DAIRY FARMER JERRY DA SILVA had a manure problem. The 500 cows on his family’s farm produced a lot of waste. He collected it in large lagoons and piped it out and used it as fertilizer on the land where he grows crops like oats, corn and walnuts every summer. But in winter, when the rains came, the lagoons were at risk of overflowing.
“The main challenge is getting through the wintertime. I need to be able to stockpile manure on my place until springtime, when I can put it to use,” said Da Silva, who farms near Modesto.
A few years ago, he applied for funding through the state to put in a sophisticated storage system that would allow him to easily separate the solid manure from the liquid and dry it out to use later. The result helped him prevent water pollution, but it also did something he didn’t expect: it greatly cut down on the climate-warming methane pollution his farm was emitting.
California is home to nearly 1,200 dairy farms — the largest number in any state in the country. The cows on those farms produce about 70 billion pounds of manure, which is 1.5 times the amount of waste produced by humans in the state every year. And all that manure has the potential to release a lot of methane, a very potent greenhouse gas. Ounce for ounce it traps 28 times more heat in the atmosphere than carbon dioxide does.
Dairy cows and livestock produce more than half of the methane emissions in California and a great deal of it comes from their manure.
But it doesn’t have to. For nearly a decade, the state has been working to change how farmers manage manure as part of its goal to lower methane emissions by 40% below 2013 levels by 2030. To achieve this goal, then-Gov. Jerry Brown signed Senate Bill 1383 in 2016. It granted power to the California Air Resources Board (CARB) to develop and implement a strategy to control sources of methane (along with landfills and the oil industry, the other major sources of methane in the state).
Since then, the state has been working with private companies to put over 130 dairy digesters — or systems that trap the methane released from large lagoons of manure — on farms. The methane from the digesters is then piped off the farm and used as biogas. Farmers get paid for the gas through the Low-Carbon Fuel Standard (LCFS), which requires that fossil fuel importers, refiners, and wholesalers buy credits to reduce the carbon intensity of their operations.
The digesters have been shown to be effective at cutting methane emissions, but they’re also increasingly controversial among environmental groups and Central Valley residents.
Now, some of those groups are suing the state’s air management board over amendments to the LCSF that went into effect in July, which they say “prioritizes dairy industry profits over effective, equitable climate action.”
The environmental and animal welfare groups, which include Food and Water Watch, Center for Food Safety, and the Animal Legal Defense Fund claim that the policy will spur larger dairy operations to expand in scope, which will cause more water contamination and air pollution in the communities near the operations.
“The current structure aggressively disincentivizes a dairy (farmer) from changing their operations to pollute less — because if they do that, they won’t get the massive, lucrative credit generation from the Low-Carbon Fuel Standard,” said Tyler Lobdell, staff attorney at Food and Water Watch.
Meanwhile, another set of solutions — designed to help dairy farmers separate, dry, and compost their manure like Da Silva is doing — stands to be just as effective at reducing methane, and is popular with farmers. But it has so far received limited funding from the state, leaving some smaller-scale farmers in the lurch.
Dairy digesters: effective but controversial
Most modern dairies collect the manure from their animals in giant lagoons, which when left to sit, release a great deal of methane emissions into the atmosphere. Digesters, which are used to cover the lagoons and often swell up like balloons full of gas, are effective at reducing emissions. In one recent study out of University of California, Riverside, researchers studied emissions from a single dairy operation for a year and found that the digesters reduced them by roughly 80 percent. The study registered minor leaks, especially from underneath the digester at the early stage, but the company that built it hastily resolved them.
“It’s a highly effective way to reduce methane emissions. The source is so large, and it’s fairly contained,” said Francesca Hopkins, a climate scientist who led the research. “So even though these digesters cost a lot of money to erect, it is actually one of the most cost-effective ways to reduce methane that we have.”
A typical digester can cost several million dollars, a fact that only makes them feasible for the largest operations, with large quantities of manure — and methane — to manage.
Farms with digesters “have a lot more funding available for them through carbon credit programs and that makes them attractive to very, very large operations,” says Colton Fagundes, the associate policy director at the California Climate and Agriculture Network (CalCAN). “A lot of the companies are coming in and covering the costs of installing digesters because they see the future potential of financial benefit from those credits.”
Many large dairy operations have also received funds from the state to help offset the cost of the digesters.
Environmental justice advocates in the Central Valley, which is already home to about 90% of the state’s dairy herd and has some of the worst air pollution in the country, worry that the Low-Carbon Fuel Standard has changed the landscape in the dairy industry in a way that will only add to consolidation in the state’s dairy industry and incentivize existing farms to take on more animals. And some of the people living in communities near the farms say that this could lead to more water pollution — as nitrates from manure get into the groundwater — and air pollution from the manure itself.
Hopkins said these communities are disproportionately burdened by dairy-related pollution compared to the rest of the state, and if the dairies were to expand, then that might add to the environmental injustice that is already in place.
“I don’t know that there’s very strong evidence that dairy farms are expanding in the San Joaquin Valley, but I do know that other regions of the state that have dairy farms are contracting,” Hopkins said.
She said digesters are not intended to reduce air pollution and she doesn’t know whether they are increasing it either.
Lawsuit puts dairy digesters in the hot seat
The lawsuit from the three nonprofits targets CARB for passing amendments to the LCFS that they say will incentivize existing dairy farms to expand and claims it will cause more agricultural pollution to occur. The groups also say the standard could cause what they call the “factory farm biogas” industry to grow outside California.
Food and Water Watch’s Lobdell said that CARB was presented with scientific evidence, community testimonies, and even alternative solutions by people and agencies about what consequences dairy expansions could cause but disregarded it.
“(CARB) is uninterested in protecting Californians from the dairy industry and their pretty extreme pollution. The agency has made the decision that Californians who have to live by mega dairies are sacrificed communities, and they will not be protected.” Tyler Lobdell, staff attorney at Food and Water Watch
In a detailed 2024 report on the topic, Food and Water Watch pointed to reporting from Reuters that showed that in the years after the Obama Administration endorsed dairy digesters as a solution to methane emissions, those emissions had risen more than 15% in the years prior, in part driven by growth in herd size.
“This agency is uninterested in protecting Californians from the dairy industry and their pretty extreme pollution,” Lobdell said. “The agency has made the decision that Californians who have to live by mega dairies are sacrificed communities, and they will not be protected.” Food and Water Watch also calls biogas a “false climate solution” and argues that the incentivization of dairy farms could undermine LCFS, which could ultimately work against California’s efforts to transition to renewable energy.
Another viable approach
CalCAN’s Fagundes isn’t focused on the environmental challenges of dairy digesters. Instead, he’s advocating for an alternative that he says works better to support small-scale dairy farmers, as well as those who use organic and pasture-based practices.
The Alternative Management Manure Program (AMMP) prevents manure solids from going into anaerobic storage — or manure lagoons. Those solids can then be dried, stored, applied to fields, or composted, resulting in a variety of benefits from water quality, soil health and air quality.
The average farm that received funding through the state’s dairy digester program has close to 6,000 cows, AMMP typically serves producers with fewer than 2,000. And while the overall methane reduction is impressive on those large farms, Fagundes says that’s because they emit a lot more methane to start with.
In 2024, AMMP was funded at $17.5 million, so the list of recipients was relatively slim compared to the demand. And this year, the program hasn’t been awarded any funding.
Lynne McBride from the California Dairy Campaign, a nonprofit that supports family dairy farms in the state, says AMMP has been very valuable for farmers who receive the funding, but it has also at times added to an uneven playing field. Da Silva is so happy with his project — which received over $500,000 in funding from the state — that he has recommended AMMP to all his neighbors and colleagues. And while most have applied multiple times, few have been granted funding because the pot is so limited.
“We want to make sure that these programs and practices work for dairies of all sizes, so that’s why we continue to be a big supporter of providing more funding to make these projects happen,” says McBride. This is key at a time when a great deal of milk is being produced by massive out-of-state operations, and dairies with fewer than 1,000 cows are struggling to stay afloat.
The California State Water Resources Control Board is working on a new dairy order regulation, which should be finalized later this year, and will require dairies to better manage their manure to keep nitrogen and other nutrients out of groundwater.
“The AMMP program is an important way for these smaller guys to be able to achieve those new benchmarks,” says McBride.
Funding for AMMP is a big question, but Fagundes says CalCAN is advocating for a permanent bucket of funding for climate-smart agriculture programs in the next reauthorization of the state’s Greenhouse Gas Reduction Fund. If that happens, it could be a boost for more dairy farmers looking to change their relationship to manure, and for California’s climate future.
“Before I applied for the AMMP program, I didn’t quite really understand well enough how the manure in my pond is creating a greenhouse gas,” said Da Silva. “My main goal was managing the manure better, but that’s a secondary benefit.”
This story was produced with support from the Climate Equity Reporting Project at Berkeley Journalism.