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A California dairy farm expansion that uses state and federal incentives to build digesters that turn manure into gas will eliminate an estimated 9% of the farm’s estimated greenhouse gas savings, according to a new pre-print study.
The study, which is in pre-print and not yet published, adds to evidence that the increasing use of anaerobic digesters to convert large amounts of manure into usable gas from large dairies and other concentrated animal feeding operations (CAFOs) across the United States is fueling the expansion of already large and concentrated farms and increasing the climate-warming emissions that digesters aim to mitigate.
Similarly, the U.S. Department of Agriculture states: issued a temporary suspension Extending loan guarantees for anaerobic digesters, many of which are issued for fertilizer digesters, until the end of 2026 due to “persistent and growing concerns” about performance and financial solvency.
Researchers used federal, state, and satellite data to analyze barn size and herd expansion on California dairy farms that received financial incentives to build manure digesters over the past decade. They found that barn area increased by an average of 19,644 square feet within three years after farms anticipated or began construction of a digester. This means each farm can accommodate an estimated 243 more mature dairy cows.
The study’s lead author, Varun Magesh, a nonresident associate at Stanford’s RegLab and a student at Harvard Law School, emphasized that the study does not actually measure the number of new cows on a farm, but rather the number of cows that can be housed in a new facility. “And we look at that as a proxy for the number of cows that a facility processes each year,” he said.
The study adds to evidence that adding digesters creates “perverse economic incentives,” said Brent Kim, a scientific assistant at the Johns Hopkins Bloomberg School of Public Health who studies digesters but was not involved in the new study.
“The value of fertilizer starts to compete with the value of milk. So if you’re a producer, you’re going to push the logic that if there’s an additional rebate on fertilizer and you’ve made this huge investment, your company is going to get even bigger,” he said.
Magesh said California dairy farms, like most farms across the country, are becoming increasingly consolidated.
“The biggest farms get bigger and the smallest farms get smaller and disappear,” he said. “Large farms that have added digesters are the most profitable, so it is difficult to untangle this from the influence of digesters.”
“The largest farms grow, the smallest farms shrink and disappear.” – Varun Magesh, Stanford Reg Lab
But state officials said the size of California’s herds fluctuates for a variety of reasons, and that the addition of manure digesters across the state has reduced industrial methane emissions.
“Herd size decisions are made by individual dairy producers based on a wide range of market and economic factors that are external to (state officials),” said Jay Van Rijn, a spokesperson for the California Department of Food and Agriculture.
Van Rijn said manure digesters remain “an important tool for reducing methane emissions from California’s dairy sector.”
fertilizer digester incentives
There is Estimation There are 394 fertilizer-based digesters in operation in the United States, with more than 70 under construction. This has increased by 55% over the past 10 years. California leads the nation in fertilizer digesters. 123 Dairy farm waste digester In isolation, this is primarily due to two incentive programs.
The state’s Dairy Digester Research and Development Program, run by the California Department of Food and Agriculture, provides grants for dairy farms to install manure digesters. even more california low carbon fuel standards (LCFS) gives credits for recovered methane to digesters in California and elsewhere.
Proponents of manure digesters point to the reduction of climate-warming emissions, particularly methane, from animal waste. According to , manure digesters reduced greenhouse gases by more than 13 million tons in 2023. Latest data available from the Environmental Protection Agency (EPA)).
In California, Researcher’s estimate Manure digesters reduce methane emissions by 80% compared to farms that use outdoor lagoons or storage pits. California Department of Food and Agriculture estimate The dairy digester will help the agency fund a nearly 30% reduction in total methane emissions from fertilizer management in California, which is projected to represent more than 8% of the state’s total agricultural greenhouse gas emissions.
The digester will also “produce renewable energy such as biogas, renewable natural gas and hydrogen, which can replace diesel and other fossil fuels and contribute to cleaner air in the Central Valley and across the state,” Van Rijn said.
The digesters “generate renewable energy, can replace diesel and other fossil fuels, and help clean the air in the Central Valley and across the state.” – Jay Van Rijn, spokesperson for the California Department of Food and Agriculture
Credit: CDFA
However, Magesh said the study shows the state may have miscalculated emissions reductions from manure digesters and may be falling short of LCFS policy targets. Expanding herds increases the amount of methane (a much more potent greenhouse gas than carbon dioxide) from farms. Methane is often converted into “carbon dioxide equivalents” to measure its impact on the climate. Magesh and his colleagues estimate that each farm will add about 1,658 tonnes of CO2-equivalent methane emissions per year as more cows fill the space in new barns.
The California Dairy Digester Research and Development Program estimates that the average emissions reduction from manure digesters is 17,563 meters of CO2-equivalent methane emissions per year. This means that increasing herd size could offset around 9% of the claimed emissions reductions.
“The industry can talk all it wants about how digesters solve all these problems, but many of these problems stem from the core problem of concentrating thousands of animals in one place,” Kim said.
“So if it makes these operations large-scale, and the evidence certainly seems to suggest that, it’s going to exacerbate all the potential public health concerns of living next to these farms,” he added.
methane leak
In addition to expanding herds, leaks from manure digesters could undermine methane emissions reductions, according to another report. study It was announced in March by researchers at the University of California, Riverside. They monitored the state’s 98 manure digesters using satellites and aircraft to track emissions.
They identified several leaks that were emitting methane at a rate 10 times higher than open fertilizer lagoons.
“For the most part, the digesters are working well,” said study lead author Alyssa Valdez, a climate scientist at the University of California, Riverside. statement. “But when you have a few breaches, it has a big impact.”
Featured image credit: Adam Fagen/flickr
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Brian Bienkowski is the editor-in-chief of The New Lede. He is a veteran journalist with over 15 years of experience covering the environment and human health. Prior to joining TNL, he was a senior editor at Environmental Health News for nearly a decade, overseeing the newsroom and two local bureaus. He was also the founder, producer, and host of the EJ podcast Agents of Change from 2020 to 2024.
Bienkowski has received multiple awards for her editing and reporting, including honors from the Healthcare Journalists Association, Columbia School of Journalism, Hunter College, and the Environmental Journalists Association. He has a master’s degree in environmental journalism from Michigan State University and lives in northern Michigan.
