# Executive Summary

An emissions inventory that identifies and quantifies a country's primary anthropogenic 1 

### 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- accep ted 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 CO 2 

### underground for

sequestration or other reasons 7 

### . 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 p lanned 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 CO 2 

### , CH 4 

### , N 2 

### O, and several other fluorine-containing halogenated substances. Although the direct

greenhouse gases CO 2 

### , CH 4 

### , and N 2 

### O 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

– 2 01 1

### 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 CO 2 

### , and therefore GWPweighted emissions are measured in teragrams (or million metric tons) of CO 2 

### equivalent (Tg CO 2 

### Eq.). 9

, 10 

### All

gases in this Executive Summary are presented in units of Tg CO 2 

### 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 CO 2 

### 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: Glo bal Warming Potentials (100-Year Time Horizon) Used in this Report

Gas GWP

CO 2 1

CH 4 * 21

N 2 O 310

HFC- 23 11,700

HFC- 32 650

HFC-1 25 2,800

HFC-134a 1,300

HFC-1 43a 3,800

HFC-152a 140

HFC-227ea 2,900

HFC-236fa 6,300

1,300

CF 4 6,500

C 2 F 6 9,200

C 4 F 10 7,000

C 6 F 14 7,400

SF 6 23,900 HFC-4310mee

Source: IPCC (1996)

* The CH 4 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 CO 2 is not included



## .

8 Albedo is a measure of the Earth’s reflectivity, and is defined as t he fraction of the total solar radiation incident on a body that

is reflected by it.

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

10 One teragram is equal to 10 12 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, NO

x 

### , NMVOCs, SO 2 

### , 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, CO 2 

### 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 CO 2 

### 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

– 2 01 1

### 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

CO 2 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 P roduction 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 CO 2 

### Eq.)

Executive Summary ES -5Soda 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 Fuels c 218.6

103.5 22 8.7

113.1 238.3

115.3 251.7

114.3 245.1

106.4 264.5

117.0 264.5

111.3

CH 4 639.9 593.6 618.6 618.8 603.8 592.7 587.2

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 Ca rbide Production

and Consumption + + + + + + +

+ + + + + + +

In cineration of Waste + + + + + + +

International Bunker Fuels c 0.1 0.1 0.1 0 .1 0.1 0.1 0.1

N 2 O 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

N 2 O 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

– 2 01 1Inc ineration of Waste 0.5

Field Burning of Agricultural

Residues 0.1

W etlands Remaining

Wetlands +

International Bunker Fuels c 0.9

HFCs 36.9

Substitution of Ozone

Depleting Substances d 0.3

HCFC-22 Production 36.4

Semiconductor Manufacture 0.2

PFCs 20.6

Semiconductor Manufacture 2.2

Aluminum Production 18.4

SF 6 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 CO 2 Eq.

a Parentheses indicate negative values or sequestration. The net CO 2 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 E thanol 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 Bu nker 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 CO 2 

### , representing approximately 83.7

percent of total greenhouse gas emissions. The largest source of CO 2 

### , and of overall greenhouse gas emissions, was

fossil fuel combustion. CH 4 

### 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 N 2 

### O emissions . O zone 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 SF 6 

### emissions.

Executive Summary ES -7

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

### Eq.)

Overall, from 1990 to 2011, total emissions of CO 2 

### increased by 504.0 Tg CO 2 

### Eq. (9.9 percent), while total

emissions of CH 4 

### decreased by 52.7 Tg CO 2 

### Eq. (8.2 percent), and N 2 

### O increased by 12.6 Tg CO 2 

### Eq. (3.6 percent).

During the same period, aggregate weighted emissions of HFCs, PFCs, and SF 6 

### rose by 55.1 Tg CO 2 

### Eq. (61.1

percent). From 1990 to 2011, HFCs increased by 92.0 Tg CO 2 

### Eq. (249.3 percent), PFCs decreased by 13.6 Tg CO 2 

### Eq. (66.1 percent), and SF 6 

### decreased by 23.3 Tg CO 2 

### Eq. (71.3 percent). Despite being emitted in smaller

quantities relative to the other principal greenhouse gases, emissions of HFCs, PFCs, and SF 6 

### are significant because

many of these gases have extremely high global warming potentials and, in the cases of PFCs and SF 6 

### , 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

CO 2 

### 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 CO 2 

### emissions in 2011 . Globally, approximately

31,780 Tg of CO 2 

### 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 CO 2 

### (e.g., through

conversion of forest land to agricultural or urban use) or can act as a sink for CO 2 

### (e.g., through net additions to

forest biomass). In addition to fossil-fuel combustion, several other sources emit significant quantities of CO 2 

### . 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 CO 2 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

– 2 01 1

### Figure ES-5 : 2011 Sources of CO 2 

### Emissions

Note: Electricity generation also includes emissions of less than 0.05 Tg CO 2 Eq. from geothermal-based generation.



### As the largest source of U.S. greenhouse gas emissions, CO 2 

### 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 CO 2 

### 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, CO 2 

### emissions from fossil fuel combustion increased from

4,748.5 Tg CO 2 

### Eq. to 5,277.2 Tg CO 2 

### Eq.

— an 11.1 percent total increase over the twenty-two-year period. From

2010 to 2011, these emissions decreased by 130.9 Tg CO 2 

### Eq. (2.4 percent).

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

emission trends. Changes in CO 2 

### emissions from fossil fuel combustion are influenced by many long-term and

sho rt -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 CO 2 

### Emissions from Fossil Fuel Combustion by Sector and Fuel Type

Figure ES-7: 2011 End -Use Sector Emissions of CO 2 

### , CH 4 

### , and N 2 

### O from Fossil Fuel

Combustion

The five major fuel consuming sectors contributing to CO 2 

### emissions from fossil fuel combustion are electricity

generation, transportation, industrial, residential, and commercial. CO 2 

### 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 CO 2 

### emissions from fossil fuel

combustion by end-use sector.

Table ES-3: CO 2 

### Emissions from Fossil Fuel Combustion by Fuel Consuming End-Use Sector

(Tg or million metric tons CO 2 

### Eq.)

ES

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

– 2 01 1 End-Use Sector 1990 2005 2007 2008 2009 2010 2011Transportation

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. Territories a 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 CO 2 

### 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 t o 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 CO 2 

### 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 CO 2 

### 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 CO 2 

### 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 CO 2 

### 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 CO 2 

### 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 CO 2 

### emissions.

Other significant CO 2 

### trends included the following:

 CO 2 

### emissions from non-energy use of fossil fuels have increased by 13.1 Tg CO 2 

### Eq. (11.2 percent) from

1990 through 2011 . Emissions from non-energy uses of fossil fuels were 130.6 Tg CO 2 

### Eq. in 2011 , which

constituted 2.3 percent of total national CO 2 

### emissions, approximately the same proportion as in 1990.

 CO 2 

### emissions from iron and steel production and metallurgical coke production increased by 8.5 Tg CO 2 

### 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 CO 2 

### Eq.). This overall decline is due to the

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

 In 2011 , CO 2 

### emissions from cement production increased by 0.7 Tg CO 2 

### 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 CO 2 

### Eq.

 Net CO 2 

### uptake from Land Use, Land-Use Change, and Forestry increased by 110.5 Tg CO 2 

### 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 (CH 4 

### ) is more than 20 times as effective as CO 2 

### at trapping heat in the atmosphere (IPCC 1996). Over the

last two hundred and fifty years, the concentration of CH 4 

### in the atmosphere increased by 158 percent (IPCC 2007).

Anthropogenic sources of CH 4 

### 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

– 2 01 1

### Figure ES-8: 2011 Sources of CH 4 

### Emissions

Some significant trends in U.S. emissions of CH 4 

### include the following:

 Natural gas systems were the largest anthropogenic source category of CH 4 

### emissions in the United States

in 2011 with 144.7 Tg CO 2 

### Eq. of CH 4 

### emitted into the atmosphere. Those emissions have decreased by

16.5 Tg CO 2 

### Eq. (10.2 percent) since 1990. The decrease in CH 4 

### 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 CH 4 

### emissions from natural gas systems in 2011.

CH 4 

### 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 CH 4 

### emissions in the United States. In

2011, enteric fermentation CH 4 

### emissions were 137.4 Tg CO 2 

### Eq. (23.4 percent of total CH 4 

### emissions),

which represents an increase of 4.6 Tg CO 2 

### 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 de crease 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 CH 4 

### emissions in the United States, accounting for

17.5 percent of total CH 4 

### emissions (103.0 Tg CO 2 

### Eq.) in 2011 . From 1990 to 2011, CH 4 

### emissions from

landfills decreased by 44.7 Tg CO 2 

### 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 CH 4 

### emissions resulting from an increase in the

amount of municipal solid waste landfilled.

 In 2011 , CH 4 

### emissions from coal mining were 63.2 Tg CO 2 

### Eq., a 9.2 Tg CO 2 

### Eq. (12.6 percent) decrease

under 2010 emission levels. The overall decline of 20.8 Tg CO 2 

### Eq. (24.8 percent) from 1990 results from

the mining of less gassy coal from underground mines and the increased use of CH 4 

### collected from

degasification systems.

 Methane emissions from manure management increased by 65.3 percent since 1990, from 31.5 Tg CO 2 

### Eq.

in 1990 to 52.0 Tg CO 2 

### 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 CH 4 

### 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

N 2 

### O 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 N 2 

### O emissions are much

lower than CO 2 

### emissions, N 2 

### O is approximately 300 times more powerful than CO 2 

### at trapping heat in the

atmosphere (IPCC 1996). Since 1750, the global atmospheric concentration of N 2 

### O has risen by approximately 19

percent (IPCC 2007). The main anthropogenic activities producing N 2 

### O 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 N 2 

### O Emissions

Some significant trends in U.S. emissions of N 2 

### O include the following:

14 The CO 2 produced from combusted landfill CH 4 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

– 2 01 1

###  Agricultural soils accounted for approximately 69.3 percent of N 2 

### O 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 CO 2 

### Eq. Annual N 2 

### O emissions from agricultural soils fluctuated between 1990 and 2011, although overall

emissions were 8.5 percent higher in 2011 than in 1990. Annual N 2 

### O 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.

 N 2 

### O emissions from stationary combustion increased 9.7 Tg CO 2 

### Eq. (79.3 percent) from 1990 through

2011 . N 2 

### O 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 , N 2 

### O emissions from mobile combustion were 18.5 Tg CO 2 

### Eq. (5.2 percent of U.S. N 2 

### O

emissions). From 1990 to 2011 , N 2 

### O 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

NO

x 

### emissions while increasing N 2 

### O emissions. Since 1998, newer control technologies have led to an

overall decline of 36.8 Tg CO 2 

### Eq. (66.6 percent) in N 2 

### O from this source.

 N 2 

### O emissions from adipic acid production were 10.6 Tg CO 2 

### 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 SF 6 

# 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 SF 6 

### , are potent greenhouse gases. In addition to having high global

warming potentials, SF 6 

### 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 CO 2 

### Eq. in 2011 . Emissions from ODS

substitutes are both the largest and the fastest growing source of HFC, PFC, and SF 6 

### 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 CO 2 

### 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.

 SF 6 

### emissions from electric power transmission and distribution systems decreased by 73.6 percent (19.6

Tg CO 2 

### Eq.) from 1990 to 2011, primarily because of higher purchase prices for SF 6 

### and efforts by industry

to reduce emissions.

 PFC emissions from aluminum production decreased by 84.0 percent (15.5 Tg CO 2 

### 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 CO 2 

### Eq. (9.1 percent), 10.3

Tg CO 2 

### Eq. (3.3 percent)

, and 47.6 Tg CO 2 

### Eq. (11.5 percent), respectively. Emissions from the Waste and Solvent

and Other Product Use sectors decreased by 40.2 Tg CO 2 

### Eq. (23.9 percent) and less than 0.1 Tg CO 2 

### 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 CO 2 

### flux from all LULUCF source categories)

increased by 87.6 Tg CO 2 

### Eq. (11.2 percent).

ES

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

– 2 01 1

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

Chapter/IPCC Sector 1990 2005 2007 2008 2009 2010 201 1

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 CO 2 

### Eq.)

* The net CO 2 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. CO 2 

### 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 CH 4 

### and N 2 

### O

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 CO 2 

### , CH 4 

### , and N 2 

### O. 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, CO 2 

### 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

SF 6 

### . 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 2 

### O 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 CO 2 

### fluxes, which are addressed in the Land Use, La nd

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. CH 4 

### and N 2 

### O were the primary greenhouse gases emitted by agricultural activities. CH 4 

### emissions from

enteric fermentation and manure management represente d 23.4 percent and 8.9 percent of total CH 4 

### 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. N 2 

### O emissions i n 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

– 2 01 1

# Land Use, Land-Use Change, and Forestry

The Land Use, Land-Use Change, and Forestry chapter contains emissions of CH 4 

### and N 2 

### O, and emissions and

removals of CO 2 

### 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 CO 2 

### 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 CO 2 

### Eq.

(Table ES-5). This represents an offset of 16.1 percent of total U.S. CO 2 

### 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 CO 2 

### 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 C O 2 

### Flux from Land Use, Land-Use Change, and Forestry (Tg or million metric

tons CO 2 

### Eq.)

Fo rest 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) La nd Converted to Cropland Sink Category 1990 2005 2007 2008 2009 2010 2011

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

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 CO 2 

### emissions of 8.1 Tg CO 2 

### Eq. (8,117 Gg). Lands undergoing peat

extraction (i.e., Peatlands Remaining Peatlands ) resulted in CO 2 

### emissions of 0.9 Tg CO 2 

### Eq. (918 Gg), and N 2 

### O

emissions of less than 0.05 Tg CO 2 

### Eq. The application of synthetic fertilizers to forest soils in 2011 resulted in

direct N 2 

### O emissions of 0.4 Tg CO 2 

### Eq. (1 Gg). Direct N 2 

### O 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 N 2 

### O emissions from fertilizer application to settlement soils in 2011 accounted for 1.5 Tg CO 2 

### Eq. (5 Gg). This represents an increase of 51 percent since 1990. Forest fires in 2011 resulted in CH 4 

### emissions of

14.2 Tg CO 2 

### Eq. ( 675 Gg), and in N 2 

### O emissions of 11.6 Tg CO 2 

### Eq. ( 37 Gg).

So urce Category 1990 2005 2007 2008 2009 2010 201 1

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 CO 2 

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

tons CO 2 

### 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 CH 4 Cropland Remaining Cropland: Urea Fertilization

Wetlands Remaining Wetlands: Peatlands Remaining

Peatlands

Forest Land Remaining Forest Land: Forest Fires

N 2 O

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 2 5.4 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 CO 2 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 fo r 80.7 percent of this chapter’s emissions, and 17.5 percent of total U.S. CH 4



### emissions. 15 

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

CH 4 

### emissions, and 1.5 percent of U.S. N 2 

### O emissions. Emissions of CH 4 

### and N 2 

### O from composting are also

accounted for in this chapter, generating emissions of 1.5 Tg CO 2 

### Eq. and 1.7 Tg CO 2 

### 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.

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

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### 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 CO 2 

### Eq.)

Note: Totals may not sum due to independent rounding. Emissions include CO 2 , CH 4 , N 2 O, HFCs, PFCs, and SF 6

. 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

ch anges 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 N 2 

### O emissions from agricultural soil management and CH 4 

### 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 CO 2 

### emissions from fossil fuel combustion. CO 2 

### 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 CO 2 

### from

fossil fuel combustion and the use of limestone and dolomite for flue gas desulfurization, CO 2 

### and N 2 

### O from

incineration of waste, CH 4 

### and N 2 

### O from stationary sources, and SF 6 

### 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, CO 2 

### 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 CO 2 

### Eq.)

Implied Sectors 1990 20 05 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

58 1.5

58.2 2,113.6

2,018.2

1,215.6

1,237.1

62 6.2

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.

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

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### 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 201 1 Growth Rate a

GDP b 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 Consumption c 100 134

Fossil Fuel Consumption c 100 119

Energy Consumption c 100 119

Population d 100 118

Greenhouse Gas Emissions e 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>

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

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### 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 CO 2 

### 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.

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