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Updated May 11, 2022
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 (MMTCO2e). 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.
international standards. Every country preparing its national
Most federal legislative proposals to reduce U.S. GHG
inventory considers the same GHG sources and sinks for
emissions would not require reductions in agriculture, but
the same standard sectors. These include an agriculture
some would incentivize voluntary actions to do so. The
sector and a land-use, land-use change and forestry
Growing Climate Solutions Act of 2021 (S. 1251/H.R.
(LULUCF) sector. The Inventory also reports estimates for
2820) would support voluntary agriculture and forestry
several EPA-defined economic sectors, including
carbon markets by establishing a voluntary certification
agriculture, transportation, electricity, industry,
program for technical assistance providers and third-party
commercial, and residential. Under this format, the
verifiers at the U.S. Department of Agriculture (USDA).
agriculture sector includes emissions from fuel-combustion
Agriculture is both a source and a sink of GHGs (Figure 1).
by farm equipment (e.g., tractors) as well as the emission
Sources generate GHG emissions that are released into the
sources already accounted for in the international standard
atmosphere and contribute to global climate change. Sinks
sector for agriculture.
remove carbon dioxide (CO2) from the atmosphere and
Agricultural GHG Emissions
store carbon through physical or biological processes.
EPA reports that agriculture sector emissions totaled 635.1
Agricultural emissions include many GHGs of interest to
MMTCO2e in 2020 (Table 1), equal to 11% of total U.S.
policymakers: CO2, methane (CH4), and nitrous oxide
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
defined by the Environmental Protection Agency (EPA),
Potentially offsetting agricultural sinks.
and the most recent data available (from 2020).
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.
Figure 1. Examples of 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.
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Greenhouse Gas Emissions and Sinks in U.S. Agriculture
Figure 2. U.S. GHG Emissions, by Economic Sector
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
matter (Figure 1). Other carbon sinks derive from a range
of land-use and land-management activities, such as
maintaining forested land, which primarily stores carbon in
above-ground biomass (e.g., trees). LULUCF is the only
Inventory sector to include GHG sinks. Net sinks in the
LULUCF sector account for both emissions and sinks from
land use and land-use change. Federal agencies—including
USDA and the Departments of Energy, Transportation, and
Defense—contribute LULUCF data to the Inventory.
EPA reports a LULUCF net sink of 758.9 MMTCO2e for
2020. This amount is equivalent to about 13% of all U.S.
GHG emissions. Most LULUCF sinks are associated with
maintaining existing forested land and converting land from
other land uses to forested land. Agricultural lands account
for a limited share of U.S. carbon sequestration. In 2020,
“cropland remaining cropland” (23.3 MMTCO2e)
accounted for about 3% of LULUCF net sinks.
Practices That Reduce GHG Emissions
Source: CRS from EPA Inventory, 2020 data.
Farming practices that sequester carbon or reduce GHG
Notes: Emissions are presented in parentheses in MMTCO
emissions could play a role in legislative proposals seeking
2e.
to reduce U.S. GHG emissions. One approach could
In 2020, three activity types accounted for 90% of U.S.
involve establishing a carbon offset or carbon banking
agriculture sector emissions:
program. For more information, see CRS Report R46956,
Agriculture and Forestry Offsets in Carbon Markets:
1. Soil management (50%, 316.2 MMTCO2e). N2O
Background and Selected Issues. Other options include
emissions from soils, associated with agricultural
regulations or tax incentives. In general, converting
practices that increase nitrogen availability, disturb
industrial land to agricultural use or keeping land in
soils, and increase oxidation (e.g., fertilization,
agriculture would sequester more carbon than would other
irrigation, drainage, cultivation, tillage, shifts in land
land-use types. For existing agricultural land, practices to
use, and deposition of livestock manure on soils).
increase carbon sequestration may include retiring or
2. Enteric fermentation (28%, 175.2 MMTCO2e). CH4
restoring land, converting it to forested land, and using
emissions from livestock occurring as part of normal
conservation tillage and other practices that increase
digestive process in ruminant animals during
biomass in soils or reduce soil. Maintaining these actions
metabolism and digestion. Associated with feed nutrient
indefinitely is a challenge; stored carbon may be released if
content and efficiency of feed use by the animal.
practices change.
3. Manure management (13%, 79.2 MMTCO2e). CH4
Practices in animal agriculture to reduce GHG emissions
and N2O emissions associated with livestock and poultry
include improved feed efficiency and manure management.
manure occurring from manure/waste that is stored and
Some livestock feed can reduce CH4 emissions from enteric
treated in systems that promote anaerobic
fermentation and increase productivity. Manure
decomposition (e.g., lagoons, ponds, tanks, pits).
management systems can reduce the CH4 that is released
U.S. agriculture sector emissions were higher in 2020
into the atmosphere when manure is collected in uncovered
despite a reduction in total U.S. emissions largely attributed
lagoons and can use the captured CH4 as an energy source.
to impacts of the Coronavirus-19 (COVID-19) pandemic on
Anaerobic digesters installed to manage manure and
travel and economic activity (Table 1).
capture and use CH4 are often part of nonfederal voluntary
Table 1. U.S. Agriculture, Related Source Emissions
and compliance carbon offset programs.
Emissions by Gas (Activity)
1990
2005
2020
Scientific research continues to investigate agricultural
Total, Agriculture Economic Sector 596.8 626.3 635.1
practices that may increase sinks and reduce emissions.
N
Voluntary and state programs have applied and illustrated
2O (soil and manure management)
330.1
330.3
336.1
CH
potential GHG emission reductions. Current research topics
4 (enteric fermentation, manure
214.7
235.5
250.9
management, rice cultivation)
related to sinks include improving estimates of (1) carbon
CO
storage in soils and (2) the effects of different management
2 (urea fertilization, liming)
7.1
7.9
7.7
CO
practices on carbon sequestration. Topics related to
2, CH4, and N2O (fuel use)
44.9
44.6
40.4
reducing sources include improving manure management
Total Agriculture w/Electricity
631.9 664.6 669.5
technology and livestock genetics and feed efficiency.
CO2, N2O, SF6 (electricity-related)
35.2
38.3
34.4
Total Emissions, All Sectors
6,453.5 7,434.8 5,981.4
Megan Stubbs, Specialist in Agricultural Conservation and
Natural Resources Policy
Source: CRS from EPA Inventory (emissions in MMTCO2e.).
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Greenhouse Gas Emissions and Sinks in U.S. Agriculture
IF11404
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