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 2011. 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 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 

use of the most recently published calculation methodologies by the IPCC, as contained in the 2006 IPCC 

Guidelines, is considered to improve the rigor and accuracy of this inventory and is fully in line with the prior IPCC 

guidance. The structure of this report is consistent 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. 

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/2006/sbsta/eng/09.pdf>. 

Executive Summary ES-1 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 this 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 United States 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 ar e 

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 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. 

On October 30, 2009, the U.S. Environmental Protection Agency (EPA) published a rule for the mandatory 

reporting of greenhouse gases (GHG) from large GHG emissions sources in the United States. Implementation of 40 

CFR Part 98 is referred to as the Greenhouse Gas Reporting Program (GHGRP). 40 CFR part 98 applies to direct 

greenhouse gas emitters, fossil fuel suppliers, industrial gas suppliers, and facilities that inject CO2 underground for 

sequestration or other reasons7. Reporting is at the facility level, except for certain suppliers of fossil fuels and 

industrial greenhouse gases. The GHGRP dataset and the data presented in this inventory report are complementary 

and, as indicated in the respective methodological and planned improvements sections in this report’s chapters, EPA 

is using the data, as applicable, to improve the national estimates presented in this inventory. 

ES.1. Background Information
 

Greenhouse gases trap heat and make the planet warmer. The most important greenhouse gases directly emitted by 

humans include CO2, CH4, N2O, and several other fluorine-containing halogenated substances. 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 2010, concentrations of these 

greenhouse gases have increased globally by 39, 158, and 18 percent, respectively (IPCC 2007 and NOAA/ESLR 

2009). This annual report estimates the total national greenhouse gas emissions and removals associated with 

human activities across the United States. 

Global Warming Potentials 

Gases in the atmosphere can contribute to the greenhouse effect both directly and indirectly. Direct effe cts 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 

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 See <http://www.epa.gov/climatechange/emissions/ghgrulemaking.html> and <http://ghgdata.epa.gov/ghgp/main.do>. 

ES-2 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2011 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

albedo).8 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. 

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 CO 2 equivalent (Tg CO2 Eq.).9,10 All 

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

The UNFCCC reporting guidelines for national inventories were updated in 2006,11 but continue to require the use 

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

estimates of aggregate greenhouse gas emissions for 1990 to 2011 are consistent with estimates developed prior to 

the publication of the IPCC Third Assessment Report (TAR) (IPCC 2001) and the IPCC Fourth Assessment Repo rt 

(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 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
 

1,300
 

CF4 6,500

C2F6 9,200

C4F10 7,000
 

C6F14 7,400

SF6 23,900

HFC-4310mee 

 

 

 

 

 

 

 

 

 

 

 

 

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.
 

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.
 

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>.
 

Executive Summary ES-3 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

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). 

ES.2. Recent Trends in U.S. Greenhouse Gas 

Emissions and Sinks 

In 2011, total U.S. greenhouse gas emissions were 6,702.3 Tg, or million metric tons, CO2 Eq. Total U.S. emissions 

have increased by 8.4 percent from 1990 to 2011, and emissions decreased from 2010 to 2011 by 1.6 percent (108.0 

Tg CO2 Eq.). The decrease from 2010 to 2011 was due to a decrease in the carbon intensity of fuels consumed to 

generate electricity due to a decrease in coal consumption, with increased natural gas consumption and a signific ant 

increase in hydropower used. Additionally, relatively mild winter conditions, especially in the South Atlantic 

Region of the United States where electricity is an important heating fuel, resulted in an overall decrease in 

electricity demand in most sectors. 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 2011. 

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

ES-4 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2011 
 

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 

 

 

Gas/Source 1990 2005 2007 2008 2009 2010 2011 

CO2 5,108.8 6,109.3 6,128.6 5,944.8 5,517.9 5,736.4 5,612.9 

Fossil Fuel Combustion 4,748.5 5,748.7 5,767.7 5,590.6 5,222.4 5,408.1 5,277.2 

Electricity Generation 1,820.8 2,402.1 2,412.8 2,360.9 2,146.4 2,259.2 2,158.5 

Transportation 1,494.0 1,891.7 1,904.7 1,816.0 1,749.2 1,763.9 1,745.0 

Industrial 848.6 823.4 844.4 802.0 722.6 780.2 773.2 

Residential 338.3 357.9 341.6 347.0 337.0 334.6 328.8 

Commercial 219.0 223.5 218.9 223.8 223.4 221.8 222.1 

U.S. Territories 27.9 50.0 45.2 41.0 43.8 49.6 49.7 

Non-Energy Use of Fuels 117.4 142.7 134.9 139.5 124.0 132.8 130.6 

Iron & Steel & Metallurgical 

Coke Production 99.8 66.7 71.3 66.8 43.0 55.7 64.3 

Natural Gas Systems 37.7 29.9 30.9 32.6 32.2 32.3 32.3 

Cement Production 33.3 45.2 44.5 40.5 29.0 30.9 31.6 

Lime Production 11.5 14.3 14.6 14.3 11.2 13.1 13.8 

Incineration of Waste 8.0 12.5 12.7 11.9 11.7 12.0 12.0 

Other Process Uses of 

Carbonates 4.9 6.3 7.4 5.9 7.6 9.6 9.2 

Ammonia Production 13.0 9.2 9.1 7.9 7.9 8.7 8.8 

Cropland Remaining Cropland 7.1 7.9 8.2 8.6 7.2 8.4 8.1 

Urea Consumption for NonAgricultural Purposes 3.8 3.7 4.9 4.1 3.4 4.4 4.3 

Petrochemical Production 3.4 4.3 4.1 3.6 2.8 3.5 3.5 

Aluminum Production 6.8 4.1 4.3 4.5 3.0 2.7 3.3 

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

tons CO2 Eq.) 

Executive Summary ES-5 
 

Soda Ash Production and 

Consumption 2.8 3.0 2.9 3.0 2.6 2.7 2.7 

Titanium Dioxide Production 1.2 1.8 1.9 1.8 1.6 1.8 1.9 

Carbon Dioxide Consumption 1.4 1.3 1.9 1.8 1.8 2.2 1.8 

Ferroalloy Production 2.2 1.4 1.6 1.6 1.5 1.7 1.7 

Glass Production 1.5 1.9 1.5 1.5 1.0 1.5 1.3 

Zinc Production 0.6 1.0 1.0 1.2 0.9 1.2 1.3 

Phosphoric Acid Production 

Wetlands Remaining 

1.5 1.3 1.2 1.2 1.0 1.1 1.2 

Wetlands 1.0 1.1 1.0 1.0 1.1 1.0 0.9 

Lead Production 0.5 0.6 0.6 0.5 0.5 0.5 0.5 

Petroleum Systems 0.4 0.3 0.3 0.3 0.3 0.3 0.3 

Silicon Carbide Production 

and Consumption 

Land Use, Land-Use Change, 

and Forestry (Sink) a 

0.4 

(794.5)

0.2 

(997.8)

0.2 

(929.2) 

0.2 

(902.6) 

0.1 

(882.6) 

0.2 

(888.8) 

0.2 

(905.0) 

Wood Biomass and Ethanol b Consumption

International Bunker Fuelsc 

218.6

103.5

228.7

113.1

238.3 

115.3 

251.7 

114.3 

245.1 

106.4 

264.5 

117.0 

264.5 

111.3 

CH4 639.9 593.6 618.6 618.8 603.8 592.7 587.2 

Natural Gas Systems 161.2 159.0 168.4 163.4 150.7 143.6 144.7 

Enteric Fermentation 132.7 137.0 141.8 141.4 140.6 139.3 137.4 

Landfills 147.8 112.5 111.6 113.6 113.3 106.8 103.0 

Coal Mining 84.1 56.9 57.9 67.1 70.3 72.4 63.2 

Manure Management 31.5 47.6 52.4 51.5 50.5 51.8 52.0 

Petroleum Systems 35.2 29.2 29.8 30.0 30.5 30.8 31.5 

Wastewater Treatment 15.9 16.5 16.6 16.6 16.5 16.4 16.2 

Forest Land Remaining Forest 

Land 2.5 8.0 14.4 8.7 5.7 4.7 14.2 

Rice Cultivation 7.1 6.8 6.2 7.2 7.3 8.6 6.6 

Stationary Combustion 7.5 6.6 6.4 6.6 6.3 6.3 6.3 

Abandoned Underground Coal 

Mines 6.0 5.5 5.3 5.3 5.1 5.0 4.8 

Petrochemical Production 2.3 3.1 3.3 2.9 2.9 3.1 3.1 

Mobile Combustion 4.6 2.4 2.1 1.9 1.8 1.8 1.7 

Composting 0.3 1.6 1.7 1.7 1.6 1.5 1.5 

Iron & Steel & Metallurgical 

Coke Production 1.0 0.7 0.7 0.6 0.4 0.5 0.6 

Field Burning of Agricultural 

Residues 0.2 0.2 0.2 0.2 0.2	 0.2 0.2 

Ferroalloy Production 

Silicon Carbide Production 

and Consumption 

+ + + + + + + 

+ + + + + + + 

Incineration of Waste + + + + + + + 

International Bunker Fuelsc 0.1 0.1 0.1 0.1 0.1 0.1 0.1 

N2O 344.3 356.1 376.1 349.7 338.7 343.9 356.9 

Agricultural Soil Management 227.9 237.5 252.3 245.4 242.8 244.5 247.2 

Stationary Combustion 12.3 20.6 21.2 21.1 20.7 22.6 22.0 

Mobile Combustion 44.0 36.9 29.0 25.5 22.7 20.7 18.5 

Manure Management 14.4 17.1 18.0 17.8 17.7 17.8 18.0 

Nitric Acid Production 18.2 16.9 19.7 16.9 14.0 16.8 15.5 

Forest Land Remaining Forest 

Land 2.1 6.9 12.1 7.4 5.0 4.2 11.9 

Adipic Acid Production 15.8 7.4 10.7 2.6 2.8 4.4 10.6 

Wastewater Treatment 3.5 4.7 4.8 4.9 5.0 5.1 5.2 

N2O from Product Uses 4.4 4.4 4.4 4.4 4.4 4.4 4.4 

Composting 0.4 1.7 1.8 1.9 1.8 1.7 1.7 

Settlements Remaining 1.0 1.5 1.6 1.5 1.4 1.5 1.5 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

ES-6 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2011 
 

Incineration of Waste 0.5 

Field Burning of Agricultural 

Residues 0.1 

Wetlands Remaining 

Wetlands + 

International Bunker Fuelsc 0.9 

HFCs 36.9 

Substitution of Ozone 

Depleting Substancesd 0.3 

HCFC-22 Production 36.4 

Semiconductor Manufacture 0.2 

PFCs 20.6 

Semiconductor Manufacture 2.2 

Aluminum Production 18.4 

SF6 32.6 

Electrical Transmission and 

Distribution 26.7 

Magnesium Production and 

Processing 5.4 2.9 2.6 1.9 1.1 1.3 1.4 

Semiconductor Manufacture 0.5 1.0 0.8 0.9 0.7 1.0 0.9 

Total 6,183.3 7,195.3 7,263.2 7,048.8 6,586.6 6,810.3 6,702.3 

Net Emissions (Sources and 

Sinks) 5,388.7 6,197.4 6,334.0 6,146.2 5,704.0 5,921.5 5,797.3 

0.4 0.4 0.4 0.4 0.4 0.4 

0.1 0.1 0.1 0.1 0.1 0.1 

+ + + + + + 

1.0 1.0 1.0 0.9 1.0 1.0 

115.0 120.0 117.5 112.0 121.3 129.0

99.0 102.7 103.6 106.3 114.6 121.7 

15.8 17.0 13.6 5.4 6.4 6.9 

0.2 0.3 0.3 0.2 0.4 0.3 

6.2 7.7 6.6 4.4 5.9 7.0 

3.2 3.8 3.9 2.9 4.4 4.1 

3.0 3.8 2.7 1.6 1.6 2.9 

15.0 12.3 11.4 9.8 10.1 9.4 

11.1 8.8 8.6 8.1 7.8 7.0 

Settlements 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

+ 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 2011. The 

primary greenhouse gas emitted by human activities in the United States was CO2, representing approximately 83.7 

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 decreased by 8.2 percent since 1990, resulted primarily from 

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

landfills. Agricultural soil management, mobile source fuel combustion and stationary 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 

from semiconductor manufacturing and as a by-product of primary aluminum production, while electrical 

transmission and distribution systems accounted for most SF6 emissions. 

Executive Summary ES-7 
 

Figure ES-4: 2011Greenhouse Gas Emissions by Gas (Percentages based on Tg CO 2 Eq.)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Overall, from 1990 to 2011, total emissions of CO2 increased by 504.0 Tg CO2 Eq. (9.9 percent), while total 

emissions of CH4 decreased by 52.7 Tg CO2 Eq. (8.2 percent), and N2O increased by 12.6 Tg CO2 Eq. (3.6 percent). 

During the same period, aggregate weighted emissions of HFCs, PFCs, and SF6 rose by 55.1 Tg CO2 Eq. (61.1 

percent). From 1990 to 2011, HFCs increased by 92.0 Tg CO2 Eq. (249.3 percent), PFCs decreased by 13.6 Tg CO2 

Eq. (66.1 percent), and SF6 decreased by 23.3 Tg CO2 Eq. (71.3 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 2011. The following sections describe each gas’s 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 roug hly 

balanced. Since the Industrial Revolution (i.e., about 1750), global atmospheric concentrations of CO 2 have risen 

about 39 percent (IPCC 2007 and NOAA/ESLR 2009), principally due to the combustion of fossil fuels. Within the 

United States, fossil fuel combustion accounted for 94.0 percent of CO2 emissions in 2011. Globally, approximately 

31,780 Tg of CO2 were added to the atmosphere through the combustion of fossil fuels in 2010, of which the United 

States accounted for about 18 percent.12 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 (2013). 

ES-8 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2011 
 

 

 

Figure ES-5: 2011 Sources of CO2 Emissions 

Note: Electricity generation also includes emissions of less than 0.05 Tg CO2 Eq. from geothermal-based generation. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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, and is approximately 79 percent of total GWPweighted emissions in 2011. Emissions of CO2 from fossil fuel combustion increased at an average annual rate of 

0.5 percent from 1990 to 2011. The fundamental factors influencing this trend include (1) a generally growing 

domestic economy over the last 22 years, and (2) an overall growth in emissions from electricity generation and 

transportation activities. Between 1990 and 2011, CO2 emissions from fossil fuel combustion increased from 

4,748.5 Tg CO2 Eq. to 5,277.2 Tg CO2 Eq.—an 11.1 percent total increase over the twenty-two-year period. From 

2010 to 2011, these emissions decreased by 130.9 Tg CO2 Eq. (2.4 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. 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 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. 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). 

Executive Summary ES-9 
 

Figure ES-6 : 2011 CO2 Emissions from Fossil Fuel Combustion by Sector and Fuel Type 

Figure ES-7: 2011End-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 or million metric tons CO2 Eq.) 

ES-10 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2011 

End-Use Sector 1990 2005 2007 2008 2009 2010 2011 
 

Transportation 

Combustion 

1,497.0 

1,494.0 

1,896.5 

1,891.7 

1,909.7 

1,904.7 

1,820.7 

1,816.0 

1,753.7 

1,749.2 

1,768.4 

1,763.9 

1,749.3 

1,745.0 

Electricity 3.0 4.7 5.1 4.7 4.5 4.5 4.3 

Industrial 1,535.3 1,560.4 1,559.9 1,499.3 1,324.6 1,421.3 1,392.1 

Combustion 848.6 823.4 844.4 802.0 722.6 780.2 773.2 

Electricity 686.7 737.0 715.4 697.3 602.0 641.1 618.9 

Residential 931.4 1,214.7 1,205.2 1,189.9 1,123.5 1,175.0 1,125.6 

Combustion 338.3 357.9 341.6 347.0 337.0 334.6 328.8 

Electricity 593.0 856.7 863.5 842.9 786.5 840.4 796.9 

Commercial 757.0 1,027.2 1,047.7 1,039.8 976.8 993.9 960.5 

Combustion 219.0 223.5 218.9 223.8 223.4 220.6 222.1 

Electricity 

U.S. Territoriesa 

538.0 

27.9 

803.7 

50.0 

828.8 

45.2 

816.0 

41.0 

753.5 

43.8 

773.3 

49.6 

738.4 

49.7 

Total 4,748.5 5,748.7 5,767.7 5,590.6 5,222.4 5,408.1 5,277.2 

Electricity Generation 1,820.8 2,402.1 2,412.8 2,360.9 2,146.4 2,259.2 2,158.5 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 33 

percent of CO2 emissions from fossil fuel combustion in 2011.

13 Virtually all of the energy consumed in this enduse 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 heavy-duty vehicles and jet fuel in aircraft. From 1990 to 2011, transportation 

emissions rose by 17 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 34 percent from 1990 to 2011, as a result of a confluence of factors including population 

growth, economic growth, urban sprawl, and low fuel prices over much of this period. It is noted that the more 

recent trend for transportation has shown a general decline in emissions, due to recent slow growth in economic 

activity, higher fuel prices, and an associated decrease in the demand for passenger transportation. 

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 2011. Approximately 56 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 manufacturing-based 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 21 

and 18 percent, respectively, of CO2 emissions from fossil fuel combustion in 2011. Both sectors relied heavily on 

electricity for meeting energy demands, with 71 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 the residential and 

commercial end-use sectors have increased by 21 percent and 27 percent since 1990, respectively, 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 

13 If emissions from international bunker fuels are included, the transportation end-use sector accounted for 34.5 percent of U.S. 

emissions from fossil fuel combustion in 2011. 

Executive Summary ES-11 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

fossil fuel combustion in 2011. 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 nonfossil options such as nuclear, hydroelectric, or geothermal energy. Electricity generators relied on coal for 

approximately 42 percent their total energy requirements in 2011, and accounted for 95 percent of all coal consumed 

for energy in the United States in 2011. Recently a decrease in the carbon intensity of fuels consumed to generate 

electricity has occurred due to a decrease in coal consumption, and increased natural gas consumption and other 

generation sources. Across the time series, changes in electricity demand and the carbon intensity of fuels used for 

electricity generation have a significant impact on CO2 emissions. 

Other significant CO2 trends included the following: 

	 CO2 emissions from non-energy use of fossil fuels have increased by 13.1 Tg CO2 Eq. (11.2 percent) from 

1990 through 2011. Emissions from non-energy uses of fossil fuels were 130.6 Tg CO2 Eq. in 2011, 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 increased by 8.5 Tg CO2 

Eq. (15.3 percent) from 2010 to 2011, continuing a two-year trend of increasing emissions primarily due to 

increased steel production associated with improved economic conditions. Despite this, from 1990 through 

2011, emissions declined by 35.6 percent (35.5 Tg CO2 Eq.). This overall decline is due to the 

restructuring of the industry, technological improvements, and increased scrap utilization. 

	 In 2011, CO2 emissions from cement production increased by 0.7 Tg CO2 Eq. (2.3 percent) from 2010. 

After decreasing in 1991 by 2.2 percent from 1990 levels, cement production emissions grew every year 

through 2006. Since 2006, emissions have fluctuated through 2011due to the economic recession and 

associated decrease in demand for construction materials. Overall, from 1990 to 2011, emissions from 

cement production have decreased by 4.9 percent, a decrease of 1.6 Tg CO2 Eq. 

	 Net CO2 uptake from Land Use, Land-Use Change, and Forestry increased by 110.5 Tg CO2 Eq. (13.9 

percent) from 1990 through 2011. 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 

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 158 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). 

ES-12 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2011 
 

Figure ES-8: 2011 Sources of CH4 Emissions 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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

	 Natural gas systems were the largest anthropogenic source category of CH4 emissions in the United States 

in 2011 with 144.7 Tg CO2 Eq. of CH4 emitted into the atmosphere. Those emissions have decreased by 

16.5 Tg CO2 Eq. (10.2 percent) since 1990. The decrease in CH4 emissions is due largely to a decrease in 

emissions from transmission and storage due to increased voluntary reductions and a decrease in 

distribution emissions due to a decrease in cast iron and unprotected steel pipelines. Emissions from field 

production accounted for approximately 37 percent of CH4 emissions from natural gas systems in 2011. 

CH4 emissions from field production decreased by 12 percent from 1990 through 2011; however, the trend 

was not stable over the time series-emissions from this source increased by 43 percent from 1990 through 

2006, and then declined by 38 percent from 2006 to 2011. Reasons for this trend include such factors as 

increased voluntary reductions, as well as the effects of the recent global economic slowdown. 

	 Enteric fermentation is the second largest anthropogenic source of CH4 emissions in the United States. In 

2011, enteric fermentation CH4 emissions were 137.4 Tg CO2 Eq. (23.4 percent of total CH4 emissions), 

which represents an increase of 4.6 Tg CO2 Eq. (3.5 percent) since 1990. This increase in emissions from 

1990 to 2011 in enteric generally follows the increasing trends in cattle populations. From 1990 to 1995 

emissions increased and then decreased from 1996 to 2001, mainly due to fluctuations in beef cattle 

populations and increased digestibility of feed for feedlot cattle. Emissions generally increased from 2002 

to 2007, though with a slight decrease in 2004, as both dairy and beef populations underwent increases and 

the literature for dairy cow diets indicated a trend toward a decrease in feed digestibility for those years. 

Emissions decreased again from 2008 to 2011 as beef cattle populations again decreased. 

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

17.5 percent of total CH4 emissions (103.0 Tg CO2 Eq.) in 2011. From 1990 to 2011, CH4 emissions from 

landfills decreased by 44.7 Tg CO2 Eq. (30.3 percent), with small increases occurring in some interim 

years. This downward trend in overall emissions can be attributed to a 21 percent reduction in the amount 

of decomposable materials (i.e., paper and paperboard, food scraps, and yard trimmings) discarded in MSW 

landfills over the time series (EPA 2010) and an increase in the amount of landfill gas collected and 

Executive Summary ES-13 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

combusted,14 which has more than offset the additional CH4 emissions resulting from an increase in the 

amount of municipal solid waste landfilled. 

	 In 2011, CH4 emissions from coal mining were 63.2 Tg CO2 Eq., a 9.2 Tg CO2 Eq. (12.6 percent) decrease 

under 2010 emission levels. The overall decline of 20.8 Tg CO2 Eq. (24.8 percent) from 1990 results from 

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

degasification systems. 

	 Methane emissions from manure management increased by 65.3 percent since 1990, from 31.5 Tg CO2 Eq. 

in 1990 to 52.0 Tg CO2 Eq. in 2011. 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. 

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 (IPCC 1996). Since 1750, the global atmospheric concentration of N2O has risen by approximately 19 

percent (IPCC 2007). The main anthropogenic activities producing N2O in the United States are agricultural soil 

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

production (see Figure ES-9). 

Figure ES-9: 2011 Sources of N2O Emissions 

 

 

 

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

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. 

ES-14 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2011 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

	 Agricultural soils accounted for approximately 69.3 percent of N2O emissions and 3.7 percent of total 

emissions in the United States in 2011. Estimated emissions from this source in 2011 were 247.2 Tg CO2 

Eq. Annual N2O emissions from agricultural soils fluctuated between 1990 and 2011, although overall 

emissions were 8.5 percent higher in 2011 than in 1990. Annual N2O emissions from agricultural soils 

fluctuated between 1990 and 2011, largely as a reflection of annual variation in weather patterns, synthetic 

fertilizer use, and crop production. 

	 N2O emissions from stationary combustion increased 9.7 Tg CO2 Eq. (79.3 percent) from 1990 through 

2011. N2O emissions from this source increased primarily as a result of an increase in the number of coal 

fluidized bed boilers in the electric power sector. 

	 In 2011, N2O emissions from mobile combustion were 18.5 Tg CO2 Eq. (5.2 percent of U.S. N2O 

emissions). From 1990 to 2011, N2O emissions from mobile combustion decreased by 58.0 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 of 36.8 Tg CO2 Eq. (66.6 percent) in N2O from this source. 

	 N2O emissions from adipic acid production were 10.6 Tg CO2 Eq. in 2011, and have decreased 

significantly in recent years due to the widespread installation of pollution control measures. Emissions 

from adipic acid production have decreased by 32.9 percent since 1990 and by 39.6 perce nt since a peak in 

1995. 

HFC, PFC, and SF6 Emissions 

HFCs and PFCs are families of synthetic chemicals that are used as alternatives to Ozone Depleting Substances, 

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). 

Figure ES- 10: 2011 Sources of HFCs, PFCs, and SF 6 Emissions 

Some significant trends in U.S. HFC, PFC, and SF 6 emissions include the following: 

Executive Summary ES-15 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

	 Emissions resulting from the substitution of ozone depleting substances (ODS) (e.g., CFCs) have been 

consistently increasing, from small amounts in 1990 to 121.7 Tg CO2 Eq. in 2011. 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-out of ODS required under the Montreal Protocol came 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 81.0 percent (29.5 Tg CO2 Eq.) from 1990 

through 2011, 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 73.6 percent (19.6 

Tg CO2 Eq.) from 1990 to 2011, primarily because of higher purchase prices for SF6 and efforts by industry 

to reduce emissions. 

	 PFC emissions from aluminum production decreased by 84.0 percent (15.5 Tg CO2 Eq.) from 1990 to 

2011, due to both industry emission reduction efforts and declines in domestic aluminum production. 

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-two-year period of 1990 to 2011, total 

emissions in the Energy, Industrial Processes, and Agriculture sectors grew by 478.4 Tg CO2 Eq. (9.1 percent), 10.3 

Tg CO2 Eq. (3.3 percent), and 47.6 Tg CO2 Eq. (11.5 percent), respectively. Emissions from the Waste and Solvent 

and Other Product Use sectors decreased by 40.2 Tg CO2 Eq. (23.9 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 (LULUCF) sector (magnitude of emissions plus CO2 flux from all LULUCF source categories) 

increased by 87.6 Tg CO2 Eq. (11.2 percent). 

ES-16 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2011 
 

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

 

 

Chapter/IPCC Sector 1990 2005 2007 2008 2009 2010 2011

5,267.3 6,251.6 6,266.9 6,096.2 5,699.2 5,889.1 5,745.7 

316.1 330.8 347.2 318.7 265.3 303.4 326.5 

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

Agriculture 413.9 446.2 470.9 463.6 459.2 462.3 461.5

Land-Use Change and Forestry 13.7 25.4 37.3 27.2 20.4 19.7 36.6

167.8 136.9 136.5 138.6 138.1 131.4 127.7 

Total Emissions 6,183.3 7,195.3 7,263.2 7,048.8 6,586.6 6,810.3 6,702.3

Land-Use Change and Forestry (Sinks) (794.5) (997.8) (929.2) (902.6) (882.6) (888.8) (905.0) 

Net Emissions (Emissions and Sinks) 5,388.7 6,197.4 6,334.0 6,146.2 5,704.0 5,921.5 5,797.3

Energy 

Industrial Processes 

 

 

 

Waste 

 

 

 

Table ES-4: Recent Trends in U.S. Greenhouse Gas Emissions and Sinks by Chapter/IPCC 

Sector (Tg or million metric tons CO2 Eq.) 

 

 

 

 

 

 

 

 

 

 

 

 

* 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 2011. In 2011, 

approximately 87 percent of the energy consumed in the United States (on a Btu basis) was produced through the 

combustion of fossil fuels. The remaining 13 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 (43 percent and 11 percent of total U.S. emissions of each gas, respectively). Overall, emission sources in 

the Energy chapter account for a combined 85.7 percent of total U.S. greenhouse gas emissions in 2011. 

Executive Summary ES-17 
 

Figure ES- 12: 2011 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, other process uses of carbonates (e.g., flux stone, flue gas 

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

phosphoric acid production, ferroalloy production, glass 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 4.9 percent of U.S. greenhouse gas 

emissions in 2011. 

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 N 2O 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 2011. 

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 23.4 percent and 8.9 percent of total CH4 emissions from 

anthropogenic activities, respectively, in 2011. Agricultural soil management activities such as fertilizer application 

and other cropping practices were the largest source of U.S. N2O emissions in 2011, accounting for 69.3 percent. In 

2011, emission sources accounted for in the Agricultural chapters were responsible for 6.9 percent of total U.S. 

greenhouse gas emissions. 

ES-18 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2011 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 92 percent of total 2011 net CO2 flux, urban trees accounted for 8 percent, 

mineral and organic soil carbon stock changes accounted for 1 percent, and landfilled yard trimmings and food 

scraps accounted for 1 percent of the total net flux in 2011. 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 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 d ue to the long-term 

accumulation of yard trimming carbon and food scraps in landfills. 

Land use, land-use change, and forestry activities in 2011 resulted in a net C sequestration of 905.0 Tg CO2 Eq. 

(Table ES-5). This represents an offset of 16.1 percent of total U.S. CO2 emissions, or 13.5 percent of total 

greenhouse gas emissions in 2011. Between 1990 and 2011, total land use, land-use change, and forestry net C flux 

resulted in a 13.9 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.) 

Forest Land Remaining Forest Land (696.8) (905.0) (859.3) 

(6.6) 

14.5 

7.1 

(9.0) 

(65.0) 

(833.3) 

(5.2) 

14.5 

7.2 

(9.0) 

(66.0) 

(811.3)

(4.6) 

14.5 

7.3 

(8.9) 

(66.9) 

(817.6)

(3.0) 

14.5 

7.3

(8.8) 

(67.9) 

(833.5) 

(2.9) 

14.5 

7.4 

(8.8) 

(68.8) 

Cropland Remaining Cropland (34.1) (20.3)

21.0 13.5

Grassland Remaining Grassland (5.3) (1.0)

Land Converted to Grassland (7.7) (10.2)

Settlements Remaining Settlements (47.5) (63.2)

Other (Landfilled Yard Trimmings 

and Food Scraps) (24.2) (11.6) (10.9) (10.9) (12.7) (13.3) (13.0) 

Land Converted to Cropland 

Sink Category 1990 2005 2007 2008 2009 2010 2011

Total (794.5) (997.8) (929.2) (902.6) (882.6) (888.8) (905.0)

 

 

 

 

 

 

 

 

 

 

 

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. Liming of agricultural soils 

and urea fertilization in 2011 resulted in CO2 emissions of 8.1 Tg CO2 Eq. (8,117 Gg). Lands undergoing peat 

extraction (i.e., Peatlands Remaining Peatlands) resulted in CO2 emissions of 0.9 Tg CO2 Eq. (918 Gg), and N2O 

emissions of less than 0.05 Tg CO2 Eq. The application of synthetic fertilizers to forest soils in 2011 resulted in 

direct N2O emissions of 0.4 Tg CO2 Eq. (1 Gg). 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 in 2011 accounted for 1.5 Tg CO2 

Eq. (5 Gg). This represents an increase of 51 percent since 1990. Forest fires in 2011 resulted in CH4 emissions of 

14.2 Tg CO2 Eq. (675 Gg), and in N2O emissions of 11.6 Tg CO2 Eq. (37 Gg). 

Source Category 1990 2005 2007 2008 2009 2010 2011 

Cropland Remaining Cropland: Liming of Agricultural 

8.1 

4.7 

8.9 

4.3 

9.2 

4.5 

9.6 

5.0

8.3 

3.7 

9.4 

4.7 

9.0 

4.5 

CO2 

Table ES-6: Emissions from Land Use, Land-Use Change, and Forestry (Tg or million metric 

tons CO2 Eq.) 

Executive Summary ES-19 
 

+ + 

19.7 36.6 

3.7 5.3

1.0 0.9 

4.7 14.2 

4.7 14.2 

5.6 13.4

3.8 11.6 

0.4 0.4 

1.5 1.5

CH4 

Cropland Remaining Cropland: Urea Fertilization 

Wetlands Remaining Wetlands: Peatlands Remaining 

Peatlands 

Forest Land Remaining Forest Land: Forest Fires 

N2O 

Forest Land Remaining Forest Land: Forest Fires 

Forest Land Remaining Forest Land: Forest Soils 

Settlements Remaining Settlements: Settlement Soils 

Wetlands Remaining Wetlands: Peatlands Remaining 

Peatlands 

2.4 

1.0 

2.5 

2.5 

3.1 

2.0 

0.1 

1.0 

+ + + + + 

Total 13.7 25.4 37.3 27.2 20.4 

3.5 3.8 3.6 3.6

1.1 1.0 1.0 1.1 

8.0 14.4 8.7 5.7 

8.0 14.4 8.7 5.7 

8.4 13.7 8.9 6.4 

6.6 11.7 7.1 4.7 

0.4 0.4 0.4 0.4 

1.5 1.6 1.5 1.4 

 

 

 

 

Soils 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

+ 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 80.7 percent of this chapter’s emissions, and 17.5 percent of total U.S. CH4 

emissions.15 Additionally, wastewater treatment accounts for 16.7 percent of Waste emissions, 2.8 percent of U.S. 

CH4 emissions, and 1.5 percent of U.S. N2O emissions. Emissions of CH4 and N2O from composting are also 

accounted for in this chapter, generating emissions of 1.5 Tg CO2 Eq. and 1.7 Tg CO2 Eq., respectively. Overall, 

emission sources accounted for in the Waste chapter generated 1.9 percent of total U.S. greenhouse gas emissions in 

2011. 

ES.4. 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 2011. 

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. 

ES-20 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2011 
 

Figure ES- 13: Emissions Allocated to Economic Sectors 

Implied Sectors 

Electric Power Industry 

Transportation 

Industry 

Agriculture 

Commercial 

Residential 

U.S. Territories 

Total Emissions 

Land Use, Land-Use Change, and Forestry 

(Sinks) 

Net Emissions (Sources and Sinks) 

1990 2005 2007 2008 2009 2010 2011

1,866.1 2,445.7 2,455.6 

2,013.1 

1,456.1 

555.6 

372.0 

358.2

52.6 

2,402.0 

1,916.0 

1,398.8 

535.3 

380.9 

366.0 

49.8 

2,187.6 

1,840.6 

1,244.2 

525.4 

382.9 

358.1 

47.9 

2,303.0 

1,852.2 

1,331.8 

528.7 

376.9 

359.6 

58.0 

2,200.9

1,829.4 

1,332.0 

546.6 

378.0 

357.3 

58.0 

1,553.2 2,012.3 

1,538.8 1,416.2 

458.0 517.4 

388.1 374.1

345.4 371.3

33.7 58.2 

6,183.3 7,195.3 7,263.2 7,048.8 6,586.6 6,810.3 6,702.3 

(794.5) (997.8) (929.2) (902.6) (882.6) (888.8) (905.0)

5,388.7 6,197.4 6,334.0 6,146.2 5,704.0 5,921.5 5,797.3 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table ES-7: U.S. Greenhouse Gas Emissions Allocated to Economic Sectors (Tg or million 

metric tons CO2 Eq.) 

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 (33 percent) of 

U.S. greenhouse gas emissions in 2011. 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 2011. 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 service-based 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 8 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 and residential sectors accounted for 6 and 5 percent, 

respectively, 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 

Executive Summary ES-21 
 

 

 

 

 

 

 

 

 

 

 

 

 

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.16 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, industrial activities account for the largest 

share of U.S. greenhouse gas emissions (28 percent) in 2011. Transportation is the second largest contributor to 

total U.S. emissions (27 percent). The residential and commercial sectors contributed the next largest shares of total 

U.S. greenhouse gas emissions in 2011. 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 2011. 

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

Emissions Distributed (Tg or million metric tons CO2 Eq.) 

Implied Sectors 1990 2005 2007 2008 2009 2010 2011 

Industry 

Transportation 

Residential 

Commercial 

Agriculture 

U.S. Territories 

2,181.3 

1,556.3 

939.5 

953.1 

519.3 

33.7 

2,102.4 

2,017.2 

1,192.4 

1,243.6

581.5 

58.2 

2,113.6 

2,018.2 

1,215.6 

1,237.1

626.2 

52.6 

2,036.3 

1,920.8 

1,211.1 

1,223.6 

607.1 

49.8 

1,789.8 

1,845.2 

1,150.8 

1,159.6 

593.3

47.9 

1,916.9 

1,856.9 

1,165.2 

1,216.3 

597.1 

58.0 

1,897.2 

1,833.7 

1,131.0 

1,169.8 

612.6 

58.0 

Total Emissions 6,183.3 7,195.3 7,263.2 7,048.8 6,586.6 6,810.3 6,702.3 

Land Use, Land-Use Change, 

and Forestry (Sinks) (794.5) (997.8) (929.2) (902.6) (882.6) (888.8) (905.0)

Net Emissions (Sources and 5,388.7 6,197.4 6,334.0 6,146.2 5,704.0 5,921.5 5,797.3 

See Table 2-14 for more detailed data. 

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

 

 

 

Sinks)

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. 

ES-22 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2011 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 2011; (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 faster 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 2005 2007 2008 2009 2010 2011 Growth Ratea 

GDPb 100 157 165 

137 

119 

120 

121 

117 

164 

136 

116 

117 

122 

114 

159 

131 

109 

111 

123 

107 

163 

137 

112 

115 

124 

110 

166 

136 

101 

102 

125 

108 

2.5% 

1.5% 

0.1% 

0.1% 

1.1% 

0.4% 

Electricity Consumptionc 100 134 

Fossil Fuel Consumptionc 100 119 

Energy Consumptionc 100 119 

Populationd 100 118 

Greenhouse Gas Emissionse 100 116 a Average annual growth rate b Gross Domestic Product in chained 2005 dollars (BEA 2012)
 c Energy content-weighted values (EIA 2013)
 d U.S. Census Bureau (2012)
 e GWP-weighted values
 

Executive Summary ES-23 

 

 

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

Product 

Source: BEA (2012), U.S. Census Bureau (2012), and emission estimates in this report. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Key Categories
 

The IPCC 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 

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 2011 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 re quest 

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. 

17 See Chapter 7 “Methodological Choice and Recalculation” in IPCC (2000). <http://www.ipccnggip.iges.or.jp/public/gp/gpgaum.htm> 

ES-24 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2011 
 

Figure ES- 16: 2011 Key Categories 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Note: 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. 

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 t he benefit of 

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

Executive Summary ES-25 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 In ventory 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 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 2011) 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. 

ES-26 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2011