United States
          Environmental Protection
          Age ncy
                                                                                                   April 2011
 Inventory  of  U.S.  Greenhouse  Gas Emissions  and  Sinks.
                                                                                  1990-2009
                                                                           Executive
                                                                              Summary
          An emissions inventory that identifies and quantifies a country's primary anthropogenic1 sources and sinks of
          greenhouse gases is essential for addressing climate change. This inventory adheres to both (1) a comprehensive
          and detailed set of methodologies for estimating sources and sinks of anthropogenic greenhouse gases, and (2) a
common and consistent mechanism that enables Parties to the United Nations Framework Convention on Climate Change
(UNFCCC) to compare the relative contribution of different emission sources and greenhouse gases to climate change.
    In 1992, the United States signed and ratified the UNFCCC.  As stated in Article 2 of the UNFCCC, "The ultimate
objective of this Convention and any related legal instruments that the Conference of the Parties may adopt is to achieve, in
accordance with the relevant provisions of the Convention, stabilization of greenhouse gas concentrations in the atmosphere
at a level that would prevent dangerous anthropogenic interference with the climate system. Such a level should be achieved
within a time-frame sufficient to  allow ecosystems to adapt naturally to climate change, to ensure that food production is not
threatened and to enable economic development to proceed in a sustainable manner."2
   All material taken from the Inventory
   of U.S. Greenhouse Gas Emissions
   and Sinks: 1990-2009,  U.S.
   Environmental Protection Agency,
   Office of Atmospheric Programs,
   EPA 430-R-11-005, April 2011. You
   may electronically download the full
   inventory report from U.S. EPA's
   Global Climate Change web page at:
   www.epa.gov/climatechange/
   emissions/usinventory.html.
                                           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 the Inventory as an opportunity to fulfill these
                                       commitments.
                                           This chapter summarizes the latest information on U.S. anthropogenic
                                       greenhouse gas emission trends from 1990 through 2009.  To ensure that the
                                       U.S. emission inventory is comparable to those of other UNFCCC Parties, the
                                       estimates presented here were calculated using methodologies consistent with
                                       those recommended in the Revised 1996 Intergovernmental Panel on Climate
                                       Change  (IPCC)  Guidelines for National  Greenhouse  Gas  Inventories
(IPCC/UNEP/OECD/IEA 1997), the IPCC Good Practice Guidance and Uncertainty Management in National Greenhouse
Gas Inventories (IPCC 2000), and the IPCC Good Practice Guidance for Land Use, Land-Use Change, and Forestry (IPCC
2003).  Additionally, the U.S. emission inventory has continued to incorporate new methodologies and data from the 2006
IPCC Guidelines for National Greenhouse Gas Inventories (IPCC 2006). The structure of the inventory report is consistent
 The 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).
r\                                                       ^
 Article 2 of the Framework Convention on Climate Change published by the UNEP/WMO Information Unit on Climate Change. See .
 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 .
                         Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2009 1

-------
with the UNFCCC guidelines for inventory reporting.4 For most source categories, the IPCC methodologies were expanded.
resulting in a more comprehensive and detailed estimate of emissions.
   Box ES-1: Methodological approach for estimating and reporting U.S. emissions and sinks
   In following the UNFCCC requirement under Article 4.1 to develop and submit national greenhouse gas emissions inventories, the emissions
   and sinks presented in the inventory report are organized by source and sink categories and calculated using internationally-accepted
   methods provided by the IPCC.5 Additionally, the calculated emissions and sinks in a given year for the U.S. are presented in a common
   manner in line with the UNFCCC reporting guidelines for the reporting of inventories under this international agreement.6 The use of
   consistent methods to calculate emissions and sinks by all nations providing their inventories to the UNFCCC ensures that these reports are
   comparable. In this regard, U.S. emissions and sinks reported in this inventory report are comparable to emissions and sinks reported by
   other countries. Emissions and sinks provided in this inventory do not preclude alternative examinations, but rather this inventory report
   presents emissions and sinks in a common format consistent with how countries are to report inventories under the UNFCCC. The inventory
   report itself follows this standardized format, and provides an explanation of the IPCC methods used to calculate emissions and sinks, and
   the manner in which those calculations are conducted.
ES.1.  Background Information
    Naturally occurring greenhouse gases include water vapor, carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O).
and ozone (O3).  Several classes of halogenated substances that  contain fluorine, chlorine, or bromine are also greenhouse
gases, but  they  are,  for the most part,  solely  a  product of industrial activities.   Chlorofluorocarbons (CFCs) and
hydrochlorofluorocarbons (HCFCs)  are  halocarbons that contain chlorine,  while halocarbons  that  contain bromine are
referred to as bromofluorocarbons (i.e., halons).  As stratospheric ozone depleting substances, CFCs, HCFCs, and halons are
covered under the Montreal Protocol on Substances that Deplete the Ozone Layer.  The UNFCCC defers  to this earlier
international treaty.   Consequently, Parties  to  the  UNFCCC are  not required to include these gases in  their national
greenhouse gas emission inventories.7 Some other fluorine-containing halogenated substances—hydrofluorocarbons (HFCs).
perfluorocarbons (PFCs), and sulfur hexafluoride (SF6)—do not deplete stratospheric ozone but are potent greenhouse gases.
These latter substances are addressed by the UNFCCC and accounted for in national greenhouse gas emission inventories.
    There are also several gases that do not have a direct global warming effect but indirectly affect terrestrial and/or solar
radiation  absorption  by influencing the  formation or  destruction  of  greenhouse gases, including  tropospheric and
stratospheric ozone.  These gases include carbon monoxide (CO), oxides of nitrogen (NOX), and non-CH4 volatile organic
compounds (NMVOCs).  Aerosols, which are extremely small particles or liquid droplets, such as those produced by sulfur
dioxide (SO2) or elemental carbon emissions, can also affect the absorptive characteristics of the atmosphere.
    Although the direct  greenhouse gases CO2, CH4, and N2O  occur naturally in the atmosphere, human  activities  have
changed their atmospheric concentrations.  From the pre-industrial era (i.e., ending about 1750)  to 2005, concentrations of
these greenhouse gases have increased globally by 36, 148, and 18 percent, respectively (IPCC 2007).
  See < http://unfccc.int/resource/docs/2006/sbsta/eng/09.pdf>.
  See < http://www.ipcc-nggip.iges.or.jp/public/index.html>.
  See < http://unfccc.int/national_reports/annex_i_ghg_inventories/national_inventories_submissions/items/5270.php>.
  Emissions estimates of CFCs, HCFCs, halons and other ozone-depleting substances are included in the annexes of the inventory
purposes.

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

-------
    Beginning in the  1950s, the use of CFCs and other stratospheric ozone depleting substances (ODS) increased by nearly
10 percent per year until the mid-1980s, when international concern about ozone depletion led to the entry into force of the
Montreal Protocol.  Since then, the production of ODS is being phased out.  In recent years, use of ODS substitutes such as
HFCs and PFCs has grown as they begin to be phased in as replacements for CFCs and HCFCs. Accordingly, atmospheric
concentrations of these substitutes have been growing (IPCC 2007).

Global Warming Potentials
    Gases in the atmosphere can contribute to the greenhouse effect both directly and indirectly. Direct effects occur when
the gas itself absorbs  radiation.  Indirect radiative forcing occurs when chemical transformations of the substance produce
other greenhouse gases, when a  gas influences the atmospheric lifetimes  of other  gases,  and/or when  a  gas affects
atmospheric processes that alter the radiative balance of the earth (e.g., affect cloud formation or albedo).8   The IPCC
developed the global warming potential (GWP) concept to compare the ability of each greenhouse gas to trap heat in the
atmosphere relative to another gas.
    The GWP of a greenhouse gas is defined as the ratio of the
time-integrated radiative forcing from the instantaneous release of
1 kilogram (kg) of a trace substance relative to that of 1 kg of a
reference gas  (IPCC 2001).   Direct radiative effects occur when
the gas itself is a greenhouse gas.  The reference gas used is CO2,
and therefore GWP-weighted emissions are measured in teragrams
(or million metric tons) of CO2 equivalent (Tg CO2 Eq.).9' 10 All
gases in this Executive Summary are presented in units of Tg CO2
Eq.
    The UNFCCC reporting guidelines  for national  inventories
were updated in 2006, * * but continue to require the use of GWPs
from the IPCC Second Assessment Report  (SAR) (IPCC 1996).
This  requirement  ensures  that current  estimates  of aggregate
greenhouse gas emissions for 1990 to 2009 are consistent with
estimates developed prior to the  publication of the IPCC  Third
Assessment Report (TAR)  (IPCC 2001) and the  IPCC Fourth
Assessment Report (AR4)  (IPCC 2007).  Therefore, to comply
with international reporting standards under the UNFCCC, official
emission estimates are reported by the United States using SAR
GWP values.  All estimates are provided throughout the inventory
report  in both CO2  equivalents  and  unweighted  units.    A
comparison of emission values using the  SAR GWPs versus the
TAR  and AR4 GWPs can be found  in Chapter 1  and, in more
detail, in Annex 6.1 of the inventory report.  The GWP values
used in the inventory report are listed below in Table ES-1.
Table ES-1:  Global Warming Potentials (100-Year
Time Horizon) Used in the Inventory Report
Gas
C02
CH;
N20
HFC-23
HFC-32
HFC-125
HFC-134a
HFC-143a
HFC-152a
HFC-227ea
HFC-236fa
HFC-4310mee
CF4
C2F6
C^FIO
C6F14
SF6
GWP
1
21
310
11,700
650
2,800
1,300
3,800
140
2,900
6,300
1,300
6,500
9,200
7,000
7,400
23,900
   Source: IPCC (1996)
   * The CH4 GWP includes the direct effects and those indirect
   effects due to the production of tropospheric ozone and
   stratospheric water vapor. The indirect effect due to the
   production of C02 is not included.
  Albedo is a measure of the earth's reflectivity, and is defined as the fraction of the total solar radiation incident on a body that is reflected by it.
  Carbon comprises 12/44*" of carbon dioxide by weight.
  One teragram is equal to 1012 grams or one million metric tons.
11
   See .
                          Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2009  3

-------
    Global warming potentials are not provided for CO, NOX, NMVOCs, SO2, and aerosols because there is no agreed-upon
method to estimate the contribution of gases that are short-lived in the atmosphere, spatially variable, or have only indirect
effects on radiative forcing (IPCC 1996).

ES.2. Recent Trends in  U.S. Greenhouse Gas  Emissions and Sinks
     In 2009, total U.S. greenhouse gas emissions were 6,633.2
Tg or million metric tons CC>2 Eq.  While total U.S. emissions
have increased by 7.3 percent from 1990 to 2009, emissions
decreased from 2008 to 2009 by  6.1 percent (427.9 Tg CO2
Eq.).  This  decrease was primarily due to  (1)  a decrease in
economic output resulting in a decrease in energy consumption
across all sectors; and (2) a decrease in the carbon intensity of
fuels used to generate electricity due to  fuel switching as the
price of coal increased, and the price of natural  gas decreased
significantly.  Since 1990, U.S. emissions have increased at an
average annual rate of 0.4 percent.
    Figure ES-1 through  Figure  ES-3  illustrate the  overall
trends in total  U.S.  emissions  by gas,  annual  changes,  and
absolute change since 1990.
    Table  ES-2  provides  a  detailed  summary  of  U.S.
greenhouse gas emissions and sinks for 1990 through 2009.
 Figure ES-1
         U.S. Greenhouse Gas Emissions by Gas
   8.000 -
   7.0DO -
   6,000 -
 uf 5,000 -
 0
 % 4,000 -
   3,000 -
   2,000
   1,000
      0
             I MFCs, PFCs, & SF.
             Nitrous Oxide

                                                                                           Methane
                                                                                          I Carbon Dioxide
                                                                                                 Bills.
 Figure ES-2
     Annual Percent Change in U.S. Greenhouse Gas
                     Emissions
 4%-,
o%

-2%
                 3.3%
                           12.8%


                   M%M%1j||   j|%M%lj|W   •
                                         •0.6%

     T-cxico^-mtnr-      _
     oioioiCTiaiaiaioioi -
Figure ES-3
   Cumulative Change in Annual U.S. Greenhouse Gas
             Emissions Relative to 1990
  1,100
  1,000
   900
   800
S 700
o~ 600
° 500
   400
   300
   200
   100
                                                              -100J
                                           1.082
                                                                    CNJ co ^- m to r*- eo
                                                                                         gggggggg
4 Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2009

-------
Table ES-2: Recent Trends in U.S. Greenhouse Gas Emissions and Sinks (Tg or million metric tons C02 Eq.)
Gas/Source
C02
Fossil Fuel Combustion
Electricity Generation
Transportation
Industrial
Residential
Commercial
U.S. Territories
Non-Energy Use of Fuels
Iron and Steel Production &
Metallurgical Coke Production
Natural Gas Systems
Cement Production
Incineration of Waste
Ammonia Production and Urea
Consumption
Lime Production
Cropland Remaining Cropland
Limestone and Dolomite Use
Soda Ash Production and
Consumption
Aluminum Production
Petrochemical Production
Carbon Dioxide Consumption
Titanium Dioxide Production
Ferroalloy Production
Wetlands Remaining Wetlands
Phosphoric Acid Production
Zinc Production
Lead Production
Petroleum Systems
Silicon Carbide Production and
Consumption
Land Use, Land-Use Change, and
Forestry (Sink) "
Biomass- Wood"
International Bunker Fuels °
Biomass - Ethanol "
CH4
Natural Gas Systems
Enteric Fermentation
Landfills
Coal Mining
Manure Management
Petroleum Systems
Wastewater Treatment
Forest Land Remaining Forest Land
Rice Cultivation
Stationary Combustion
Abandoned Underground Coal Mines
Mobile Combustion
Composting
Petrochemical Production
Iron and Steel Production &
Metallurgical Coke Production
Field Burning of Agricultural Residues
Ferroalloy Production

1990
5,099.7
4,738.4
1,820.8
1,485.9
846.5
338.3
219.0
27.9
118.6

99.5
37.6
33.3
8.0|

16.sl
11.5
7.1
5.1

4.1
6.8
3.3
1.4
1.2
2.2
1.0
1.5
0.7
0.5
0.6

0.4

(861.5)
215.2
111.8
4.2\
674.9
2000
5,975.0
5,594.8
2,296.9
1,809.5
851.1
370.7
230.8
35.9
144.9

85.9
29.9
40.4
1 11.1

1 16.4
14.1
7.5
5.1

4.2
6.1
4.5
1.4
1.8
1.9
1.2
1.4
1.0
0.6
0.5

0.2

(576.6)
218.1
98.5
9.4\
659.9
189.8 209.3
132.1 136.5
147.41
84.1
31.7
35.4
23.5
3.2|
7.1|
7.4l
6.0|
4.7l
0.3|
0.9l

1.0!
o.sl
+|

111.7
60.4
42.4
31.5
25.2
1 14.3
1 7.5
6.6l
1 7.4
3.4l
1 1.3
1.2l

1 0.9
1 0.3
+
2005
6,113.8
5,753.2
2,402.1
1,896.6
1823.1
357.9
223.5
50.0
143.4

65.9
29.9
45.2
1 12.5

1 12.8
14.4
7.9
6.8

4.2
4.1
4.2
1.3
1.8
1.4
1.1
1.4
1.1
0.6
0.5

0.2

(1,056.5)
206.9
109.7
23.0
631.4
190.4
136.5
112.5
56.9
46.6
29.4
24.3
9.8
6.8
6.6
1 5.5
2.5
1 1.6
1.1

1 0.7
1 0.2
| +

2006
6,021.1
5,653.1
2,346.4
1,878.1
848.2
321.5
208.6
50.3
145.6

68.8
30.8
45.8
12.5

12.3
15.1
7.9
8.0

4.2
3.8
3.8
1.7
1.8
1.5
0.9
1.2
1.1
0.6
0.5

0.2

(1,064.3)
203.8
128.4
31.0
672.1
217.7
138.8
111.7
58.2
46.7
29.4
24.5
21.6
5.9
6.2
5.5
2.3
1.6
1.0

0.7
0.2
+

2007
6,120.0
5,756.7
2,412.8
1,894.0
842.0
342.4
219.4
46.1
137.2

71.0
31.1
44.5
12.7

14.0
14.6
8.2
7.7

4.1
4.3
3.9
1.9
1.9
1.6
1.0
1.2
1.1
0.6
0.5

0.2

(1,060.9)
203.3
127.6
38.9
664.6
205.2
141.0
111.3
57.9
50.7
30.0
24.4
20.0
6.2
6.5
5.6
2.2
1.7
1.0

0.7
0.2
+

2008
5,921.4
5,565.9
2,360.9
1,789.9
802.9
348.2
224.2
39.8
141.0

66.0
32.8
40.5
12.2

11.9
14.3
8.7
6.3

4.1
4.5
3.4
1.8
1.8
1.6
1.0
1.2
1.2
0.6
0.5

0.2

(1,040.5)
198.4
133.7
54.8
676.7
211.8
140.6
115.9
67.1
49.4
30.2
24.5
11.9
7.2
6.5
5.9
2.0
1.7
0.9

0.6
0.3
+

2009
5,505.2
5,209.0
2,154.0
1,719.7
730.4
339.2
224.0
41.7
123.4

41.9
32.2
29.0
12.3

11.8
11.2
7.8
7.6

4.3
3.0
2.7
1.8
1.5
1.5
1.1
1.0
1.0
0.5
0.5

0.1

(1,015.1)
183.8
123.1
61.2
686.3
221.2
139.8
117.5
71.0
49.5
30.9
24.5
7.8
7.3
6.2
5.5
2.0
1.7
0.8

0.4
0.2
+

                          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 C02 Eq.) (continued)
Gas/Source
Silicon Carbide Production and
Consumption
Incineration of Waste
International Bunker Fuels0
N20
Agricultural Soil Management
Mobile Combustion
Manure Management
Nitric Acid Production
Stationary Combustion
Forest Land Remaining Forest Land
Wastewater Treatment
N20 from Product Uses
Adipic Acid Production
Composting
Settlements Remaining Settlements
Incineration of Waste
Field Burning of Agricultural Residues
Wetlands Remaining Wetlands
International Bunker Fuels °
MFCs
Substitution of Ozone Depleting
Substances d
HCFC-22 Production
Semiconductor Manufacture
PFCs
Semiconductor Manufacture
Aluminum Production
SF6
Electrical Transmission and
Distribution
Magnesium Production and
Processing
Semiconductor Manufacture
Total
Net Emissions (Sources and Sinks)
1990
:
0.2l
315.2
197.8
43.9
14.5















JD.^t
0.2l
20.8
2.2l
18.51
34.4

28.41


u.og
6,181.8
5,320.3
2000
+
o./|
341.0
206.8
53.2
17.1
19.41
14.6
12.1
4.5l
4.9l
5.5
1.4l
1.ll
0.4l
0.1!
+1
0.9
103.2

74.31
28.6
o.sl
13.5
4.9l
8. el
20.1

16.0

3.0
j j ^1
7,112.7
6,536.1
2005
*
0.1
322.9
211.3
36.9
17.3
16.5
14.7
8.4
4.8
4.4
5.0
1.7
1.5
0.4
0.1
+
1.0
120.2

104.2
15.8
0.2
6.2
3.2
3.0
19.0

15.1

2.9
1.0
7,213.5
6,157.1
2006
*
0.2
326.4
208.9
33.6
18.0
16.2
14.4
18.0
4.8
4.4
4.3
1.8
1.5
0.4
0.1
+
1.2
123.5

109.4
13.8
0.3
6.0
3.5
2.5
17.9

14.1

2.9
1.0
7,166.9
6,102.6
2007
*
0.2
325.1
209.4
30.3
18.1
19.2
14.6
16.7
4.9
4.4
3.7
1.8
1.6
0.4
0.1
+
1.2
129.5

112.3
17.0
0.3
7.5
3.7
3.8
16.7

13.2

2.6
0.8
7,263.4
6,202.5
2008
*
0.2
310.8
210.7
26.1
17.9
16.4
14.2
10.1
5.0
4.4
2.0
1.9
1.5
0.4
0.1
+
1.2
129.4

115.5
13.6
0.3
6.6
4.0
2.7
16.1

13.3

1.9
0.9
7,061.1
6,020.7
2009
*
0.1
295.6
204.6
23.9
17.9
14.6
12.8
6.7
5.0
4.4
1.9
1.8
1.5
0.4
0.1
+
1.1
125.7

120.0
5.4
0.3
5.6
4.0
1.6
14.8

12.8

1.1
1.0
6,633.2
5,618.2
  + Does not exceed 0.05 Tg C02 Eq.
  a Parentheses indicate negative values or sequestration. The net C02 flux total includes both emissions and sequestration, and constitutes a net sink in the
  United States.  Sinks are only included in net emissions total.
  b Emissions from Wood Biomass and Ethanol Consumption are not included specifically in summing energy sector totals. Net carbon fluxes from changes in
  biogenic carbon reservoirs are accounted for in the estimates for Land Use, Land-Use Change, and Forestry.
  c Emissions from International Bunker Fuels are not included in totals.
  d Small amounts of RFC emissions also result from this source.
  Note: Totals may not sum due to independent rounding.

    Figure ES-4 illustrates the relative contribution of the direct greenhouse gases to total U.S.  emissions in 2009.  The
primary greenhouse gas emitted by human activities in the United States was  CO2, representing approximately 83.0 percent
of total greenhouse gas emissions.  The  largest source of CO2,  and of overall  greenhouse gas emissions, was fossil fuel
combustion.   Methane emissions, which have increased by 1.7 percent  since  1990, resulted primarily from natural  gas
systems, enteric fermentation associated with domestic livestock, and  decomposition of wastes in landfills.  Agricultural  soil
management and  mobile source fuel combustion were  the major sources  of N2O  emissions.  Ozone depleting substance
substitute emissions and emissions of HFC-23 during the production of HCFC-22 were the primary contributors to aggregate
HFC  emissions.  PFC emissions resulted as a byproduct of  primary  aluminum production  and  from semiconductor
manufacturing, while electrical transmission and distribution systems accounted for most SF6 emissions.
6  Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2009

-------
                                                              Figure ES-4
                                                                     2009 Greenhouse Gas Emissions by Gas
                                                                          (percents based on Tg C02 Eq.)
    Overall, from 1990 to 2009, total emissions of CO2 and
CH4 increased by 405.5 Tg CO2 Eq.  (8.0 percent) and 11.4 Tg
CO2 Eq. (1.7 percent), respectively. Conversely, N2O emissions
decreased by 19.6 Tg CO2 Eq. (6.2 percent).  During the same
period, aggregate weighted emissions of HFCs, PFCs, and SF6
rose by 54.1 Tg CO2 Eq. (58.8 percent).   From 1990 to 2009,
HFCs increased by 88.8 Tg  CO2 Eq. (240.41  percent), PFCs
decreased by 15.1 Tg CO2 Eq. (73.0 percent), and SF6 decreased
by  19.5 Tg CO2 Eq. (56.8  percent).  Despite being emitted in
smaller quantities relative  to the  other  principal greenhouse
gases, emissions of HFCs, PFCs, and SF6 are significant because
many of  these  gases  have  extremely high global warming
potentials and, in the cases  of PFCs and SF6, long atmospheric
lifetimes.   Conversely,  U.S.  greenhouse  gas emissions were
partly offset by  carbon sequestration in forests, trees in urban
areas, agricultural soils, and landfilled yard trimmings and food
scraps,  which,  in  aggregate,  offset  15.3   percent of total
emissions in 2009.  The following sections describe each gas:
contribution to total U.S. greenhouse gas emissions in more detail.

Carbon Dioxide  Emissions
    The global carbon cycle is made up of large carbon flows and reservoirs.  Billions of tons of carbon in the form of CO2
are absorbed by oceans and living biomass (i.e.,  sinks) and are emitted to the atmosphere annually through natural processes
(i.e., sources).  When in equilibrium, carbon fluxes  among these various reservoirs are roughly balanced.  Since the Industrial
Revolution (i.e., about 1750), global atmospheric concentrations of CO2 have risen about 36 percent (IPCC 2007), principally
due to the combustion of fossil fuels.  Within the  United States, fossil fuel combustion accounted for 94.6 percent of CO2
emissions in 2009.  Globally, approximately 30,313 Tg  of CO2 were added to the atmosphere through the combustion of
fossil fuels in 2009, of which the United States accounted for about 18 percent.12 Changes in land use and forestry practices
can also emit CO2 (e.g., through conversion of forest land to agricultural or urban use)  or can act as a sink for CO2  (e.g.,
through net additions to forest biomass). In addition  to  fossil-fuel combustion, several  other  sources emit  significant
quantities of CO2. These sources include, but are not limited to non-energy use of fuels, iron and steel production and cement
production (Figure ES-5).
     As the largest  source of U.S. greenhouse  gas emissions,  CO2  from  fossil fuel combustion  has  accounted for
approximately 78 percent of GWP-weighted emissions since 1990, growing slowly from 77 percent of total GWP-weighted
emissions in 1990 to  79 percent in 2009. Emissions  of CO2 from fossil fuel combustion increased at an  average annual rate
of 0.4 percent from 1990 to 2009. The fundamental factors influencing this trend include: (1) a generally growing domestic
economy over the last 20 years, and (2) overall growth in emissions from electricity generation and transportation activities.
Between 1990 and 2009, CO2 emissions from fossil fuel combustion increased from 4,738.4 Tg CO2 Eq. to 5,209.0 Tg CO2
Eq.—a 9.9 percent total increase over the twenty-year period.  From 2008 to 2009, these emissions decreased by 356.9 Tg
CO2 Eq. (6.4 percent), the largest decrease in any year over the twenty-year period.
  Global CO2 emissions from fossil fuel combustion were taken from Energy Information Administration International Energy Statistics 2010
 El A (201 Oa).
                          Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2009  1

-------
                                                            Figure ES-5
                                                                           2009 Sources of CO, Emissions
         Fossil Fuel Combustion
        Non-Energy Jseof Fuels
        Iron and Steel Production
    & Metallurgical Coke Production
           Natural Gas Systems
            Cement Production
          Incineration of Waste •
        Ammonia Production and _
            Urea Consomption •
             Lime Production |
     Cropland Remaining Cropland •
      Limestone and Dolomite Use •
Soda Ash Production and Consomption I
          Aluminum Production I
        Petrochemical Production
      Carbon Dioiide Consomption
      Titanium Dioiide Production
          Ferroalloy Production
     Wetlands Remaining Wetlands
      Phosphoric Acid Production
             Zinc Production
             Lead Production |
            Petroleum Systems
     Silicon Carbide Production and
               Consumption
                                                                                                                   5,209
                                                                                                 CO; as a Portion
                                                                                                 of all Emissions
    Historically, changes in emissions from fossil fuel
combustion have been the dominant factor affecting U.S.
emission trends.  Changes in CC>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 consumption than a year with  poor
economic   performance,   high   fuel   prices,    mild
temperatures,  and increased output  from  nuclear and
hydroelectric   plants.     In  the  long  term,  energy
consumption patterns respond to changes that affect the
scale of consumption  (e.g., population, number of cars.
and size of houses),  the efficiency with which energy is
used  in  equipment (e.g., cars,  power plants, steel  mills.
and light bulbs) and behavioral choices  (e.g.,  walking.
bicycling, or telecommuting to work instead of driving).
    The five major fuel consuming  sectors contributing
to  CO2  emissions  from fossil  fuel  combustion  are  electricity generation,  transportation,  industrial, residential, and
commercial.  Carbon dioxide emissions are produced by the electricity  generation sector as they consume fossil fuel to
provide  electricity to  one of the other four  sectors,  or "end-use" sectors.  For the discussion below, electricity generation
emissions  have been  distributed  to each end-use  sector on  the  basis  of each sector's  share of aggregate electricity
consumption.  This method of distributing emissions assumes that each end-use sector consumes electricity that is generated
from the national average mix of fuels  according to their carbon intensity. Emissions from electricity generation are also
addressed separately after the end-use sectors have been discussed.
    Note that  emissions from U.S. territories are calculated  separately due to a lack of specific consumption data for the
individual end-use sectors.
    Figure ES-6, Figure ES-7, and  Table ES-3 summarize CO2 emissions from fossil fuel combustion by end-use sector.
                                                                                      <0.5
                                                                                          25
                                                                                                    To   100   125    15D
8  Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2009

-------
Figure ES-6
                                                   Figure ES-7
   2009 C02 Emissions from Fossil Fuel Combustion by
                  Sector and Fuel Type
                                                     2009 End-Use Sector Emissions of C02, CH4, and N20
                                                                 from Fossil Fuel Combustion
   2,500 -



   2,000 -


Sj.500 -
o"
O
i?
   1,000 -



    500 -
Relative Contribution
   by Fuel Type
                    Petroleum
                   I Coal
                    Natural Gas
2,154
                                1,720
                        730
                   224
           42
                339

               •
                 I
                 I
Note: Electricity generation also includes emissions of less than 0.5 Tg C02
Eq. from geothermal-based electricity generation.
              2,000 -,
                                                     1,500 -
                                                     1,000 -
                                                                  500 -
I From Direct Fossil
 Fuel Combustion
 From Electricity
 Consumption
                                                                        990
                                                                                                     1,750
                                                                                 1,132
                                                                          42
Table ES-3:  C02 Emissions from Fossil Fuel Combustion by Fuel Consuming End-Use Sector (Tg or million metric tons C02 Eq.)
End-Use Sector
Transportation
Combustion
Electricity
Industrial
Combustion
Electricity
Residential
Combustion
Electricity
Commercial
Combustion
Electricity
U.S. Territories a
Total
Electricity Generation
1990
1,489.0
1,485.9 1
3.0
1,533.2
846.5 1
686.7 1
931.4 1
338.3 1
593.0 1
757.0
219.0 1
538.0
27.9
4,738.4
1,820.8
2000
1,813.0
1,809.5
3.4
1,640.8
851.1
789.8
1,133.1
370.7
762.4
972.1
230.8
741.3
35.9
5,594.8
2,296.9
2005
1,901.3
1,896.6
4.7
1,560.0
823.1
737.0
1,214.7
357.9
856.7
1,027.2
223.5
803.7
50.0
5,753.2
2,402.1
2006
1,882.6
1,878.1
4.5
1,560.2
848.2
712.0
1,152.4
321.5
830.8
1,007.6
208.6
799.0
50.3
5,653.1
2,346.4
2007
1,899.0
1,894.0
5.0
1,572.0
842.0
730.0
1,198.5
342.4
856.1
1,041.1
219.4
821.7
46.1
5,756.7
2,412.8
2008
1,794.6
1,789.9
4.7
1,517.7
802.9
714.8
1,182.2
348.2
834.0
1,031.6
224.2
807.4
39.8
5,565.9
2,360.9
2009
1,724.1
1,719.7
4.4
1,333.7
730.4
603.3
1,123.8
339.2
784.6
985.7
224.0
761.7
41.7
5,209.0
2,154.0
     a Fuel consumption by U.S. territories (i.e., American Samoa, Guam, Puerto Rico, U.S. Virgin Islands, Wake Island, and other U.S. Pacific
     Islands) is included in the inventory report.
     Note: Totals may not sum due to independent rounding. Combustion-related emissions from electricity generation are allocated based
     on aggregate national electricity consumption by each end-use sector.


     Transportation  End-Use Sector.   Transportation  activities  (excluding international bunker fuels) accounted  for  33
percent of CO2 emissions from fossil fuel combustion in 2009.13  Virtually all  of the energy consumed in this end-use sector
came from petroleum products.  Nearly 65 percent of the emissions resulted from gasoline consumption for personal vehicle
use.  The remaining emissions came from other transportation activities, including the combustion of diesel fuel in  heavy-
   If emissions from international bunker fuels are included, the transportation end-use sector accounted for 35 percent of U.S. emissions from fossil fuel
combustion in 2009.
                             Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2009  9

-------
duty vehicles and jet fuel in aircraft.  From 1990 to 2009, transportation emissions rose by 16 percent due, in large part, to
increased demand for travel and the stagnation of fuel efficiency across the U.S. vehicle fleet.  The number of vehicle miles
traveled by light-duty motor vehicles (passenger cars and light-duty trucks) increased 39 percent from 1990 to 2009, as a
result of a confluence of factors including population growth, economic growth, urban sprawl, and low fuel prices over much
of this period.
    Industrial End-Use Sector.  Industrial CO2 emissions, resulting both directly from the combustion of fossil  fuels and
indirectly from the generation of electricity that is consumed by industry, accounted for 26 percent of CO2 from fossil fuel
combustion in 2009.  Approximately 55 percent of these emissions resulted from direct fossil fuel combustion to produce
steam and/or heat for industrial processes.  The remaining emissions resulted from consuming electricity for motors, electric
furnaces, ovens, lighting, and  other applications.  In contrast to  the other end-use sectors,  emissions from industry have
steadily declined since 1990. This decline is due to structural changes in the U.S. economy (i.e., shifts from a 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 22 and 19
percent, respectively, of CO2 emissions from fossil fuel combustion in 2009. Both sectors relied heavily on electricity for
meeting energy demands, with 70 and 77 percent, respectively, of their emissions attributable to electricity consumption for
lighting,  heating, cooling, and  operating appliances.  The remaining emissions were due to the consumption of natural gas
and petroleum for heating and cooking.  Emissions from these end-use sectors have increased 25 percent since 1990, due to
increasing electricity consumption for lighting, heating, air conditioning, and operating appliances.
    Electricity Generation.  The United States relies on electricity to meet a significant portion  of its  energy  demands.
Electricity generators consumed 36 percent of U.S. energy from fossil fuels and emitted 41 percent of the CO2 from fossil
fuel combustion in 2009. The type of fuel combusted by electricity generators has a significant effect on their emissions. For
example, some electricity is generated with low CO2 emitting energy technologies, particularly non-fossil options such as
nuclear, hydroelectric, or geothermal energy. However, electricity generators rely on coal for over half of their total energy
requirements and accounted for 95 percent of all coal consumed for energy in the United  States in  2009.  Consequently.
changes in electricity demand have a significant impact on coal consumption and associated CO2 emissions.
    Other significant CO2 trends included the following:
    •   Carbon dioxide emissions from non-energy use of fossil fuels have increased 4.7 Tg CO2 Eq. (4.0 percent) from
         1990  through 2009.   Emissions from  non-energy uses  of fossil fuels  were 123.4 Tg CO2 Eq. in 2009, which
        constituted 2.2 percent of total national CO2 emissions, approximately the same proportion as in 1990.
    •   Carbon dioxide emissions from iron and steel production and metallurgical coke production  decreased by 24.1 Tg
        CO2 Eq.  (36.6 percent) from 2008 to 2009, continuing a trend of decreasing emissions from  1990 through 2009 of
        57.9 percent  (57.7 Tg  CO2  Eq.).   This  decline  is due  to the restructuring of  the  industry, technological
        improvements, and increased scrap utilization.
    •   In 2009,  CO2  emissions from cement production decreased by 11.5 Tg CO2 Eq. (28.4 percent) from 2008.  After
        decreasing  in 1991 by two percent from 1990 levels, cement production emissions grew every year through 2006;
        emissions  decreased in the last  three years.  Overall, from 1990 to 2009, emissions from  cement production
        decreased by 12.8 percent, a decrease of 4.3 Tg CO2 Eq.
    •   Net CO2 uptake from Land Use, Land-Use Change, and Forestry increased by 153.5 Tg CO2 Eq. (17.8 percent) from
         1990 through 2009. This increase was primarily due to an increase in the rate of net carbon accumulation in forest
        carbon stocks, particularly in aboveground and belowground tree biomass, and harvested wood pools.  Annual
10  Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2009

-------
        carbon accumulation in landfilled yard trimmings and food scraps slowed over this period, while the rate of carbon
        accumulation in urban trees increased.
Methane Emissions
    Methane (CH4) is more than 20 times as effective as CO2 at
trapping heat in the atmosphere (IPCC 1996).  Over the last two
hundred and  fifty years, the concentration  of CH4 in  the
atmosphere  increased   by   148   percent   (IPCC  2007).
Anthropogenic  sources   of  CH4  include  natural   gas  and
petroleum systems, agricultural activities, landfills, coal mining.
wastewater treatment,  stationary  and mobile  combustion, and
certain industrial processes (see Figure ES-8).
    Some significant trends in U.S.  emissions of CH4 include
the following:
    •   In 2009, CH4 emissions from coal mining were 71.0 Tg
        CO2 Eq., a 3.9 Tg CO2 Eq. (5.8 percent) increase over
        2008 emission levels.  The overall decline of 13.0 Tg
        CO2 Eq.  (15.5  percent) from  1990  results from  the
        mining of less gassy coal from underground mines and
        the increased use of CH4 collected from degasification
        systems.
    •   Natural  gas  systems were the largest  anthropogenic
        source category of CH4 emissions in  the United States
        in 2009 with 221.2 Tg CO2 Eq. of CH4 emitted into the
Figure ES-8
            2009 Sources of CH, Emissions
             Natural Gas Systems
             Enteric Fermentation
                    Landfills
                  Coal Mining
             Manure Management
              Petroleum Systems ^^|
            Waslewater Treatment ^H
     Foresl Land Remaining Forest Land |
                Rice Cultivation |
            Stationary Combustion |
     Abandoned Underground Coal Mines |
              Mobile Combustion [
                  Composting |
           Petrochemical Production |
           Iron and Steel Production i-««
       S Metallurgical Coke Production I
-------
        emissions is the result of increases in the amount of landfill gas collected and combusted,14 which has more than
        offset the additional CH4 emissions resulting from an increase in the amount of municipal solid waste landfilled.
                                                             Figure ES-9
Nitrous Oxide  Emissions
     Nitrous  oxide is produced by biological processes that
occur in soil and water and by a variety of anthropogenic
activities  in  the  agricultural, energy-related,  industrial, and
waste management fields.  While total N2O emissions are much
lower than CO2 emissions,  N2O is approximately  300 times
more powerful than CO2 at trapping heat in  the atmosphere
(IPCC 1996).  Since 1750, the global atmospheric concentration
of N2O  has risen by approximately 18  percent (IPCC 2007).
The main anthropogenic activities producing N2O in the United
States are  agricultural  soil  management,  fuel combustion  in
motor vehicles, manure management, nitric acid production and
stationary fuel combustion, (see Figure ES-9).
    Some significant trends  in U.S. emissions  of N2O include
the following:
    •   In 2009, N2O emissions from mobile combustion were
        23.9 Tg CO2 Eq. (approximately  8.1 percent of U.S.
        N2O emissions).  From 1990 to 2009, N2O emissions
        from mobile combustion decreased by 45.6 percent.  However, from 1990 to 1998 emissions increased by 25.6
        percent, due to control technologies that reduced NOX emissions while increasing N2O emissions.  Since 1998.
        newer control technologies have led to an overall decline in N2O from this source.
    •   Nitrous oxide emissions from adipic acid production were 1.9 Tg CO2 Eq. in 2009, and have decreased significantly
        since 1996 from the widespread installation  of pollution control measures.  Emissions from adipic acid production
        have decreased by 87.7 percent since 1990, and emissions from adipic acid production have remained consistently
        lower than pre-1996 levels since 1998.
    •   Agricultural soils accounted for approximately 69.2 percent of N2O emissions  in  the  United States in 2009.
        Estimated emissions from this source in 2009 were 204.6 Tg CO2 Eq. Annual N2O emissions from agricultural soils
        fluctuated between 1990 and 2009, although overall emissions were 3.4  percent higher in 2009 than in 1990.
2009 Sources of N20 Emissions

Nitric Acid Production ^^^^H
Stationary Combustion ^^^^H
N,0 as a Portion
Forest Land Remaining Forest Land ^^| of all Emissions
Wastewater Treatment ^| /" »^\
N.O from Product Uses ^| / \
Adipic Acid Production | 1 4'5* j
Composting | \ 	 /
Settlements Remaining Settlements |
Incineration of Waste
Field Burning of Agricultural Residues
Wetlands Remaining Wetlands
I I I I
0 10 20 30 40
Tg C0; Eq.
205

50
  The CO2 produced from combusted landfill CH4 at landfills is not counted in national inventories as it is considered part of the natural C cycle of
decomposition.
12 Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2009

-------
                                    Figure ES-10
                                         2009 Sources of MFCs, PFCs, and SF6 Emissions
                                      Substitution of Ozone
                                      Depleting Substances
                                     Electrical Transmission
                                          and Distribution
                                       HCFC-22 Production
                                          Semiconductor
                                            Manufacture
                                      Aluminum Production  I

                                          and Processing
Magnesium Production I
                               MFCs, PFCs, and
                               SF, as a Portion of
                                all Emissions

                               0
                                                          10
                                                                20     30
                                                                 TgCO,Eq.
                                                                            40
                                                                                  50
HFC, PFC, and SF6 Emissions
    HFCs and PFCs are families of synthetic chemicals that are
used as alternatives to ODS, which are being phased out under
the Montreal Protocol and Clean Air Act Amendments of 1990.
HFCs and PFCs do not deplete the stratospheric  ozone layer.
and are therefore  acceptable alternatives under the Montreal
Protocol.
    These compounds,  however,  along with  SF6, are potent
greenhouse gases.   In addition to  having high global warming
potentials, SF6 and PFCs have  extremely  long  atmospheric
lifetimes, resulting in their essentially irreversible accumulation
in the atmosphere once emitted.  Sulfur hexafluoride is the most
potent greenhouse gas the IPCC has evaluated (IPCC 1996).
    Other emissive sources of these  gases include  electrical
transmission  and distribution systems, HCFC-22 production.
semiconductor  manufacturing,   aluminum  production,  and
magnesium production and processing (see Figure ES-10).
     Some significant trends in U.S. HFC, PFC, and SF6 emissions include the following:
    •   Emissions  resulting from the substitution of ODS (e.g., CFCs)  have been  consistently increasing, from small
        amounts in 1990 to 120.0 Tg CO2 Eq. in 2009.  Emissions from ODS substitutes are both the largest and the fastest
        growing source of HFC,  PFC, and SF6 emissions.  These emissions have been increasing as phase-outs required
        under the Montreal Protocol come into effect, especially after 1994, when full  market penetration was made for the
        first generation of new technologies featuring ODS substitutes.
    •   HFC emissions from the production of HCFC-22 decreased by 85.2 percent (31.0 Tg CO2 Eq.) from  1990 through
        2009, due to a steady decline  in the emission rate of HFC-23 (i.e., the amount of HFC-23 emitted per kilogram of
        HCFC-22 manufactured) and the use of thermal oxidation at some plants to reduce HFC-23 emissions.
    •   Sulfur hexafluoride emissions from electric power transmission and distribution systems decreased by 54.8 percent
        (15.6 Tg CO2 Eq.) from 1990 to 2009, primarily because of higher purchase prices for SF6 and efforts by industry to
        reduce emissions.
    •   PFC emissions from aluminum production decreased by 91.5 percent  (17.0 Tg CO2 Eq.) from 1990 to 2009, due to
        both industry emission reduction efforts and lower domestic aluminum production.
Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2009  13

-------
            ES.3.  Overview of Sector Emissions  and  Trends
                 In accordance with the Revised 1996IPCC Guidelines for
            National Greenhouse Gas Inventories (IPCC/UNEP/OECD/IEA
            1997), and the 2003  UNFCCC Guidelines  on Reporting and
            Review  (UNFCCC  2003), Figure  ES-11  and  Table  ES-4
            aggregate emissions and  sinks by these chapters. Emissions of
            all gases can be summed from each source category from IPCC
            guidance. Over the twenty-year period of 1990 to 2009, total
            emissions in the Energy and Agriculture sectors grew by 463.3
            Tg  CO2  Eq.  (9 percent), and 35.7 Tg CO2 Eq. (9 percent),
            respectively.  Emissions  decreased in the Industrial Processes,
            Waste, and Solvent and Other Product Use sectors by 32.9 Tg
            CO2 Eq. (10 percent), 24.7 Tg CO2 Eq.  (14 percent) and less
            than 0.1 Tg CO2 Eq. (0.4 percent), respectively.  Over the same
            period, estimates of net C sequestration in the Land Use, Land-
            Use  Change, and Forestry sector (magnitude of emissions plus
            CO2 flux from all LULUCF  source  categories) increased by
            143.5 Tg CO2 Eq. (17  percent).
Figure ES-11
      U.S. Greenhouse Gas Emissions and Sinks by
                 Chapter/IPCC Sector
            Industrial Processes
                           Waste
                                 LULUCF (sources)
   7,500
   7,000
   6.500
   6.000
   5,500
   5,000
  . 4,500
   4,000
  ' 3,500
  , 3,000
   2,500
   2,000
   1,500
   1,000
     500 -
      0
   (500) -
  (1,000)
  (1,500) J
Land Use. Land-Use Change and Forestry (sinks)
S
           oioioi
                      SSSS
                                s
Note: Relatively smaller amounts of GWP-weighted emissions are also
emitted from the Solvent and Other Product Use Sectors.
            Table ES-4:  Recent Trends in U.S. Greenhouse Gas Emissions and Sinks by Chapter/IPCC Sector (Tg or million metric tons C02
            Eq.)
Chapter/IPCC Sector
Energy
Industrial Processes
Solvent and Other Product Use
Agriculture
Land Use, Land-Use Change, and Forestry (Emissions)
Waste
Total Emissions
Net C02 Flux from Land Use, Land-Use Change, and
Forestry (Sinks)3
Net Emissions (Sources and Sinks)

5,




6,

(5
5,
1990
287.8
315.8
44
383.6
15.0
175.2
181.8

161.5)
320.3











6




7

(
6
2000
,168.0
348.8
4.9
410.6
36.3
143.9
,112.7

576.6)
,536.1
2005
6,282.8
334.1
4.4
418.8
28.6
144.9
7,213.5

(1,056.5)
6,157.1
2006
6,210.2
339.4
4.4
418.8
49.8
144.4
7,166.9

(1,064.3)
6,102.6
2007
6,290.7
350.9
4.4
425.8
47.5
144.1
7,263.4

(1,060.9)
6,202.5
2008
6,116.6
331.7
4.4
426.3
33.2
149.0
7,061.1

(1,040.5)
6,020.7
2009
5,751.1
282.9
4.4
419.3
25.0
150.5
6,633.2

(1,015.1)
5,618.2
             a The net C02 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.
            14  Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2009

-------
                                    Figure ES-12
                                        2009 U.S. Energy Consumption by Energy Source
                                             Nuclear Electric
Energy
    The  Energy chapter contains emissions of all greenhouse
gases resulting from  stationary  and mobile  energy activities
including fuel combustion and fugitive fuel emissions.  Energy-
related activities, primarily fossil fuel combustion, accounted for
the vast majority of U.S. CO2 emissions for the period of 1990
through 2009. In 2009,  approximately 83 percent of the energy
consumed in the United States (on a Btu basis) was produced
through  the  combustion of fossil fuels.   The remaining 17
percent came from other energy sources such as hydropower.
biomass, nuclear, wind, and solar energy (see Figure ES-12).
Energy-related activities are also responsible for CH4 and N2O
emissions (49 percent and 13 percent of total U.S. emissions of
each gas, respectively). Overall, emission sources in the Energy
chapter account  for  a  combined 87 percent of  total  U.S.
greenhouse gas emissions in 2009.

Industrial Processes
    The Industrial Processes chapter contains byproduct or fugitive emissions of greenhouse gases from industrial processes
not directly related to energy activities such as fossil fuel combustion.  For example, industrial processes can chemically
transform raw materials, which often release waste gases such as CO2, CH4, and N2O. These processes include iron and steel
production and metallurgical coke  production,  cement  production, ammonia production  and  urea consumption, lime
production,  limestone and  dolomite  use (e.g., flux stone, flue gas desulfurization, and  glass manufacturing),  soda ash
production  and  consumption, titanium  dioxide  production,  phosphoric  acid production,  ferroalloy  production, CO2
consumption, silicon  carbide production and consumption, aluminum  production, petrochemical  production, nitric acid
production, adipic acid production, lead production, and zinc production.  Additionally, emissions from industrial processes
release HFCs, PFCs, and SF6.  Overall, emission sources in the Industrial Process chapter account for 4 percent of U.S.
greenhouse gas emissions in 2009.

Solvent and Other Product Use
    The  Solvent and  Other Product Use chapter contains greenhouse gas emissions that  are produced as a byproduct  of
various solvent and other product uses.  In the United States,  emissions from N2O from product uses, the only source  of
greenhouse  gas emissions from this  sector, accounted for about 0.1 percent of total U.S. anthropogenic greenhouse gas
emissions on a carbon equivalent basis in 2009.

Agriculture
    The Agriculture chapter contains anthropogenic emissions  from agricultural activities (except fuel combustion, which is
addressed in the Energy chapter,  and agricultural CO2 fluxes, which are addressed in the Land Use, Land-Use Change, and
Forestry Chapter).  Agricultural activities contribute directly to emissions of greenhouse gases through a variety of processes.
including the following  source categories: enteric fermentation in domestic livestock, livestock manure management, rice
cultivation,  agricultural  soil management, and field burning  of agricultural  residues.   CH4 and N2O were  the primary
greenhouse gases emitted by agricultural activities.  Methane emissions from enteric fermentation and manure management
represented 20 percent and  7  percent of total  CH4 emissions from  anthropogenic  activities,  respectively, in  2009.
Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2009 15

-------
Agricultural soil management activities such as fertilizer application and other cropping practices were the largest source of
U.S. N2O emissions in 2009, accounting for 69 percent. In 2009, emission sources accounted for in the Agriculture chapter
were responsible for 6.3 percent of total U.S. greenhouse gas emissions.

Land Use,  Land-Use Change, and Forestry
    The Land Use, Land-Use Change, and Forestry chapter contains emissions of CH4 and N2O, and emissions and removals
of CO2 from forest management, other land-use activities, and land-use change.  Forest management practices, tree planting
in urban areas, the management of agricultural soils, and the landfilling of yard trimmings and food scraps resulted in a net
uptake (sequestration) of C in the United States. Forests (including vegetation, soils, and harvested wood) accounted for 85
percent of total 2009 net  CO2 flux, urban trees accounted for 9 percent, mineral and  organic soil carbon  stock changes
accounted for 4 percent, and landfilled yard trimmings and food scraps accounted for 1 percent of the total net flux in 2009.
The net forest  sequestration is a result of net forest  growth and increasing forest area, as well as a net accumulation of carbon
stocks in harvested wood  pools.  The net sequestration in urban forests is  a result of net tree growth in these areas.  In
agricultural  soils, mineral  and organic soils sequester approximately 5.5  times  as much C as is emitted from these soils
through liming and urea fertilization.  The mineral soil  C sequestration is largely due to the conversion of cropland to
permanent pastures and hay production, a reduction in summer fallow areas in semi-arid areas, an increase in the adoption of
conservation tillage practices, and an increase in the amounts of organic fertilizers (i.e., manure and sewage sludge) applied
to agriculture lands. The landfilled yard trimmings and food scraps net sequestration is due to the long-term accumulation of
yard trimming carbon and food scraps in landfills.
    Land use, land-use change, and forestry activities in 2009 resulted in a net C sequestration of 1,015.1 Tg CO2 Eq. (Table
ES-5). This represents an offset of 18 percent of total U.S. CO2 emissions, or 15 percent of total greenhouse gas emissions in
2009. Between 1990 and 2009, total land use, land-use change, and forestry net C flux resulted in a 17.8 percent increase in
CO2 sequestration, primarily due to  an increase  in the  rate of net C  accumulation in forest C stocks, particularly in
aboveground and belowground tree biomass, and harvested wood pools. Annual C accumulation in landfilled yard trimmings
and food scraps slowed over this period, while the rate of annual C accumulation increased in urban trees.

Table ES-5: Net C02 Flux from Land Use, Land-Use Change, and Forestry (Tg or million metric tons C02 Eq.)

Sink Category
Forest Land Remaining Forest Land
Cropland Remaining Cropland
Land Converted to Cropland
Grassland Remaining Grassland
Land Converted to Grassland
Settlements Remaining Settlements
Other (Landfilled Yard Trimmings and Food
Scraps)
Total
1990
(681.1)
(29.4)
2.2
(52.2)
(19.8)
(57.1)

(24.2)
(861.5)







2000
(378.3)
(30.2)
2.4
(52.6)
(27.2)
(77.5)

(13.2)
(576.6)







2005
(911.5)
(18.3)
5.9
(8.9)
(24.4)
(87.8)

(11.5)
(1,056.5)
2006
(917.5)
(19.1)
5.9
(8.8)
(24.2)
(89.8)

(11.0)
(1,064.3)
2007
(911.9)
(19.7)
5.9
(8.6)
(24.0)
(91.9)

(10.9)
(1,060.9)
2008
(891.0)
(18.1)
5.9
(8.5)
(23.8)
(93.9)

(11.2)
(1,040.5)
2009
(863.1)
(17.4)
5.9
(8.3)
(23.6)
(95.9)

(12.6)
(1,015.1)
  Note: Totals may not sum due to independent rounding. Parentheses indicate net sequestration.


    Emissions from Land Use, Land-Use Change, and Forestry  are shown in Table ES-6.  The application of crushed
limestone and dolomite to managed land (i.e., liming of agricultural soils) and urea fertilization resulted in CO2 emissions of
7.8 Tg CO2 Eq.  in 2009, an increase of 11 percent relative to 1990.  The application of synthetic fertilizers to forest and
settlement soils in 2009 resulted in direct N2O emissions of 1.9 Tg CO2 Eq.  Direct N2O emissions from fertilizer application
to forest soils have increased by 455 percent since 1990, but still account for a relatively small portion of overall emissions.
Additionally, direct N2O emissions from fertilizer application to settlement soils increased by 55 percent since 1990.  Forest
16  Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2009

-------
fires resulted in CH4 emissions of 7.8 Tg CO2 Eq., and in N2O emissions of 6.4 Tg CO2 Eq.  in 2009. Carbon dioxide and
N2O emissions from peatlands totaled 1.1 Tg CO2 Eq. and less than 0.01 Tg CO2 Eq. in 2009, respectively.

Table ES-6:  Emissions from Land Use, Land-Use Change, and Forestry (Tg or million metric tons C02 Eq.)

  Source Category                                         1990      2000       2005   2006    2007   2008   2009
  C02                                                     8.1       8.8        8.9    8.8     9.2    9.6     8.9
  Cropland Remaining Cropland: Liming of Agricultural Soils           4./B      4.3B      4.3    4.2     4.5    5.0     4.2
  Cropland Remaining Cropland: Urea Fertilization                   2AM      3.2U      3.5    3.7     3.7    3.6     3.6
  Wetlands Remaining Wetlands: Peatlands Remaining Peatlands      1.ol      1.2l      1.1    0.9     1.0    1.0     1.1
  CH4                                                     3.2      14.3        9.8   21.6    20.0   11.9     7.8
  Forest Land Remaining Forest Land: Forest Fires                  3.2l     14.sB      9.8   21.6    20.0   11.9     7.8
  N20                                                     3.?l     13.2        9.8   19.5    18.3   11.6     8.3
  Forest Land Remaining Forest Land: Forest Fires                  2.6l     11.7M      8.0   17.6    16.3    9.8     6.4
  Forest Land Remaining Forest Land: Forest Soils                  0.11      0.4l      0.4    0.4     0.4    0.4     0.4
  Settlements Remaining Settlements: Settlement Soils               1.ol      1.11      1.5    1.5     1.6    1.5     1.5
  Wetlands Remaining Wetlands: Peatlands Remaining Peatlands	+	+	+	+	+	+	+_
  Total	15.0      36.3       28.6   49.8    47.5   33.2    25.0
  + Less than 0.05 Tg C02 Eq.
  Note:  Totals may not sum due to independent rounding.



Waste

    The Waste chapter  contains emissions  from waste management  activities (except incineration of waste,  which  is
addressed in the Energy chapter).  Landfills were the largest source of anthropogenic greenhouse gas emissions in the Waste
chapter, accounting for just over 78 percent of this chapter's emissions,  and 17 percent of total U.S.  CH4  emissions.15
Additionally, wastewater treatment accounts for 20  percent of Waste  emissions, 4 percent of U.S. CH4 emissions, and 2
percent of  U.S. N2O emissions.  Emissions of CH4 and  N2O from composting are  also accounted for in this chapter;
generating emissions of 1.7 Tg CO2 Eq. and 1.8 Tg  CO2 Eq., respectively.  Overall, emission sources  accounted for in the
Waste chapter generated 2.3 percent of total U.S. greenhouse gas emissions in 2009.


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 2009.
  Landfills also store carbon, due to incomplete degradation of organic materials such as wood products and yard trimmings, as described in the Land-Use.
Land-Use Change, and Forestry chapter of the inventory report.

                          Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2009  17

-------
 Table ES-7: U.S. Greenhouse Gas Emissions Allocated to Economic Sectors (Tg or million metric tons C02 Eq.)
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
1,868.9
1,545.2
1,564.4
429.0
395.5
345.1
33.7
6,181.8

(861.5)
5,320.3
2000
2,337.6
1,932.3
1,544.0
485.1
381.4
386.2
46.0
7,112.7

(576.6)
6,536.1
2005
2,444.6
2,017.4
1,441.9
493.2
387.2
371.0
1 58.2
7,213.5

(1,056.5)
6,157.1
2006
2,388.2
1,994.4
1,497.3
516.7
375.2
335.8
59.3
7,166.9

(1,064.3)
6,102.6
2007
2,454.0
2,003.8
1,483.0
520.7
389.6
358.9
53.5
7,263.4

(1,060.9)
6,202.5
2008
2,400.7
1,890.7
1,446.9
503.9
403.5
367.1
48.4
7,061.1

(1,040.5)
6,020.7
2009
2,193.0
1,812.4
1,322.7
490.0
409.5
360.1
45.5
6,633.2

(1,015.1)
5,618.2
  Note: Totals may not sum due to independent rounding. Emissions include C02, CH4, N20, MFCs, PFCs, and SF6.
  See Table 2-12 of the inventory report for more detailed data.
        Emissions Allocated to Economic Sectors
   2,500 -,
   2,000
   1,500-
   1,000
    500
Electric Power Industry
     ^^^ ^^"^^
     Transportation
         —\

          Industry
        Agriculture
       Commercial

        —~*_-~—•
        Residential
Figure ES-13                                                   Using this categorization,  emissions  from electricity
                                                          generation accounted for the largest portion (33 percent)  of
                                                          U.S.  greenhouse  gas  emissions in  2009.   Transportation
                                                          activities, in  aggregate,  accounted  for the  second largest
                                                          portion (27 percent), while emissions from industry accounted
                                                          for the third largest portion (20 percent) of U.S. greenhouse
                                                          gas emissions in 2009.  In contrast to electricity generation and
                                                          transportation, emissions  from  industry  have  in  general
                                                          declined over the past decade.  The long-term decline in these
                                                          emissions has been  due to structural  changes in  the  U.S.
                                                          economy (i.e., shifts from a manufacturing-based to a 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 7  percent  of  U.S.  emissions;  unlike  other
economic sectors, agricultural sector emissions were dominated by N2O  emissions from agricultural soil management and
CH4 emissions from enteric fermentation. The commercial sector accounted for 6 percent of emissions while the residential
sector accounted for 5 percent of emissions and U.S. territories accounted for 1 percent of emissions; emissions from these
sectors primarily consisted of CO2 emissions from fossil fuel combustion.
    Carbon dioxide was also emitted and sequestered by a variety of activities related to forest management practices, free
planting in urban areas, the management of agricultural soils, and landfilling of yard trimmings.
    Electricity is ultimately consumed in  the  economic  sectors described above.  Table  ES-8 presents greenhouse gas
emissions from  economic sectors with emissions related to  electricity generation distributed into end-use categories  (i.e..
emissions from  electricity generation are allocated to the economic sectors in which the  electricity  is consumed).  To
distribute electricity emissions among end-use sectors, emissions from the source categories assigned to electricity generation
were  allocated to the residential, commercial, industry, transportation, and agriculture economic sectors according to retail
Note: Does not include U.S. Territories.
18  Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2009

-------
sales of electricity.16 These source categories include CO2 from fossil fuel combustion and the use of limestone and dolomite
for flue gas desulfurization, CO2 and N2O from incineration of waste, CH4 and N2O from  stationary sources, and SF6 from
electrical transmission and distribution systems.

Table ES-8: U.S. Greenhouse Gas Emissions by Economic Sector with Electricity-Related Emissions Distributed (Tg or million
metric tons C02 Eq.)
Implied Sectors 1990 2000 2005
Industry 2,238.3 2,314.4 2,162.5
Transportation 1,548.3 1,935.8 2,022.2
Commercial 947.7( 1,135.8 1,205.1
Residential 953.8 1,162.2 1,242.9
Agriculture 460.0 518.4 522.7
U.S. Territories 33.7 46.0 I 58.2
Total Emissions 6,181.8 7,112.7 7,213.5
Land Use, Land-Use Change,
and Forestry (Sinks) (861.5) (576.6) (1,056.5)
Net Emissions (Sources
and Sinks) 5,320.3 6,536.1 6,157.1
See Table 2-14 of the inventory report for more detailed data.
2006 2007
2,194.6 2,192.9
1,999.0 2,008.9
1,188.5 1,225.3
1,181.5 1,229.6
544.1 553.2
59.3 53.5
7,166.9 7,263.4

(1,064.3) (1,060.9)

6,102.6 6,202.5

2008 2009
2,146.5 1,910.9
1,895.5 1,816.9
1,224.5 1,184.9
1,215.1 1,158.9
531.1 516.0
48.4 45.5
7,061.1 6,633.2

(1,040.5) (1,015.1)

6,020.7 5,618.2

When emissions from electricity are distributed among Figure ES-14
these sectors, industrial activities account for the largest share
of U.S. greenhouse gas emissions (29 percent) in 2009.
T +U J1 +'t, +1TTC
transportation is tne second largest contributor to total u.o.
emissions (28 percent). The commercial and residential sectors
contributed the next largest shares of total U.S. greenhouse gas
emissions in 2009. Emissions from these sectors increase

substantially when emissions from electricity are included, due
to their relatively large share of electricity consumption (e.g.,
lighting, appliances, etc.). In all sectors except agriculture, CO2

accounts for more than 80 percent of greenhouse gas emissions,
primarily from the combustion of fossil fuels. Figure ES-14
shows the trend in these emissions by sector from 1990 to 2009.




2,500 -

2,000 -


5^ 1,500-
o'
ES
(21
1,000-

cfin
3UU
o-

Economic Sectors



^ 	 " 	 —
^^^
-^--*^
^>*^
^_^-^
---
^ ^-^
_ — -— — •*" ^ 	




isiiillslli



^^ Industry
• 	 r — TT^O
Transportation \»

^^--Residential
	 	 -~^-* 	 «x.

- Commercial

Agriculture

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

                          Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2009  19

-------
  Box ES-2: Recent Trends in Various U.S. Greenhouse Gas Emissions-Related Data
  Total emissions can be compared to other economic and social indices to highlight changes over time. These comparisons include:  (1)
  emissions per unit of aggregate energy consumption, because energy-related activities are the largest sources of emissions; (2) emissions per
  unit of fossil fuel consumption, because almost all energy-related emissions involve the combustion of fossil fuels; (3) emissions per unit of
  electricity consumption, because the electric power industry—utilities and nonutilities combined—was the largest source of U.S. greenhouse
  gas emissions in 2009; (4) emissions  per unit of total gross domestic product as a measure of national economic activity; and (5) emissions
  per capita.
  Table ES-9 provides data on various statistics related to U.S. greenhouse gas emissions normalized to 1990 as a baseline year.  Greenhouse
  gas emissions in the United States have grown at an average annual rate of 0.4 percent since 1990. This rate is slightly slower than that for
  total energy and for fossil fuel consumption, and much  slower than that for electricity consumption, overall gross domestic product and
  national population (see Figure ES-15).

  Table ES-9:  Recent Trends in Various U.S. Data (Index 1990 = 100)
Variable
GDPb
Electricity Consumption c
Fossil Fuel Consumption c
Energy Consumption c
Population d
Greenhouse Gas Emissions e
1990
100
100
100
100
100
100
2000
140
127
117
116
113
115
2005
157
134
119
118
118
117
2006
162
135
117
118
120
116
2007
165
138
119
120
121
117
2008
165
138
116
118
122
114
2009
160
132
108
112
123
107
Growth
Rate3
2.5%
1.5%
0.5%
0.6%
1.1%
0.4%
  a Average annual growth rate
  b Gross Domestic Product in chained 2005 dollars (BEA 2010)
  c Energy content-weighted values (EIA 201 Ob)
  d U.S. Census Bureau (2010)
  e GWP-weighted values
                         Figure ES-15
                              U.S. Greenhouse Gas Emissions Per Capita and Per Dollar of Gross
                                                       Domestic Product
   1701
   160
   150-
_ 140
§ 130-
£  100-
•o
-  90-
   80-
   70-
   60
                                                                                      Real GDP
                                                                                      Emissions
                                                                                      per $GDP
                                 o  T—  cMco^-mtof-cocj)
                                                                      i—  CM  CO
                                                                   CM  CM  CM
                                                                                   CM  CM  CM  CM  CM
                         Source: BEA (2010), U.S. Census Bureau (2010), and emission estimates in the inventory report.
20  Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2009

-------
Indirect Greenhouse Gases (CO, NOX,  NMVOCs, and S02)

    The reporting requirements of the UNFCCC  request that information be provided on indirect greenhouse gases, which
include CO, NOX,  NMVOCs, and  SO2.   These gases do  not have a direct  global  warming effect, but indirectly affect
terrestrial radiation absorption by influencing the formation and destruction of tropospheric and stratospheric ozone, or, in the
case of SO2, by affecting the absorptive characteristics of the atmosphere.  Additionally, some of these gases may react with
other chemical compounds in the atmosphere to form compounds that are greenhouse gases.

    Since 1970, the United States has published estimates of annual emissions of CO, NOX, NMVOCs, and SO2 (EPA 2010,
EPA 2009),18 which are regulated  under the Clean Air Act.  Table ES-10 shows that fuel combustion accounts for the
majority of emissions of these indirect greenhouse gases.  Industrial processes—such as the manufacture of chemical and
allied products, metals processing, and industrial uses of solvents—are also significant sources of CO, NOX, and NMVOCs.

Table ES-10: Emissions of  NOX, CO, NMVOCs, and S02 (Gg)
  Gas/Activity
1990
2000
2005
2006
2007
2008
2009
  NOX
    Mobile Fossil Fuel Combustion
    Stationary Fossil Fuel Combustion
    Industrial Processes
    Oil and Gas Activities
    Incineration of Waste
    Agricultural Burning
    Solvent Use
    Waste
  CO
    Mobile Fossil Fuel Combustion
    Stationary Fossil Fuel Combustion
    Industrial Processes
    Incineration of Waste
    Agricultural Burning
    Oil and Gas Activities
    Waste
    Solvent Use
  NMVOCs
    Mobile Fossil Fuel Combustion
    Solvent Use
    Industrial Processes
    Stationary Fossil Fuel Combustion
    Oil and Gas Activities
    Incineration of Waste
    Waste
    Agricultural Burning
  S02
    Stationary Fossil Fuel Combustion
    Industrial Processes
    Mobile Fossil Fuel Combustion
    Oil and Gas Activities
    Incineration of Waste
    Waste
    Solvent Use
    Agricultural Burning	
  NA (Not Available)
  Note: Totals may not sum due to independent rounding.
  Source: (EPA 2010, EPA 2009) except for estimates from field burning of agricultural residues.
                                             14,380
                                              7,965
                                              5,432
                                                537
                                                318
                                                114
                                         13,547
                                          7,441
                                          5,148
                                            520
                                            318
                                            106
  See .
                                     11,468
                                      6,206
                                      4,159
                                       568
                                       393
                                       128
18
  NOX and CO emission estimates from field burning of agricultural residues were estimated separately, and therefore not taken from EPA (2008).
                          Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2009  21

-------
Key Categories
     The 2006IPCC Guidelines for National Greenhouse Gas Inventories (IPCC 2006) defines a key category as a "[source
or sink category] that is prioritized within the national inventory system because its estimate has a significant influence on a
country's total inventory of direct greenhouse gases in terms of the absolute level of emissions, the trend in emissions, or
both."19  By definition, key categories are sources or sinks that have the greatest contribution to the absolute overall level of
national emissions in any of the years  covered by the time series.  In addition, when an entire time  series of emission
estimates is prepared, a thorough investigation of key categories must also account for the influence of trends of individual
source and sink categories.  Finally, a qualitative evaluation of key categories should be performed, in order to capture any
key categories that were not identified in either of the quantitative analyses.
 Figure ES-16
                                                     2009 Key Categories
                       CO; Emissions Irom Stationary Combustion - Coal
                         C0? Emissions from Mobile Combustion - Road
                        CO, Emissions from Stationary Combustion - Gas
                        CO, Emissions from Stationary Combustion - Oil
                       Fugitive CH4 Emissions from Natural Gas Systems
                  Direct N,0 Emissions from Agricultural Soil Management  |
                       CO; Emissions from Mobile Combustion - Aviation  |
                             CH, Emissions from Enteric Fermentation  |
                           C0;, Emissions from Non-Energy Use of Fuels  |
                Emissions from Substitutes for Ozone Depleting Substances  |
                                      CH, Emissions from Landfills  |
                          C02 Emissions from Mobile Combustion: Other  |
                              Fugitive CH, Emissions from Coal Mining  |
                             CH, Emissions from  Manure Management  |
                           Indirect N,0  Emissions from Applied Nitrogen  |
   C0? Emissions from Iron and Steel Production & Metallurgical Coke Production  |
                             CO, Emissions from Natural Gas Systems  |
                        Fugitive CH, Emissions from Petroleum Systems
                            CH, Emissions from Wastewater Treatment
                        Non-CD, Emissions from Stationary Combustion
                                 CH, Emissions from Rice Cultivation
 Key Categories as a
Portion of all Emissions
                                                                  i
                                                                 200
                                                                                                I
                                                                                                      T
                                                                                                            T
                                                                       400    600    800   1,000   1,200  1,400  1,600  1,800  2,000
                                                                                       Tg CO, Eq.
 Note: For a complete discussion of the key category analysis, see Annex 1 of the inventory report. Darker bars indicate a Tier 1 level assessment key category.
 Lighter bars indicate a Tier 2 level assessment key category.
     Figure ES-16 presents 2009 emission estimates for the key categories as defined by a level analysis (i.e., the contribution
of each source or sink category to the total inventory level).  The UNFCCC reporting guidelines request that key category
analyses be reported at an appropriate level of disaggregation,  which may lead to source  and sink category names which
differ from those used elsewhere in the inventory report.  For more information regarding key categories, see section 1.5 and
Annex 1.
19
   See Chapter 7 "Methodological Choice and Recalculation" in IPCC (2000). .
22  Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2009

-------
Quality Assurance and Quality Control  (QA/QC)
    The United  States  seeks to  continually improve the quality, transparency, and credibility  of the Inventory of U.S.
Greenhouse Gas Emissions and Sinks.  To assist in these efforts, the United States implemented a systematic approach to
QA/QC.  While QA/QC has  always been an  integral part  of the  U.S. national  system for inventory development,  the
procedures followed for the current inventory have been formalized  in accordance with the QA/QC plan and the UNFCCC
reporting guidelines.

Uncertainty Analysis of Emission Estimates
    While the current U.S.  emissions inventory provides a solid foundation for the development of a more detailed and
comprehensive national inventory, there  are  uncertainties associated  with the emission estimates.  Some of  the  current
estimates, such as those  for CO2 emissions from energy-related activities and cement processing, are considered to have low
uncertainties.   For some other categories  of emissions, however, a lack of data or an incomplete understanding  of how
emissions are generated increases the uncertainty associated with the estimates presented. Acquiring a better understanding
of the uncertainty associated with inventory estimates is an important step in helping to prioritize future work and improve
the overall quality of the inventory  report. Recognizing the benefit of conducting an uncertainty analysis, the UNFCCC
reporting guidelines follow the recommendations  of the IPCC Good Practice Guidance (IPCC  2000) and  require  that
countries provide single  estimates of uncertainty for source and sink categories.
    Currently, a qualitative discussion of uncertainty is presented for  all source and sink categories. Within the discussion of
each emission source, specific factors affecting the uncertainty surrounding the estimates are discussed.  Most sources also
contain a quantitative uncertainty assessment, in accordance with UNFCCC reporting guidelines.
   Box ES-3: Recalculations of Inventory Estimates
   Each year, emission and sink estimates are recalculated and revised for all years in the Inventory of U.S. Greenhouse Gas Emissions and
   Sinks, as attempts are made to improve both the analyses themselves, through the use of better methods or data, and the overall usefulness
   of the inventory report.  In this effort, the United States follows the 2006 IPCC Guidelines (IPCC 2006), which states, "Both methodological
   changes and refinements overtime are an essential part of improving inventory quality. It is good practice to change or refine methods"
   when: available data have changed; the previously used method is not consistent with the IPCC guidelines for that category; a category has
   become key; the previously used method is insufficient to reflect mitigation activities in a transparent manner; the capacity for inventory
   preparation has increased;  new inventory methods become available; and for correction of errors." In general, recalculations are made to the
   U.S. greenhouse gas emission estimates either to incorporate new methodologies or, most commonly, to update recent historical data.
   In each inventory report, the results of all methodology changes and historical data updates are presented in the "Recalculations and
   Improvements" chapter; detailed descriptions of each recalculation are contained within each source's description contained in the report, if
   applicable. In general, when methodological changes have been implemented, the entire time series (in the case of the most recent inventory
   report, 1990 through 2009) has been recalculated to reflect the change, per the 2006 IPCC  Guidelines (IPCC 2006). Changes in historical
   data are generally the result of changes in statistical data supplied by other agencies. References for the data are provided for additional
   information.
                          Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2009  23

-------
References


BEA (2010) 2009 Comprehensive Revision of the National Income and Product Accounts: Current-dollar and "real" GDP,
1929-2009. Bureau of Economic Analysis (BEA), U.S. Department of Commerce, Washington, DC. July 29, 2010.
Available online at < http://www.bea.gov/national/index.htnrfgdp >.

EIA (2010) Supplemental Tables on Petroleum Product detail. Monthly Energy Review, September 2010, Energy
Information Administration, U.S. Department of Energy, Washington, DC. DOE/EIA-0035(2009/09).

EIA (2009) International Energy Annual 2007. Energy Information Administration (EIA), U.S. Department of Energy.
Washington, DC. Updated October 2008. Available online at
.

EPA (2010) "2009 Average annual emissions, all criteria pollutants in MS Excel." National Emissions Inventory (NEI) Air
Pollutant Emissions Trends Data. Office of Air Quality Planning and Standards.

EPA (2009) "1970 - 2008 Average annual emissions, all criteria pollutants in MS Excel." National Emissions Inventory
(NEI) Air Pollutant Emissions Trends Data. Office of Air Quality Planning and Standards. Available online at


IPCC (2007) Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment
Report of the Intergovernmental Panel on Climate Change. S. Solomon, D. Qin, M. Manning, Z. Chen, M. Marquis, K.B.
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
Programme, The Intergovernmental Panel on Climate Change, H.S. Eggleston,  L. Buendia, K. Miwa, T. Ngara, and K.
Tanabe (eds.). Hayama, Kanagawa, Japan.

IPCC (2003) Good Practice Guidance for Land Use, Land-Use Change, and Forestry. National Greenhouse Gas Inventories
Programme, The Intergovernmental Panel on Climate Change, J. Penman, et al. (eds.).  Available online at
. August 13, 2004.

IPCC (2001) Climate Change 2001: The Scientific Basis. Intergovernmental Panel on Climate Change,  J.T. Houghton, Y.
Ding, D. J. Griggs, M. Noguer, P. J. van der Linden, X. Dai, C. A. Johnson, and K.  Maskell (eds.). Cambridge University
Press.  Cambridge, United Kingdom.

IPCC (2000) Good Practice Guidance and Uncertainty Management in National  Greenhouse Gas Inventories. , National
Greenhouse Gas Inventories Programme, Intergovernmental Panel on Climate Change. Montreal. May 2000.  IPCC-XVI/Doc.
10 (1.IV.2000).

IPCC (1996) Climate Change 1995: The Science of Climate Change. Intergovernmental Panel on Climate Change, J.T.
Houghton, L.G. Meira Filho, B.A. Callander, N. Harris, A. Kattenberg, and K. Maskell. (eds.). Cambridge University Press.
Cambridge, United Kingdom.

IPCC/UNEP/OECD/IEA (1997) Revised 1996 IPCC Guidelines for National Greenhouse Gas Inventories.
Intergovernmental Panel on Climate Change, United Nations Environment Programme, Organization for Economic Co-
Operation and Development, International Energy Agency. Paris, France.

UNFCCC (2003) National Communications: Greenhouse Gas Inventories from Parties included in Annex I to the
Convention, UNFCCC Guidelines on Reporting and Review.  Conference of the Parties, Eighth Session, New Delhi.
(FCCC/CP/2002/8).  March 28, 2003.

U.S. Census Bureau (2010) U.S. Census Bureau International Database (IDE). Available online at
. August 15, 2010.
24 Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2009

-------

-------

-------

-------
United States
Environmental Protection Agency

EPA 430-S-11-001
April 2011
Office of Atmospheric Programs (6207J)
Washington, DC 20460

Official Business
Penalty for Private Use

-------