What Is Methane?
Methane is a powerful greenhouse gas. Methane is flammable, and is used as a fuel worldwide. Methane is a hydrocarbon that is naturally found below ground or under the sea floor. Once it reaches the surface, it is known as atmospheric methane and it then becomes one of the most potent greenhouse gases on Earth¹. Methane doesn't linger as long in the atmosphere as carbon dioxide, but it nevertheless is far more devastating to the climate because of how effectively it absorbs heat. Taking that into account, scientists calculate that over a 100-year period the “global-warming potential” of methane is 28 times greater than for carbon dioxide¹. Methane in the atmosphere, before it converts into carbon dioxide, a two decade-long period, is 84 times as potent as carbon dioxide in terms of trapping and absorbing heat and radiation².
Atmospheric methane concentrations have risen from 722 parts per billion in pre-industrial times to now 1887.65 ppb as of November 2017, a 2.6-fold increase and the highest level reached in human history³. Depending on the source, scientists estimate that anywhere from 25-40% of global warming is due to methane emissions².
Atmospheric methane concentrations have risen from 722 parts per billion in pre-industrial times to now 1887.65 ppb as of November 2017, a 2.6-fold increase and the highest level reached in human history³. Depending on the source, scientists estimate that anywhere from 25-40% of global warming is due to methane emissions².
How Does Methane Relate to Our Food?
In the past decade or so, atmospheric levels of methane have steadily risen. From an outsiders perspective, the source of this rise in methane would likely be increases in fossil fuel production or the burning of organic material, as methane is the main component of natural gas. However, scientists have recently identified agriculture as the culprit of these rising methane levels⁴.
Methane is released during various processes of agricultural production, emitting from ruminant animals to rice paddies and wetlands.
Methane is released during various processes of agricultural production, emitting from ruminant animals to rice paddies and wetlands.
Livestock Methane Emissions
Ruminant animals are livestock, such as cows and sheep, and they contain bacteria in their gastrointestinal systems that help to break down plant material. While bacteria are breaking down plant material, such as grass cattle graze on, methane is created in a process called enteric fermentation. This methane is then released into the air when the animal releases gas, such as when they defecate or belch⁵. Enteric fermentation accounted for 26% of methane emissions in 2016¹.
Manure Management
The U.S. contributes almost to half of worldwide manure management methane emissions.
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Livestock manure also contributes to methane emissions. In a traditional farm, animals were kept on farms that also grew crops. These systems are sustainable and self-sufficient in that animal waste was used as a natural fertilizer for these crops, and the crops were used as animal feed. In industrial agriculture, however, manure is often stored by industrial farms in massive closed-air containers called “lagoons”, in which methane is produced as the manure decomposes⁴. This type of methane emission is categorized as “manure management” and accounts for 10% of all U.S. methane emissions as of 2016¹. The United Nations’ Food and Agriculture Organization estimates that livestock production accounts for some 2.2 billion tons of carbon dioxide equivalent greenhouse⁴. The United States greatly surpasses every country on Earth for its contributions to methane emissions from manure management practices, even though U.S. population accounts for less than 5% of the world's population.
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Rice Production & Methane Emissions
Rice production is also a methane-intensive activity, as rice plants secrete carbohydrates during photosynthesis. When rice paddies are flooded, the lack of oxygen becomes an ideal place for bacteria to feed off of those carbohydrates, releasing methane in the process⁴. As such, wetlands are also ideal places for methane production because of the lack of oxygen, high temperatures, and the large number of microbes⁶. Wetland methane emissions are the largest natural source of methane emissions, contributing to roughly one third of total natural and anthropogenic emissions⁶.
- EPA. (2016). Overview of Greenhouse Gases.
- Hamburg, S. Methane: The other important greenhouse gas.
- NOAA. Trends in Atmospheric Methane [Chart]. Retrieved from Earth System Research Laboratory Global Monitoring Division database.
- Geiling, N. (2016, March 17). Methane Emissions Are Spiking, But It Might Be More Cow Than Car. Think Progress.
- Mooney, C. (2017, September 29). Scientists may have found a solution to the atmosphere’s methane mystery. The Washington Post.
- Poulter, B., et. al (2017). Global wetland contribution to 2000–2012 atmospheric methane growth rate dynamics. Environmental Research Letters, 12(9).