Dairy farms can join the climate fight by trapping methane

A year-long experiment on a Central Valley dairy farm has confirmed that sealing manure lagoons under gas-tight tarps can trap roughly 80 percent of the methane they would otherwise release.

By capturing the gas and sending it to fuel markets, the system turns a potent climate threat into a usable resource.

Led by researchers from the University of California, Riverside (UCR), the study gives the first independent, year-over-year check on dairy “digesters” that California regulators have counted on to meet aggressive methane-cutting goals.

More than 130 such systems already dot the state’s milk belt. Until now, officials had relied mainly on engineering models to judge their effectiveness.

Capturing methane gas on a dairy farm

The test site sits in Tulare County, the nation’s top milk-producing region. Hot summers keep open manure ponds bubbling like low-grade cauldrons, releasing methane that warms the planet more than 80 times faster than carbon dioxide over two decades.

Engineers solved the problem by floating a heavy, flexible cover across the lagoon and piping the captured gas through scrubbers before sending it to truck fleets as a low-carbon diesel replacement.

“The digesters can leak, and they sometimes do,” said Francesca Hopkins, the UCR climate scientist who led the work. “But when the system is built well and managed carefully, the emissions really drop. That’s what we saw here.”

Measuring the invisible

Hopkins’ team set up mobile gas analyzers inside a white research van. For 12 months before construction and twelve months after, they drove grid patterns around the dairy, logging hundreds of methane readings under different winds and temperatures.

The before-and-after comparison showed an 80 percent decline in methane drifting off the property once the cover and piping were in place.

That figure lines up closely with the reduction assumed in California’s official climate inventory.

Most earlier studies had relied on short snapshots or on-site sensors. The new roaming approach captured seasonal swings, day-night cycles, and operational hiccups, providing a more realistic picture of performance over time.

Leaks, fixes, and fast improvements

During early tests the team picked up sudden methane spikes. They alerted California Bioenergy, the company that built and operates the digester. Technicians located torn seams and loose joints, repaired them, and the plumes vanished on subsequent drives.

“This was a textbook case of adaptive management,” Hopkins said. “The partnership between scientists, the company, and the farmer really made a huge difference.”

The episode underlines a broader lesson: digesters work best when operators monitor them closely and move quickly to plug leaks.

California’s new fleet of methane-tracking satellites could help, flagging large plumes so ground crews can respond in days instead of months.

Other pollutants remain untouched

Digesters leave other pollution untouched. They do not curb ammonia, a lung-irritating gas, or tiny airborne particles that can hang over dairy counties on still summer days.

The hardware is also expensive. Farmers need permits, financing, and maintenance contracts to keep covers inflated and engines running.

“They’re not for every farm,” Hopkins said. “But for dairies that can make it work, this is one of the most cost-effective ways we have to cut these greenhouse gas emissions.”

California’s climate program helps in this regard by awarding low-carbon fuel credits for each ton of methane kept out of the air. Those credits, sold to oil companies that need to hit clean-fuel targets, can repay installation costs in a few years.

Slashing methane emissions from dairy farms

State agencies plan to slash dairy methane 40 percent below 2013 levels by 2030. The new study suggests that target remains within reach if existing digesters keep performing and more come online.

The research also shows that rigorous, transparent monitoring can build confidence among regulators, industry, and local communities.

“There’s so much division in the climate space,” Hopkins said. “But this is a real example of cooperation that leads to measurable results.”

Digesters will not solve every problem tied to large-scale dairying, yet the Tulare County project proves they can deliver the climate benefit promised on their labels.

With careful design, vigilant upkeep, and open data, farms can turn what was once a methane plume into fuel for trucks, revenue for operators, and progress toward a lower-carbon future.

The study is published in the journal Global Change Biology Bioenergy.

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