What comes to mind when you hear the term engineered climate technology? For me, it’s usually an expensive metal machine sucking carbon out of the air with a lot of moving parts, a lot of engineering schematics and a lot of complicated chemical explanations. 

A less popular image of carbon removal is a hole in the ground filled with tree trimmings. But biomass burial, the technical term for this hole, is one of the most promising and uncharacteristically simple engineered approaches to removing carbon from the atmosphere. 

"We call this a hybrid nature engineering method," said Ning Zeng, professor at the Department of Atmospheric and Oceanic Science and the Earth System Science Interdisciplinary Center at the University of Maryland. "It doesn't really fall neatly into any particular big boxes they have defined."

But it is, in fact, an engineered solution to climate change. Burying wood trimmings about 6.5 feet underground prevents the decomposition process, as it preserves the carbon in the wood instead of releasing it into the atmosphere. 

"[Without biomass burial], you waste all that photosynthesis capacity from a carbon point of view," Zeng said. "The plants pump CO2 into their body, but then they die, it goes back [into the atmosphere]."

Nature’s already tackled the hard part of capturing CO2 from the atmosphere, leaving us to configure a storage solution. But how durable that storage is depends on engineering the wood vault where the trimmings are stored in a specific way, and using materials that create an anaerobic (oxygen-free) environment. 

The vault itself can be created from the soils at the site of burial if the soil can insulate from termites, fungi and water. According to Daniel Sanchez, chief scientist for biomass carbon removal and storage at Carbon Direct, dense, nonporous soils such as clay, silt and sand are the best for keeping an underground environment stable in this way. 

"You absolutely need to think about how you design different vaults," he said. "They're going to have different considerations and different abilities. The science of the wood vault is still really evolving." 

But with good engineering, the carbon stored in wood vaults can be preserved for thousands of years, according to scientific models. That number has pricked the ears of companies, investors and sustainability experts alike. And the carbon crediting machine has already started lurching into motion on biomass burial. Puro.Earth has a few biomass burial projects listed on its marketplace, including the Potomac Project of Carbon Lockdown a startup founded by Zeng’s demo projects in Montreal where the carbon removal is selling for $170 a ton. And last March, Puro released a methodology for biomass burial, specifying where the wood can come from, how to ensure additionality and making sure to remove other greenhouse gasses such as methane. 

Biomass burial is one of the most promising and uncharacteristically simple engineered approaches to removing carbon from the atmosphere.

Of course, the climate tech startup ecosystem has already started roaring to life around this technology, including newcomer Kodama Systems. They are hoping to go beyond carbon accounting and solve three problems at once — decreasing the amount of carbon in the air, reducing wildfire risks and increasing the workforce for forest manageme