Direct agricultural emissions

Extra facts

• Non-CO₂ agricultural emissions are primarily nitrous oxide (N₂O) from soil management, including the application of inorganic and organic fertilizers, and methane (CH₄) from rice production and farm animal digestion.
• Agriculture’s responsibility for non-CO₂ greenhouse gas emissions is expected to grow about 20 percent by 2030, reaching 7,313 MtCO₂e per year.

Emissions by agricultural source:

Agricultural soils (N₂O):

• Between 1990 and 2005, N₂O emissions from agricultural soil management have increased 10 percent, from 1,804 to 1,984 MtCO₂e, which corresponds to 32.5 percent of total agricultural emissions.
• Underlying this trend are increases in crop production and fertilizer use and other nitrogen sources such as crop residues.
• From 2005 to 2030, N₂O emissions from agricultural soils are projected to increase 34 percent, from 1,984 to 2,666 MtCO₂e. This projection assumes continued increases in fertilizer usage. Over the projection period, emissions are expected to increase in all regions (US-EPA 2011 p. 5-4).

Emissions from digestion in ruminant animals (enteric fermentation) (CH₄):

• Global CH₄ emissions from enteric fermentation increased by 6 percent between 1990 and 2005, from 1,755 to 1,864 MtCO₂e, corresponding to 30.5 percent of total agricultural emissions.
• From 2005 to 2030, CH₄ emissions from enteric fermentation are projected to increase 23 percent, from 1,864 to 2,289 MtCO₂e (US-EPA 2011 p. 5-6).

Rice cultivation (CH₄):

• CH₄ emissions from rice production have increased 6 percent between 1990 and 2005, from 670 to 710 MtCO₂e, corresponding to 11.6 percent of total agricultural emissions. Underlying this trend has been a similar increase in the land area of harvested rice.
• From 2005 to 2030, CH₄ emissions from this source are projected to increase 4 percent from 710 to 739 MtCO₂e (this projection assumes a further increase in rice area harvested over the projection period) (US-EPA 2011 p. 5-8).

Manure management (CH₄, N₂O):

• Between 1990 and 2005, CH₄ and N₂O emissions from manure management decreased by 5 percent, from 408 to 389 MtCO₂e, corresponding to 6.4 percent of total agricultural emissions.
• From 2005 to 2030, global CH₄ and N₂O emissions from manure management are projected to increase by 17 percent, from 389 to 455 MtCO₂e (US-EPA 2011 p. 5-10).

Other agriculture sources of non-CO₂ emissions (CH₄, N₂O):

• Between 1990 and 2005, total emissions from other agricultural sources decreased from 1,283 to 1,164 MtCO₂e (US-EPA 2011 p. 5-13), corresponding to 19 percent of total agricultural emissions.

Methods, caveats and issues

Definitions

• Agricultural soils:
  N₂O is produced naturally in soils through the microbial process of denitrification and nitrification. A number of anthropogenic activities add nitrogen to the soils, thereby increasing the amount of nitrogen available for nitrification and denitrification, and ultimately the amount of N₂O emitted (US-EPA 2011 p. 5-3).
• Enteric fermentation:
  Normal digestive processes in animals result in CH₄ emissions. Enteric fermentation refers to a fermentation process whereby microbes in an animal’s digestive system ferment food. CH₄ is produced as a byproduct and can be exhaled by the animal. Domesticated ruminants such as cattle, buffalo, sheep, goats and camels account for the majority of CH₄ emissions in this sector (US-EPA 2011 p. 5-6).
• Rice cultivation:
  The anaerobic decomposition of organic matter in flooded rice fields produces CH₄. When fields are flooded, aerobic decomposition of organic material gradually depletes the oxygen present in the soil and flood water, causing anaerobic conditions in the soil to develop. Once the environment becomes anaerobic, CH₄ is produced through anaerobic decomposition of soil organic matter by methanogenic bacteria. Several factors influence the amount of CH₄ produced, including water management practices and the quantity of organic material available to decompose (US-EPA 2011 p. 5-8).
• Manure management:
  Manure management produces CH₄ and N₂O. CH₄ is produced during the anaerobic decomposition of manure, while N₂O is produced by the nitrification and denitrification of the organic nitrogen content in livestock manure and urine (US-EPA 2011 p. 5-9).
• Other agricultural emissions:
  This category includes emission sources from the agricultural sector that are relatively small compared to the sector overall. The data presented include the following sources of CH₄ and N₂O: Agricultural soils (CH₄), field burning of agricultural residues (CH₄, N₂O), prescribed burning of savannas (CH₄, N₂O) and open burning from forest clearing (CH₄).

Method

US-EPA (2011):

For each source and country, estimates are based on country-reported estimates (CR* or CR), Intergovernmental Panel on Climate Change (IPCC) Tier 1 estimates (T1) or other methodologies (O). If emissions for a given country and source are not estimated or are equal to zero, the corresponding cell is left blank. Appendix F in the report provides a brief overview of the methods used to estimate historical and projected emissions of methane (CH₄) and nitrous oxide (N₂O) by country and source.

The US-EPA notes that data for other agricultural sources are based only on country reports. Data are not fully comparable between countries or to data in the remainder of the US-EPA report since emissions are not calculated for countries not reporting emissions data (US-EPA 2011 p.5-13).

Sources

• Greenpeace. 2008. Cool farming: climate impacts of agriculture and mitigation potential. Amsterdam: Greenpeace International. (Available from http://www.greenpeace.org/international/en/publications/reports/cool-farming-full-report/)
• Popp A, Lotze-Campen H, Bodirsky B. 2010. Food consumption, diet shifts and associated non-CO₂ greenhouse gases from agricultural production. Global Environmental Change 20:451–462. (Available from http://doi:10.1016/j.gloenvcha.2010.02.001)
• Smith P, Martino D, Cai Z, Gwary D, Janzen H, Kumar P, McCarl B, Ogle S, O’Mara F, Rice C, Scholes B, Sirotenko O. 2007. Agriculture. In: Climate Change 2007: Mitigation. Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Metz B, Davidson OR, Bosch PR, Dave R, Meyer LA, eds. Cambridge, United Kingdom, New York, New York: Cambridge University Press.
• [US-EPA] United States Environmental Protection Agency. 2011. Global anthropogenic non-CO₂ greenhouse gas emissions: 1990 – 2030 EPA 430-D-11-003. (Draft.) Office of Atmospheric Programs, Climate Change Division. Washington, DC: U.S. Environmental Protection Agency. (Available from http://www.epa.gov/climatechange/EPAactivities/economics/nonco₂projections.html)
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