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Emissions of Greenhouse Gases Report
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Methane Emissions
Total Emissions | Energy Use | Agriculture | Waste Management | Industrial Processes |
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Total Emissions |
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The major sources of U.S. methane emissions are energy production, distribution,
and use; agriculture; and waste management (Figure 15 on right). |
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U.S. methane emissions in 2008 totaled 737.4 MMTCO2e, 2.0 percent higher
than the 2007 total of 722.7 MMTCO2e (Table 16 below). |
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Methane emissions declined steadily from 1990 to 2001, as emissions from
coal mining and landfills fell. |
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From 2002 to 2008, methane emissions rose as a result of moderate increases
in emissions related to energy, agriculture, and waste management that
more than offset a decline in industrial emissions of methane over the
same period. |
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The energy sectorincluding coal mining, natural gas systems, petroleum
systems, and stationary and mobile combustionis the largest source of
U.S. methane emissions, accounting for 295.7 MMTCO2e in 2008. |
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Agricultural emissions (primarily from livestock management) and emissions
from waste management (primarily landfills) also are large sources of U.S.
methane emissions, contributing 225.0 and 212.1 MMTCO2e, respectively,
in 2008. |
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figure data
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Energy Use |
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Natural gas systems and coal mines are the major sources of methane emissions
in the energy sector (Figure 16 on right and Table 17 below).
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U.S. methane emissions from natural gas systems grew from 1990 to 2008,
largely because of increases in natural gas consumption. |
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Emissions from coal mines declined from 1990 to 2002 and remained nearly
steady through 2007. In 2008, emissions from ventilation of underground
mines jumped by 24.6 percent, leading to a 15.3-percent increase in total
mining emissions over their 2007 level. Much of the 2008 increase can be
attributed to the larger number of gassy mines in operation throughout
the year and to the fact that, as mining proceeds into deeper seams, more
methane emissions tend to be produced per ton of coal mined. |
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With domestic oil production dropping by 30 percent from 1990 to 2008,
methane emissions from petroleum systems also declined. |
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Residential wood consumption accounted for nearly 45 percent of U.S. methane
emissions from stationary combustion in 2008. |
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Methane emissions from passenger cars fell by 51.3 percent from 1990 to
2008, as the use of catalytic converters increased. A 9.2-percent drop
in annual miles traveled by passenger cars from 2002 to 2008 also contributed
to the decrease in emissions.
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Agriculture |
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Livestock managementincluding emissions from enteric fermentation (66
percent) and management of animal wastes (29 percent)accounts for most
of the U.S. methane emissions from agricultural activities (Table 18 below). |
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Since 1990, there has been a shift in livestock management to larger facilities
that manage waste in liquid systems, increasing the amount of methane generated
from livestock waste. Increases in the U.S. swine population since 1990
have also contributed to the rise in methane emissions. Emissions of methane
from animal waste rose by 2.0 percent from 2007 to 2008. Swine accounted
for 45.9 percent (29.7 MMTCO2e) and dairy cattle 36.2 percent (23.3 MMTCO2e)
of the 2008 total. |
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Enteric fermentation (food digestion) in ruminant animals also produces
methane emissions, and digestion by cattle accounts for 95 percent of U.S.
methane emissions from this source. With little change in the cattle population
since 1990, the level of emissions from enteric fermentation has been relatively
stable. Small declines in cattle and goat populations in 2008 were offset
by increases in horse, goat and swine poulations, which caused methane
emissions from enteric fermentation to increase slightly (by 0.5 MMTCO2e,
or 0.3 percent) from their 2007 level. |
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Despite lower crop yields, U.S. rice production rose by 7 percent in 2008
as a result of increases in area harvested in Missouri, Texas, Arkansas,
Louisiana, and Mississippi. Consequently, emissions from this source increased
by 7.1 percent from 2007 to 2008. |
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Although emissions from crop residue burning grew by 2.0 percent in 2008,
residue burning remains the smallest contributor to methane emissions from
agriculture, representing less than 1 percent of total U.S. methane emissions
from agriculture (Figure 17 on right). |
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Waste Management |
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Methane emissions from waste management are dominated by the decomposition
of solid waste in municipal and industrial landfills (Table 19 below). |
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Emissions from landfills declined substantially from 1990 to 2001 as a
result of increases in recycling and in the recovery of landfill methane
for energy; since 2001, increases in the total amount of waste deposited
in landfills have resulted in increasing methane emissions (Figure 18 on right). |
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Rapid growth in methane recovery during the 1990s can be traced in part
to the Federal Section 29 tax credit for alternative energy sources, which
provided a subsidy of approximately 1 cent per kilowatthour for electricity
generated from landfill gas before June 1998. |
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The U.S. EPAs New Source Performance Standards and Emission Guidelines,
which require large landfills to collect and burn landfill gas, have also
played an important role in the growth of methane recovery. |
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The American Recovery and Reinvestment Act of 2009, signed into law on
February 17, 2009, included a 2-year extension (through December 31, 2012)
of the production tax credit (PTC) for renewable energy, including waste-to-energy
and landfill gas combustion. |
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Wastewater treatment, including both domestic wastewater (two-thirds) and
industrial wastewater (one-third), is responsible for 13.1 percent (27.8
MMTCO2e) of methane emissions from waste management. |
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Emissions from the treatment of wastewater from ethanol production and
from petroleum refineries are included for the first time in the 2008 inventory,
increasing the estimates of methane emissions from industrial wastewater
in previous years by 8.0 to 11.4 percent. In 2008, emissions from wastewater
at petroleum refineries accounted for 7.3 percent (0.7 MMTCO2e) of total
emissions from industrial wastewater, and emissions from ethanol production
accounted for 2.9 percent (0.3 MMTCO2e). |
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figure data
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Industrial Processes |
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Methane emissions are generated by industrial processes in the production
of iron and steel and in chemical production (Figure 19 on right and Table 20 below). |
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Methane emissions from industrial processes declined by a net 0.6 MMTCO2e
(10.7 percent) from 2007 to 2008, as a result of declines in both chemical
production and iron and steel production. |
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Since 1990, methane emissions from industrial processes have increased
by 0.1 MMTCO2e (2.4 percent). A 32.4-percent decline (0.4 MMTCO2e) in emissions
from iron and steel production since 1990 has been offset by an increase
of 0.5 MMTCO2e (13.9 percent) in emissions from chemical production. |
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Estimates of industrial emissions of methane in the 2008 inventory are
approximately 50 to 65 percent higher for all years, as a result of applying
the IPCCs revised emissions factors for methane from ethylene, ethylene
dichloride, and methanol production in the chemical industry and for methane
from sinter and coke in iron and steel production. |
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