anthropogenic1

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.”

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. 

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

 

A

This chapter summarizes the latest information on U.S. anthropogenic 

greenhouse gas emission trends from 1990 through 2009. To ensure that the 

U.S. emission 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 Intergovernmental Panel on Climate 

Change (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 continued to incorporate new methodologies and data from the 2006 

IPCC Guidelines for National Greenhouse Gas Inventories (IPCC 2006). The structure of the inventory report is consistent 

 

The United States views the Inventory as an opportunity to fulfill these 

commitments.

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>.

All material taken from the Inventory 

of U.S. Greenhouse Gas Emissions 

and Sinks: 1990–2009, U.S. 

Environmental Protection Agency, 

Office of Atmospheric Programs, 

EPA 430-R-11-005, April 2011. You 

may electronically download the full 

inventory report from U.S. EPA’s 

Global Climate Change web page at: 

www.epa.gov/climatechange/

emissions/usinventory.html. 
2 Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2009

with the UNFCCC guidelines for inventory reporting.4 For most source categories, the IPCC methodologies were expanded, 

resulting in a more comprehensive and detailed estimate of emissions.

Box ES-1: Methodological approach for estimating and reporting U.S. emissions and sinks

In following the UNFCCC requirement under Article 4.1 to develop and submit national greenhouse gas emissions inventories, the emissions 

and sinks presented in the inventory report are organized by source and sink categories and calculated using internationally-accepted 

methods provided by the IPCC.5 Additionally, the calculated emissions and sinks in a given year for the U.S. are presented in a common 

manner in line with the UNFCCC reporting guidelines for the reporting of inventories under this international agreement.6 The use of 

consistent methods to calculate emissions and sinks by all nations providing their inventories to the UNFCCC ensures that these reports are 

comparable. In this regard, U.S. emissions and sinks reported in this inventory report are comparable to emissions and sinks reported by 

other countries. Emissions and sinks provided in this inventory do not preclude alternative examinations, but rather this inventory report 

presents emissions and sinks in a common format consistent with how countries are to report inventories under the UNFCCC. The inventory 

report itself follows this standardized format, and provides an explanation of the IPCC methods used to calculate emissions and sinks, and 

the manner in which those calculations are conducted.

ES.1. 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.7

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.

 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.

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). 

 

4 See < http://unfccc.int/resource/docs/2006/sbsta/eng/09.pdf>.

5 See < http://www.ipcc-nggip.iges.or.jp/public/index.html>.

6 See < http://unfccc.int/national_reports/annex_i_ghg_inventories/national_inventories_submissions/items/5270.php>.

7 Emissions estimates of CFCs, HCFCs, halons and other ozone-depleting substances are included in the annexes of the inventory report for informational 

purposes.
Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2009 3 

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).8

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 GWP-weighted emissions are measured in teragrams 

(or million metric tons) of CO2 equivalent (Tg CO2 Eq.).

 The IPCC 

developed the global warming potential (GWP) concept to compare the ability of each greenhouse gas to trap heat in the 

atmosphere relative to another gas.

9, 10

The UNFCCC reporting guidelines for national inventories 

were updated in 2006,

All 

gases in this Executive Summary are presented in units of Tg CO2

Eq. 

11

 

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 2009 are consistent with 

estimates developed prior to the publication of the IPCC Third 

Assessment Report (TAR) (IPCC 2001) and the IPCC Fourth 

Assessment Report (AR4) (IPCC 2007). 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 inventory 

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 the inventory report. The GWP values 

used in the inventory report are listed below in Table ES-1.

Table ES-1: Global Warming Potentials (100-Year

Time Horizon) Used in the Inventory 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.

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

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

11 See <http://unfccc.int/resource/docs/2006/sbsta/eng/09.pdf>.

8 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.
4 Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2009

Global warming potentials are not provided for CO, NOx, NMVOCs, SO2, and aerosols because there is no agreed-upon 

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).

ES.2. Recent Trends in U.S. Greenhouse Gas Emissions and Sinks 

In 2009, total U.S. greenhouse gas emissions were 6,633.2 

Tg or million metric tons CO2 Eq. While total U.S. emissions 

have increased by 7.3 percent from 1990 to 2009, emissions 

decreased from 2008 to 2009 by 6.1 percent (427.9 Tg CO2

Eq.). This decrease was primarily due to (1) a decrease in 

economic output resulting in a decrease in energy consumption 

across all sectors; and (2) a decrease in the carbon intensity of 

fuels used to generate electricity due to fuel switching as the 

price of coal increased, and the price of natural gas decreased 

significantly. Since 1990, U.S. emissions have increased at an 

average annual rate of 0.4 percent. 

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 2009. 

Figure ES-1 

U.S. Greenhouse Gas Emissions by Gas

Figure ES-2 Figure ES-3 

Annual Percent Change in U.S. Greenhouse Gas 

Emissions

Cumulative Change in Annual U.S. Greenhouse Gas 

Emissions Relative to 1990
Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2009 5 

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

Gas/Source 1990 2000 2005 2006 2007 2008 2009

CO2 5,099.7 5,975.0 6,113.8 6,021.1 6,120.0 5,921.4 5,505.2 

Fossil Fuel Combustion 4,738.4 5,594.8 5,753.2 5,653.1 5,756.7 5,565.9 5,209.0 

Electricity Generation 1,820.8 2,296.9 2,402.1 2,346.4 2,412.8 2,360.9 2,154.0 

Transportation 1,485.9 1,809.5 1,896.6 1,878.1 1,894.0 1,789.9 1,719.7

Industrial 846.5 851.1 823.1 848.2 842.0 802.9 730.4

Residential 338.3 370.7 357.9 321.5 342.4 348.2 339.2

Commercial 219.0 230.8 223.5 208.6 219.4 224.2 224.0

U.S. Territories 27.9 35.9 50.0 50.3 46.1 39.8 41.7 

Non-Energy Use of Fuels 118.6 144.9 143.4 145.6 137.2 141.0 123.4

Iron and Steel Production & 

Metallurgical Coke Production 99.5 85.9 65.9 68.8 71.0 66.0 41.9

Natural Gas Systems 37.6 29.9 29.9 30.8 31.1 32.8 32.2 

Cement Production 33.3 40.4 45.2 45.8 44.5 40.5 29.0

Incineration of Waste 8.0 11.1 12.5 12.5 12.7 12.2 12.3 

Ammonia Production and Urea 

Consumption 16.8 16.4 12.8 12.3 14.0 11.9 11.8 

Lime Production 11.5 14.1 14.4 15.1 14.6 14.3 11.2 

Cropland Remaining Cropland 7.1 7.5 7.9 7.9 8.2 8.7 7.8 

Limestone and Dolomite Use 5.1 5.1 6.8 8.0 7.7 6.3 7.6 

Soda Ash Production and 

Consumption 4.1 4.2 4.2 4.2 4.1 4.1 4.3 

Aluminum Production 6.8 6.1 4.1 3.8 4.3 4.5 3.0 

Petrochemical Production 3.3 4.5 4.2 3.8 3.9 3.4 2.7 

Carbon Dioxide Consumption 1.4 1.4 1.3 1.7 1.9 1.8 1.8 

Titanium Dioxide Production 1.2 1.8 1.8 1.8 1.9 1.8 1.5

Ferroalloy Production 2.2 1.9 1.4 1.5 1.6 1.6 1.5

Wetlands Remaining Wetlands 1.0 1.2 1.1 0.9 1.0 1.0 1.1 

Phosphoric Acid Production 1.5 1.4 1.4 1.2 1.2 1.2 1.0 

Zinc Production 0.7 1.0 1.1 1.1 1.1 1.2 1.0 

Lead Production 0.5 0.6 0.6 0.6 0.6 0.6 0.5 

Petroleum Systems 0.6 0.5 0.5 0.5 0.5 0.5 0.5 

Silicon Carbide Production and 

Consumption 0.4 0.2 0.2 0.2 0.2 0.2 0.1 

Land Use, Land-Use Change, and 

Forestry (Sink) a (861.5) (576.6) (1,056.5) (1,064.3) (1,060.9) (1,040.5) (1,015.1)

Biomass – Wood b 215.2 218.1 206.9 203.8 203.3 198.4 183.8

International Bunker Fuels c 111.8 98.5 109.7 128.4 127.6 133.7 123.1

Biomass – Ethanol b 4.2 9.4 23.0 31.0 38.9 54.8 61.2

CH4 674.9 659.9 631.4 672.1 664.6 676.7 686.3

Natural Gas Systems 189.8 209.3 190.4 217.7 205.2 211.8 221.2 

Enteric Fermentation 132.1 136.5 136.5 138.8 141.0 140.6 139.8 

Landfills 147.4 111.7 112.5 111.7 111.3 115.9 117.5 

Coal Mining 84.1 60.4 56.9 58.2 57.9 67.1 71.0 

Manure Management 31.7 42.4 46.6 46.7 50.7 49.4 49.5 

Petroleum Systems 35.4 31.5 29.4 29.4 30.0 30.2 30.9 

Wastewater Treatment 23.5 25.2 24.3 24.5 24.4 24.5 24.5 

Forest Land Remaining Forest Land 3.2 14.3 9.8 21.6 20.0 11.9 7.8 

Rice Cultivation 7.1 7.5 6.8 5.9 6.2 7.2 7.3 

Stationary Combustion 7.4 6.6 6.6 6.2 6.5 6.5 6.2 

Abandoned Underground Coal Mines 6.0 7.4 5.5 5.5 5.6 5.9 5.5 

Mobile Combustion 4.7 3.4 2.5 2.3 2.2 2.0 2.0 

Composting 0.3 1.3 1.6 1.6 1.7 1.7 1.7 

Petrochemical Production 0.9 1.2 1.1 1.0 1.0 0.9 0.8 

Iron and Steel Production & 

Metallurgical Coke Production 1.0 0.9 0.7 0.7 0.7 0.6 0.4 

Field Burning of Agricultural Residues 0.3 0.3 0.2 0.2 0.2 0.3 0.2 

Ferroalloy Production + + + + + + + 
6 Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2009

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

Gas/Source 1990 2000 2005 2006 2007 2008 2009

Silicon Carbide Production and 

Consumption + + + + + + + 

Incineration of Waste + + + + + + + 

International Bunker Fuelsc 0.2 0.1 0.1 0.2 0.2 0.2 0.1 

N2O 315.2 341.0 322.9 326.4 325.1 310.8 295.6 

Agricultural Soil Management 197.8 206.8 211.3 208.9 209.4 210.7 204.6 

Mobile Combustion 43.9 53.2 36.9 33.6 30.3 26.1 23.9 

Manure Management 14.5 17.1 17.3 18.0 18.1 17.9 17.9 

Nitric Acid Production 17.7 19.4 16.5 16.2 19.2 16.4 14.6 

Stationary Combustion 12.8 14.6 14.7 14.4 14.6 14.2 12.8 

Forest Land Remaining Forest Land 2.7 12.1 8.4 18.0 16.7 10.1 6.7 

Wastewater Treatment 3.7 4.5 4.8 4.8 4.9 5.0 5.0 

N2O from Product Uses 4.4 4.9 4.4 4.4 4.4 4.4 4.4 

Adipic Acid Production 15.8 5.5 5.0 4.3 3.7 2.0 1.9 

Composting 0.4 1.4 1.7 1.8 1.8 1.9 1.8 

Settlements Remaining Settlements 1.0 1.1 1.5 1.5 1.6 1.5 1.5 

Incineration of Waste 0.5 0.4 0.4 0.4 0.4 0.4 0.4 

Field Burning of Agricultural Residues 0.1 0.1 0.1 0.1 0.1 0.1 0.1 

Wetlands Remaining Wetlands + + + + + + + 

International Bunker Fuels c 1.1 0.9 1.0 1.2 1.2 1.2 1.1 

HFCs 36.9 103.2 120.2 123.5 129.5 129.4 125.7 

Substitution of Ozone Depleting 

Substances d 0.3 74.3 104.2 109.4 112.3 115.5 120.0 

HCFC-22 Production 36.4 28.6 15.8 13.8 17.0 13.6 5.4 

Semiconductor Manufacture 0.2 0.3 0.2 0.3 0.3 0.3 0.3 

PFCs 20.8 13.5 6.2 6.0 7.5 6.6 5.6 

Semiconductor Manufacture 2.2 4.9 3.2 3.5 3.7 4.0 4.0 

Aluminum Production 18.5 8.6 3.0 2.5 3.8 2.7 1.6 

SF6 34.4 20.1 19.0 17.9 16.7 16.1 14.8 

Electrical Transmission and 

Distribution 28.4 16.0 15.1 14.1 13.2 13.3 12.8 

Magnesium Production and 

Processing 5.4 3.0 2.9 2.9 2.6 1.9 1.1 

Semiconductor Manufacture 0.5 1.1 1.0 1.0 0.8 0.9 1.0 

Total 6,181.8 7,112.7 7,213.5 7,166.9 7,263.4 7,061.1 6,633.2 

Net Emissions (Sources and Sinks) 5,320.3 6,536.1 6,157.1 6,102.6 6,202.5 6,020.7 5,618.2 

+ 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 net sink in the 

United States. Sinks are only included in net emissions total. b Emissions from Wood Biomass and Ethanol Consumption are not included specifically in summing energy sector totals. Net carbon fluxes from changes in 

biogenic carbon reservoirs are accounted for in the estimates for Land Use, Land-Use Change, and Forestry. c Emissions from International Bunker Fuels are not included in totals.

d Small amounts of PFC emissions also result from this source.

Note: Totals may not sum due to independent rounding. 

Figure ES-4 illustrates the relative contribution of the direct greenhouse gases to total U.S. emissions in 2009. The 

primary greenhouse gas emitted by human activities in the United States was CO2, representing approximately 83.0 percent 

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

combustion. Methane emissions, which have increased by 1.7 percent since 1990, resulted primarily from natural gas 

systems, enteric fermentation associated with domestic livestock, and decomposition of wastes in landfills. 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 byproduct of primary aluminum production and from semiconductor 

manufacturing, while electrical transmission and distribution systems accounted for most SF6 emissions. 
Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2009 7 

Overall, from 1990 to 2009, total emissions of CO2 and 

CH4 increased by 405.5 Tg CO2 Eq. (8.0 percent) and 11.4 Tg 

CO2 Eq. (1.7 percent), respectively. Conversely, N2O emissions 

decreased by 19.6 Tg CO2 Eq. (6.2 percent). During the same 

period, aggregate weighted emissions of HFCs, PFCs, and SF6

rose by 54.1 Tg CO2 Eq. (58.8 percent). From 1990 to 2009, 

HFCs increased by 88.8 Tg CO2 Eq. (240.41 percent), PFCs 

decreased by 15.1 Tg CO2 Eq. (73.0 percent), and SF6 decreased 

by 19.5 Tg CO2 Eq. (56.8 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 15.3 percent of total 

emissions in 2009. The following sections describe each gas’ 

contribution to total U.S. greenhouse gas emissions in more detail. 

Figure ES-4 

2009 Greenhouse Gas Emissions by Gas 

(percents based on Tg CO2 Eq.)

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 94.6 percent of CO2

emissions in 2009. Globally, approximately 30,313 Tg of CO2 were added to the atmosphere through the combustion of 

fossil fuels in 2009, of which the United States accounted for about 18 percent.12

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

approximately 78 percent of GWP-weighted emissions since 1990, growing slowly from 77 percent of total GWP-weighted 

emissions in 1990 to 79 percent in 2009. Emissions of CO2 from fossil fuel combustion increased at an average annual rate 

of 0.4 percent from 1990 to 2009. The fundamental factors influencing this trend include: (1) a generally growing domestic 

economy over the last 20 years, and (2) overall growth in emissions from electricity generation and transportation activities. 

Between 1990 and 2009, CO2 emissions from fossil fuel combustion increased from 4,738.4 Tg CO2 Eq. to 5,209.0 Tg CO2

Eq.—a 9.9 percent total increase over the twenty-year period. From 2008 to 2009, these emissions decreased by 356.9 Tg 

CO2 Eq. (6.4 percent), the largest decrease in any year over the twenty-year period. 

 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). 

 

12 Global CO2 emissions from fossil fuel combustion were taken from Energy Information Administration International Energy Statistics 2010

<http://tonto.eia.doe.gov/cfapps/ipdbproject/IEDIndex3.cfm> EIA (2010a).
8 Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2009

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. In the short term, the overall 

consumption of fossil fuels in the United States fluctuates 

primarily in response to changes in general economic 

conditions, energy prices, weather, and the availability of 

non-fossil 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. In the long term, energy 

consumption patterns respond to changes that affect the 

scale of consumption (e.g., population, number of cars, 

and size of houses), the efficiency with which energy is 

used in equipment (e.g., cars, power plants, steel mills, 

and light bulbs) and behavioral choices (e.g., walking, 

bicycling, or telecommuting to work instead of driving). 

The five major fuel consuming sectors contributing 

to CO2 emissions from fossil fuel combustion are electricity generation, transportation, industrial, residential, and 

commercial. Carbon dioxide 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.

Figure ES-5 

2009 Sources of CO2 Emissions
Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2009 9 

Figure ES-6 Figure ES-7 

2009 CO2 Emissions from Fossil Fuel Combustion by 

Sector and Fuel Type

2009 End-Use Sector Emissions of CO2, CH4, and N2O 

from Fossil Fuel Combustion

Note: Electricity generation also includes emissions of less than 0.5 Tg CO2

Eq. from geothermal-based electricity generation.

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

End-Use Sector 1990 2000 2005 2006 2007 2008 2009

Transportation 1,489.0 1,813.0 1,901.3 1,882.6 1,899.0 1,794.6 1,724.1 

Combustion 1,485.9 1,809.5 1,896.6 1,878.1 1,894.0 1,789.9 1,719.7

Electricity 3.0 3.4 4.7 4.5 5.0 4.7 4.4

Industrial 1,533.2 1,640.8 1,560.0 1,560.2 1,572.0 1,517.7 1,333.7 

Combustion 846.5 851.1 823.1 848.2 842.0 802.9 730.4

Electricity 686.7 789.8 737.0 712.0 730.0 714.8 603.3

Residential 931.4 1,133.1 1,214.7 1,152.4 1,198.5 1,182.2 1,123.8 

Combustion 338.3 370.7 357.9 321.5 342.4 348.2 339.2

Electricity 593.0 762.4 856.7 830.8 856.1 834.0 784.6

Commercial 757.0 972.1 1,027.2 1,007.6 1,041.1 1,031.6 985.7 

Combustion 219.0 230.8 223.5 208.6 219.4 224.2 224.0

Electricity 538.0 741.3 803.7 799.0 821.7 807.4 761.7

U.S. Territories a 27.9 35.9 50.0 50.3 46.1 39.8 41.7 

Total 4,738.4 5,594.8 5,753.2 5,653.1 5,756.7 5,565.9 5,209.0 

Electricity Generation 1,820.8 2,296.9 2,402.1 2,346.4 2,412.8 2,360.9 2,154.0

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 the inventory report. 

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.

Transportation End-Use Sector. Transportation activities (excluding international bunker fuels) accounted for 33 

percent of CO2 emissions from fossil fuel combustion in 2009.13

 

 Virtually all of the energy consumed in this end-use sector 

came from petroleum products. Nearly 65 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 heavy13 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 2009.
10 Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2009

duty vehicles and jet fuel in aircraft. From 1990 to 2009, transportation emissions rose by 16 percent due, in large part, to 

increased demand for travel and the stagnation of fuel efficiency across the U.S. vehicle fleet. The number of vehicle miles 

traveled by light-duty motor vehicles (passenger cars and light-duty trucks) increased 39 percent from 1990 to 2009, as a 

result of a confluence of factors including population growth, economic growth, urban sprawl, and low fuel prices over much 

of this period. 

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 26 percent of CO2 from fossil fuel 

combustion in 2009. Approximately 55 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. In contrast to the other end-use sectors, emissions from industry have 

steadily declined since 1990. This decline is due to structural changes in the U.S. economy (i.e., shifts from a manufacturingbased to a service-based economy), fuel switching, and efficiency improvements. 

Residential and Commercial End-Use Sectors. The residential and commercial end-use sectors accounted for 22 and 19 

percent, respectively, of CO2 emissions from fossil fuel combustion in 2009. Both sectors relied heavily on electricity for 

meeting energy demands, with 70 and 77 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. Emissions from these end-use sectors have increased 25 percent since 1990, due to 

increasing electricity consumption for lighting, heating, air conditioning, and operating appliances. 

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

Electricity generators consumed 36 percent of U.S. energy from fossil fuels and emitted 41 percent of the CO2 from fossil 

fuel combustion in 2009. 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 2009. Consequently, 

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

Other significant CO2 trends included the following: 

• Carbon dioxide emissions from non-energy use of fossil fuels have increased 4.7 Tg CO2 Eq. (4.0 percent) from 

1990 through 2009. Emissions from non-energy uses of fossil fuels were 123.4 Tg CO2 Eq. in 2009, which 

constituted 2.2 percent of total national CO2 emissions, approximately the same proportion as in 1990. 

• Carbon dioxide emissions from iron and steel production and metallurgical coke production decreased by 24.1 Tg 

CO2 Eq. (36.6 percent) from 2008 to 2009, continuing a trend of decreasing emissions from 1990 through 2009 of 

57.9 percent (57.7 Tg CO2 Eq.). This decline is due to the restructuring of the industry, technological 

improvements, and increased scrap utilization. 

• In 2009, CO2 emissions from cement production decreased by 11.5 Tg CO2 Eq. (28.4 percent) from 2008. After 

decreasing in 1991 by two percent from 1990 levels, cement production emissions grew every year through 2006; 

emissions decreased in the last three years. Overall, from 1990 to 2009, emissions from cement production 

decreased by 12.8 percent, a decrease of 4.3 Tg CO2 Eq.

• Net CO2 uptake from Land Use, Land-Use Change, and Forestry increased by 153.5 Tg CO2 Eq. (17.8 percent) from 

1990 through 2009. 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 
Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2009 11 

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

Methane (CH4) is more than 20 times as effective as CO2 at 

trapping heat in the atmosphere (IPCC 1996). 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 natural gas and 

petroleum systems, agricultural activities, landfills, coal mining, 

wastewater treatment, stationary and mobile combustion, and 

certain industrial processes (see Figure ES-8). 

Some significant trends in U.S. emissions of CH4 include 

the following: 

• In 2009, CH4 emissions from coal mining were 71.0 Tg 

CO2 Eq., a 3.9 Tg CO2 Eq. (5.8 percent) increase over 

2008 emission levels. The overall decline of 13.0 Tg 

CO2 Eq. (15.5 percent) from 1990 results from the 

mining of less gassy coal from underground mines and 

the increased use of CH4 collected from degasification 

systems.

• Natural gas systems were the largest anthropogenic 

source category of CH4 emissions in the United States

in 2009 with 221.2 Tg CO2 Eq. of CH4 emitted into the 

atmosphere. Those emissions have increased by 31.4 Tg CO2 Eq. (16.6 percent) since 1990. Methane emissions 

from this source increased 4 percent from 2008 to 2009 due to an increase in production and production wells. 

• Enteric Fermentation is the second largest anthropogenic source of CH4 emissions in the United States. In 2009, 

enteric fermentation CH4 emissions were 139.8 Tg CO2 Eq. (20 percent of total CH4 emissions), which represents an 

increase of 7.7 Tg CO2 Eq. (5.8 percent) since 1990. 

• Methane emissions from manure management increased by 55.9 percent since 1990, from 31.7 Tg CO2 Eq. in 1990 

to 49.5 Tg CO2 Eq. in 2009. 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. 

• Landfills are the third largest anthropogenic source of CH4 emissions in the United States, accounting for 17 percent 

of total CH4 emissions (117.5 Tg CO2 Eq.) in 2009. From 1990 to 2009, CH4 emissions from landfills decreased by 

29.9 Tg CO2 Eq. (20 percent), with small increases occurring in some interim years. This downward trend in overall 

Figure ES-8 

2009 Sources of CH4 Emissions
12 Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2009

emissions is the result of increases in the amount of landfill gas collected and combusted,14 which has more than 

offset the additional CH4 emissions resulting from an increase in the amount of municipal solid waste landfilled. 

Nitrous Oxide Emissions

Nitrous oxide 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

(IPCC 1996). 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, manure management, nitric acid production and 

stationary fuel combustion, (see Figure ES-9).

Some significant trends in U.S. emissions of N2O include 

the following:

• In 2009, N2O emissions from mobile combustion were 

23.9 Tg CO2 Eq. (approximately 8.1 percent of U.S. 

N2O emissions). From 1990 to 2009, N2O emissions 

from mobile combustion decreased by 45.6 percent. However, from 1990 to 1998 emissions increased by 25.6 

percent, due to control technologies that reduced NOx emissions while increasing N2O emissions. Since 1998, 

newer control technologies have led to an overall decline in N2O from this source.

• Nitrous oxide emissions from adipic acid production were 1.9 Tg CO2 Eq. in 2009, and have decreased significantly 

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

have decreased by 87.7 percent since 1990, and emissions from adipic acid production have remained consistently 

lower than pre-1996 levels since 1998. 

• Agricultural soils accounted for approximately 69.2 percent of N2O emissions in the United States in 2009. 

Estimated emissions from this source in 2009 were 204.6 Tg CO2 Eq. Annual N2O emissions from agricultural soils 

fluctuated between 1990 and 2009, although overall emissions were 3.4 percent higher in 2009 than in 1990. 

 

Figure ES-9 

2009 Sources of N2O Emissions

14 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.
Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2009 13 

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 (IPCC 1996). 

Other emissive sources of these gases include electrical 

transmission and distribution systems, HCFC-22 production, 

semiconductor manufacturing, aluminum production, and 

magnesium production and processing (see Figure ES-10). 

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 120.0 Tg CO2 Eq. in 2009. 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.

• HFC emissions from the production of HCFC-22 decreased by 85.2 percent (31.0 Tg CO2 Eq.) from 1990 through 

2009, 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. 

• Sulfur hexafluoride emissions from electric power transmission and distribution systems decreased by 54.8 percent 

(15.6 Tg CO2 Eq.) from 1990 to 2009, primarily because of higher purchase prices for SF6 and efforts by industry to 

reduce emissions.

• PFC emissions from aluminum production decreased by 91.5 percent (17.0 Tg CO2 Eq.) from 1990 to 2009, due to 

both industry emission reduction efforts and lower domestic aluminum production. 

Figure ES-10 

2009 Sources of HFCs, PFCs, and SF6 Emissions
14 Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2009

ES.3. 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 IPCC 

guidance. Over the twenty-year period of 1990 to 2009, total 

emissions in the Energy and Agriculture sectors grew by 463.3 

Tg CO2 Eq. (9 percent), and 35.7 Tg CO2 Eq. (9 percent), 

respectively. Emissions decreased in the Industrial Processes, 

Waste, and Solvent and Other Product Use sectors by 32.9 Tg 

CO2 Eq. (10 percent), 24.7 Tg CO2 Eq. (14 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, LandUse Change, and Forestry sector (magnitude of emissions plus 

CO2 flux from all LULUCF source categories) increased by 

143.5 Tg CO2 Eq. (17 percent). 

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

Eq.)

Figure ES-11 

U.S. Greenhouse Gas Emissions and Sinks by 

Chapter/IPCC Sector

Note: Relatively smaller amounts of GWP-weighted emissions are also 

emitted from the Solvent and Other Product Use Sectors.

Chapter/IPCC Sector 1990 2000 2005 2006 2007 2008 2009

Energy 5,287.8 6,168.0 6,282.8 6,210.2 6,290.7 6,116.6 5,751.1 

Industrial Processes 315.8 348.8 334.1 339.4 350.9 331.7 282.9 

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

Agriculture 383.6 410.6 418.8 418.8 425.8 426.3 419.3 

Land Use, Land-Use Change, and Forestry (Emissions) 15.0 36.3 28.6 49.8 47.5 33.2 25.0 

Waste 175.2 143.9 144.9 144.4 144.1 149.0 150.5 

Total Emissions 6,181.8 7,112.7 7,213.5 7,166.9 7,263.4 7,061.1 6,633.2 

Net CO2 Flux from Land Use, Land-Use Change, and 

Forestry (Sinks)a (861.5) (576.6) (1,056.5) (1,064.3) (1,060.9) (1,040.5) (1,015.1)

Net Emissions (Sources and Sinks) 5,320.3 6,536.1 6,157.1 6,102.6 6,202.5 6,020.7 5,618.2 

a 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.
Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2009 15 

Energy 

The Energy chapter contains emissions of all greenhouse 

gases resulting from stationary and mobile energy activities 

including fuel combustion and fugitive fuel emissions. Energyrelated activities, primarily fossil fuel combustion, accounted for 

the vast majority of U.S. CO2 emissions for the period of 1990 

through 2009. In 2009, approximately 83 percent of the energy 

consumed in the United States (on a Btu basis) was produced 

through the combustion of fossil fuels. The remaining 17 

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 (49 percent and 13 percent of total U.S. emissions of 

each gas, respectively). Overall, emission sources in the Energy 

chapter account for a combined 87 percent of total U.S. 

greenhouse gas emissions in 2009. 

Figure ES-12 

2009 U.S. Energy Consumption by Energy Source

Industrial Processes

The Industrial Processes chapter contains byproduct 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 4 percent of U.S. 

greenhouse gas emissions in 2009. 

Solvent and Other Product Use

The Solvent and Other Product Use chapter contains greenhouse gas emissions that are produced as a byproduct 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 2009. 

Agriculture

The Agriculture 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, Land-Use 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. Methane emissions from enteric fermentation and manure management 

represented 20 percent and 7 percent of total CH4 emissions from anthropogenic activities, respectively, in 2009. 
16 Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2009

Agricultural soil management activities such as fertilizer application and other cropping practices were the largest source of 

U.S. N2O emissions in 2009, accounting for 69 percent. In 2009, emission sources accounted for in the Agriculture chapter 

were responsible for 6.3 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 resulted in a net 

uptake (sequestration) of C in the United States. Forests (including vegetation, soils, and harvested wood) accounted for 85 

percent of total 2009 net CO2 flux, urban trees accounted for 9 percent, mineral and organic soil carbon stock changes 

accounted for 4 percent, and landfilled yard trimmings and food scraps accounted for 1 percent of the total net flux in 2009. 

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 5.5 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. 

Land use, land-use change, and forestry activities in 2009 resulted in a net C sequestration of 1,015.1 Tg CO2 Eq. (Table 

ES-5). This represents an offset of 18 percent of total U.S. CO2 emissions, or 15 percent of total greenhouse gas emissions in 

2009. Between 1990 and 2009, total land use, land-use change, and forestry net C flux resulted in a 17.8 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 or million metric tons CO2 Eq.)

Sink Category 1990 2000 2005 2006 2007 2008 2009

Forest Land Remaining Forest Land (681.1) (378.3) (911.5) (917.5) (911.9) (891.0) (863.1)

Cropland Remaining Cropland (29.4) (30.2) (18.3) (19.1) (19.7) (18.1) (17.4)

Land Converted to Cropland 2.2 2.4 5.9 5.9 5.9 5.9 5.9 

Grassland Remaining Grassland (52.2) (52.6) (8.9) (8.8) (8.6) (8.5) (8.3)

Land Converted to Grassland (19.8) (27.2) (24.4) (24.2) (24.0) (23.8) (23.6)

Settlements Remaining Settlements (57.1) (77.5) (87.8) (89.8) (91.9) (93.9) (95.9)

Other (Landfilled Yard Trimmings and Food 

Scraps) (24.2) (13.2) (11.5) (11.0) (10.9) (11.2) (12.6)

Total (861.5) (576.6) (1,056.5) (1,064.3) (1,060.9) (1,040.5) (1,015.1)

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 

7.8 Tg CO2 Eq. in 2009, an increase of 11 percent relative to 1990. The application of synthetic fertilizers to forest and 

settlement soils in 2009 resulted in direct N2O emissions of 1.9 Tg CO2 Eq. Direct N2O emissions from fertilizer application 

to forest soils have increased by 455 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 by 55 percent since 1990. Forest 
Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2009 17 

fires resulted in CH4 emissions of 7.8 Tg CO2 Eq., and in N2O emissions of 6.4 Tg CO2 Eq. in 2009. Carbon dioxide and 

N2O emissions from peatlands totaled 1.1 Tg CO2 Eq. and less than 0.01 Tg CO2 Eq. in 2009, respectively. 

Table ES-6: Emissions from Land Use, Land-Use Change, and Forestry (Tg or million metric tons CO2 Eq.)

Source Category 1990 2000 2005 2006 2007 2008 2009

CO2 8.1 8.8 8.9 8.8 9.2 9.6 8.9

Cropland Remaining Cropland: Liming of Agricultural Soils 4.7 4.3 4.3 4.2 4.5 5.0 4.2 

Cropland Remaining Cropland: Urea Fertilization 2.4 3.2 3.5 3.7 3.7 3.6 3.6 

Wetlands Remaining Wetlands: Peatlands Remaining Peatlands 1.0 1.2 1.1 0.9 1.0 1.0 1.1

CH4 3.2 14.3 9.8 21.6 20.0 11.9 7.8

Forest Land Remaining Forest Land: Forest Fires 3.2 14.3 9.8 21.6 20.0 11.9 7.8

N2O 3.7 13.2 9.8 19.5 18.3 11.6 8.3

Forest Land Remaining Forest Land: Forest Fires 2.6 11.7 8.0 17.6 16.3 9.8 6.4

Forest Land Remaining Forest Land: Forest Soils 0.1 0.4 0.4 0.4 0.4 0.4 0.4 

Settlements Remaining Settlements: Settlement Soils 1.0 1.1 1.5 1.5 1.6 1.5 1.5 

Wetlands Remaining Wetlands: Peatlands Remaining Peatlands + + + + + + + 

Total 15.0 36.3 28.6 49.8 47.5 33.2 25.0

+ Less than 0.05 Tg CO2 Eq.

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 78 percent of this chapter’s emissions, and 17 percent of total U.S. CH4 emissions.15

ES.4. Other Information

 

Additionally, wastewater treatment accounts for 20 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 2009. 

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 2009.

 

15 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.
18 Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2009

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

Implied Sectors 1990 2000 2005 2006 2007 2008 2009

Electric Power Industry 1,868.9 2,337.6 2,444.6 2,388.2 2,454.0 2,400.7 2,193.0

Transportation 1,545.2 1,932.3 2,017.4 1,994.4 2,003.8 1,890.7 1,812.4

Industry 1,564.4 1,544.0 1,441.9 1,497.3 1,483.0 1,446.9 1,322.7

Agriculture 429.0 485.1 493.2 516.7 520.7 503.9 490.0

Commercial 395.5 381.4 387.2 375.2 389.6 403.5 409.5

Residential 345.1 386.2 371.0 335.8 358.9 367.1 360.1

U.S. Territories 33.7 46.0 58.2 59.3 53.5 48.4 45.5

Total Emissions 6,181.8 7,112.7 7,213.5 7,166.9 7,263.4 7,061.1 6,633.2

Land Use, Land-Use Change, and Forestry 

(Sinks) (861.5) (576.6) (1,056.5) (1,064.3) (1,060.9) (1,040.5) (1,015.1)

Net Emissions (Sources and Sinks) 5,320.3 6,536.1 6,157.1 6,102.6 6,202.5 6,020.7 5,618.2

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

See Table 2-12 of the inventory report for more detailed data.

Using this categorization, emissions from electricity 

generation accounted for the largest portion (33 percent) of 

U.S. greenhouse gas emissions in 2009. Transportation 

activities, in aggregate, accounted for the second largest 

portion (27 percent), while emissions from industry accounted 

for the third largest portion (20 percent) of U.S. greenhouse 

gas emissions in 2009. 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 changes in the U.S. 

economy (i.e., shifts from a manufacturing-based to a servicebased economy), fuel switching, and energy efficiency 

improvements. The remaining 20 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.

Carbon dioxide 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 

Figure ES-13 

Emissions Allocated to Economic Sectors

Note: Does not include U.S. Territories.
Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2009 19 

sales of electricity.16

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

metric tons CO2 Eq.)

 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. 

Implied Sectors 1990 2000 2005 2006 2007 2008 2009

Industry 2,238.3 2,314.4 2,162.5 2,194.6 2,192.9 2,146.5 1,910.9

Transportation 1,548.3 1,935.8 2,022.2 1,999.0 2,008.9 1,895.5 1,816.9

Commercial 947.7 1,135.8 1,205.1 1,188.5 1,225.3 1,224.5 1,184.9

Residential 953.8 1,162.2 1,242.9 1,181.5 1,229.6 1,215.1 1,158.9

Agriculture 460.0 518.4 522.7 544.1 553.2 531.1 516.0

U.S. Territories 33.7 46.0 58.2 59.3 53.5 48.4 45.5

Total Emissions 6,181.8 7,112.7 7,213.5 7,166.9 7,263.4 7,061.1 6,633.2

Land Use, Land-Use Change, 

and Forestry (Sinks) (861.5) (576.6) (1,056.5) (1,064.3) (1,060.9) (1,040.5) (1,015.1)

Net Emissions (Sources 

and Sinks) 5,320.3 6,536.1 6,157.1 6,102.6 6,202.5 6,020.7 5,618.2

See Table 2-14 of the inventory report for more detailed data.

When emissions from electricity are distributed among 

these sectors, industrial activities account for the largest share 

of U.S. greenhouse gas emissions (29 percent) in 2009. 

Transportation is the second largest contributor to total U.S. 

emissions (28 percent). The commercial and residential sectors 

contributed the next largest shares of total U.S. greenhouse gas 

emissions in 2009. Emissions from these sectors increase 

substantially when emissions from electricity are included, due 

to their relatively large share of electricity consumption (e.g., 

lighting, appliances, etc.). 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 2009.

 

Figure ES-14 

U.S. Emissions with Electricity Distributed to 

Economic Sectors

Note: Does not include U.S. Territories.

16 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.
20 Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2009

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 2009; (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 0.4 percent since 1990. This rate is slightly slower than that for 

total energy and for fossil fuel consumption, and much slower than that for electricity consumption, overall gross domestic product and 

national population (see Figure ES-15). 

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

Variable 1990 2000 2005 2006 2007 2008 2009

Growth 

Ratea

GDP b 100 140 157 162 165 165 160 2.5%

Electricity Consumption c 100 127 134 135 138 138 132 1.5%

Fossil Fuel Consumption c 100 117 119 117 119 116 108 0.5%

Energy Consumption c 100 116 118 118 120 118 112 0.6%

Population d 100 113 118 120 121 122 123 1.1%

Greenhouse Gas Emissions e 100 115 117 116 117 114 107 0.4%

a

 Average annual growth rate

b

 Gross Domestic Product in chained 2005 dollars (BEA 2010)

c

 Energy content-weighted values (EIA 2010b) d

 U.S. Census Bureau (2010)

e

 GWP-weighted values

Figure ES-15 

U.S. Greenhouse Gas Emissions Per Capita and Per Dollar of Gross 

Domestic Product

Source: BEA (2010), U.S. Census Bureau (2010), and emission estimates in the inventory report. 
Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2009 21 

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

The reporting requirements of the UNFCCC17

Since 1970, the United States has published estimates of annual emissions of CO, NOx, NMVOCs, and SO2 (EPA 2010, 

EPA 2009),

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.

18 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 2000 2005 2006 2007 2008 2009

NOx 21,707 19,116 15,900 15,039 14,380 13,547 11,468

Mobile Fossil Fuel Combustion 10,862 10,199 9,012 8,488 7,965 7,441 6,206

Stationary Fossil Fuel Combustion 10,023 8,053 5,858 5,545 5,432 5,148 4,159

Industrial Processes 591 626 569 553 537 520 568

Oil and Gas Activities 139 111 321 319 318 318 393

Incineration of Waste 82 114 129 121 114 106 128

Agricultural Burning 8 8 6 7 8 8 8

Solvent Use 1 3 3 4 4 4 3

Waste 0 2 2 2 2 2 2

CO 130,038 92,243 70,809 67,238 63,625 60,039 51,452

Mobile Fossil Fuel Combustion 119,360 83,559 62,692 58,972 55,253 51,533 43,355

Stationary Fossil Fuel Combustion 5,000 4,340 4,649 4,695 4,744 4,792 4,543

Industrial Processes 4,125 2,216 1,555 1,597 1,640 1,682 1,549

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

Agricultural Burning 268 259 184 233 237 270 247

Oil and Gas Activities 302 146 318 319 320 322 345

Waste 1 8 7 7 7 7 7

Solvent Use 5 45 2 2 2 2 2

NMVOCs 20,930 15,227 13,761 13,594 13,423 13,254 9,313

Mobile Fossil Fuel Combustion 10,932 7,229 6,330 6,037 5,742 5,447 4,151

Solvent Use 5,216 4,384 3,851 3,846 3,839 3,834 2,583

Industrial Processes 2,422 1,773 1,997 1,933 1,869 1,804 1,322

Stationary Fossil Fuel Combustion 912 1,077 716 918 1,120 1,321 424

Oil and Gas Activities 554 388 510 510 509 509 599

Incineration of Waste 222 257 241 238 234 230 159

Waste 673 119 114 113 111 109 76

Agricultural Burning NA NA NA NA NA NA NA

SO2 20,935 14,830 13,466 12,388 11,799 10,368 8,599

Stationary Fossil Fuel Combustion 18,407 12,849 11,541 10,612 10,172 8,891 7,167

Industrial Processes 1,307 1,031 831 818 807 795 798

Mobile Fossil Fuel Combustion 793 632 889 750 611 472 455

Oil and Gas Activities 390 287 181 182 184 187 154

Incineration of Waste 38 29 24 24 24 23 24

Waste 0 1 1 1 1 1 1

Solvent Use 0 1 0 0 0 0 0

Agricultural Burning NA NA NA NA NA NA NA

NA (Not Available)

Note: Totals may not sum due to independent rounding.

Source: (EPA 2010, EPA 2009) except for estimates from field burning of agricultural residues.

 

17 See <http://unfccc.int/resource/docs/cop8/08.pdf>.

18 NOx and CO emission estimates from field burning of agricultural residues were estimated separately, and therefore not taken from EPA (2008).
22 Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2009

Key Categories

The 2006 IPCC Guidelines for National Greenhouse Gas Inventories (IPCC 2006) 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 inventory of direct greenhouse gases in terms of the absolute level of emissions, the trend in emissions, or 

both.”19 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 

2009 Key Categories

Note: For a complete discussion of the key category analysis, see Annex 1 of the inventory report. Darker bars indicate a Tier 1 level assessment key category. 

Lighter bars indicate a Tier 2 level assessment key category.

 

Figure ES-16 presents 2009 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. 

19 See Chapter 7 “Methodological Choice and Recalculation” in IPCC (2000). <http://www.ipcc-nggip.iges.or.jp/public/gp/gpgaum.htm>. 
Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2009 23 

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 report. 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.

Box ES-3: 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 inventory report. In this effort, the United States follows the 2006 IPCC Guidelines (IPCC 2006), which states, “Both methodological 

changes and refinements over time are an essential part of improving inventory quality. It is good practice to change or refine methods” 

when: available data have changed; the previously used method is not consistent with the IPCC guidelines for that category; a category has 

become key; the previously used method is insufficient to reflect mitigation activities in a transparent manner; the capacity for inventory 

preparation has increased; new inventory methods become available; and for correction of errors.” 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.

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 2009) has been recalculated to reflect the change, per the 2006 IPCC Guidelines (IPCC 2006). 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.
24 Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2009

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