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Updated September 2, 2021
Greenhouse Gas Emissions and Sinks in U.S. Agriculture
Agriculture and land-use activities continue to play a
reports GHG estimates by sector, source, and GHG type.
central role in the broader debate about energy and climate
The Inventory presents GHG estimates as CO2-equivalents,
policy options in the United States and abroad. Such
aggregated to millions of metric tons (MMTCO2-Eq.). CO2-
activities offer opportunities to remove greenhouse gases
equivalents convert an amount of a GHG, such as N2O, to
(GHGs) from the atmosphere, potentially reducing the
the amount of CO2 that could have a similar impact on
nation’s net emissions: the metric of emissions targets for
global temperature over a specific duration (100 years in
the Paris Agreement (PA), the binding international climate
the Inventory). This common measurement can help
change treaty. Pursuant to the PA, the Biden Administration
compare the magnitudes of various GHG sources and sinks.
released a Nationally Determined Contribution (NDC) in
The Inventory presents GHG estimates for two types of
2021 specifying a new U.S. target of reducing net GHG
sector classifications. One classification follows
emissions by 50%-52% below 2005 levels by 2030. Most
international standards. Every country preparing its national
federal legislative proposals to reduce U.S. GHG emissions
inventory considers the same GHG sources and sinks for
would not require reductions in agriculture, but some would
the same standard sectors. These include an agriculture
incentivize voluntary actions to do so. For example, the
sector and a land-use, land-use change and forestry
Growing Climate Solutions Act (S. 1251/H.R. 2820, 117th)
(LULUCF) sector. The Inventory also reports estimates for
would support the creation and use of agriculture and
several EPA-defined economic sectors, including
forestry offset credits in carbon markets by establishing
agriculture, transportation, electricity, industry,
qualifications for technical assistance providers and third-
commercial, and residential. Under this format, the
party verifiers and by developing a list of U.S. Department
agriculture sector includes emissions from fuel-combustion
of Agriculture (USDA)-backed offset protocols.
by farm equipment (e.g., tractors) as well as the emission
Agriculture is both a source and a sink of GHGs (Figure 1).
sources already accounted for in the international standard
Sources generate GHG emissions that are released into the
sector for agriculture.
atmosphere and contribute to global climate change. Sinks
remove carbon dioxide (CO
Agricultural GHG Emissions
2) from the atmos phere and
store carbon through physical or biological processes.
EPA reports that agriculture sector emissions totaled 669.5
Agricultural emissions include many GHGs of interest to
MMTCO2-Eq. in 2019 (Table 1), equal to 10.2% of total
policymakers: CO2, methane (CH4), and nitrous oxide
U.S. GHG emissions (Figure 2). This estimate is based on
(N2O). Agricultural sinks remove CO2 through
certain assumptions and includes direct emissions from
photosynthesis and store carbon in plants and soil. Despite
agricultural activities (see text below for major emissions
these sinks, U.S. agriculture is a net GHG source. This In
sources in agriculture). It does not include
Focus discusses emissions from the agriculture sector, as
Potentially offsetting agricultural sinks.
defined by the Environmental Protection Agency (EPA),
and the most recent data available (from 2019).
Forestry activities, which are accounted for in LULUCF.
U.S. GHG Inventory
Emissions from generating the electricity that farms use.
Since the 1990s, EPA has prepared an annual Inventory of
Emissions from activities in the food system more
U.S. GHG Emissions and Sinks. USDA and other federal
broadly, such as production of agricultural inputs and
agencies contribute data and analyses. The Inventory
post-harvest transportation and processing of foods.
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Greenhouse Gas Emissions and Sinks in U.S. Agriculture
Figure 1. Greenhouse Gas Emission Sources and Sinks from Agricultural Activities
Source: CRS. Note: Enteric fermentation refers to digestive processes in ruminant animals, which result in GHG emissions.
Figure 2. U.S. GHG Emissions, by Economic Sector
stored and treated in systems that promote anaerobic
decomposition (e.g., lagoons, ponds, tanks, pits).
U.S. agriculture sector emissions were higher in 2019
compared with 1990, 2000, and 2010 (Table 1).
Table 1. U.S. Agriculture and Related Source Emissions
Emissions by Gas (Activity)
1990
2000
2010
2019
Total, Ag. Econ. Sector
600.2 598.1 644.5 669.5
N2O (soil and manure mgmt.)
330.1 311.0
341.7 364.4
CH4 (enteric ferment., manure 218.2 238.3
246.1 256.4
mgmt., rice cultivation)
CO2 (urea fertilization, liming)
7.1
7.5
8.6
7.8
CO2, CH4, and N2O (fuel use)
44.8
41.2
48.2
40.8
Total Ag. w/Electricity-
635.2 640.0 685.1 704.6
Related
CO2, N2O, SF6 (electric.-rel.)
35.1
41.9
40.6
35.2
Tot. Emissions, All Sectors 6,442.7 7,313.6 6,991.1 6,558.3
Source: CRS from EPA Inventory (emissions in MMTCO2-Eq.).
Agricultural GHG Sinks
On agricultural lands, carbon can enter the soil through
plant roots, litter, cover crops, harvest residues, and animal
manure. This carbon can be stored, primarily as soil organic
Source: CRS from EPA Inventory, 2019 data.
matter (Figure 1). Other carbon sinks derive from a range
Notes: Emissions are presented in parentheses in MMTCO2-Eq.
of land-use and land-management activities, such as
maintaining fores ted land, which primarily stores carbon in
In 2019, three activity types accounted for 90.4% of U.S.
above-ground biomass (e.g., trees). The Inventory accounts
agriculture sector emissions:
for U.S. GHG sinks in the LULUCF sector. LULUCF net
1. Soil management (51.5%, 344.6 MMTCO2-Eq.). N2O
sinks account for both emissions and sinks from land use
emissions from soils, associated with agricultural
and land-use change. Federal agencies—including USDA
practices that disturb soils and increase oxidation,
and the Departments of Energy, Transportation, and
releasing emissions into the atmosphere. Associated
Defense—contribute LULUCF data to the Inventory.
with fertilization, irrigation, drainage, cultivation and
EPA reports a LULUCF net sink of 789.2 MMTCO
tillage, shifts in land use, and application and/or
2-Eq.
for 2019. The magnitude of this net sink is equivalent to
deposition of livestock manure and other organic
about 12% of all U.S. GHG emissions. Most LULUCF
materials on cropland and other farmland soils.
sinks are associated with maintaining existing forested land
2. Enteric fermentation (26.7%, 178.6 MMTCO2-Eq.).
and converting land from other land uses to forested land.
CH4 emissions from livestock occurring as part of
normal digestive process in ruminant animals during
Agricultural lands account for a limited share of U.S.
metabolism and digestion. Associated with feed nutrient
carbon sequestration. In 2019, “cropland remaining
cropland” (
content and efficiency of feed use by the animal.
14.5 MMTCO2-Eq.) accounted for about 1.8%
of LULUCF net sinks, decreased from 2.1% in 2018.
3. Manure management (12.2%, 82.0 MMTCO2-Eq.).
CH4 and N2O emissions associated with livestock and
poultry manure occurring from manure/waste that is
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Greenhouse Gas Emissions and Sinks in U.S. Agriculture
Practices That Reduce GHG Emissions
Some livestock feed can reduce CH4 emissions from enteric
fermentation and increase productivity. Manure
Farming practices that sequester carbon or reduce GHG
management systems can reduce the CH4 that is released
emissions could play a role in legislative proposals seeking
into the atmosphere when manure is collected in uncovered
to reduce U.S. GHG emissions. One approach could
lagoons and can use the captured CH
involve establishing a carbon offset or carbon banking
4 as an energy s ource.
Anaerobic digesters installed to manage manure and
program. Other options include regulations or tax
capture and use the CH4 emissions are often part of non-
incentives. In general, converting industrial land to
federal voluntary and compliance carbon offset programs.
agricultural use, or keeping land in agriculture, would
sequester more carbon in the soil than would other types of
Scientific research continues to investigate agricultural
industrial, commercial, or residential land uses. For existing
practices that may increase sinks and reduce emissions.
agricultural land, practices to increase carbon sequestration
Voluntary and state programs have applied and documented
may include retiring or restoring land, converting it to
potential GHG emission reductions. Current research topics
forested land, using conservation tillage and other practices
related to sinks include improving estimates of (1) carbon
that increase biomass retention in soils or reduce soil
storage in soils and (2) the effects of different management
disturbance, and installing vegetative windbreaks.
practices on carbon sequestration. Topics related to
Maintaining these actions indefinitely is a challenge; stored
reducing sources include improving manure management
carbon may be released if practices change.
technology and livestock genetics and feed efficiency.
Practices in animal agriculture to reduce GHG emissions
Genevieve K. Croft, Analyst in Agricultural Policy
include improved feed efficiency and manure management.
IF11404
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