The Connecticut River cuts between the Green Mountains of Vermont and the White Mountains of New Hampshire and rushes into the heart of Massachusetts, where Denise Barstow Manz stands in the wind, surveying the land her family has farmed for 217 years.

“We have some of the best soil in the entire world,” says Barstow Manz. “It’s called Hadley silt loam.” She explains how the rich Connecticut River flood plain that’s wedged between the river and the Mount Holyoke mountain range behind her nourished tobacco, asparagus, broom corn and squash for her 1800s ancestors, and how it now grows hay and corn for the current farm’s 600 dairy cows.

Her dad, David Barstow, co-owns the farm with his brother, Steve Barstow, and his niece and nephew, Shannon and Steve II. David is “the director of special projects,” his daughter teases. “Anytime we are doing anything that is unusual, which is almost always, Dad is in charge.”

In the early 2000s, when the price of milk plummeted and dairy farms everywhere were trying to find a way to diversify, the Barstows began thinking about how to stay alive. They decided to take full advantage of an underutilized commodity the cows produced in abundance, and build something called an anaerobic digester—basically, a manure-fueled power plant.

It was a business decision that happened to have profound environmental consequences. Cows produce milk, but microorganisms in one of their four stomach compartments also produce methane. They belch methane out of their mouths, and when mountains of manure pile up in oxygen-free lagoons or pits, the micro-organisms keep producing methane there, too.

Global climate policy hasn’t focused as much on methane as carbon dioxide, partly because methane only stays in the atmosphere for about 12 years, while carbon dioxide lingers for centuries. But methane is many times more effective than carbon dioxide at warming the atmosphere, and its concentration has been rapidly increasing, according to the United Nations Environment Programme (UNEP). Interestingly, many measures for reducing methane have low operating costs or quickly pay for themselves. That’s because captured methane can be used as power.

In front of the Barstows’ cow barn sits a 550,000-gallon underground tank into which about 9,000 tons of manure flow from the cow barn each year. There, it’s mixed in an oxygen-free environment heated to between 95 and 105 degrees Fahrenheit. Micro-organisms break down the organic material in the manure, and the machinery captures the biogas produced in the process. Pipes move the methane into one of two engines on the farm that burns it to create heat and electricity. This provides all the farm’s heating needs. The organic matter left over after digestion is used as fertilizer on the fields, which has increased crop yields considerably. With the volatility of fertilizer prices since Russia’s invasion of Ukraine, free fertilizer is a welcome cost savings.

“When you talk about sustainability, you have to talk about soil health and water quality and all of that, but you also have to talk about being able to make a profit,” Barstow Manz says, pushing breeze-blown strands of hair back into her ponytail. A few cows lie on the field in front of the farm store chewing their cud. There’s a steady wind stirring on that cloudy June day, and the chimes on the farm store tinkle. Yet the air blowing across the farm smells like … nothing.

The digester had turned all the manure into money.

Three-and-a-half billion years ago—when the Earth was a mess of crust and ocean—there was about 1,000 times as much methane in the air as there is today. Scientists think early micro-organisms helped warm the new planet by releasing methane as they went about their business. The sun was only 70 or 80 percent as bright back then, and the oceans should have been frozen. But some scientists believe that because of heat trapped by methane and other greenhouse gases, they weren’t.

A methane molecule has one carbon atom surrounded by four hydrogen atoms. Desirée Plata, an environmental chemist at MIT, compares it to a person with four limbs. “There’s a lot of different ways they could move,” says Plata. “I like to say methane has great dance moves, so it’s got these vibrational and rotational modes, where its atoms are moving around the central atom.”

When ultraviolet and visible light waves reach the Earth’s surface, the ground absorbs them and sends the energy up as infrared radiation, or heat. The methane grabs onto that energy, says Plata, and keeps some of it trapped in the atmosphere. A molecule of carbon dioxide doesn’t absorb as much infrared radiation as methane. “Methane, molecule for molecule or pound for pound, is much better at absorbing that outgoing energy that’s trying to leave the Earth,” says Plata. “So a little bit of methane can do a lot of damage relative to CO2.”

About a third of the methane emitted each year comes from natural sources, especially wetlands, which pump out megatons of methane. Methane-making bacteria also thrive in hydrothermal vents and hot springs. But the majority of methane emitted into the air today is generated by human activity. Oil, natural gas and coal-mining infrastructure contribute about 35 percent of human-caused methane emissions; human waste and landfills contribute another 20 percent.

Agriculture produces much of the rest. “We have seen essentially the number of livestock around the world inexorably go up for many, many decades by now,” says Drew Shindell, an earth scientist at Duke University and the chair of the Climate and Clean Air Coalition Scientific Advisory Panel coordinated by the UNEP. If nothing changes, human-caused methane emissions are expected to increase by more than 15 percent over 2010 levels by 2030.

Since a lot of the methane humans are adding to the atmosphere comes from waste and leaky infrastructure, it’s easier to reduce than carbon dioxide, which is a byproduct of combustion in essential machines and power plants. And since methane only stays in the atmosphere for about 12 years, cutting it down will bring fast rewards. “If you want to tangibly reduce people’s suffering over the next 20 to 30 years, then methane is by far your most potent leverage to do that,” Shindell says, noting that fires, heat waves, floods and droughts are increasing at a faster rate than the climate scientists’ worst-case projections. On the ground, methane also oxidizes to form ozone, a respiratory hazard.

Shindell’s 2021 UNEP Global Methane Assessment showed that a combination of strategies—from better manure management to capturing gas escaping from the energy infrastructure—could reduce human-caused methane emissions by up to 45 percent. According to the UNEP report, that 45 percent reduction in human-caused methane emissions would “prevent 255,000 premature deaths, 775,000 asthma-related hospital visits, 73 billion hours of lost labour from extreme heat, and 26 million [metric tons] of crop losses” annually.

When it comes to agriculture, the methane from belching cows is difficult to eliminate unless consumers start eating less meat and drinking less milk. Methane from manure, though a much smaller portion of livestock emissions, can be reduced more effectively right now.

Anaerobic digesters can also tackle another problem: Americans throw out 30 to 40 percent of all the food we grow and make—as much as 80 million tons a year. Food waste is the largest category dumped in municipal landfills, and some states are running out of space. In 2014, Massachusetts—which now has fewer than ten active landfills, according to the Environmental Protection Agency—banned the dumping of food and other organic waste for institutions and businesses that produce one ton or more a week: grocery stores, food processors, wholesalers and large restaurants. Since November 2022, the ban has applied even to institutions that produce half a ton of organic waste.

Before the Massachusetts ban, there was only one small anaerobic digester in the state. By 2020, there were nine, five of them belonging to Vanguard Renewables. The company’s co-founder, John Hanselman, first laid eyes on anaerobic digesters in the early 2010s, when he went to Europe to examine solar panel technologies. “I kept seeing these domes. I said, ‘What are these things?’ And they said, ‘It’s an anaerobic digester. We take organic materials and cow manure and we make renewable energy.’”

When he got back to Boston, Hanselman decided to develop a new company, with colleague Kevin Chase, that focused on building digesters, but raising money was difficult. “Big energy investors were like, ‘Yeah, that doesn’t work, we don’t do that,’” he recalls. The United States did have some digesters, especially at wastewater treatment facilities and a few on farms, but the technology had never really taken off stateside.

As large companies like Unilever started talking about food waste and carbon footprints, Vanguard bought two existing manure digesters—including the Barstows’—which had been processing manure for a short time, and improved their capacity and efficiency. Then Vanguard built digesters on other farms. It also built a recycling facility in Agawam, Massachusetts, where companies or restaurants send food waste: pallets of packaged food, dozens of half-empty kegs of beer, mountains of boxed soup. An auger compactor and a hammer mill the size of a bus break food out of its packaging. The facility processes 100 tons of food per day, sending it to digesters to make power.

In 2013, Vanguard started trucking more than 24,000 tons of food waste each year, from local companies, such as Cabot Creamery and HP Hood, to the Barstows’ farm. “Manure is really just food waste that’s been digested once,” says Patrick Serfass, executive director of the American Biogas Council. “So when you take food waste that hasn’t been digested at all, it has 10 to 35 times more energy in it.” Allocating just 10 percent of a digester’s volume to food waste doubles the biogas yield. “If we don’t recycle this food waste, it’s just going to be buried,” Serfass says.

Instead, the generator helps turn the local food and farming industries into a highly efficient loop. The crops on the Barstow farm hold the sun’s power, which cows eat to produce milk that Cabot Creamery uses to make butter. Cabot sends its food waste back to the Barstows’, and then buys some of the energy to help power its butter plant. Waste is squeezed for resources until it has nothing left to give. The digester sends more than 6,000 megawatt hours of electricity per year into the grid, enough to power 550 homes. The American Biogas Council estimates that at least 15,000 anaerobic digestion systems like this could be built across the country.

Vanguard won’t divulge how much money it’s making from the energy it sells and the fees it collects from food companies. But it now has contracts with 130 farms across the country, with $800 million in projects in progress nationwide. It has tripled its employees in the past year.

“For 400 years, this country picked up garbage and either put it in a hole and buried it, or burned it. When people tried to do it before us, they ran right into a brick wall of an industry that didn’t want to change,” says Hanselman. “We try to price it so that we can get people to disrupt what they’ve been doing.”

What happens when this approach is scaled up? Massachusetts has 9,500 dairy cows producing 200 million pounds of milk each year. In contrast, California, the largest producer of milk in the U.S., has 1.7 million dairy cows that produce 42 billion pounds of milk each year. Especially in the agricultural San Joaquin Valley, many farms are concentrated animal feeding operations, or CAFOs, with more than 700 dairy cows confined to a small area and manure frequently thrown into a pit or lagoon.

In 2016, the California legislature passed a bill requiring that the state reduce disposal of organic waste 75 percent from 2014 levels by 2025 and reduce methane emissions from dairy and livestock 40 percent from 2013 levels by 2030. The state started giving out more grant money to dairy digester projects, most of which went to three biogas companies that build on huge dairy farms. California allows gas produced by anaerobic digesters not just to be sold but also to generate credits when used for vehicle fuel. A digester in California can pay for itself in a little over three years, while dramatically reducing a CAFO’s methane emissions.

Some environmental groups take issue with this. They acknowledge that digesters can help mitigate damage but worry that subsidies encourage CAFOs to keep polluting the air and water, overusing hormones and mistreating animals. They argue that the simplest way to reduce methane is to keep farms small and expose manure to the air. (When manure isn’t put into a pit or lagoon, oxygen prevents methanogens from surviving.) Many environmentalists would also like to see people consuming less meat and dairy.

Hanselman, who calls himself “an old Sierra Club guy,” has heard these complaints from friends. His retort: “Hey guys, you can ignore this or wish it away; they’re not leaving. Let’s attack the problem and try to work with the industry to create a solution that puts us as a country in a much better place.”

Burning methane natural gas from the digesters also emits CO2 as a byproduct, though a lot less than burning fuel oil or coal. And since CO2 is a much weaker greenhouse gas than methane, burning the methane heats the Earth far less than letting it float into the atmosphere untouched. “Unfortunately, there is no replacement for natural gas that can possibly work in the next 20 years,” says Hanselman. The methane filling the pipelines might as well come from non-fossil sources that actually cut down on emissions, he says, and be used alongside all the other sources of renewable energy. The results in California have been striking: Projects subsidized by California’s digester grants will sequester as much greenhouse gas as removing almost 500,000 gas-powered cars from the road each year.

Third-generation farmer Danielle Goodrich Gingras walks past a humming, barn-red anaerobic digester on her way to visit the cows at her farm in Salisbury, Vermont. The sun is powerful on this early summer day, and the small, brand-new power plant shines. A Vanguard representative is there, too, and he explains that this plant came online in 2021 and is now the biggest anaerobic plant in the Northeast. The natural gas produced by its two 925,430-gallon digesters is purified on-site and fed into Vermont pipelines.

By partnering with Vanguard, farmers relieve themselves of the construction and operating burdens but still reap significant benefits. Their manure is handled in a way that reduces nutrient runoff into local watersheds, which is regulated by the state. Neighbors are happy, since there’s little odor. The solid plant-fiber byproducts from the digester can be used as bedding for the cows (the price of sawdust keeps increasing), and the liquid digestate is rich in nitrogen, which makes it an excellent fertilizer. Farms receive a 20-year guaranteed lease payment from Vanguard, and some also receive credits from their energy providers.

Peter Melnik, a fourth-generation farmer in Deerfield, Massachusetts, partnered with Vanguard early on to build a digester. “Sustainability to me means not importing nitrogen from Russia, not relying on an outside sawmill for bedding, being a better neighbor because we aren’t adding manure to our fields,” he says. “I’ve also never felt so interconnected with my community and the food system. And it feels really good to know that we make enough electricity to power almost every home in this community.”

On a wet September morning a few months later, a thick fog cloaks the mountainside trees behind the Barstows’ milking barn. A tanker truck is parked nearby, its waste flowing into the digester. The family is about to bring in their fifth cutting of hay fertilized with the digester’s organic matter. “We used to get four,” Barstow Manz says, “but because of the anaerobic digester we are now getting five.”