Why Humans Are Putting a Bunch of ‘Coal’ and ‘Oil’ Back in the Ground

Because the reactor removes the carbohydrates that microbes love, creating charcoal, the carbon that goes into the ground doesn’t become food, so it persists. “If you’re just burying carbohydrates, you always have this risk that you don’t have it in the right conditions,” says Paul Dauenhauer, senior adviser and cofounder of Carba and a chemical engineer at the University of Minnesota, Twin Cities. “And so if 10, 20, or 30 percent of the material that you bury ends up degrading, that’s a loss of a lot of credibility.”

You don’t even need an abandoned coal mine to get rid of the processed biomass—Carba is burying it in landfills, too—so the technique could be used pretty much anywhere. “Every municipality has wastepaper waste, tree clippings, and grasses, all that kind of stuff,” says Dauenhauer. “But also, you can imagine packaging centers, where they have all the waste cardboard. That’s all carbohydrate and cellulose also.”

When applied to agricultural fields, this sort of carbon is known as biochar, which also improves soils. Biochar can boost crop yields in some cases, says Sanjai Parikh, who created the Biochar Database, an open-access tool at UC Davis for those that make and use biochar. “It’s sequestering carbon still, even though it’s at the surface,” Parikh adds. “That biochar, some of it will degrade, but we’re talking stability of hundreds to thousands of years.”

The material also helps retain water in sandy soils, for instance, which tend to drain quickly otherwise. “Biochar is a highly, highly absorbent material,” says Wendy Lu Maxwell-Barton, executive director of the International Biochar Initiative. “This is why biochar is such an extraordinary soil amendment … it makes it more resilient to both drought conditions as well as flooding.”

Biochar is also quantifiable, Maxwell-Barton says: With a certain amount of biomass, you create a certain amount of carbon to store in soils or underground. Indeed, biochar accounts for 90 percent of the carbon removal market, in which companies pay to offset their greenhouse gas emissions.

Alternatively, it’s harder to quantify exactly how much carbon you’re sequestering by restoring a complex forest ecosystem. Not that humans shouldn’t also protect these habitats—such “nature-based solutions” sequester carbon, bolster species, reduce flooding, and boost tourism industries. The unfortunate risk, though, is that a wildfire might destroy a protected forest, returning the carbon to the atmosphere. Burying carbon as charcoal theoretically protects it better in the long run.

In addition to burying solid carbon or sprinkling it on fields, researchers are also turning waste biomass into liquid carbon—oil, essentially, that they pump back into the ground instead of pumping the fossil variety up. “What we do at the highest level is we make barbecue sauce—or liquid smoke for barbecue sauce—and then we inject it into old oil wells,” says Peter Reinhardt, CEO and cofounder of the carbon removal company Charm.

They also do this with pyrolysis, which spits out solid char for agriculture, but also liquid oil. That’s shipped to abandoned wells and pumped underground, where it solidifies. “There’s about 2 to 3 million abandoned, end-of-life oil and gas wells across the United States,” says Reinhardt. “It’s quite a problem, actually—a lot of them are methane emitters or improperly sealed, with fluid leaking up to the surface.” By pumping its biomass oil underground at these sites, Charm both sequesters carbon and seals up wells that have been leaking greenhouse gases.