California Dairy’s Carbon Footprint Steadily Shrinking
The U.S. dairy industry proudly touts the fact that its carbon footprint is shrinking per gallon of milk due to ever increasing efficiency gains in milk and feed production. On a per gallon basis, it is now only about a third of what it was in 1944.
Yet overall greenhouse gas emissions (GHG), due to rising milk production, have not taken as a steep a decline.
California, however, is making the claim that both emissions per gallon and total emissions are on the decline. In a new study released in late summer, University of California (UC) researchers say state dairy emissions likely peaked over a decade ago when cow numbers reached their zenith. There are now 1.72 million cows on California dairies, down about 7% from when they peaked in 20008 at 1.85 million head.
In addition, California now lays claim to 213 dairy methane reduction projects—mostly in the form of anaerobic digestors and renewable natural gas (RNG) recapture projects on large dairy farms—that will further reduce the industry’s methane contributions.
Still, California’s dairy industry is huge. Scientists estimate California’s dairy industry is contributing about 4% of the state’s total GHG emissions. (Nationally, the U.S. dairy industry contributes about 2% of the nation’s total.)
About 80% of dairy’s GHG emissions come from methane. Methane is potent, producing 28 times the global warming potential of carbon dioxide (CO₂). But methane from dairies is also “biogenic” and short-lived. “Biogenic methane from cows is a part of a natural carbon cycle, where after 12 years it is removed from the atmosphere,” explains Frank Mitloehner, an air quality specialist with UC-Davis.
“This means that for a steady rate of methane release—as emitted by a constant number of dairy cows, for example—the amount of methane in the atmosphere stays at the same level and does not increase,” he says. “As a result, when a steady amount of methane is emitted for more than 12 years, no additional warming occurs.
“This does not mean that methane can or should be ignored,” he notes. “Put simply, a reduction in methane emissions has climate cooling effects.”
The more than 200 RNG projects already on the books are expected to lower the industry’s output of GHGs by 2.2 million metric tons annually. Hundreds more such project are expected in the future, further reducing methane emissions.
Dairy farms also emit CO₂ and nitrous oxide when they burn fossil fuels to mix feed, scrape manure alleys and grow and harvest crops for feed. Here, greater efficiency can reduce emissions. One estimate suggests fossil fuel use per gallon of milk has already dropped almost 60% over the past half century. Using solar energy and electricity to mix feed and pump water should further reduce fossil fuel use.
But methane reduction remains key. “California is seeking to reduce dairy methane emissions by roughly 7.2 million metric tons per year by 2030 (a 40% reduction),” says Mitloehner.
“These reductions will be critical to mitigate continually accumulating CO₂ emissions from other sectors of the economy, and the achievement of California’s ‘net zero’ long-term goal,” he says.
State subsidies are critical to making the RNG re-capture projects on dairies financially viable. One study suggests the projects need at least 90% subsidization to make them work. Mitloehner and his colleagues estimate a minimum of $85 million per year of state subsidies is needed to fully fund the California Climate Investment Programs.