«EPA
United States
Environmental Protection
Agency
April 2005
Executive
Summary
of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2003
Central to any study of climate change is the development of an emissions inventory that identifies and quantifies
a country's primary anthropogenic1 sources and sinks of greenhouse gases. This inventory adheres to both
1) a comprehensive and detailed methodology 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.. .is to achieve.. .stabilization of greenhouse gas concentrations in the atmosphere at a level
that would prevent dangerous anthropogenic interference with the climate system. Such a level should be achieved
within a time-frame sufficient to allow ecosystems to adapt naturally to climate change, to ensure that food production
is not threatened and to enable economic development to proceed in a sustainable manner."2
Parties to the Convention, by ratifying, "shall develop, periodically update, publish and make available...national
inventories of anthropogenic emissions by sources and removals by sinks of all greenhouse gases not controlled by
the Montreal Protocol, using comparable methodologies.. ."3 The United States views this report as an opportunity to
fulfill these commitments. ,
*
This chapter summarizes the latest information on U.S. anthropogenic greenhouse gas emission trends from
1990 through 2003. To ensure that the U.S. emissions inventory is comparable to those of other UNFCCC Parties, the
estimates presented here were calculated using methodologies consistent with those recommended in the Revised 1996
IPCC Guidelines for National Greenhouse Gas Inventories (IPCC/DNEP/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). The structure of this report is consistent
with the UNFCCC guidelines for inventory reporting? For most
source categories, the IPCC methodologies were expanded,
All material taken from the Inventory of U.S. ... -* _ , . .. ,
resulting in ,a more comprehensive and detailed estimate of
Greenhouse Gas Emissions and Sinks: ^missions. '*
1990 -2003, U.S. Environmental Protection
Agency, Office of Atmospheric Programs,
EPA 43G-R-05-GQ3, April 2005. You may
electronically download this document
from U.S. EPA's Global Warming web
page at: www.epa.gov/globalw3rming/
publications/emissions.
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).
" 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 1 Parties in preparing national inventories. See .
See .
Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2003 1
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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 are not required to include these
gases in their national greenhouse gas emission inventories.5
Some other fluorine-containing halogenated substances—
hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and
sulfur hexafl uoride (SF5)—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 other greenhouse gases, including tropospheric
and stratospheric ozone. These gases include carbon
monoxide (CO), oxides of nitrogen (NOX), and non-methane
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. Since the
pre-industrial era (i.e., ending about 1750), concentrations
of these greenhouse gases have increased by 31, 150, and 16
percent, respectively (IPCC 2001).
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 2001).
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).6
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 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 of CO2 equivalent (Tg CO2 Eq.).7
All gases in this Executive Summary are presented in units
of Tg CO2 Eq. The relationship between gigagrams (Gg) of
a gas and Tg CO2 Eq. can be expressed as follows:
Tg CO2 Eq = (Gg of gas) x (GWP) x
i ,000 Ge
3 Emissions estimates of CFCs, HCFCs, halons and other ozone-depleting substances are included in this document for informational purposes.
6 Albedo is a measure of the Earth's reflectivity; see the Glossary (Annex 6.8) for definition.
7 Carbon comprises 12/44*5 of carbon dioxide by weight.
2 Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2003
T *
-------
Table ES-1: Global Warming Potentials (100-Year Time
Horizon) Used in this Report
Figure ES-1
Gas
C02
CH4*
N20
HFC-23
HFC-32
HFC-125
HFC-134a
HFC-143a
HFC-152a
HFC-227ea
HFC-236fa
HFC-4310mee
CF4
C2F6
C^io
C6Fi4
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 methane 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.
The UNFCCC reporting guidelines for national
inventories were updated in 2002,8 but continue to require
the use of GWPs from the IPCC Second Assessment Report
(SAR). This requirement ensures that current estimates of
aggregate greenhouse gas emissions for 1990 to 2003 are
consistent with estimates developed prior to the publication
of the IPCC Third Assessment Report (TAR). Therefore,
to comply with international reporting standards under the
UNFCCC, official emission estimates are reported by the
United States using SAR GWP values. All estimates are
provided throughout the report in both CO2 equivalents and
unweighted units. A comparison of emission values using the
SAR GWPs versus the TAR GWPs can be found in Chapter
1 and in more detail in Annex 6.1. The GWP values used in
this report are listed in Table ES-1.
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).
U.S. Greenhouse Gas Emissions by Gas
8,000
7,000
6,000
... 5,000
LLJ
g~ 4,000
"~ 3,000
2,000 -
1,000
0 J
MFCs, PFCs, & SF,
Nitrous Oxide
Methane
Carbon Dioxide
..,,6,2516,3436,407
138 6,121
6,621 6,678 6,720 6,752 6'953 6,807 6,858 6,900
Figure ES-2
Annual Percent Change in U.S. Greenhouse Gas Emissions
3.3%
3.0%
2.0% -
1.0% -
0.5% -
0.0%
-1.0% -
-2.0% -
-3.0%
3.0%
2.1%
«%•«*
Illilii.
0.8%
0.5% • « 0-6%
-0.8%
III
f
i— CM co ^mcor^oooicaT— CMCO
0)0)0) O)0)O)O)O)O)OOOO
Figure ES-3
Cumulative Change in U.S. Greenhouse Gas
Emissions Relative to 1990
8
See .
1000
800
600-
400-
200-
0
-200 J
O) O> O) O> O) O) O>
O) O) O) 0> O) 0> O)
5 S 8
Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2003 3
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Table ES-2: Recent Trends in U.S. Greenhouse Gas Emissions and Sinks (Tg C02 Eq.)
Gas/Source 1990
C02 5,009.6
Fossil Fuel Combustion 4,71 1 .7
Non-Energy Use of Fuels 1 08.0
Iron and Steel Production 85.4
Cement Manufacture 33.3
Waste Combustion 10.9
Ammonia Production and Urea Application 1 9.3
Lime Manufacture 11.2
Natural Gas Flaring 5.8
Limestone and Dolomite Use 5.5
Aluminum Production 6.3
Soda Ash Manufacture and Consumption 4.1
Petrochemical Production 2.2
Titanium Dioxide Production 1 .3
Phosphoric Acid Production 1 .5
Ferroalloy Production 2.0
Carbon Dioxide Consumption 0.9
Land-Use Change and Forestry (Sinks)*
International Bunker Fuels'* 113.5
Biomass Combustion13 216.7
CH4 605.3
Landfills 172.2
Natural Gas Systems 128.3
Enteric Fermentation 117.9
Coal Mining 81.9
Manure Management 31.2
Wastewater Treatment 24.8
Petroleum Systems 20.0
Rice Cultivation 7.1
Stationary Sources 7.8
Abandoned Coal Mines 6.1
Mobile Sources 4.8
Petrochemical Production 1.2
Iron and Steel Production 1 .3
Agricultural Residue Burning 0.7
Silicon Carbide Production +
International Bunker Fuelsb 0.2
N20 382.0
Agricultural Soil Management 253.0
Mobile Sources 43.7
Manure Management 16.3
Human Sewage 13.0
Nitric Acid Production 17.8
Stationary Sources 12.3
Settlements Remaining Settlements 5.5
Adipic Acid Production 15.2
N20 Product Usage 4.3
Waste Combustion 0.4
Agricultural Residue Burning 0.4
Forest Land Remaining Forest Land 0.1
International Bunker Fuelsb 1.0
MFCs, PFCs, and SF6 91.2
Substitution of Ozone Depleting Substances 0.4
Electrical Transmission and Distribution 29.2
HCFC-22 Production 35.0
Semiconductor Manufacture 2.9
Aluminum Production 18.3
Magnesium Production and Processing 5.4
Total 6,088.1
Net Emissions (Sources and Sinks) 5,046.1
1997 1998
5,580.0 5,607.2
5,263.2 5,278.7
120.3 135.4
71.9 67.4
38.3 39.2
17.8 17.1
20.7 21.9
13.7 13.9
7.9 6.6
7.2 7.4
5.6 5.8
4.4 4.3
2.9 3.0
1.8 1.8
1.5 1.6
2.0 2.0
0.8 0.9
(930.0) (881.0)
109.9 114.6
233.2 217.2
579.5 569.1
147.4 138.5
133.6 131.8
118.3 116.7
62.6 62.8
36.4 38.8
31.7 32.6
18.8 18.5
7.5 7.9
7.4 6.9
8.1 7.2
4.0 3.9
1.6 1.7
1.3 1.2
0.8 0.8
+ +
0.1 0.2
396.3 407.8
252.0 267.7
55.2 55.3
17.3 17.4
14.7 15.0
21.2 20.9
13.5 13.4
6.1 6.1
10.3 6.0
4.8 4.8
0.4 0.3
0.4 0.5
0.3 0.4
1.0 1.0
121.7 135.7
46.5 56.6
21.7 17.1
30.0 40.1
6.3 7.1
11.0 9.1
8 6.3 5.8
6,677.5 6,719.7
m 5.747.5 5,838.8
1999
5,678.0
5,345.9
141.6
64.4
40.0
17.6
20.6
13.5
6.9
8.1
5.9
4.2
3.1
1.9
1.5
2.0
0.8
(826.1)
105.3
222.3
557.3
134.0
127.4
116.8
58.9
38.8
33.6
17.8
8.3
7.1
7.3
3.6
1.7
1.2
0.8
+
0.1
382.1
243.4
54.6
17.4
15.4
20.1
13.5
6.2
5.5
4.8
0.3
0.4
0.5
0.9
134.8
65.8
16.4
30.4
7.2
9.0
6.0
6,752.2
5,926.1
2000
5,858 ?
5,545.1
124.7
65.7
41.2
18.0
19.6
13.3
5.8
6.0
5.7
4.2
3.0
1.9
1.4
1.7
1.0
(822.4)
101.4
226.8
554.2
130.7
132.1
115.6
56.2
38.1
34.3
17.6
7.5
7.3
7.7
3.4
1.7
1.2
0.8
+
0.1
401.9
263.9
53.2
17.8
15.6
19.6
14.0
6.0
6.0
4.8
0.4
0.5
0.4
0.9
138.9
75.0
15.6
29.8
6.3
9.0
3.2
6,953.2
6,130.8
2001
5,744.8
5,448.0
120.1
58.9
41.4
18.8
16.7
12.8
6.1
5.7
4.1
4.1
2.8
1.9
1.3
1.3
0.8
(826.9)
97.9
200.5
546.8
126.2
131.8
114.5
55.6
38.9
34.7
17.4
7.6
6.7
6.9
3.1
1.4
1.1
0.8
+
0.1
385.8
257.1
49.0
18.0
15.6
15.9
13.5
5.8
4.9
4.8
0.4
0.5
0.4
0.9
129.5
83.3
15.4
19.8
4.5
4.0
2.6
6,806.9
5,980.1
2002
5,796.8
5,501.4
118.8
55.1
42.9
18.8
18.6
12.3
6.2
5.9
4.2
4.1
2.9
2.0
1.3
1.2
1.0
(826.5)
89.5
207.2
542.5
126.8
130.6
114.6
52.4
39.3
35.8
17.1
6.8
6.4
6.4
2.9
1.5
1.0
0.7
+
0.1
380.5
252.6
45.6
17.9
15.7
17.2
13.5
6.0
5.9
4.8
0.5
0.4
0.4
0.8
138.3
91.5
14.7
19.8
4.4
5.2
2.6
6,858.1
6,031.6
2003
5,841.5
5,551.6
118.0
53.8
43.0
18.8
15.6
13.0
6.0
4.7
4.2
4.1
2.8
2.0
1.4
1.4
1.3
(828.0)
84.2
216.8
545.0
131.2
125.9
115.0
53.8
39.1
36.8
17.1
6.9
6.7
6.4
2.7
1.5
1.0
0.8
+
0.1
376.7
253.5
42.1
17.5
15.9
15.8
13.8
6.0
6.0
4.8
0.5
0.4
0.4
0.8
137.0
99.5
14.1
12.3
4.3
3.8
3.0
6,900.2
6,072.2
+ Does not exceed 0.05 Tg C02 Eq.
a Sinks are only included in net emissions total, and are based partially on projected activity data. Parentheses indicate negative values (or sequestration).
b Emissions from International Bunker Fuels and Biomass combustion are not included in totals.
Note: Totals may not sum due to independent rounding.
4 Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2003
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ES.2. Recent Trends in U.S.
Greenhouse Gas Emissions
and Sinks
Figure ES-4
2003 Greenhouse Gas Emissions by Gas
In 2003, total U.S. greenhouse gas emissions were
6,900.2 Tg CO2 Eq. Overall, total U.S. emissions have
risen by 13 percent from 1990 to 2003, while the U.S.
gross domestic product has increased by 46 percent over
the same period (BEA 2004). Emissions rose slightly from
2002 to 2003, increasing by 0.6 percent (42.2 Tg CO2 Eq.).
The following factors were primary contributors to this
increase: 1) moderate economic growth in 2003, leading to
increased demand for electricity and fossil fuels, 2) increased
natural gas prices, causing some electric power producers
to switch to burning coal, and 3) a colder winter, which
caused an increase in the use of heating fuels, primarily in
the residential end-use sector.
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 2003.
Figure ES-4 illustrates the relative contribution of the
direct greenhouse gases to total U.S. emissions in 2003.
The primary greenhouse gas emitted by human activities
in the United States was CO2, representing approximately
85 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 steadily declined since 1990, resulted primarily from
decomposition of wastes in landfills, natural gas systems,
and enteric fermentation associated with domestic livestock.
Agricultural soil management and mobile source fossil fuel
combustion were the major sources of N2O emissions. The
emissions of substitutes for ozone depleting substances and
emissions of HFC-23 during the production of HCFC-22
were the primary contributors to aggregate HFC emissions.
Electrical transmission and distribution systems accounted
for most SF6 emissions, while PFC emissions resulted from
semiconductor manufacturing and as a by-product of primary
aluminum production.
Overall, from 1990 to 2003, total emissions of CO2
increased by 832.0 Tg CO2 Eq. (17 percent), while CH4 and
MFCs, PFCs, & SF6
N20
CH4
CO,
2.0%
5.5%
7.9%
84.7%
N2O emissions decreased by 60.4 Tg CO9 Eq. (10 percent)
and 5.2 Tg CO2 Eq. (1 percent), respectively. During the
same period, aggregate weighted emissions of HFCs, PFCs,
and SF6 rose by 45.8 Tg CO2 Eq. (50 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 them 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
12 percent of total emissions in 2003. 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, atmospheric concentrations of CO2
have risen about 31 percent (IPCC 2001), principally due to
the combustion of fossil fuels. Within the United States, fuel
combustion accounted for 95 percent of CO2 emissions in
2003. Globally, approximately 24,240 Tg of CO2 were added
Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2003 5
-------
Figure ES-5
2003 Sources of CO,
Fossil Fuel Combustion
Iron and Steel Production
Cement Manufacture
Waste Combustion
Ammonia Production and Urea Application B
Lime Manufacture H
Natural Gas Flaring I
Limestone and Dolomite Use H
Aluminum Production |
Soda Ash Manufacture and •
Titanium Dioxide Production |
Phosphoric Add Production |
Ferroalloy Production
Carbon Dioxide Consumption |
5,552
C02 as a Portion
of all Emissions
10 20 30 40 50 60
Tg C02 Eq.
to the atmosphere through the combustion of fossil fuels in
2000, of which the United States accounted for about 23
percent.9 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).
As the largest source of U.S. greenhouse gas emissions,
CO2 from fossil fuel combustion has accounted for a nearly
constant 80 percent of GWP weighted emissions since 1990.
Emissions of CO2 from fossil fuel combustion increased at
an average annual rate of 1.3 percent from 1990 to 2003.
The fundamental factors influencing this trend include (1) a
generally growing domestic economy over the last 13 years,
and (2) significant growth in emissions from transportation
activities and electricity generation. Between 1990 and 2003,
CO2 emissions from fossil fuel combustion increased from
4,711.7 Tg CO2 Eq. to 5,551.6 Tg CO2 Eq.—an 18 percent
total increase over the thirteen-year period. Historically,
changes in emissions from fossil fuel combustion have been
the dominant factor affecting U.S. emission trends.
From 2002 to 2003, these emissions increased by 50.2
Tg CO2 Eq. (1 percent). A number of factors played a major
role in the magnitude of this increase. The U.S. economy
experienced moderate growth from 2002, causing an increase
in the demand for fuels. The price of natural gas escalated
dramatically, causing some electric power producers to
switch to coal, which remained at relatively stable prices.
Colder winter conditions brought on more demand for
heating fuels, primarily in the residential sector. Though a
cooler summer partially offset demand for electricity as the
use of air-conditioners decreased, electricity consumption
continued to increase in 2003. The primary drivers behind
this trend were the growing economy and the increase in U.S.
housing stock. Use of nuclear and renewable fuels remained
relatively stable. Nuclear capacity decreased slightly, for the
first time since 1997. Use of renewable fuels rose slightly due
to increases in the use of hydroelectric power and biofuels.
The four major end-use sectors contributing to CO2
emissions from fossil fuel combustion are industrial,
transportation, residential, and commercial. Electricity
generation also emits CO2, although these emissions are
produced as they consume fossil fuel to provide electricity
to one of the four 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. In reality, sources of
Figure ES-6
2003 C02 Emissions from Fossil Fuel
Combustion by Sector and Fuel Type
2,500 -i
2,000 -
1,500
1,000-
500-
Relative Contribution
by Fuel Type
>
Natural Gas
Petroleum
H Coal
Residential Commercial Industrial Transportation Electricity U.S.
Generation Territories
Note: Electricity generation also includes emissions of less than
1 Tg C02 Eq. from geothermal-based electricity generation.
9 Global CO2 emissions from fossil fuel combustion were taken from Marland et al. (2003) .
6 Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2003
-------
electricity vary widely in carbon intensity. By assuming the
same carbon intensity for each end-use sector's electricity
consumption, for example, emissions attributed to the
residential end-use sector may be underestimated, while
emissions attributed to the industrial end-use sector may
be overestimated. 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.
Transportation End-Use Sector. Transportation activities
(excluding international bunker fuels) accounted for 32
percent of CO2 emissions from fossil fuel combustion in
2003.10 Virtually all of the energy consumed in this end-use
sector came from petroleum products. Over 60 percent of the
emissions resulted from gasoline consumption for personal
vehicle use. The remaining emissions came from other
transportation activities, including the combustion of diesel
fuel in heavy-duty vehicles and jet fuel in aircraft.
Figure ES-7
2003 End-Use Sector Emissions of C02 from
Fossil Fuel Combustion
2000-
1750-
1500-
. 1250 -
LLJ
o 1000
"~ 750-
500
250-
0
From Electricity
Consumption
H From Direct Fossil
Fuel Combustion
Residential Commercial Industrial Transportation U.S.
Territories
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 28 percent of CO2 from fossil fuel
combustion in 2003. About half of these emissions resulted
from direct fossil fuel combustion to produce steam and/or
heat for industrial processes. The other half of the emissions
Table ES-3: C02 Emissions from Fossil Fuel Combustion by End-Use Sector (Tg C02 Eq.)
End-Use Sector
Transportation
Combustion
Electricity
Industrial
Combustion
Electricity
Residential
Combustion
Electricity
Commercial
Combustion
Electricity
U.S. Territories
Total
1997
1,606.4
1,603.3
3.1
1,703.0
963.8
739.2
1,040.7
370.6
670.2
876.7
237.2
639.5
36.4
5,263.2
2,051.9
1998
1,636.5
1,633.4
3.1
1,668.5
911.6
757.0
1,044.4
338.6
705.8
892.9
219.7
673.2
36.3
5,278.7
2,139.0
1999
1,693.9
1,690.8
3.2
1,651.2
888.1
763.1
1,063.5
359.3
704.2
901.2
222.3
678.9
36.2
5,345.9
2,149.3
2000
1,741.0
1,737.7
3.4
1,684.4
905.0
779.4
1,124.2
379.1
745.0
959.5
235.2
724.3
35.9
5,545.1
2,252.1
2001
1,723.1
1,719.7
3.4
1,587.4
878.2
709.3
1,116.2
367.0
749.2
972.7
226.7
745.9
48.6
5,448.0
2,207.8
2002
1,755.4
1,752.3
3.2
1,579.0
876.6
702.4
1,145.0
371.4
773.6
973.9
230.0
743.9
48.1
5,501.4
2,223.0
2003
1,770.4
1,767.2
3.2
1,572.9
858.6
714.3
1,168.9
385.1
783.8
983.1
234.0
749.2
56.2
5,551.6
2,250.5
Electricity Generation
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.
10 If emissions from international bunker fuels are included, the transportation end-use sector accounted for 33 percent of U.S. emissions from fossil fuel
combustion in 2003.
Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2003 7
-------
resulted from consuming electricity for motors, electric
furnaces, ovens, lighting, and other applications.
Residential and Commercial End-Use Sectors. The
residential and commercial end-use sectors accounted for
21 and 18 percent, respectively, of CO2 emissions from
fossil fuel combustion in 2003. Both sectors relied heavily
on electricity for meeting energy demands, with 67 and
76 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.
Electricity Generation. The United States relies on
electricity to meet a significant portion of its energy demands,
especially for lighting, electric motors, heating, and air
conditioning. Electricity generators consumed 35 percent of
U.S. energy from fossil fuels and emitted 41 percent of the
CO2 from fossil fuel combustion in 2003. 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 93
percent of all coal consumed for energy in the United States
in 2003. Consequently, changes in electricity demand have
a significant impact on coal consumption and associated
CCX, emissions.
Figure ES-8
2003 U.S. Sources of CH,
Landfills
Natural Gas Systems
Enteric Fermentation
Coal Mining
Manure Management
Wastewater Treatment
Petroleum Systems m
Rice Cultivation |
Stationary Sources I
Abandoned Coal Mines i
Mobile Sources I
Petrochemical Production |
Iron and Steel Production I
Agricultural Residue Burning I
Silicon Carbide Production I < 0.05
CH, as a Portion of
all Emissions
7.9%
O
Other significant CO, trends included the following:
Carbon dioxide emissions from iron and steel production
decreased to 53.8 Tg CO2 Eq. in 2003, and have declined
by 31.7 Tg CO2 Eq. (37 percent) from 1990 through
2003, due to reduced domestic production of pig iron,
sinter, and coal coke.
• Carbon dioxide emissions from waste combustion (18.8
Tg CO2 Eq. in 2003) increased by 7.9 Tg CO2 Eq. (72
percent) from 1990 through 2003, as the volume of
plastics and other fossil carbon-containing materials in
municipal solid waste grew.
• Net CO2 sequestration from land-use change and forestry
decreased by 214.0 Tg CO2 Eq. (21 percent) from 1990
through 2003. This decline was primarily attributable
to forest soils, a result of the slowed rate of forest area
increases after 1997.
Methane Emissions
According to the IPCC, CH4 is more than 20 times as
effective as CO2 at trapping heat in the atmosphere. Over the
last two hundred and fifty years, the concentration of CH4
in the atmosphere increased by 150 percent (IPCC 2001).
Experts believe that over half of this atmospheric increase
was due to emissions from anthropogenic sources, such as
landfills, natural gas and petroleum systems, agricultural
activities, 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:
Landfills are the largest anthropogenic source of CH4
emissions in the United States. In 2003, landfill CH4
emissions were 131.2 Tg CO2 Eq. (approximately 24
percent of total CH4 emissions), which represents a
decline of 41.1 Tg CO2 Eq., or 24 percent, since 1990.
• Methane emissions from coal mining declined by 28.1
Tg CO2 Eq. (34 percent) from 1990 to 2003, as a result
of the mining of less gassy coal from underground
mines and the increased use of methane collected from
degasification systems.
8 Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2003
-------
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. Since 1750, the atmospheric concentration of
N2O has risen by approximately 16 percent (IPCC 2001). The
main anthropogenic activities producing N2O in the United
States are agricultural soil management, fuel combustion in
motor vehicles, manure management, nitric acid production,
human sewage, and stationary fuel combustion (see Figure
ES-9).
Some significant trends in U.S. emissions of N2O
include the following:
• Agricultural soil management activities such as fertil-
izer application and other cropping practices were the
largest source of U.S. N2O emissions, accounting for
67 percent (253.5 Tg CO2 Eq.).
• In 2003, N2O emissions from mobile combustion were
42.1 Tg CO2 Eq. (approximately 11 percent of U.S. N2O
emissions). From 1990 to 2003, N2O emissions from
mobile combustion decreased by 4 percent.
HFC, RFC, and SF6 Emissions
HFCs and PFCs are families of synthetic chemicals
that are being used as alternatives to the ODSs, 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.
Other emissive sources of these gases include HCFC-22
production, electrical transmission and distribution systems,
semiconductor manufacturing, aluminum production, and
magnesium production and processing (see Figure ES-10).
Figure ES-9
2003 U.S. Sources of N20
Agricultural Soil Management
Mobile Sources
Manure Management
Human Sewage I
Nitric Acid ••
Stationary Sources I
Settlements Remaining Settlements H
Adipic Acid |
NZ0 Product Usage |
Waste Combustion <1.0
Agricultural Residue Burning
Forest Land Remaining Forest Land
10 20 30 40 50 60 70
Figure ES-10
2003 U.S. Sources of HFCs, PFCs, and SF6
Substitution of Ozone
Depleting Substances
Electrical Transmission
and Distribution
HCFC-22
Production
Semiconductor
Manufacture
Aluminum
Production
Magnesium Production
and Processing
1
n
HFCs, PFCs, and
SF6 as a Portion of
all Emissions
2.0%
20 40 60 80
Tg C02 Eq.
100
Some significant trends in U.S. HFC, PFC, and SF6
emissions include the following:
• Emissions resulting from the substitution of ozone
depleting substances (e.g., CFCs) have been increas-
ing from small amounts in 1990 to 99.5 Tg CO2 Eq. in
2003. Emissions from substitutes for ozone depleting
substances are both the largest and the fastest growing
source of HFC, PFC and SF6 emissions.
• The increase in ODS emissions is offset substantially
by decreases in emission of HFCs, PFCs, and SF6 from
other sources. Emissions from aluminum production
decreased by 79 percent (14.5 Tg CO2 Eq.) from 1990 to
2003, due to both industry emission reduction efforts and
Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2003 9
-------
lower domestic aluminum production. Emissions from
the production of HCFC-22 decreased by 65 percent
(22.6 Tg CO2 Eq.), due to a steady decline in the emis-
sion 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. Emissions from electric power transmission
and distribution systems decreased by 52 percent (15.1
Tg CO2 Eq.) from 1990 to 2003, primarily because of
higher purchase prices for SF6 and efforts by industry
to reduce emissions.
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), this Inventory of
U.S. Greenhouse Gas Emissions and Sinks is segregated into
six sector-specific chapters. Figure ES-11 and Table ES-4
aggregate emissions and sinks by these chapters.
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 2003. In 2003, approximately
86 percent of the energy consumed in the United States
was produced through the combustion of fossil fuels. The
remaining 14 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 (39 percent and 15 percent of
total U.S. emissions, respectively). Overall, emission sources
in the Energy chapter account for a combined 87 percent of
total U.S. greenhouse .gas emissions in 2003.
Figure ES-11
U.S. Greenhouse Emissions by Ghapter/IPCC Sector
7,000
6,000
5,000
4,000
3,000 -
2,000
1,000
0
It.DDOf-
Industrial Processes Agriculture
Waste
Energy
Land-Use Change and Forestry (sink)
§ 1
Table ES-4: Recent Trends in U.S. Greenhouse Gas Emissions and Sinks by Chapter/IPCC Sector (Tg C02 Eq.)
Chapter/IPCC Sector
Energy
Industrial Processes
Solvent and Other Product Use
Agriculture
Land-Use Change and Forestry
(Emissions)
Waste
Total
Land-Use Change and Forestry
(Sinks)
Net Emissions (Sources and Sinks)
1990
5,141.7
299.9
4.3
426.5
5.6
210.1
6,088.1
(1042.0)
5,046.1
1997
5,712.8
327.1
4.8
432.8
6.4
193.7
6,677.5
(930.0)
5,747.5
1998
5,737.7
334.9
4.8
449.8
6.5
186.0
6,719.7
(881.0)
5,838.8
1999
5,802.6
329.2
4.8
425.9
6.6
183.1
6,752.2
(826.1)
5,926.1
2000
5,985.3
332.1
4.8
444.1
6.3
180.6
6,953.2
(822.4)
6,130.8
2001
5,877.3
304.7
4.8
437.5
6.2
176.5
6,806.9
(826.9)
5,980.1
2002
5,920.7
315.4
4.8
432.4
6.4
178.3
6,858.1
(826.5)
6,031.6
2003
5,963.4
308.6
4.8
433.3
6.4
183.8
6,900.2
(828.0)
6,072.2
* Sinks are only included in net emissions total, and are based partially on projected activity data.
Note: Totals may not sum due to independent rounding. Parentheses indicate negative values (or sequestration).
10 Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2003
-------
Figure ES-12
2003 U.S. Energy Consumption by Energy Source
6.1% Renewable
8.0% Nuclear
22.5% Natural Gas
22.8% Coal
39.1% Petroleum
Industrial Processes
The Industrial Processes chapter contains by-product
or fugitive emissions of greenhouse gases from industrial
processes not directly related to energy activities such as
fossil fuel combustion. For example, industrial processes
can chemically transform raw materials, which often
release waste gases such as CO2, CH4, and N2O. The
processes include iron and steel production, cement
manufacture, ammonia manufacture and urea application,
lime manufacture, limestone and dolomite use (e.g., flux
stone, flue gas desulfurization, and glass manufacturing),
soda ash manufacture and use, titanium dioxide production,
phosphoric acid production, ferroalloy production, CO2
consumption, aluminum production, petrochemical
production, silicon carbide production, nitric acid production,
and adipic acid production. Additionally, emissions from
industrial processes release MFCs, PFCs and SF6. Overall,
emission sources in the Industrial Process chapter account
for 4.5 percent of U.S. greenhouse gas emissions in 2003.
Solvent and Other Product Use
The Solvent and Other Product Use chapter contains
greenhouse gas emissions that are produced as a by-product
of various solvent and other product uses. In the United
States, emissions from N2O Product Usage, the only source
of greenhouse gas emissions from this sector, accounted for
less than 0.1 percent of total U.S. anthropogenic greenhouse
gas emissions on a carbon equivalent basis in 2003.
Agriculture
The Agricultural chapter contains anthropogenic
emissions from agricultural activities (except fuel combustion,
which is addressed in the Energy 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.
Methane and N2O were the primary greenhouse gases
emitted by agricultural activities. Methane emissions from
enteric fermentation and manure management represented
about 21 percent and 7 percent of total CH4 emissions from
anthropogenic activities, respectively in 2003. Agricultural
soil management activities such as fertilizer application
and other cropping practices were the largest source of U.S.
N2O emissions in 2003, accounting for 67 percent. In 2003,
emission sources accounted for in the Agricultural chapters
were responsible for 6.3 percent of total U.S. greenhouse
gas emissions.
Land-Use Change and Forestry
The Land-Use Change and Forestry chapter contains
emissions and removals of CO7 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 have resulted in a net uptake (sequestration) of
carbon in the United States. Forests (including vegetation,
soils, and harvested wood) accounted for approximately 91
percent of total 2003 sequestration, urban trees accounted for
7 percent, agricultural soils (including mineral and organic
soils and the application of lime) accounted for 1 percent,
and landfilled yard trimmings and food scraps accounted for
1 percent of the total sequestration in 2003. 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 soils account for a net carbon sink that is
approximately one and a third times larger than the sum of
Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2003 11
-------
Table ES-5: Net C02 Flux from Land-Use Change and Forestry (Tg C02 Eq.)
Sink Category
Forest Land Remaining Forest Land
Changes in Forest Carbon Stocks
Cropland Remaining Cropland
Changes in Agricultural Soil Carbon Stocks
Settlements Remaining Settlements
Urban Trees
Landfilled Yard Trimmings and Food Scraps
Total
1990
(949.3)
(949.3)
(8.1)
(8.1)
(84.7)
(58.7)
(26.0)
(1,042.0)
1997
(851.0)
(851.0)
(7.4)
(7.4)
(71.6)
(58.7)
(12.9)
(930.0)
1998
(805.5)
(805.5)
(4.3)
(4.3)
(71.2)
(58.7)
(12.5)
(881.0)
1999
(751.7)
(751.7)
(4.3)
(4.3)
(70.0)
(58.7)
(11.4)
(826.1)
2000
(747.9)
(747.9)
(5.7)
(5.7)
(68.9)
(58.7)
(10.2)
(822.4)
2001
(750.9)
(750.9)
(7.1)
(7.1)
(68.9)
(58.7)
(10.3)
(826.9)
2002
(751.5)
(751.5)
(6.2)
(6.2)
(68.8)
(58.7)
(10.2)
(826.5)
2003
(752.7)
(752.7)
(6.6)
(6.6)
(68.7)
(58.7)
(10.1)
(828.0)
Note: Totals may not sum due to independent rounding. Parentheses indicate net sequestration.
emissions from organic soils and liming. The mineral soil
carbon sequestration is largely due to 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
2003 resulted in a net carbon sequestration of 828.0 Tg CO2
Eq. (Table ES-5). This represents an offset of approximately
14 percent of total U.S. CO2 emissions, or 12 percent of
total gross greenhouse gas emissions in 2003. Total land
use, land-use change, and forestry net carbon sequestration
declined by approximately 21 percent between 1990 and
2003. This decline was primarily due to a decline in the rate
of net carbon accumulation in forest carbon stocks. Annual
carbon accumulation in landfilled yard trimmings and food
scraps also slowed over this period, as did annual carbon
accumulation in agricultural soils. As described above, the
constant rate of carbon accumulation in urban trees is a
reflection of limited underlying data (i.e., this rate represents
an average for 1990 through 1999).
Land use, land-use change, and forestry activities in
2003 also resulted in emissions of N2O (6.4 Tg CO2 Eq.).
Total N9O emissions from the application of fertilizers
to forests and settlements increased by approximately 14
percent between 1990 and 2003.
Waste
The Waste chapter contains emissions from waste
management activities (except waste incineration, which is
addressed in the Energy chapter). Landfills were the largest
source of anthropogenic CH4 emissions, accounting for 24
percent of total U.S. CH4 emissions.1' Wastewater treatment
systems are a potentially significant source of N2O emissions;
however, methodologies are not currently available to
develop a complete estimate. Nitrous oxide emissions from
the treatment of the human sewage component of wastewater
were estimated, however, using a simplified methodology.
Overall, in 2003, emission sources accounted for in the Waste
chapter generated 2.7 percent of total U.S. greenhouse gas
emissions.
ES.4. Other Information
Emissions by Economic Sector
Throughout this report, emission estimates are grouped
into six sectors (i.e., chapters) defined by the IPCC: Energy,
Industrial Processes, Solvent Use, Agriculture, 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
1' Landfills also store carbon, due to incomplete degradation of organic materials such as wood products and yard trimmings, as described in the Land-
Use Change and Forestry chapter.
12 Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2003
-------
emissions by the following economic sectors: Residential,
Commercial, Industry, Transportation, Electricity Generation,
and Agriculture, and U.S. Territories. Table ES-6 summarizes
emissions from each of these sectors, and Figure ES-13
shows the trend in emissions by sector from 1990 to 2003.
Using this categorization, emissions from electricity
generation accounted for the largest portion (33 percent)
of U.S. greenhouse gas emissions in 2003. Transportation
activities, in aggregate, accounted for the second largest
portion (27 percent). Emissions from industry accounted
for 19 percent of U.S. greenhouse gas emissions in 2003. In
contrast to electricity generation and transportation, emissions
from industry have declined over the past decade, as structural
Figure ES-13
Emissions Allocated to Economic Sectors
2500
2000
1500
1000
Electricity Generation
Transportation
Industry
griculture
Residential
ST-CM
oiot
OT-
oo
changes have occurred in the U.S. economy (i.e., shifts from
a manufacturing based to a service-based economy), fuel
switching has occurred, and efficiency improvements have
been made. The remaining 21 percent of U.S. greenhouse gas
emissions were contributed by the residential, agriculture,
and commercial economic sectors, plus emissions from
U.S. Territories. Residences accounted for about 6 percent,
and primarily consisted of CO2 emissions from fossil fuel
combustion. Activities related to agriculture accounted for
roughly 7 percent of U.S. emissions; these emissions were
dominated by N2O emissions from agricultural soils instead
of CO2 from fossil fuel combustion. The commercial sector
accounted for about 7 percent of emissions, while U.S.
territories accounted for 1 percent.
Carbon dioxide was also emitted and sequestered by a
variety of activities related to forest management practices,
tree planting in urban areas, the management of agricultural
soils, and landfilling of yard trimmings.
Electricity is ultimately consumed in the economic
sectors described above. Table ES-7 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
Table ES-6: U.S. Greenhouse Gas Emissions Allocated to Economic Sectors (Tg C02 Eq.)
Economic Sector
Electric Power Industry
Transportation
Industry
Agriculture
Commercial
Residential
U.S. Territories
Total
Land-Use Change and Forestry Sinks
Net Emissions (Sources and Sinks)
1
1
1
6
0-
1990
,841.8
,506.8
,446.1
473.3
435.4
350.9
33.8
,088.1
042.0)
5,046.1
1997
2,104.6
1,693.0
1,509.1
492.0
445.2
391.0
42.7
6,677.5
(930.0)
5,747.5
1998
2,186.8
1,728.7
1,470.6
508.4
424.2
358.4
42.7
6,719.7
(881.0)
5,838.8
1999
2,197.3
1,790.0
1,427.9
486.9
426.8
379.5
43.9
6,752.2
(826.1)
5,926.1
2000
2,299.0
1,839.6
1,431.8
495.3
440.7
399.7
47.0
6,953.2
(822.4)
6,130.8
2001
2,254.9
1,819.8
1,371.0
488.6
431.4
387.1
54.1
6,806.9
(826.9)
5,980.1
2002
2,269.7
1,851.6
1,365.7
485.6
440.2
391.6
53.6
6,858.1
(826.5)
6,031.6
2003
2,296.2
1,864.4
1,331.4
486.4
453.5
406.1
62.3
6,900.2
(828.0)
6,072.2
Note: Totals may not sum due to independent rounding. Emissions include C02, CH4, HFCs, PFCs, and SFB.
Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2003 13
-------
Table ES-7: U.S. Greenhouse Gas Emissions by Economic Sector with Electricity-Related Emissions Distributed (Tg C02 Eq.)
Economic Sector
Industry
Transportation
Commercial
Residential
Agriculture
U.S. Territories
Total
Land-Use Change and Forestry Sinks
Net Emissions (Sources and Sinks)
2,075.7
1,509.9
981.6
953.0
534.1
33.8
6,088.1
(1,042.
5,046.1
1997
2,247.3
1,696.1
1,083.8
1,060.3
547.4
42.7
6,677.5
(930.0)
5,747.5
1998
2,223.2
1,731.8
1,093.5
1,060.0
568.6
42.7
6,719.7
(881.0)
5,838.8
1999
2,190.1
1,793.2
1,104.9
1,082.9
537.3
43.9
6,752.2
(826.1)
5,926.1
2000
2,207.7
1,843.0
1,161.8
1,141.4
552.3
47.0
6,953.2
(822.4)
6,130.8
2001
2,074.0
1,823.2
1,170.6
1,129.6
555.5
54.1
6,806.9
(826.9)
5,980.1
2002
2,062.9
1,854.8
1,178.5
1,159.5
548.8
53.6
6,858.1
(826.5)
6,031.6
2003
2,040.1
1,867.6
1,196.8
1,183.7
549.8
62.3
6,900.2
(828.0)
6,072.2
according to retail sales of electricity.12 These source
categories include CO2 from fossil fuel combustion and the
use of limestone and dolomite for flue gas desulfurization,
CO2 and N2O from waste combustion, CH4 and N2O from
stationary sources, and SF6 from electrical transmission and
distribution systems.
When emissions from electricity are distributed among
these sectors, industry accounts for the largest share of U.S.
greenhouse gas emissions (30 percent) in 2003. Emissions
from the residential and commercial sectors also increase
substantially due to their relatively large share of electricity
consumption (e.g., lighting, appliances, etc.). Transportation
activities remain the second largest contributor to emissions.
In all sectors except agriculture, CO2 accounts for more than
75 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 2003.
Ambient Air Pollutant Emissions
In the United States, CO, NOX, NMVOCs, SO2 are
referred to as "ambient air pollutants," and are regulated
under the Clean Air Act in an effort to protect human
health and the environment. These pollutants 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 pollutants 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
ambient air pollutants (EPA 2004).13 Table ES-9 shows that
fuel combustion accounts for the majority of emissions of
these 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.
Figure ES-14
Emissions with Electricity Distributed
to Economic Sectors
2500-
zooo-
ri- 1500-
1000-
500-
(H
Industrial
Transportation
, Commercial
Residential
Agriculture
r~ co o> o T— cvi CO
SOI 0> O O O O
o> o> o o o o
Note: Docs 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.
NOX and CO emission estimates from field burning of agricultural residues were estimated separately, and therefore not taken from EPA (2004).
14 Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2003
-------
Box ES-1: 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 overtime. 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 2003; 4) emissions per unit of total gross domestic product as a measure of national economic activity; or 5) emissions
per capita.
Table ES-8 provides data on various statistics related to U.S. greenhouse gas emissions normalized to 1990 as a baseline year. Green-
house gas emissions in the United States have grown at an average annual rate of 1.0 percent since 1990. This rate is slower than that for total
energy or fossil fuel consumption and much slower than that for either electricity consumption or overall gross domestic product. Total U.S.
greenhouse gas emissions have also grown more slowly than national population since 1990 (see Figure ES-15). Overall, global atmospheric
C02 concentrations—a function of many complex anthropogenic and natural processes—are increasing at 0.5 percent per year.
Table ES-8: Recent Trends in Various U.S. Data (Index 1990 = 100) and Global Atmospheric C02 Concentration
Variable
Greenhouse Gas Emissions3
Energy Consumption"
Fossil Fuel Consumption11
Electricity Consumption11
GDPC
Population11
Atmospheric C02 Concentration6
1991 1
99
100
99
102 :
100
101 1
100 1
1997
110
112
112
117
122
109
103
1998
110
113
113
121
127
110
104
1999
111
114
114
124
133
112
104
2000
114
117
117
128
138
113
104
2001
112
114
115
125
139
114
105
2002
113
116
116
129
142
115
105
2003
113
116
116
130
146
116
106
Growth Rate'
1.0%
1.2%
1.2%
2.1%
3.0%
1.1%
0.5%
a GWP weighted values
b Energy content weighted values (EIA 2004)
c Gross Domestic Product in chained 2000 dollars (BEA 2004)
" (U.S. Census Bureau 2004)
e Mauna Loa Observatory, Hawaii (Keeling and Wnorf 2004)
' Average annual growth rate
Figure ES-15
U.S. Greenhouse Gas Emissions Per Capita and Per
Dollar of Gross Domestic Product
50
40
30-
20-
10
00
90
80
70-
60-
Real GDP
Population
Emissions per capita
Emissions per $GDP
O T— CVIC*?^mcD
o>a>a>o)a)a>a>
Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2003 15
-------
Table ES-9: Emissions of NOX, CO, NMVOCs, and S02 (Gg)
Gas/Activity
1990
1997 1998 1999 2000 2001 2002 2003
NO,
Stationary Fossil Fuel Combustion
Mobile Fossil Fuel Combustion
Oil and Gas Activities
Waste Combustion
Industrial Processes
Solvent Use
Agricultural Burning
Waste
CO
Stationary Fossil Fuel Combustion
Mobile Fossil Fuel Combustion
Oil and Gas Activities
Waste Combustion
Industrial Processes
Solvent Use
Agricultural Burning
Waste
NMVOCs
Stationary Fossil Fuel Combustion
Mobile Fossil Fuel Combustion
Oil and Gas Activities
Waste Combustion
Industrial Processes
Solvent Use
Agricultural Burning
Waste
S02
Stationary Fossil Fuel Combustion
Mobile Fossil Fuel Combustion
Oil and Gas Activities
Waste Combustion
Industrial Processes
Solvent Use
Agricultural Burning
Waste
22,860
9,884
12,134
139
82
591
1
28
0
130,580
4,999
119,482
302
978
4,124
4
689
1
20,937
912
10,933
555
222
2,426
5,217
NA
673
20,936
18,407
793
390
39
1,306
0
NA
0
22,284
9,578
11,768
130
140
629
3
34
3
101,138
3,927
90,284
333
2,668
3,153
1
767
5
16,994
1,016
7,928
442
313
2,038
5,100
NA
157
17,091
15,104
659
312
29
985
1
NA
1
21,964
9,419
11,592
130
145
637
3
35
3
98,984
3,927
87,940
332
2,826
3,163
1
789
5
16,403
1,016
7,742
440
326
2,047
4,671
NA
161
17,189
15,191
665
310
30
991
1
NA
1
20,530
8,344
11,300
109
143
595
3
34
3
94,361
5,024
83.484
145
2,725
2,156
46
767
13
15,869
1,045
7,586
414
302
1,813
4,569
NA
140
15,917
13,915
704
283
30
984
1
NA
1
20,288
8,002
11,395
111
114
626
3
35
2
92,895
4,340
83,680
146
1,670
2,217
46
790
8
15,228
1,077
7,230
389
257
1,773
4,384
NA
119
14,829
12,848
632
286
29
1,031
1
NA
1
19,414
7,667
10,823
113
114
656
3
35
2
89,329
4,377
79,972
147
1,672
2,339
45
770
8
15,048
1,080
6,872
400
258
1,769
4,547
NA
122
14,452
12,461
624
289
30
1,047
1
NA
1
18,850
7,523
10,389
135
134
630
5
33
2
87,451
4,020
78,574
116
1,672
2,308
46
707
8
14,222
926
6,560
340
281
1,725
4,256
NA
133
13,928
11,946
631
315
24
1,009
2
NA
1
18,573
7,222
10,418
124
121
648
4
33
2
85,077
4,454
75,526
125
1,674
2,431
65
794
8
13,939
1.007
6,351
345
263
1,711
4,138
NA
125
14,463
12,477
634
293
28
1,029
2
NA
1
Source: (EPA 2004) except for estimates from field burning of agricultural residues.
+ Does not exceed 0.5 Gg
NA (Not Available)
Note: Totals may not sum due to independent rounding.
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
16 Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2003
-------
Figure ES-16
2003 Key Sources- Tier 1 Level Assessment
C02-Stalionary Combustion-Coal
C0?-Mobile Combustion: Road & Other
C02-Stationary Combustion-Gas
(^•Stationary Combustion-Oil
C02-Mobile Combustion: Aviation _
Direct N20 Emissions from Agricultural Soils •
CHj-Solid Waste Disposal Sites g
CH^-Fugitive Emissions from Natural Gas Operations 9
C02 Non-Energy Dse of Fuel •
CH4-Enteric Fermentation in Domestic Livestock ™
Various-Substitutes for Ozone Depleting Substances ?
Indirect N20 Emissions from Nitrogen Used in Agriculture -
C02-lron and Steel Production |
COj-Cement Production |
N,0-Mobile Combustion: Road & Other 1
500 1,000 1,500
Tg C02 Eq.
2,000
Note: For a complete discussion of the key source analysis see Annex 1.
estimates, such as those for CO2 emissions from energy-
related activities and cement processing, are considered
to have low uncertainties. For some other categories
of emissions, however, a lack of data or an incomplete
understanding of how emissions are generated increases
the uncertainty associated with the estimates presented.
Acquiring a better understanding of the uncertainty
associated with inventory estimates is an important step
in helping to prioritize future work and improve the
overall quality of the inventory. Recognizing the benefit of
conducting an uncertainty analysis, the UNFCCC reporting
guidelines follow the recommendations of the IPCC Good
Practice Guidance and Uncertainty Management in National
Greenhouse Gas Inventories and require that countries
provide single point estimates of uncertainty for many 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.
Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2003 17
-------
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18 Executive Summary of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2003
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United States
Environmental Protection
Agency
United States
Environmental Protection Agency
EPA 430^845401
April 2005
Office of Atmospheric Programs (62Q4J)
Washington, DC 20460
Official Business
Penatty far Private Use
------- |