Cows vs. cars: Methane from livestock differs from greenhouse gases

DAVIS, Calif. — Methane produced by livestock is different from greenhouse gases produced by other sources.

“Greenhouse gases like carbon dioxide, methane, nitrous oxide and others form a blanket over our atmosphere and hold the heat from the sun to prevent the heat from escaping back into space,” said Frank Mitloehner, professor of animal science and air quality Extension specialist at University of California, Davis.

“This is a really important function for these greenhouse gases because without them life on earth would not be possible since it would be too cold,” Mitloehner explained during a presentation at the Driftless Region Beef Conference, organized by University of Illinois Extension, Iowa State University Extension and Outreach and University of Wisconsin-Madison Extension.

“The problem is human activity is producing too many greenhouse gases and therefore the blanket is getting too thick,” he said during the virtual event.

For the global methane budget, which includes sources that produce gas such fossil fuel production, agricultural waste, biomass burning and so forth, there are 560 teragrams of methane produced by all the sources in the world per year, Mitloehner said.

“Methane is not just produced; it is also destroyed, and that is why it is so different from carbon dioxide, nitrous oxide and other gases,” he said. “Once methane is in the atmosphere, it meets another molecule that steals away the hydrogen on the methane and destroys it and that destruction occurs in a 10-year time frame.”

Through this process, Mitloehner said, 550 teragrams of methane are destroyed each year.

“Then you arrive at 10 teragrams globally emitted and going into the atmosphere, which is a number that is still too high,” he said. “Methane is a short-lived climate pollutant that is only active for 10 years whereas the other greenhouse gases stay in the atmosphere for a long time.”

The biogenic carbon cycle explains why methane from livestock is different from greenhouse gases produced from other sources.

“It starts with the plants that need sunlight, water and carbon and the carbon comes from the air in the form of carbon dioxide which goes into the plants during photosynthesis,” Mitloehner said. “The plants convert it into carbohydrates, a bovine eats those carbohydrates and a small fraction of the carbohydrates are converted into methane by belching or from animal manure.”

Not only is this methane recycled, Mitloehner said, if there is a constant number of livestock, the amount of methane produced and destroyed is in balance.

“This is completely overlooked because people are not considering the process of photosynthesis in the carbon cycle,” he said.

In addition, Mitloehner said, livestock methane is different from fossil fuel derived methane.

“Fossil fuels like oil, coal and gas are stored in the ground for a long time and when we extract and burn them, that’s new, additional carbon added to the atmosphere,” Mitloehner said.

“That is the main human culprit of climate change — taking vast amounts of carbon out of the ground and burning them,” he said. “Do not allow people to compare cows to cars because that is a flawed comparison.”

Every time a vehicle is driven, Mitloehner said, new carbon dioxide is produced into the atmosphere.

“That’s why carbon dioxide is referred to as a stock gas because it stays there for 1,000 years,” he said.

Methane is a flow gas, Mitloehner said, because it is not just produced; it is also destroyed.

“The only way methane concentrations in the atmosphere go up is if we increase the size of the herd,” he said.

Reducing methane, which has a cooling effect on the earth’s atmosphere, is already occurring in California.

“Our state legislature approved an incentive approach to help farmers invest in technologies that reduce methane from dairies,” Mitloehner said.

“Dairies are covering the lagoons, biogas is produced and then converted into renewable natural gas which is used to fuel vehicle fleets,” he said. “This is reducing 2.2 million metric tons of methane per year.”

Mitloehner stressed the importance to consider the contributions of greenhouse gases by countries around the world since it is a global issue.

“In many countries, milk production of dairy cows is very low at 1,000 pounds of milk per cow per year, compared to the U.S., where it is 23,000 pounds of milk per cow per year,” Mitloehner said. “There is a direct relationship with the less milk produced the higher the carbon footprint.”

“The U.S. has the lowest carbon footprint per unit of livestock as anyplace in the world because we have an improved veterinary system, we’ve improved the genetics of both plants and animals and we’ve learned to feed more energy dense diets to animals,” he said. “That has allowed us to shrink the number of livestock to produce food.”

For example, in 1950, there were 25 million dairy cows in the United States, and today that number is around 9 million head.

“But we are producing 60% more milk, so a glass of milk has shrunk its carbon footprint by two-thirds,” Mitloehner said.

“The U.S. beef herd has gone from 140 million head to 90 million head today and we’re producing the same amount of beef as in 1970,” he said. “The U.S. produces 18% of the global beef with 6% of the cattle.”

Sustainability means producing more with less.

“Production intensity and emission intensity are inversely related so when productivity goes up, emissions go down,” Mitloehner said.