### Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990 –2009 1 n emissions inventory that identifies and quantifies a country's primary anthropogenic 1



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

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

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

at a level that would prevent dangerous anthropogenic interference with the climate system. Such a level should be achieved

within a time

- frame sufficient to allow ecosystems to adapt naturally to climate change, to ensure that food production is not

threatened and to enable economic development to proceed in a sustainable manner.” sources and sinks of

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

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

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

(UNFCCC) to compare the relative contribution of different e mission sources and greenhouse gases to climate change.

2



### Parties to the Convention, by ratifying, “shall develop, periodically

update, publish and make available...national inventories of anthropogenic

emissions by sources and removals by sinks of all greenhouse gases not

controlled by the Montreal Protocol , using comparable methodologies...” 3 

# A

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

greenhouse gas emission trends from 1990 through 200 9 . To ensure that the

U.S. emi ssion 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 I ntergovernmental P anel on C limate

C hange (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 (IP CC 2006). The structure of the i nventory report is consistent The United States views the Inventory as an opportunity to fulfill these

commitments.

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

natural processes that have been affec ted 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 <h ttp://unfccc.int>.

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

of the Parties elaborated the role of Annex I Parties in preparing national inventories. See <http://unfccc.int>. 

### All material taken from the Inventory

of U.S. Greenhouse Gas Emissions

and Sinks: 1990

– 2009 , U.S.

Environmental Protection Agency,

Offi ce of Atmospheric Programs,

EPA 430 -R- 11

- 005 , April 2011. You

may el ectronicall y download the full

i nventory report from U.S. EPA’s

Global Climate Change web page at:

www.epa.gov/climatechange/

emissions/usinventory.html.2 Executive Summary of th e **Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990**

**– 2009**  

### with the UNFCCC gui delines for inventory reporting. 4 

### For most source categories, the IPCC methodologies were expanded,

resulting in a more comprehensive and detailed estimate of emissions.

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

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

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

- accepted

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

manner in line with the UNFCCC reporting guidelines for the reporting of i nventories 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 the se reports are

comparable. In this regard, U.S. emissions and sinks rep orted in this i nventory report are comparable to emissions and sinks reported by

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

presents emissions and sinks in a c ommon format consistent with how countries are to report inventories under the UNFCCC. The i nventory

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

the manner in which those calculations are conducted.



# ES.1. Background Information

Naturally occurring greenhouse gases include water vapor, carbon dioxide (CO 2 

### ), methane (CH 4 

### ), nitrous oxide (N 2 

### O),

and ozone (O 3 

### ). Several classes of halogenated substances that contain fluorine, chlorine, or bromine are also greenhouse

gases, but they are, for the most part, solely a product of industrial activities. Chlorofluorocarbons (CFCs) and

hydrochlorofluorocarbons (HCFCs) are halocarbons that contain chlorine, while halocarbons that contain bromine are

referred to as bromofluorocarbons (i.e., halons). As stratospheric ozone depleting substances, CFCs, HCFCs, and halons are

covered under the Montreal Protocol on Substances that Deplete the Ozone Layer. The UNFCCC defers to this earlier

international treaty. Consequently, Parties to the UNFCCC are not required to include these gases in their national

greenhouse gas emission inventories. 7



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

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

stratospheric ozone. These gases include carbon monoxide (CO), oxides of nitrogen (NO

x 

### ), and non -CH 4 

### volatile organic

compounds (NMVOCs). Aerosols, which are extremely small particles or liquid droplets, such as those produced by sulfur

dioxide (SO 2 

### ) or elemental carbon emissions, can also affect the absorptive characteristics of the atmosphere. Some other fluorine

- containing halogenated substances

— hydrofluorocarbons (HFCs),

perfluoroc arbons (PFCs), and sulfur hexafluoride (SF 6 

### )— do not deplete stratospheric ozone but are potent greenhouse gases.

These latter substances are addressed by the UNFCCC and accounted for in national greenhouse gas emission inventories.

Although the direct greenhouse gases 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 2005, concentrations of

these greenhouse gases have increased globally by 36, 148, and 18 percent, respectively (IPCC 2007).

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

5 See < http://www.ipcc

- nggip.iges.or.jp/public/index.html>.

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

7 Emissions estimates of CFCs, HCFCs, halons and other ozone -d epleting substances are include d in the annexes of the i nventory report for informational

purposes.

### Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990 –2009 3 Beginning in the 1950s, the use of CFCs and other stratospheric ozone depleting substances (ODS) increased by nearly

10 p ercent per year until the mid

- 1980s, when international concern about ozone depletion led to the entry into force of the

Montreal Protocol . Since then, the production of ODS is being phased out. In recent years, use of ODS substitutes such as

HFCs and PF Cs has grown as they begin to be phased in as replacements for CFCs and HCFCs. Accordingly, atmospheric

concentrations of these substitutes have been growing (IPCC 2007).



# Global Warming Potentials

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

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

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

atmospheric processes that alter the radiative balance of the earth (e.g., affect cloud formation or albedo). 8



### The GWP of a greenhouse gas is defined as the rat io 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 refere nce gas used is CO 2 

### ,

and therefore GWP

- weighted emissions are measured in teragrams

(or million metric tons) of CO 2 

### equivalent (Tg CO 2 

### Eq.)

. The IPCC

developed the g lobal warming p otential (GWP) concept to compare the ability of each green house gas to trap heat in the

atmosphere relative to another gas.

9

, 10



### The UNFCCC reporting guidelines for national inventories

were updated in 2006, All

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



### Eq.

11 

### but continue to require the use of GWPs

from the IPCC Second Assessment Report (SAR) (IPCC 1996).

This requirement ensures that current estimates of aggregate

greenhouse gas emissions for 1990 to 200 9 are consis tent with

estimates developed prior to the publication of the IPCC Third

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

Assessment Report (AR4) (IPCC 2007) . Therefore, to comply

with international reporting standards under the UNFCCC, official

em ission estimates are reported by the United States using SAR

GWP values. All estimates are provided throughout the i nventory

report in both CO 2 

### equivalents and unweighted units. A

comparison of emission values using the SAR GWPs versus the

TAR and AR4 GW Ps can be found in Chapter 1 and, in more

detail, in Annex 6.1 of the i nventory report. The GWP values

used in th e i nventory report are listed below in Table ES -1. Table ES -1 : Global Warming Potentials (100

- Year

T ime Horizon) Used in the Inventory Report

Gas GWP

CO

2 1

CH

4 * 21

N

2 O 310

HFC

- 23 11,700

HFC

- 32 650

HFC

- 125 2,800

HFC

- 134a 1,300

HFC

- 143a 3,800

HFC

- 152a 140

HFC

- 227ea 2,900

HFC

- 236fa 6,300

HFC

- 4310mee 1,300

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

Source: IPCC (1996)

* The C H 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.

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>. 8 Albedo is a measure of the earth’s reflectivity, and is defined as the fraction of the total solar radiation incident on a bo dy that is reflected by it.4 Executive Summary of th e **Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990**

**– 2009**  

### Global warming potentials are not provided for CO, NO

x 

### , NMVOCs, SO 2 

### , and aerosols because there is no agreed -upon

method to estimate the contribution of gases that are short

- lived in the atmosphere, spatially variable, or have only indirect

effects on radiative forcing (IPCC 1996).



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

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

Tg or million metric tons CO 2 

### Eq. While total U.S. emissions

have increased by 7. 3 percent from 1990 to 2009, emi ssions

decreased from 2008 to 2009 by 6. 1 percent (42 7.9 Tg CO 2



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

economic output resulting in a decrease in energy consumption

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

fuel s used to generate electricity due to fuel switching as the

price of coal increase d , and the price of natural gas decreased

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

average annual rate of 0.4 percent.

Figure ES

- 1 through Figure ES -3 illustrate the overall

trends in total U.S. emissions by gas, annual changes, and

absolute change since 1990.

Table ES -2 provides a detailed summary of U.S.

greenhouse gas emissions and sinks for 1990 through 200 9. Figure ES -1

U.S. Greenhouse Gas Emissions by Gas

Figure ES -2 F igure ES -3

Annual Percent Change in U.S. Greenhouse Gas

Emissions Cumulative Change in Annual U.S. Greenhouse Gas

Emissions Relative to 1990

### Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990 –2009 5 Table ES -2 : Recent Trends in U.S. Greenhouse Gas Emissions and Sinks (Tg or million metric tons CO

2 

### Eq.)

Gas/Source 1990 2000 2005 2006 2007 2008 2009

CO

2 5,099.7 5,97 5.0 6,11 3.8 6,021.1 6,120.0 5,921.4 5,505.2

Fossil Fuel Combustion 4,738 .4 5,59 4.8 5,75 3.2 5,65 3.1 5,756 .7 5,56 5.9 5,209 .0

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

Transportation 1,485.9 1,809.5 1,896.6 1,878.1 1,894.0 1,789 .9 1,71 9

. 7

Industrial 84 6

. 5 85 1

. 1 82 3

. 1 8 48

. 2 84 2

. 0 80 2.9 73 0.4

Residential 338.3 370.7 357.9 321.5 342.4 348.2 3 39.2

Commercial 219.0 230.8 223.5 208.6 219.4 224.2 2 24.0

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

Non

- Energy Use of Fuels 11 8

. 6 14 4

. 9 14 3

. 4 14 5

. 6 13 7

. 2 1 41.0 12 3.4

Iron and Steel Production &

Metallurgical Coke Production 99.5 85.9 65.9 68.8 71.0 66.0 4 1.9

Natural Gas Systems 37.6 29. 9 29.9 30.8 31.1 32.8 32.2

Cement Production 33.3 40.4 45. 2 4 5.8 44.5 4 0.5 29. 0

Incineration of Waste 8.0 11. 1 12.5 12.5 12.7 12.2 12.3

Ammonia Production and Urea

Consumption 16.8 16.4 12.8 12.3 14.0 11.9 11.8

Lime Production 11. 5 14.1 14.4 15.1 14.6 14.3 11.2

Cropland Remaining Cropland 7.1 7.5 7.9 7.9 8.2 8.7 7.8

Limestone and Dolomite Use 5.1 5.1 6.8 8.0 7.7 6.3 7.6

Soda Ash Production and

Consumption 4.1 4.2 4.2 4.2 4.1 4.1 4.3

Aluminum Production 6.8 6.1 4.1 3.8 4.3 4.5 3.0

Petrochemical Production 3.3 4.5 4.2 3.8 3.9 3.4 2.7

Carbon Dioxide Consumption 1.4 1.4 1.3 1.7 1.9 1.8 1.8

Titanium Dioxide Production 1.2 1.8 1.8 1.8 1.9 1.8 1.5

Ferroalloy Production 2.2 1.9 1.4 1.5 1.6 1.6 1. 5

Wetlands Remaining Wetlands 1.0 1.2 1.1 0.9 1.0 1.0 1.1

Phosphoric Acid Production 1.5 1.4 1.4 1.2 1.2 1.2 1.0

Zinc Production 0. 7 1.0 1.1 1.1 1.1 1.2 1.0

Lead Production 0.5 0.6 0.6 0.6 0.6 0.6 0.5

Petroleum Systems 0.6 0.5 0.5 0.5 0.5 0.5 0.5

Silicon Carbide Production and

Consumption 0.4 0.2 0.2 0.2 0.2 0.2 0.1

Land Use, Land

- Use Change, and

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

Biomass

– Wood b 215.2 218.1 206.9 203.8 203.3 198.4 183.8

International Bunker Fuels c 111.8 98.5 1 09.7 12 8.4 127. 6 13 3.7 1 23.1

Biomass

– Ethanol b 4. 2 9. 4 2 3

. 0 31.0 3 8.9 5 4 .8 61.2

CH

4 674.9 659.9 631.4 672.1 664.6 676.7 686. 3

Natural Gas Systems 189.8 209.3 190.4 217.7 205.2 211.8 221.2

Enteric Fermentation 132.1 136.5 136.5 138.8 141.0 140.6 139.8

Landfills 147.4 111.7 112. 5 111.7 111.3 115.9 117.5

Coal Mining 84.1 60.4 56.9 58.2 57.9 67.1 71.0

Manure Management 31.7 42.4 46.6 46.7 50.7 49.4 49.5

Petroleum Systems 35.4 31.5 29.4 29.4 30.0 30.2 30.9

Wastewater Treatment 23.5 25 .2 24.3 24.5 24.4 24.5 24.5

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

Rice Cultivation 7.1 7.5 6.8 5.9 6.2 7.2 7.3

Stationary Combustion 7.4 6.6 6.6 6.2 6.5 6.5 6.2

Abandoned Underground Coal Mines 6.0 7.4 5.5 5.5 5.6 5.9 5.5

Mobile Combustion 4.7 3.4 2.5 2.3 2.2 2.0 2.0

Composting 0.3 1.3 1.6 1.6 1.7 1.7 1.7

Petrochemical Production 0.9 1.2 1.1 1.0 1.0 0.9 0.8

Iron and Steel Production &

Me tallurgical Coke Production 1.0 0.9 0.7 0.7 0.7 0.6 0.4

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

Ferroalloy Production + + + + + + +6 Executive Summary of th e **Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990**

**– 2009**  

### Table ES

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

2 

### Eq. ) ( continued)

Gas/Source 1990 2000 2005 2006 2007 2008 2009

Silicon Carbide Production and

Consumption + + + + + + +

Incineration of Waste + + + + + + +

International Bunker Fuels c 0.2 0.1 0.1 0.2 0.2 0.2 0.1

N

2 O 315.2 341.0 322.9 326.4 325.1 310.8 295.6

Agricultural Soil Management 197.8 206.8 211.3 208.9 209.4 210.7 204.6

Mobile Combustion 43.9 53.2 36.9 33.6 30.3 26.1 23.9

Manure Management 14.5 17.1 17.3 18.0 18.1 17.9 17.9

Nitric Acid Production 17.7 19.4 16.5 16.2 19.2 16.4 14.6

Stationary Combustion 12.8 14.6 14.7 14.4 14.6 14.2 12.8

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

Wastewater Treatment 3.7 4.5 4.8 4.8 4.9 5.0 5.0

N

2 O from Product Uses 4.4 4.9 4.4 4.4 4.4 4.4 4.4

Adipic Acid Production 15.8 5.5 5.0 4.3 3.7 2.0 1.9

Composting 0.4 1.4 1.7 1.8 1.8 1.9 1.8

Settlements Remaining Settlements 1.0 1.1 1.5 1.5 1.6 1.5 1.5

Incineration of Waste 0.5 0.4 0.4 0.4 0.4 0.4 0.4

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

Wetlands Re maining Wetlands + + + + + + +

International Bunker Fuels c 1.1 0.9 1.0 1.2 1.2 1.2 1.1

HFCs 36.9 103.2 120.2 123.5 129.5 129.4 125.7

Substitution of Ozone Depleting

Substances d 0.3 74.3 104.2 109.4 112.3 115.5 120.0

HCFC

- 22 Production 36.4 28.6 15.8 13.8 17.0 13.6 5.4

Semiconductor Manufacture 0.2 0.3 0.2 0.3 0.3 0.3 0.3

PFCs 20.8 13.5 6.2 6.0 7.5 6.6 5.6

Semiconductor Manufacture 2.2 4.9 3.2 3.5 3.7 4.0 4.0

A luminum Production 18.5 8.6 3.0 2.5 3.8 2.7 1.6

SF

6 34.4 20.1 19.0 17.9 16.7 16.1 14.8

Electrical Transmission and

Distribution 28.4 16.0 15.1 14.1 13.2 13.3 12.8

Magnesium Production and

Processing 5.4 3.0 2.9 2.9 2.6 1.9 1.1

Semiconductor Manufacture 0.5 1.1 1.0 1.0 0.8 0.9 1.0

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

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

+ Does not exceed 0.05 Tg 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 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 -Us e 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 200 9 . The

primary greenhouse gas emitted by human activities in the United States was CO 2 

### , representing approximately 83.0 percent

of total greenhouse gas emissions. The largest sourc e of CO 2 

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

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

systems

, enteric fermentation associated with domestic livestock, and dec omposition of wastes in landfills. Agricultural soil

management and mobile source fuel combustion were the major sources of N 2 

### O emissions. Ozone depleting substance

substitute emissions and emissions of HFC

- 23 during the production of HCFC

- 22 were the pr imary contributors to aggregate

HFC emissions. PFC emissions resulted as a byproduct of primary aluminum production and from semiconductor

manufacturing, while electrical transmission and distribution systems accounted for most SF 6 

### emissions.

### Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990 –2009 7 Overall, from 1990 to 200 9, total emissions of CO 2 

### and

CH 4 

### i ncreased by 405.5 Tg CO 2 

### Eq. ( 8.0 percent) and 11.4 Tg

CO 2 

### Eq. ( 1.7 percent), respectively

. Conversely, N 2 

### O emissions

d ecreased by 19.6 Tg CO 2 

### Eq. ( 6.2 percent). During the same

period, aggregate weighted emissions of HFCs, PFCs, and SF 6



### rose by 54.1 Tg CO 2 

### Eq. ( 58.8 percent). From 1990 to 200 9

, HFCs increased by 88.8 Tg CO 2 

### Eq. ( 240.41 percent), PFCs

decreased by 15.1 T g CO 2 

### Eq. ( 73.0 percent), and SF 6 

### decreased

by 19.5 Tg CO 2 

### Eq. (5 6.8 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 landfill ed yard trimmings and food

scraps, which, in aggregate, offset 15.3 percent of total

emissions in 200 9 . The following sections describe each gas’

contribution to total U.S. greenhouse gas emissions in more detail. Figure ES -4

2009 Greenhouse Gas Emissions by Gas

(percents based on Tg CO

2 

### Eq.)



# Carbon Dioxide Emissions

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

Revolution (i.e., about 1750), global atmospheric concentrations of CO 2 

### have risen about 36 percent (IPCC 2007), principally

due to the combustion of fos sil fuels. Within the United States, fossil fuel combustion accounted for 94. 6 percent of CO 2



### emissions in 200 9

. Globally, approximately 30, 313 Tg of CO 2 

### were added to the atmosphere through the combustion of

fossil fuels in 200 9 , of which the United Sta tes accounted for about 1 8 percent. 12



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

### from fossil fuel combustion has accounted for

approximately 7 8 percent of GWP

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

emissions in 1990 to 79 percent in 2009. Emissions of CO 2 

### from fo ssil fuel combustion increased at an average annual rate

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

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

Between 1990 and 2009, CO 2 

### emissions from fossil fuel combustion increased from 4, 738.4 Tg CO 2 

### Eq. to 5, 209.0 Tg CO 2



### Eq.— a 9.9 percent total increase over the twenty

- year period. From 2008 to 2009, thes e emissions decreased by 356.9 Tg

CO 2 

### Eq. ( 6.4 percent), the largest decrease in any year over the twenty

- year period. Changes in land use and forestry practices

can also emit 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 Ener gy Information Administration International Energy Statistics 2010

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

**– 2009**  

### H istorically, changes in emissions from fossil fuel

combustion have been the dominant f actor affecting U.S.

emission trends. Changes in CO 2 

### emissions from fossil

fuel combustion are influenced by many long

- term and

short

- term factors, including population and economic

growth, energy price fluctuations, technological changes,

and seasonal temperatures. In the short term , the overall

consumption of fossil fuels in the United States fluctuates

primarily in response to changes in general economic

conditions, energy prices, weather, and the availability of

non

- fossil alternatives. For example, in a year with

increased consumption of goods and services, low fuel

prices, severe summer and winter weather conditions,

nuclear plant closures, and lower precipitation feeding

hydroelectric dams, there would likely be proportionally

greater fossil fuel c onsumption 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 driv ing).

The five major fuel consuming sectors contributing

to CO 2 

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

commercial. Carbon dioxide emissions are produced by the electricity generation sector as they consume fossil fuel to

provide electricity to one of the other four sectors, or “end

- use” sectors. For the discussion below, electricity generation

emissions have been distributed to each end

- use sector on the basis of each sector’s share of aggregate electricity

consumption. This method of distributing emissions assumes that each end

- use sector consumes electricity that is generated

from the national average mix of fuels according to their carbon intensity. Emissions from electricity gen eration 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. Figure ES -5

2009 Sources of CO

2 

### Emissions

### Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990 –2009 9 Fi gure ES -6 F igure ES -7

2009 CO

2 

### Emissions from Fossil Fuel Combustion by

Sector and Fuel Type 2009 End

- Use Sector Emissions of CO

2 

### , CH

4 

### , and N

2 

### O

from Fossil F uel Combustion

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

- based electricity generation.



### T able ES -3 : CO

2 

### Emissions from Fossil Fuel Combustion by Fuel Consuming En d- Use Sector (Tg or million metric tons CO

2 

### Eq.)

End

- Use Sector 1990 2000 2005 2006 2007 2008 2009

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

Combustion 1,485. 9 1,809.5 1,896.6 1,878.1 1,894.0 1,789.9 1 ,719.7

Electricity 3.0 3.4 4.7 4.5 5.0 4.7 4.4

Industrial 1,5 33.2 1,640.8 1,560.0 1,560.2 1,572.0 1,517.7 1,333.7

Combustion 846.5 851.1 823.1 848.2 842.0 802.9 730.4

Electricity 686.7 789.8 737.0 712.0 730.0 714.8 603.3

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

Combustion 338.3 370.7 357.9 321.5 342.4 348.2 339.2

Electricity 593.0 762.4 856.7 830.8 856.1 834.0 784.6

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

Combustion 219 .0 230.8 223.5 208.6 219.4 224.2 224.0

Electricity 538.0 741.3 803.7 799.0 821.7 807.4 761.7

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

Total 4,7 38.4 5,59 4.8 5,75 3.2 5,65 3.1 5,7 56.7 5,5 65.9 5,2 09 .0

Electricity Generation 1,82 0.8 2,296.9 2,402.1 2,346.4 2,412.8 2,360.9 2,154.0

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

Islands) is included in th e inventory report

. Note: Totals m ay not sum due to independent rounding. Combustion

- related emissions from electricity generation are allocated based

on aggregate national electricity consumption by each end

- use sector.



### Transportation End

- Use Sector. Transportation activities (exclu ding international bunker fuels) accounted for 33

percent of CO 2 

### emissions from fossil fuel combustion in 2009. 13 

### Virtually all of the energy consumed in this end

- use sector

c ame from petroleum products. N e arly 65 percent of the emissions resulted from gas oline consumption for personal vehicle

use. The remaining emissions came from other transportation activities, including the combustion of diesel fuel in heavy

13 If emissions from international bunker fuels are included, the transportation end

- use sector accounted for 35 perc ent of U.S. emissions from fossil fuel

combustion in 2009.10 Executive Summary of th e **Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990**

**– 2009**  

### duty vehicles and jet fuel in aircraft. From 1990 to 200 9 , transportation emissions rose by 16 percent due, in large part, to

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

traveled by light

- duty motor vehicles (passenger cars and light

- duty trucks) increased 39 percent from 1990 to 200 9 , as a

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

of this period.

Industrial End

- Use Sector. Industrial CO 2 

### emissions, resulting both directly from the com bustion of fossil fuels and

indirectly from the generation of electricity that is consumed by industry, accounted for 2 6 percent of CO 2 

### from fossil fuel

combustion in 200 9 . Approximately 5 5 percent of these emissions resulted from direct fossil fuel combu stion 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 indu stry 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 S ectors. The residential and commercial end

- use sectors accounted for 2 2 and 19

percent, respectively, of CO 2 

### emissions from fossil fuel combustion in 200 9 . Both sectors relied heavily on electricity for

meeting energy demands, with 7 0 and 7 7 percent, res pectively, of their emissions attributable to electricity consumption for

lighting, heating, cooling, and operating appliances. The remaining emissions were due to the consumption of natural gas

and petroleum for heating and cooking. Emissions from these end

- use sectors have increased 25 percent since 1990, due to

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

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

Electricity generators consumed 3 6 percent of U.S. energy from fossil fuels and emitted 4 1 percent of the CO 2 

### from fossil

fuel combustion in 200 9 . 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 non

- fossil options such as

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

requirements and accounted for 95 percent of all coal consumed for energy in the United States in 2009. Consequently,

changes in electricity demand have a significant impact on coal consumption and associated CO 2 

### emissions.

Other signif icant CO 2 

### trends included the following:

**•** Carbon dioxide emissions from non

- energy use of fossil fuels have increased 4.7 Tg CO 2 

### Eq. ( 4.0 percent) from

1990 through 200 9 . Emissions from non

- energy uses of fossil fuels were 123.4 Tg CO 2 

### Eq. in 200 9 , which

constituted 2. 2 percent of total national CO 2 

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

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

CO 2 

### Eq. (36.6 percent ) from 200 8 to 200 9 , continuing a trend of decreasing emissions from 1990 through 200 9 of

57.9 percent (57.7 Tg CO 2 

### Eq.) . This decline is due to the restructuring of the industry, technological

improvements, and increased scrap utilization.

**•** In 200 9 , CO 2 

### emissions from cement production decreased by 11.5 Tg CO 2 

### Eq. ( 28.4 percent) from 200 8 . After

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

emissions decreased in the last three years. Overall, from 1990 to 20 09 , emissions from cement production

de creased by 12.8 percent, a de crease of 4.3 Tg CO 2 

### Eq.

**•** Net CO 2 

### uptake from Land Use, Land

- Use Change, and Forestry increased by 153.5 Tg CO 2 

### Eq. (17.8 percent) from

1990 through 200 9 . This increase was primarily due t o an increase in the rate of net carbon accumulation in forest

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

### Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990 –2009 11 carbon accumulation in landfilled yard trimmings and food scraps slowed over this peri od, 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 148 percent (IPCC 2007).

Anthropogenic sources of CH 4 

### include natural gas and

petroleum systems

, agricultural activities, landfills

, coal mining,

wastewater treatment, statio nary and mobile combustion, and

certain industrial processes (see Figure ES -8).

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

### include

the following:

**•** In 200 9 , CH 4 

### emissions from coal mining were 71.0 Tg

CO 2 

### Eq., a 3.9 Tg CO 2 

### Eq. ( 5.8 percent) increase o ver

2008 emission levels. The overall decline of 13.0 Tg

CO 2 

### Eq. ( 15.5 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.

**•** N atural gas systems were the la rgest anthropogenic

source category of CH 4 

### emissions in the United States

in 2009 with 221.2 Tg CO 2 

### Eq. of CH 4 

### emitted into the

atmosphere. Those emissions have increased by 31.4 Tg CO 2 

### Eq. ( 16.6 percent) since 1990. Methane emissions

from this source inc reased 4 percent from 2008 to 2009 due to an increase in production and production wells

.

**•** Enteric Fermentation is the second largest anthropogenic source of CH 4 

### emissions in the United States. In 200 9

,

enteric fermentation CH 4 

### emissions were 1 39 .8 Tg CO 2 

### Eq. (2 0 percent of total CH 4 

### emissions), which represents an

increase of 7.7 Tg CO 2 

### Eq. ( 5.8 percent) since 1990.

**•** Methane emissions from manure management increased by 55.9 percent since 1990, from 31.7 Tg CO 2 

### Eq. in 1990

to 49.5 Tg CO 2 

### Eq. in 200 9 . 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 s pread to manure managed

and stored on site.

**•** Landfills are the third largest anthropogenic source of CH 4 

### emissions in the United States, accounting for 17 percent

of total CH 4 

### emissions ( 117.5 Tg CO 2 

### Eq.) in 200 9 . From 1990 to 200 9 , CH 4 

### emissions from la ndfills decreased by

29.9 Tg CO 2 

### Eq. ( 20 percent), with small increases occurring in some interim years. This downward trend in overall F igure ES -8

2009 Sources of CH

4 

### Emissions12 Executive Summary of th e **Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990**

**– 2009**  

### emissions is the result of increases in the amount of landfill gas collected and combusted, 14 

### which has more than

offset the additional CH 4 

### emissions resulting from an increase in the amount of municipal solid waste landfilled.



# Nitrous Oxide Emissions

Nit rous oxide is produced by biological processes that

occur in soil and water and by a variety of anthropogenic

activities in the agricultural, energy

- related, industrial, and

waste management fields. While total 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 18 percent (IPCC 2007).

The main anthropogenic activities producing N 2 

### O in the United

States are agricultural soil management, fuel com bustion in

motor vehicles, manure management

, nitric acid production and

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

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

### O include

the following:

**•** In 200 9 , N 2 

### O emissions from mobile combustion were

23.9 Tg CO 2 

### E q. (approximately 8.1 percent of U.S.

N 2 

### O emissions). From 1990 to 200 9 , N 2 

### O emissions

from mobile combustion decreased by 45.6 percent. However, from 1990 to 1998 emissions increased by 2 5.6

percent, due to control technologies that reduced NO

x 

### emission s while increasing N 2 

### O emissions. Since 1998,

newer con trol technologies have led to an overall decline in N 2 

### O from this source.

**•** Nitrous oxide emissions from adipic acid production were 1.9 Tg CO 2 

### Eq. in 200 9 , and have decreased significantly

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

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

lower than pre

- 1996 levels since 1998.

**•** Ag ricultural soils accounted for approximately 69.2 percent of N 2 

### O emissions in the United States in 200 9

.

Estimated emissions from this source in 200 9 were 204.6 Tg CO 2 

### Eq. Annual N 2 

### O emissions from agricultural soils

fluctuated between 1990 and 200 9 , alt hough overall emissions were 3.4 percent higher in 200 9 than in 1990. Figure ES -9

2009 Sources of N

2 

### O Emissions

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.

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

# HFC, PFC, and SF

6 

# Emissions

HFCs and PFCs are families of synthetic chemicals that are

used as alternatives to ODS, whi ch 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 wi th 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 hexafluorid e 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 prod uction and processing (see Figure ES

- 10 ).

Some significant trends in U.S. HFC, PFC, and SF 6 

### emissions include the following:

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

amounts in 1990 to 120 .0 Tg CO 2 

### Eq. in 200 9 . 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

- outs required

under the Montreal Protocol come into effect, especially after 1994, when full market penetration was made for the

first generation of new technologies featuring ODS substitutes.

**•** HFC emissions from the production of HCFC

- 22 decreased by 85.2 percent ( 31.0 Tg CO 2 

### Eq.) from 1990 through

2009 , due to a steady decline in the emission rate of HFC

- 23 (i.e., the amount of HFC

- 23 emitted per kilogram of

HCFC

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

- 23 emissions.

**•** Sulfur hexafluoride emis sions from electric power transmission and di stribution systems decreased by 54.8 percent

(15.6 Tg CO 2 

### Eq.) from 1990 to 200 9 , primarily because of higher purchase prices for SF 6 

### and efforts by industry to

reduce emissions.

**•** PFC emissions from aluminum production decreased by 91.5 percent (1 7.0 Tg CO 2 

### Eq.) from 1990 to 200 9 , due to

both industry emission reduction efforts and lower domestic aluminum production. Figure ES -10

2009 Sources of HFCs, PFCs, and SF

6 

### Emissions14 Executive Summary of th e **Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990**

**– 2009**  

# ES.3. Overview of Sector Emissions and Trends

In accordance with the Revised 1996 IPCC Guidelines for

National Greenhouse Gas Inventories (IPCC/UNEP/OECD/IEA

1997), and the 2003 UNFCCC Gui delines on Reporting and

Review (UNFCCC 2003), Figure ES

- 11 and Table ES -4

aggregate emissions and sinks by these chapters. Emissions of

all gases can be summed from each source category from IPCC

guidance. Over the twenty

- year period of 1990 to 200 9 , total

emissions in the Energy and Agriculture sectors grew by 463.3

Tg CO 2 

### Eq. ( 9 percent), and 3 5 .7 Tg CO 2 

### Eq. ( 9 percent),

respectively. Emissions decreased in the Industrial Processes,

Waste

, and Solvent and Othe r Product Use sectors by 32.9 Tg

CO 2 

### Eq. ( 10 percent) , 24.7 Tg CO 2 

### Eq. (1 4 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 sector (mag nitude of emissions plus

CO 2 

### flux from all LULUCF source categories) increased by

143.5 Tg CO 2 

### Eq. ( 17 percent).

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

2 

### Eq.) Figure ES -11

U.S. Greenhouse Gas Emissions and Sinks by

Chapter/IPCC Sector

Note : Relativ ely smaller amounts of GWP

- weighted emissions are also

emitted from the Solvent and Other Product Use Sectors.

Chapter/IPCC Sector 1990 2000 2005 2006 2007 2008 2009

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

Industrial Processes 315.8 348.8 334.1 339.4 350.9 331.7 282.9

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

Agriculture 383.6 410.6 418.8 418.8 425.8 426.3 419.3

Land Use, Land

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

Waste 175.2 143.9 144.9 144.4 14 4.1 149.0 150.5

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

Net CO

2 Flux from Land Use, Land

- Use Change, and

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

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

a The net CO

2 flux total includes both emissions and sequestration, and constitutes a sink in the United States. Sinks are only included i n net

emissions total.

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

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

# Energy

The Energy chapter contains emissions of all greenhouse

gases resulting from stationary and mobile energy activities

including fuel combustion and fugitive fuel emissions. Energy

related activities, primarily fossil fuel combustion, accounted for

the vast m ajority of U.S. CO 2 

### emissions for the period of 1990

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

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

through the combustion of fossil fuels. The remaining 17

percent came from other energy sources such as hydropower,

biomass, nuclear, wind, and solar energy (see Figure ES -12 ).

Energy- related activities are also responsible for CH 4 

### and N 2 

### O

emissions ( 49 percent and 1 3 percent of total U.S. emissions of

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

chapter account for a combined 8 7 percent of total U.S.

greenhouse gas emissions in 200 9. F igure ES -12

2009 U.S. Energy Consumption by Energy Source



# Industrial Processes

The Industrial Processes chapter contains byproduct or fugitive emissions of greenhouse gases from industrial processes

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

transform raw materials, which often release waste gases such as 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, limestone and dolomite use (e.g., flux stone, flue gas desulfurization, and glass manufacturing), soda ash

production and consumption, titanium dioxide production, phosphoric acid production, ferroal loy 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 proce sses

release HFCs, PFCs, and SF 6 

### . Overall, emission sources in the Industrial Process chapter account for 4 percent of U.S.

greenhouse gas emissions in 200 9.



# Solvent and Other Product Use

The Solvent and Other Product Use chapter contains greenhouse gas e missions that are produced as a byproduct 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. an thropogenic greenhouse gas

emissions on a carbon equivalent basis in 200 9

.



# Agriculture

The Agricultur e chapter contains anthropogenic emissions from agricultural activities (except fuel combustion, which is

addressed in the Energy chapter, and agricultura l CO 2 

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

- Use Change, and

Forestry Chapter). Agricultural activities contribute directly to emissions of greenhouse gases through a variety of process es,

including the following source categories: enteric ferm entation 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. Methane emissions f rom enteric fermentation and manure management

represented 20 percent and 7 percent of total CH 4 

### emissions from anthropogenic activities, respectively, in 200 9

.16 Executive Summary of th e **Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990**

**– 2009**  

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

U.S. N 2 

### O emissions in 200 9 , accounting for 6 9 percent. In 200 9 , emission sources accounted for in the Agricultur e chapter

were responsible for 6. 3 percent of total U.S. greenhouse gas emissions.



# Land Use, Land

- Use Change, and Forestry

The Land Use, Land

- Use Change, and Forestry chapter contains emissions of 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 ur ban 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 8 5

percent o f total 200 9 net CO 2 

### flux, urban trees accounted for 9 percent, mineral and organic soil carbon stock changes

accounted for 4 percent , and landfilled yard trimmings and food scraps accounted for 1 percent of the total net flux in 200 9

. The net forest sequ estration 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, mi neral and organic soils sequester approximately 5. 5 times as much C as is emitted from these soils

through liming and urea fertilization. The mineral soil C sequestration is largely due to the conversion of cropland to

permanent pastures and hay production, a reduction in summer fallow areas in semi

- arid areas, an increase in the adoption of

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

to agriculture lands. The landfilled ya rd trimmings and food scraps net sequestration is due to the long

- term accumulation of

yard trimming carbon and food scraps in landfills.

Land use, land

- use change, and forestry activities in 200 9 resulted in a net C sequestration of 1,015.1 Tg CO 2 

### Eq. ( Table

ES -5 ). This represents an offset of 1 8 percent of total U.S. CO 2 

### emissions, or 1 5 percent of total greenhouse gas emissions in

2009 . Between 1990 and 200 9 , total land use, land

- use change, and forestry net C flux resulted in a 17.8 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 CO

2 

### Flux from Land Use, Land

- Use Change, and Forestry (Tg or million metric tons CO

2 

### Eq.)

Sink Category 1990 2000 2005 2006 2007 2008 2009

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

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

Land Converted to Cropland 2.2 2.4 5.9 5.9 5.9 5.9 5.9

Grassland Remaining Grassland (52. 2 ) (52.6) (8.9) (8.8) (8.6) (8.5) (8.3)

Land Converted to Grassland (19.8) (27. 2 ) (24.4) (24.2) (24.0) (23.8) (23.6)

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

Other (Landfilled Yard Trimmings and Food

Scraps) (2 4.2 ) (1 3.2 ) (11.5) (11.0) (10.9) (11.2) (12.6)

Total (861.5) (576.6) (1

, 056.5) (1

, 064.3) (1

, 060.9) (1

, 040.5) (1

, 015.1)

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



### Emissions from Land Use, Land

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

limestone and dolomite to managed land (i.e., liming of agricultural soils) and urea fertilization resulted in CO 2 

### emissions of

7.8 Tg CO 2 

### Eq. in 200 9 , an increase of 11 percent relative to 1990. The application of synthetic fertilizers to forest and

settlement soils in 2009 resulted in direct N 2 

### O emissions of 1 .9 Tg CO 2 

### Eq. 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 emissio ns.

Additionally, direct N 2 

### O emissions from fertilizer application to settlement soils increased by 55 percent since 1990. F orest

### Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990 –2009 17 fires resulted in CH 4 

### emissions of 7.8 Tg CO 2 

### Eq., and in N 2 

### O emissions of 6.4 Tg CO 2 

### Eq. in 2009. Carbon dioxide and

N 2 

### O emissions from peatlands totaled 1.1 Tg CO 2 

### Eq. and less than 0.01 Tg CO 2 

### Eq. in 2009, respectively

.

Table ES -6 : Emissions from Land Use, Land

- Use Change, and Forestry (Tg or million metric tons CO

2 

### Eq.)

Source Category 1990 2000 2005 2006 2007 2008 2009

CO

2 8.1 8.8 8.9 8 .8 9.2 9.6 8.9

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

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

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

CH

4 3.2 14.3 9.8 21.6 20.0 11.9 7.8

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

N

2 O 3.7 13.2 9.8 19.5 18.3 11.6 8.3

Forest Land Rema ining Forest Land: Forest Fires 2.6 11.7 8.0 17.6 16.3 9. 8 6.4

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

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

W etlands Remaining Wetlands: Peatlands Remaining Peatlands + + + + + + +

Total 15.0 36.3 28.6 49.8 47.5 33. 2 25.0

+ Less than 0.05 Tg CO

2 Eq.

Note: Totals may not sum due to independent rounding.



# Waste

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

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

chapter, accounting for just over 7 8 percent of this chapter’s emissions, and 17 percent of total U.S. CH 4 

### emissions. 15



# ES. 4. Other Information Additionally, wastewater treatment accounts for 20 percent of Waste emissions, 4 percent of U.S. CH 4 

### emissions, and 2

percent of U.S. N 2 

### O emissions. Emissions of CH 4 

### and N 2 

### O from com posting are also accounted for in this chapter;

generating emissions of 1.7 Tg CO 2 

### Eq. and 1.8 Tg CO 2 

### Eq., respectively. Overall, emission sources accounted for in the

Waste chapter generated 2.3 percent of total U.S. greenhouse gas emissions in 200 9.



# 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. Th is section reports

emissions by the following economic sectors: Residential, Commercial, Industry, Transportation, Electricity Generation,

Agriculture, and U.S. Territories.

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

from 1990 to 2009.

15 Landfills also store carbon, d ue to incomplete degradation of organic materials such as wood products and yard trimmings, as described in the Land

- Use,

Land

- Use Chang e, and Forestry chapter of the inventory report.18 Executive Summary of th e **Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990**

**– 2009**  

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

2 

### Eq.)

Imp lied Sectors 1990 2000 2005 2006 2007 2008 2009

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

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

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

Agriculture 429.0 485.1 493.2 516.7 520.7 503.9 490.0

Commercial 395.5 381.4 387.2 375.2 389.6 403.5 409.5

Residential 345.1 386.2 371.0 335.8 358.9 367.1 360.1

U.S. Territories 33.7 46.0 58.2 59.3 53.5 48.4 45. 5

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

Land Use, Land

- Use Change, and Forestry

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

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

Note: Totals may not sum due to independent rounding. Emissions include CO

2 , CH

4 , N

2 O, HFCs, PFCs, and SF

6

. See Table 2

- 12 of the inventory report for more detailed data.



### U sing this categorization, emissions from electricity

generation accounted for the largest portion (33 percent) of

U.S. greenhouse gas emissions in 2009. Transportation

activities, in aggre gate, accounted for the second largest

portion (2 7 percent), while emissions from industry accounted

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

gas emissions in 2009. In contrast to electricity generation and

transportation, emissions f rom 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 ef ficiency

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

ac counted for 7 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 sector accounted for 6 perc ent of emissions while the residential

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

sectors primarily consisted of CO 2 

### emissions from fossil fuel combustion.

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

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

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

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

- use categories (i.e.,

emissions from electricity generation are allocated to the economic sectors in which the electricity is consumed). To

distribute electricity emissions among end

- use sectors, emissions from the source categories assigned to electricity generation

were allocated to the residential, commercial, industry, transportation, and agriculture economic sectors according to retail Figure ES -13

Emissions Allocated to Economic Sectors

Note: Does not include U.S. Territories.

### Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990 –2009 19 sales of electricity. 16



### Table ES -8 : U.S

. Greenhouse Gas Emissions by Economic Sector with Electricity

- Related Emissions Distri buted (Tg or million

metric tons CO

2 

### Eq.) 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.

Implied Sectors 1990 2000 2005 2006 2007 2008 2009

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

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

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

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

Agriculture 460.0 518.4 522.7 544.1 553.2 531.1 516.0

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

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

Land Use, Land

- Use Change,

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

Net Emissions (Sources

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

See Table 2

- 14 of the inventory report for more detailed data.



### W

hen emissions from electricity are distributed among

these sectors, industrial activities account for the largest share

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

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

emissions (2 8 percent) . The commerci al and residential sectors

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

emissions in 2009. Emissions from these sectors increase

substantially when emissions from electricity are included, due

to their relatively large share of electric ity 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 se ctor from 1990 to 2009. Figure ES -14

U.S. Emissions with Electricity Distributed to

Economic Sectors

Note: Does not include U.S. Territories.

16 Emissions were not distributed to U.S. territories, since the electri city generation sector only includes emissions related to the generation of electricity in

the 50 states and the District of Columbia.20 Executive Summary of th e **Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990**

**– 2009**  

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

- Related Data

Total emissions can be compared to other economic and social indices to highlight changes over time. These comparisons incl ude: (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 f ossil 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 200 9 ; (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. Greenhou se

gas emissions in the United States have grown at an average annual rate of 0. 4 percent since 1990. This rate is slightly slower than that for

total energy and for fossil fuel consumption, and much slower than that for electricity consumption

, overall gro ss domestic product and

national population (see Figure ES

- 15 ).



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

Variable 1990 2000 2005 2006 2007 2008 2009 Growth

Rate a

GDP b 100 1 40 157 162 165 165 160 2.5%

Electricity Consumption c 100 1 27 134 135 138 138 132 1.5%

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

Energy Consumption c 100 1 16 118 118 120 118 112 0.6%

Population d 100 1 13 118 120 121 122 123 1.1%

Greenhouse Gas Emis sions e 100 1 15 117 116 11 7 114 107 0.4%

a Average annual growth rate

b Gross Domestic Product in chained 2005 dollars (BEA 2010)

c Energy content

- weighted values (EIA 2010b)

d U.S. Census Bureau (2010)

e GWP

- weighted values



### Figure ES -15

U.S. Gr eenhouse Gas Emissions Per Capita and Per Dollar of Gross

Domestic Product

Source: BEA (2010), U.S. Census Bureau (2010), and emission estimates in the inventory report

.

### Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990 –2009 21 

# Indirect Greenhouse Gases (CO, NO

x 

# , NMVOCs, and SO

2 

# )

The reporting requirements of the UNFCCC 17



### Since 1970, the United States has published estimates of annual emissions of CO, NO

x 

### , NMVOCs, and SO 2 

### (EPA 2010,

EPA 2009), request that information be provided on indirect greenhouse gases, which

include CO, NO

x 

### , NMVOCs, and SO 2 

### . These gases do not have a direct global warming effect, but indirectly affect

terrestrial radiation ab sorption by influencing the formation and destruction of tropospheric and stratospheric ozone, or, in the

case of SO 2 

### , by affecting the absorptive characteristics of the atmosphere. Additionally, some of these gases may react with

other chemical compounds in the atmosphere to form compounds that are greenhouse gases.

18 

### Table ES -10 which are regulated under the Clean Air Act. shows that fuel combustion accounts for the

majority of emissions of these indirect greenhouse gases. Industrial processes

— such as the manufacture of chemical and

allied products, metals processing, and industrial uses of solvents

— are also significant sources of CO, NO

x 

### , and NMVOCs.

Table ES -10 : Emissions of NO

x 

### , CO, NMVOCs, and SO

2 

### (Gg)

Gas/Activity 1990 2000 2005 2006 2007 2008 2009

NO

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

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

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

Industrial Processes 591 626 569 553 537 520 568

Oil and Gas Activities 13 9 111 321 319 318 318 393

Incineration of Waste 82 114 129 121 114 106 128

Agricultural Burning 8 8 6 7 8 8 8

Solvent Use 1 3 3 4 4 4 3

Waste 0 2 2 2 2 2 2

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

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

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

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

Incineration of Waste 978 1,670 1,40 3 1,412 1,421 1,430 1,403

Agricultural Burning 268 259 184 233 237 270 247

Oil and Gas Activities 302 146 318 319 320 322 345

Waste 1 8 7 7 7 7 7

Solvent Use 5 45 2 2 2 2 2

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

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

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

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

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

Oil and Gas Activities 554 388 510 510 509 509 599

Incineration of Waste 222 257 241 238 234 230 159

Waste 673 119 114 113 111 109 76

Agricultural Burning NA NA NA NA NA NA NA

SO

2 20,935 14,830 13,466 12 ,388 11,799 10,368 8,599

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

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

Mobile Fossil Fuel Combustion 793 632 889 750 611 472 455

Oil and Gas Activiti es 390 287 181 182 184 187 154

Incineration of Waste 38 29 24 24 24 23 24

Waste 0 1 1 1 1 1 1

Solvent Use 0 1 0 0 0 0 0

Agricultural Burning NA NA NA NA NA NA NA

NA (Not Available)

Note: Totals may not sum due to independent r ounding.

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

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

18 NO

x and CO emission estimates from field burning of agricultural r esidues were estimated separately, and therefore not taken from EPA (2008).22 Executive Summary of th e **Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990**

**– 2009**  

# Key Categories

The 2006 IPCC Guidelines for National Greenhouse Gas Inventories (IPCC 2006) defines a key category as a “[source

or sink cat egory] that is prioritized within the national inventory system because its estimate has a significant influence on a

country’s total inventory of direct greenhouse gases in terms of the absolute level of emissions, the trend in emissions, or

both.” 19 

### By definitio n, 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 prepar ed, 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 wer e not identified in either of the quantitative analyses.

Figure ES -16

2009 Key Categories

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

Lighter bars indicate a Tier 2 level assessment key category.



### Figure ES -16 presents 200 9 emission estimates for the key categories as defined by a level analysis (i.e., the contribution

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

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

differ from those used elsewhere in the inventory report . For more information regarding key categories, see section 1.5 and

Annex 1.

19 See Chapter 7 “Methodological Choice and Recalculation” in IPCC (2000). <http://www.ipcc

- nggip.iges.or.jp/public/gp/gpgaum.htm>

.

### Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990 –2009 23 

# Quality Assurance and Quality Control (QA/QC)

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

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

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

procedures followed for the current inventory have been formalized in accordance with the QA/QC plan and the UNFCCC

reporting guidelines.



# Uncertainty Analysis of Emission Estimates

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

comprehensive national inventor y, 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 report . Recognizing the benefit of conducting an uncertainty analysis, the UNFCCC

reporting guidelines follow the recommendations of the IPCC Good Pra ctice 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 : Re calculations of Inventory Estimates

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

Sinks, as attempts are made to improve both the analyses themselves, through the use of better methods or data, and the overall usefulness

of the inventory report

. In this effort, the United States follows the 2006 IPCC Guidelines (IPCC 2006), which states, “Both methodological

changes and refinements over time are an essential part of i mproving 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 i s 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. greenhous e 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

Impr ovements" chapter; detailed descriptions of each recalculation are contained within each source's description contained in th e 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 200 9 ) 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. Refere nces for the data are provided for additional

information.24 Executive Summary of th e **Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990**

**– 2009**  

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Available online at < http://www.bea.gov/national/index.htm#gdp >.

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Averyt, M. Tignor and H.L. Miller (eds.). Cambridge University Press. Cambridge, United Kingdom 996 pp.

IPCC (2006) 2006 IPCC Guidelines for National Greenhouse Gas Inventories . The National Greenhouse Gas Inventories

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IPCC/UNEP/OECD/IEA (1997) Revised 1996 IPCC Guidelines for National Greenhouse Gas Inventories

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Convention, UNFCCC Guidelines on Reporting and Review. Conference of the Parties, Eighth Session, New Delhi.

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### United States

Environmental Protection Agency

EPA 430 -S- 11

- 001

April 201 1

Office of Atmospheric Programs ( 6207J)

Washington, DC 20460

Official Business

Penalty for Private Use