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U.S. Greenhouse
Gas Emissions
Of U.S.
greenhouse gas emissions, 87% are related to energy consumption. Since
1990, greenhouse gas emissions in the United States have grown by about 1%
per year. In 2005, about 21% of the world’s total energy-related carbon
dioxide was emitted by the United States.
What
Specific Kinds of Greenhouse Gases Does the United States Emit?
Seven
kinds of greenhouse gases are emitted by the United States.
- Carbon
dioxide (CO2)
- Methane
(CH4)
- Nitrous
oxide (N2O)
- High-GWP
gases, which are:
- Hydrofluorocarbons
(HFCs)
- Perfluorocarbons
(PFCs)
- Sulfur
hexafluoride (SF6)
- Water
vapor
(H2O)
Electricity
generation and transportation are the biggest sources of energy-related
greenhouse gases.
Petroleum
is the fossil fuel that accounts for the most carbon dioxide emissions
How
Much of Total U.S. Greenhouse Gas Emissions Are Energy Related?
Of
the total amount of greenhouse gases emitted in 2006, about 5.9 billion
metric tons were carbon dioxide from energy consumption (the burning of
fossil fuels). Another 0.3 billion metric tons CO2e came from
energy-related greenhouse gases other than carbon dioxide for a total of
6.2 out of 7.1 billion metric tons CO2e or about 87%.
Which
Fuel Accounts for the Largest Share of Energy-Related Carbon Dioxide
Emissions?
Petroleum
is the largest fuel source of carbon dioxide emissions from energy
consumption in the United States. Petroleum carbon dioxide emissions were
2.6 billion metric tons, or 44% of the total, in 2006.
Other
important fossil fuel sources of carbon dioxide emissions include:
- Coal–accounting
for 2.1 billion metric tons (36%) in 2006
- Natural
gas–accounting for 1.2 billion metric tons (20%) in 2006
What
Are the Important Non-Carbon Dioxide (Non-CO2)
Greenhouse Gases Related to the Production and Consumption of Energy?
Of
the non-CO2
gases that contribute to energy-related greenhouse gas emissions, methane
contributes most of the 0.3 billion metric tons CO2e—mainly
from emissions that leak out of natural gas pipelines, coal mines, and
petroleum exploration and production facilities.
How
Are Energy-Related Greenhouse Gas Emissions Distributed Throughout Our
Economy and What Sector of Our Economy Is Responsible for the Most
Emissions?
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Electric
power generation and transportation are the biggest sources of
energy-related greenhouse gas emissions in our nation, with respective
shares of 39.8% and 33.7% of our total energy-related emissions in
2006. Taken together, emissions in power generation and transportation
increased at an average annual rate of 1.5% between 1990 and 2006. The
rest of our emissions result from direct use of fossil fuels in homes,
commercial buildings, and industry. These emissions are virtually
unchanged since 1990.
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Since
electric power is ultimately used in homes, commercial buildings, and
industry, emissions associated with power generation can be allocated
to each end-use sector based on their electricity consumption to
obtain another perspective. Using this approach, the transportation
sector is currently the largest emitter. Our cars, trucks, planes,
trains, ships, and barges produced 2.0 billion metric tons CO2e
(1.9 billion metric tons of carbon dioxide plus 0.1 billion metric
tons CO2e
in other gases) in 2006. Emissions from this sector have grown at an
average rate of 1.4% since 1990.
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The
industrial sector—which consists of activities such as
manufacturing, construction, mining, and agriculture—emits almost as
much as the transportation sector—a total of 1.9 billion metric tons
of energy-related CO2e
(1.7 billion metric tons of carbon dioxide plus 0.2 billion metric
tons CO2e
in other gases). Its emissions have been largely stable since 1990 due
primarily to the loss of energy-intensive industries such as steel.
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The
commercial sector—which includes such sources as schools, office
buildings, and shopping malls—emits a total of 1.0 billion metric
tons CO2e
of energy-related carbon dioxide, with almost 80% of it coming from
the power plants providing the electricity used in the buildings. Its
emissions have grown the fastest since 1990, at an average annual rate
of 1.8%.
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The
residential sector—the homes we live in—emits 1.2 billion metric
tons of CO2e,
almost all of which is energy-related carbon dioxide, over 70% of
which is produced at power plants providing homes electricity.
Residential sector emissions have grown at an average annual rate of
1.4% since 1990.
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Total
Emissions
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| Total
U.S. greenhouse gas emissions in 2006 were 1.5 percent below the
2005 total—the first annual drop since 2001 and only the third
since 1990. |
| The
total emissions reduction, from 7,181.4 million metric tons carbon
dioxide equivalent (MMTCO2e) in 2005 to 7,075.6 MMTCO2e in 2006,
was largely a result of reductions in carbon dioxide (CO2)
emissions. There were smaller reductions in emissions of methane
(CH4) and man-made gases with high global warming potentials
(high-GWP gases) (Table 1 below). |
| U.S.
carbon dioxide emissions in 2006 were 110.6 million metric tons (MMT)
below their 2005 level of 6,045.0 MMT, due to favorable weather
conditions; higher energy prices; a decline in the carbon
intensity of electric power generation that resulted from
increased use of natural gas, the least carbon-intensive fossil
fuel; and greater reliance on non-fossil energy sources. |
| Methane
emissions totaled 605.1 MMTCO2e in 2006 (Figure 1 on right), down
by 2.3 MMTCO2e from 2005, with decreases in emissions from energy
sources, agriculture, and industrial processes. |
| U.S.
emissions of high-GWP gases, which totaled 157.6 MMTCO2e in 2006,
were 3.6 MMTCO2e below the 2005 total, as the result of a drop in
hydrofluorocarbon (HFC) emissions. |
| Emissions
of nitrous oxide (N2O), unlike the other greenhouse gases,
increased by 10.6 MMTCO2e from 2005 to a 2006 total of 378.6
MMTCO2e. The increase is attributed primarily to an increase of
9.9 MMTCO2e in emissions from agricultural sources. |
| In
2005, the latest year for which data are available, U.S. land use,
land-use change, and forestry activities resulted in total carbon
sequestration of 828.5 MMTCO2e, equal to 11.5 percent of U.S.
greenhouse gas emissions in 2005. |
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U.S. Carbon
Dioxide Emissions
| Total
Emissions |
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The important
factors that contributed to a drop in carbon dioxide emissions in
2006 included: total energy consumption in 2006 that was 0.5
percent below the 2005 total—due in part to favorable weather
conditions (both heating and cooling degree-days were below 2005
levels) and in part to higher energy prices that helped to dampen
energy demand.
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A
decline in the carbon intensity of electric power generation that
resulted from increased use of natural gas, the least
carbon-intensive fossil fuel, and greater reliance on non-fossil
energy sources also contributed to the decrease.
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Relatively
small increases in emissions from other sources of carbon dioxide,
such as industrial processes, and from the U.S. Territories, which
in total represent only a minor share of U.S. emissions, were not
enough to offset the declines from major energy sources.
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Energy-related
carbon dioxide, including emissions resulting from nonfuel uses of
energy fuels (primarily petroleum) and adjustments for U.S.
Territories and international bunker fuels, account for 98 percent
of carbon dioxide emissions
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Emissions
from other sources, such as industrial processes, account for 2
percent of carbon dioxide emissions.
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Credit:EIA
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