Specialists discuss livestock and greenhouse gases

Issue Date: March 27, 2019
By Bob Johnson
Frank Mitloehner, a professor and Cooperative Extension air quality specialist at UC Davis, studies how livestock operators and particularly dairy farmers can reduce production of greenhouse gases. He says livestock account for only about 4 percent of total U.S. greenhouse gas emissions.
Photo/Bob Johnson

Science is steadily progressing toward a better understanding of how much animal agriculture contributes to the greenhouse gases linked to climate change, and what can be done to minimize the problem.

Though some activists have claimed cows and other livestock emit as many greenhouse gases as the entire transportation sector, the federal Environmental Protection Agency has a far more modest estimate.

"All livestock combined accounts for approximately 4 percent of total U.S. greenhouse gas emissions, according to the EPA, and most of that is from cattle," said Frank Mitloehner, professor and Cooperative Extension air quality specialist in the Department of Animal Science at the University of California, Davis.

National Cattlemen's Beef Association senior director of sustainable beef production research Sara Place, who was Mitloehner's doctoral student and collaborates with him on occasion, took a deep dive into the most recent EPA catalog of greenhouse gases to find details about animal agriculture.

"The vast majority of CO2 emissions, 76 percent, come from burning fossil fuels," Place said. "Most of the fossil fuel is combusted for use in electricity generation and transportation, but the type of fuel used across economic sectors varies."

The gases for which cows have received considerable publicity lately are, although significant, not a major driver of climate change, she said.

"Methane emissions represent 10.6 percent of total U.S. greenhouse gas emissions in CO2 equivalents, with enteric fermentation, also known as ruminant burps, not farts, representing 26 percent of total methane emissions, followed by natural gas systems," Place said.

Mitloehner specializes in working to understand how the state's $6.5 billion dairy sector can reduce its contribution to climate change, and said it begins with increasing use of digesters to turn manure into fuel or electricity.

"Last year, there were 20 anaerobic digesters in California, and only half of them were in use," Mitloehner said. "Now there are 40 in California, counting the ones that are new or in construction."

The main reason for increased use of the digesters is Senate Bill 1383, which requires agriculture to reduce methane emissions 40 percent by 2030.

"The use of anaerobic digesters is one way to reach that goal, and alternative manure management practices is the other," Mitloehner said. "The digesters might have the most promise. If you manage a digester right and leave the manure in long enough, you should have good efficiency."

Anaerobic digesters cost $2 million to $5 million, depending on what the technology is asked to do, but Mitloehner said the benefits make them more financially viable than ever.

"You make the gases into power or fuels," he said. "Fuel is the largest use in California."

In addition to incentives available for putting in an anaerobic digester, dairies can also receive substantial renewable natural gas credits that might be a financial incentive for developers and/or dairy producers. The resulting fuels can be used in vehicle fleets instead of diesel.

"The answer in the past was, we were not sure if they pencil out," Mitloehner said. "Because of the high credits for renewable natural gas, they do seem to have financial potential. You're converting the methane into a fuel that can be used instead of a fossil fuel. It's a double benefit. That's why it pencils out now."

He also reported progress in finding feed supplements that could significantly reduce the methane cows burp as part of their digestion process.

"There are a couple experimental technologies and studies that indicate reductions of the methane from enteric fermentation of 20 to 30 percent are possible," Mitloehner said. "Not all of them are available yet, because some need FDA approval, and that takes time."

Progress by the U.S. dairy sector in breeding more productive cows and managing them more efficiently has already resulted in a sharp reduction in the number of animals raised to produce milk.

"The number of dairy cows peaked in the U.S. in 1945, at 27.8 million," Place said. "From 1945 to 2018, the lactating dairy cow herd shrunk 66 percent, but total milk production in 2018 was 81 percent higher than in 1945."

Cows are often singled out because the methane they burp is 28 times more powerful as a greenhouse gas than carbon dioxide. Once in the atmosphere, however, the methane changes naturally into carbon dioxide in a decade.

And while fossil fuels put carbon into the atmosphere that had been locked in the earth for millions of years, Mitloehner said bovine burps are part of a cycle that does not really add new carbon into the system.

"It's a cycle that goes from the plant to the animal, and back to the plant and then to the animal," he said. "The carbon dioxide from methane destruction will sooner or later go back into plants. Mathematically, it is unlike the fossil fuel carbon dioxide, which adds new carbon dioxide into the system."

Dairy production also involves the gases emitted in production of feed, which Mitloehner said vary, depending on what the animals are fed and how the fertilizer to produce it is managed.

"The next most important source of emissions is the feed production, the nitrous oxide from the fertilizer," he said.

Costs involved in technologies to reduce greenhouse gases in dairy production are generally shared by the public, in order to improve the environment without driving up the price of milk and cheese.

"Half a billion dollars has been spent by this state on digesters and alternative manure practices," Mitloehner said.

Though California has been more committed than other states in investment in greenhouse gas reduction, he said Germany has adopted a far more ambitious program.

"Germany has 9,000 anaerobic digesters," Mitloehner said. "Germany is about the same size as California, has about twice as many people, and is in better shape economically. They are investing in renewable energy and have reached a 40 percent level already."

(Bob Johnson is a reporter in Davis. He may be contacted at bjohn11135@aol.com.)

Permission for use is granted, however, credit must be made to the California Farm Bureau Federation when reprinting this item.

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