A new study shows that systems designed to capture methane from cow manure, called dairy digesters, are highly effective. But on the rare occasions they fail, the leaks are large enough to offset their climate benefits.
"I think manure emissions on dairies are underestimated. These digesters seem to be a solution that captures a lot of methane," said Alyssa Valdez, a University of California, Riverside climate scientist and lead study author. "But I wanted to make sure they were working properly."
The findings of her study, published in Environmental Research Letters, draw on eight years of satellite and airborne observations of 98 dairies across California. By tracking emissions before, during, and after digester installation, Valdez and her research team were able to see how these systems perform over time and at scale.
Digesters are widely seen as a key climate solution. By sealing manure ponds and capturing the gas they produce, these systems convert methane into usable fuel instead of allowing it to escape into the atmosphere where it has a tremendous effect on the climate.
Methane is shorter lived than carbon dioxide, but it is 80 times more powerful at trapping heat in the atmosphere, making even small releases significant.
A previous study led by UCR climate scientist Francesca Hopkins examined emissions at a single dairy using ground-based measurements. Hopkins found that a well-managed digester can cut methane emissions by as much as 80%. This new research builds on that work by showing how digesters perform across dozens of farms, including what happens when things go wrong.
Across the dairies studied, the number of strong methane plumes declined after digesters were installed, suggesting the systems are effective overall. However, the researchers also detected occasional leaks that were far more intense than emissions from traditional manure storage.
"For the most part, the digesters are working well," Valdez said. "But the few leaks that happen, they make a huge impact."
In some cases, the team observed methane escaping at rates around 1,000 kilograms per hour. By comparison, typical emissions from open manure lagoons ranged from 20 to 100 kilograms per hour.
The contrast highlights a central challenge: digesters concentrate methane in one place, making it easier to capture, but they also increase the risk of powerful releases if something goes wrong.
Those large releases are not limited to system failures. The study also captured spikes in emissions during digester construction and installation, a phase that is rarely measured but can produce substantial short-term increases.
To capture these patterns, the researchers relied on satellite and aircraft data. Satellite images allowed them to track changes across dozens of dairies over long periods, which is not possible with traditional ground-based monitoring. Aircraft measurements were then used to identify concentrated methane plumes over specific infrastructure locations, making the approach especially useful for spotting leaks.
"A farmer might not know their digester is leaking," Valdez said. "This gives us a way to detect issues early and prevent them from becoming long-term problems."
However, this method does not capture all emissions. It cannot measure more diffuse methane releases from sources such as lagoons or fields. For that reason, the researchers say satellite and airborne observations are most effective when combined with on-the-ground measurements, which provide a fuller picture.
This need for comprehensive monitoring comes as California continues to invest in digesters as part of its strategy to reduce emissions of heat-trapping gases. Hundreds of these systems are already operating or in development across the state.
In some cases, methane releases are not accidental. Operators may vent gas when it cannot be flared due to air quality regulations or when systems require maintenance. These process-related emissions add another layer of complexity to managing digester performance.
Even so, the study shows that most systems are working well and that large leaks are relatively uncommon. But for Valdez, who spent years living in California's Central Valley, and whose family lives there, the work is about ensuring that climate solutions deliver real benefits in a region critical to the nation's food system.
"This region is the backbone of our food supply, but people there also carry a lot of fear about air quality," she said. "And they have good reasons for that."
More broadly, the study highlights the need to pay closer attention to agricultural waste.
"We need to start caring about poop," Valdez said. "And we need to keep verifying that these solutions are actually working. If we monitor them carefully, we can make sure they deliver on their promise."
