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Is California Overstating the Climate Benefit of Dairy Manure Methane Digesters?


A California state grant program designed to reduce greenhouse gas emissions results in the direct release of approximately 225,000 to 300,000 metric tons of carbon dioxide into the air each year, according to an Inside Climate News analysis of state data. The pollution, which comes from burning biomethane fuel that was captured from decomposing cow manure, is equal to the annual greenhouse gas emissions of between 50,000 and 65,000 automobiles.

However, the emissions aren’t counted in the state’s annual greenhouse gas inventory. Rather, the California Department of Food and Agriculture considers the pollution to be the opposite—part of the emissions reductions that come from its $200 million dairy digester program

Critics of the program note that burning methane, the biggest component of natural gas, releases carbon dioxide emissions regardless of whether the gas comes from cow manure or from underground fossil gas reservoirs. They argue that using biomethane fuel in vehicles should not be counted as a source of emissions reductions.

“It treats a compressed-natural-gas heavy duty truck emitting greenhouse gas emissions as though it were a direct carbon capture technology, which of course it is not,” Tyler Lobdell, an attorney with Food and Water Watch, said of the state’s dairy digester program.

The California Air Resources Board (CARB) also considers this CO2 pollution negative emissions, counting the same volume of carbon dioxide as part of the emission reductions achieved by the state’s Low Carbon Fuel Standard program. The program is designed to decrease the carbon intensity of California’s transportation fuel.  

Roughly a dozen of the dairy digesters that received funding from the state’s Department of Food and Agriculture are part of a third program, the Aliso Canyon Mitigation Agreement set up to offset emissions from a massive leak at an underground gas storage facility in southern California from 2015 to 2016.

In effect, critics argue, dairy digesters that received funding from the state of California are getting double, and in some cases, triple credit for reducing the same greenhouse gas emissions, for something they say is actually contributing to, rather than combating, climate change.

“It’s a complete mess,” said Danny Cullenward, a climate economist at the University of Pennsylvania and American University and the vice chair of California’s Independent Emissions Market Advisory Committee.  “There’s multiple overlapping claims being attributed to the same tons from the same fundamental activity.”

A report published in 2021 by California’s Legislative Analyst’s Office (LAO), a nonpartisan government agency that provides fiscal and policy advice to the state Legislature, found the Department of Food and Agriculture dairy digester program likely overstates its greenhouse gas benefits due in part to other government programs that also count the climate benefits of the same dairy digesters.

The report also reiterated that burning methane fuel, whether it comes from cow manure or underground sources, releases carbon dioxide, whether-or-not the state counts those emissions in its greenhouse gas inventory.  However, the LAO found that state regulators did not count emission reductions more than once at the sectoral level in its annual greenhouse gas inventory.  

CARB declined a request to make someone available for an interview. However, David Clegern, a spokesman, said in a written response that their accounting practices regarding carbon dioxide from biomethane are consistent with Intergovernmental Panel on Climate Change (IPCC) inventory methods and there is “no double counting of the emissions in the [state greenhouse gas] inventory.”  

The Air Board is currently considering changes to its Low Carbon Fuel Standards program and on December 19 proposed it would phase out incentives for biomethane from dairies and other sources by the end of 2045.

Advocates for environmental justice communities near the digesters and the industrial scale dairies that feed them, say the incentives are fueling a further concentration of cows and manure that pollute the environment and should end immediately.

“It’s creating sacrifice zones, where certain communities in the Central Valley get to carry the load for the rest of the state so it can boast about its methane reductions,” Lobdell said.  “That’s unjust. CARB can do better and it’s choosing not to.”

One hundred miles southeast of CARB headquarters in Sacramento, the California Dairy Farms, a large dairy in the heart of California’s Central Valley, received $1.6 million from the state’s Department of Food and Agriculture in 2022 to help turn manure from the facility’s 5,250 milking cows into “biomethane” fuel.

A dairy digester, a thick rubber membrane covering a pool of liquid manure, will capture biogas that, once upgraded, can be used interchangeably with conventional fossil gas. The fuel will be used to power vehicles that run on compressed natural gas in the Central Valley and elsewhere in the state, according to information posted by the Department of Food and Agriculture.  

The project, the largest of 14 dairy digesters funded in part by the California Department of Food and Agriculture in 2022, will reduce greenhouse gas emissions equal to 31,659 metric tons of carbon dioxide equivalent per year when it is completed in 2024, according to the department.

The majority of these reductions will come from a direct decrease in the dairy’s methane emissions that would otherwise be released into the atmosphere.

However, approximately 10 to 13 percent of the emission reductions from each of the dairy digester projects come from “avoided CO2,” when biomethane is used as fuel instead of fossil gas or diesel fuel, according to Steve Lyle, a spokesman for the department, who added that the percent of emission reductions that come from avoided CO2 can be highly variable across projects.

For the California Dairy Farms digester, the emissions cuts translate to being credited for roughly 3,000 to 4,000 tons of avoided fossil fuel carbon dioxide per year, when biomethane from the facility is burned as fuel.

The California Air Resources Board previously counted carbon dioxide emissions from biomethane and other biofuels used in the transportation sector in its annual greenhouse gas emissions inventory no differently than carbon dioxide emissions from any other fuel source. Then in 2016, the agency changed its accounting methods to exclude these emissions.  

The change resulted in a reduction in emissions for the transportation sector in 2016, a year when they otherwise would have increased, according to a preprint study posted on the Social Science Research Network by Stanford University climate researcher Leehi Yona that has not yet received full peer review.

Clegern, of the Air Board, said the agency made the change to be consistent with IPCC inventory methods that were first developed in the 1990s. “This is done so we have consistent inventory methodologies across jurisdictions,” Clegern said.

While burning biomethane or other biofuels produces carbon dioxide similar to the CO2 emissions from fossil fuels, biofuels have historically been considered to be carbon neutral. This is because the carbon that is released during combustion of the fuel was sequestered from the atmosphere by plants that went into making the fuel.

However, recent studies suggest greenhouse gas emissions associated with biofuels may actually exceed those of fossil fuels. Yona said continued reliance on the outdated IPCC guidelines no longer makes sense.

“These methodologies, while they were the best that we could have decades ago, are woefully inadequate in comparison to the scientific information we have available to us today,” she said.

Also at issue is whether emission reductions from the dairy digesters are being counted more than once by different state agencies.

The Department of Food and Agriculture counts the total greenhouse gas emission reductions—including methane and “avoided carbon dioxide”—from the digesters it has subsidized in the state.

The Air Board also includes these same emission reductions, including both methane and “avoided carbon dioxide,” in its Low Carbon Fuel Standard, which incentivizes the use of biomethane in the transportation sector. A portion of the dairy digester emission reductions are also counted in a program designed to displace emissions from the Aliso Canyon natural gas storage leak that occurred nearly a decade ago.

While multiple state agencies count the emission reductions as a climate benefit for their individual programs, the Air Board stated that emission reductions are only counted once in the state’s annual inventory of greenhouse gas emissions.

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Under the inventory, for example, methane emission reductions from the digesters are counted as reductions in the agriculture sector, where the emission reduction occurs.   Meanwhile, avoided carbon dioxide emissions are counted as reductions in the transportation sector or other sectors where the fuel is burned. Emissions reductions from digesters that are part of the Aliso Canyon mitigation agreement are counted in the natural gas sector, Clegern said.  

Clegern added that reductions claimed at the program level “are for either credit generation or for informational purposes as part of administering those respective incentive programs.”

Critics say such double or triple counting at the program level overstates the cost effectiveness of individual programs because it exaggerates the climate benefits of each program by not acknowledging that others also helped fund the same emission reductions.

A recent Air Board report on the Department of Food and Agriculture’s dairy digester program stated it “delivered some of the most cost-effective GHG emissions reductions on a per-metric ton CO2e [carbon dioxide equivalent] basis” compared to other programs.

Dairy Cares, an industry group, called the program “the most cost-effective effort in the fight against climate change.”

Sasan Saadat, a policy analyst with Earthjustice, said it’s a misrepresentation.

“California loves to brag ‘this program, for every eight dollars we spend on it, gets us this many tons of CO2 reductions,’ he said. “What’s missing from that is the fact that these programs are triple counting those reductions.”

At least 210 more dairy digesters will have to be built in California in the coming years, along with other measures, to reach the state’s 2030 target for methane emission reductions from agriculture, according to a 2022 report by the Air Board.

In addition to subsidizing additional digesters, CARB will have the authority to regulate methane emissions from dairies as of Jan. 1, 2024. Yet, it is unclear if, or when, the agency will begin to exercise its authority.

The Air Board “has not yet designed a new regulation,” Clegern said.

Peter Aldhous contributed additional reporting to this article.



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