Cows receive a lot of attention in climate change discussions because one of the greenhouse gases they produce in the rumen is methane. Progress in our understanding of greenhouses gases, however, may provide new perspective on the role methane—and livestock—play in global warming and cooling.
There are three greenhouse gases: carbon dioxide (CO2), nitrous oxide (NO2) and methane (CH4). According to the U.S. Environmental Protection Agency, the U.S. dairy industry accounts for approximately 1.4% of total U.S emissions. While some older studies claim agriculture is responsible for a greater percentage of emissions, many have been found to be misleading because of the way they were calculated. Others go beyond the U.S. to look at global agricultural emissions, which represent a much higher percent of total emissions. Why the difference in U.S. and global estimates? For one, the livestock industry in the U.S. is much more efficient than the rest of the world. We need fewer animals to produce a gallon of milk or pound of meat. We also consume fossil fuels at a much higher rate than many parts of the world, which changes the percent contributions.
Methane is a potent greenhouse gas with a warming potential more than 28 times that of CO2. Often authors criticize the livestock industry because of this potential. However, when it comes to livestock and climate change, several researchers are questioning the comparison and are changing the way we look at methane from cows.
Dr. Frank Mitloehner, an air quality specialist from UC Davis has highlighted why we need to look at methane from cows differently than we used to. He argues many other characteristics set methane apart from CO2. For starters, methane stays in our atmosphere for about 12 years before returning to the atmosphere as CO2. At that point, 80-89 percent of methane is removed by oxidation with hydroxyl radicals. As a result, methane is only significantly warming our atmosphere for those 12 years, making it a short-lived climate pollutant. As methane is being emitted it is also being destroyed in the atmosphere. This is very different from CO2 produced from burning fossil fuels. CO2 is a stock gas, which means it builds up in the atmosphere where it can remain for a thousand years.
The warming impact of methane is not determined by how much is being emitted—since it’s destroyed relatively quickly—but by how much more or less methane is being emitted over a period of time. After 12 years, methane is converted into CO2 again, taken up by the grass, corn, alfalfa and recycled back through the biological system we call the dairy cow. The amount of methane emitted can equal the amount destroyed in the atmosphere.
While the impact might not be as significant as many presumed, the dairy industry is still working to reduce rumen methane contributions. New tools such as feed additives and digesters could decrease the amount of methane produced and even create a short-term cooling effect.
If you’d like to learn more about the role methane plays in climate change, check out Rethinking Methane at: https://www.youtube.com/watch?v=UOPrF8oyDYw
Troy Downing, OSU Dairy Extension Specialist
Tillamook, Oregon
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