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Cutting methane emissions, which account for 12 percent of US climate emissions, is a crucial component of the country’s efforts to slow down global warming.

One of the biggest sources of methane gas is America’s cows — and their poop. Dairy farms keep their massive volumes of manure in giant open-air lagoons, the most common and cheapest storage method, spurring a climate problem: As the manure decomposes, it produces methane, a highly potent “super pollutant” that accelerates climate change at a much faster rate than carbon dioxide. 

In recent years, the livestock industry has turned to a slate of novel technologies to reduce its carbon footprint, and one involves turning that poop into energy. 

Today on Vox, I’m looking at biodigesters, the machines these dairy operations are using to contain manure and trap the methane and other gasses it gives off to produce what’s known as “biogas.” Like fossil fuel-derived natural gas, biogas can be used to fuel cars and trucks, generate electricity, or heat homes and businesses. 

The technology shows some promise in reducing methane emissions: As of 2019, California’s dairy biodigester program was cutting one-quarter of its dairy methane emissions each year, the equivalent of taking nearly half a million cars off the road, according to an analysis by the state.

From 2020 to 2024, the number of manure biodigesters nationwide nearly doubled from 175 to 343. The technology looks so promising that a slew of generous federal and state grants, tax credits, technical assistance programs, and loan guarantees have been developed to build out biodigester infrastructure. President Biden’s Inflation Reduction Act funneled over $150 million in subsidies to biogas projects in 2023 alone.

But a coalition of environmental, public health, and agriculture groups — and some lawmakers — is pushing back against biogas, which they’ve renamed “factory farm gas.”

So are biodigesters and biogas potential game-changers in the fight against climate change, or is the technology’s win-win narrative too good to be true? 

Here are a few key takeaways from my reporting: 

It costs an estimated $1,130 per cow per year to build and operate a biodigester that generates just $128 worth of gas per cow, according to a widely cited analysis by University of California, Berkeley agricultural economist Aaron Smith.

Public investment in this highly inefficient gas, some energy wonks have argued, has also come at the expense of faster vehicle electrification. Manure biogas has gained an outsize share of valuable carbon credits in California, for example, capital that might have otherwise been used toward electrification projects, such as EV charging stations.

“If we would completely shake the Etch-A-Sketch and start over, I wouldn't prioritize anaerobic digesters on dairy farms as being where I would want to invest a lot of money,” Smith told me. “I would want to have a lot of research and development into better and more efficient ways to handle manure so as to reduce methane emissions.”

Over the next decade, greenhouse gas emissions are expected to decline in every sector except agriculture, where emissions are projected to slightly increase. Instead of incentivizing farmers to grow more climate-friendly foods or finally regulating farm pollution, as some other countries have begun to do, US policymakers — using funds from the Inflation Reduction Act and elsewhere — have doubled down on throwing money at technologies like manure biodigesters. They provide some modest albeit expensive short-term environmental benefits, but at the cost of further locking us into the animal factory farming model. The fact is that the US has long had an oversupply of milk, due in part to significant government involvement in the dairy industry; we could meet dairy demand with fewer methane-generating cows.

Instead, critics say, the biogas craze could end up incentivizing dairy farms to grow herd sizes in order to produce more manure and thus receive more lucrative federal and state credits from the gas that these “cash cows” generate. In 2021, for example, Iowa passed a bill that lifts the cap on the number of animals a farm can house if it has a biodigester, which directly led to increased herd sizes. Other analyses have found that some dairy farms in Wisconsin and California increased their herd sizes, and thus their overall pollution, after installing biodigesters.

Patrick Serfass, executive director of the trade group American Biogas Council, dismissed the argument that biodigesters incentivize farms to get bigger: “I don't think anyone's shown causation,” he told me. “I think there might be some correlation.”

One set of possibilities for curbing livestock emissions include feed additives, such as Bovaer — a product that when fed to dairy cows daily can reduce methane from their burps by around 30 percent — which are much more cost effective in reducing methane than manure biodigesters. 

The government could also simply pay dairy farmers to raise fewer cows, which some environmental groups say would be cheaper than funding biodigesters. The Netherlands has begun paying farmers to stop raising pigs and other livestock to reduce the nation’s nitrogen pollution. 

The simplest solution would be to make the dairy industry reduce its methane however it sees fit, at its own expense. After all, cow manure doesn’t inherently need to contain methane. So-called “dry” manure management systems in which the manure is stacked in outdoor mounds and exposed to oxygen — as opposed to the poop lagoon systems used by most commercial dairies — largely avoid releasing methane. 

But common sense has been hard to find in US climate-agriculture policy, with policymakers and business leaders doing anything to avoid the cow in the room: that we need to raise fewer cows.

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