How a soil additive called biochar can help fight the climate crisis by locking away carbon for centuries

• Biochar is a soil additive that can help store carbon dioxide for centuries.
• Cities in Minnesota and Nebraska plan to build biochar plants similar to those in Nordic countries.

A decade ago, Jim Doten was on a tour in Afghanistan with the Army National Guard searching for ways to help farmers improve soils depleted of nutrients and carbon.

The geohydrologist came across some studies on biochar, a material not unlike the burnt remains of a campfire.

Doten's biochar program in Afghanistan was short-lived, but the idea stuck. He's since convinced Minneapolis, Minnesota officials of biochar's value as governments search for ways to not only reduce greenhouse gas emissions but also remove them from the atmosphere.

"It took a few years to build credibility because people didn't understand why this was a carbon-negative technology," said Doten, the carbon-sequestration program manager for Minneapolis.

The rationale for biochar being carbon-negative goes like this: Through photosynthesis, trees absorb carbon dioxide from the atmosphere, and it's released when they decay or are burned. Gathering forest or yard waste, converting it into biochar using a process known as pyrolysis, and returning it to the soil can trap carbon for centuries and retain water while helping plants absorb nutrients.

Doten first worked with the Shakopee Mdewakanton Sioux Community, a tribe in Minneapolis that owns a compost facility and develops urban gardens to promote food security. The city paid for biochar trucked in from Missouri to be mixed with compost.

"That's a great way to demonstrate the work, but from a climate aspect, trucking biochar across the country negates its climate benefits," Doten said. "So we need local supply."

Minneapolis is among seven cities that received a $400,000 grant from Bloomberg Philanthropies this week to invest in biochar. The city is matching the grant to fund the construction of a production plant that will convert wood from nearby ash trees — which are getting decimated by an invasive pest — into biochar, Doten said. The plant will be powered by a low-carbon electric grid.

"Instead of burning the wood for energy, which is also bad for the climate, we're turning it into a soil amendment," Doten said.

The $50 billion global industry that combusts wood for power has been panned by scientists and environmentalists, even as governments in the US, the European Union, and elsewhere categorize it as renewable. While some biochar on the market is a byproduct of that industry, Doten said most production was from plants like the one coming to Minneapolis, which will use the nearly zero-emissions pyrolysis process. That's the case in Stockholm, the original recipient of a Bloomberg Philanthropies grant, where yard waste is being converted into biochar and enough energy to heat 80 apartments.

Bloomberg Philanthropies said all the projects combined would yield enough biochar suppliers to sequester nearly 10,000 metric tons of carbon dioxide each year. It's a help though it's only a tiny amount relative to the scale of what's needed to keep global warming below catastrophic levels. Scientists predict that 10 billion metric tons of carbon will need to be removed from the atmosphere annually by 2050.

"Work like this, no matter the size, is important because it engages everyday people in finding solutions," Jim Anderson, the government-innovation lead at Bloomberg Philanthropies, said.

For now, Doten said government agencies with big public-works projects would be the main customers for biochar. A pilot project in Minneapolis demonstrated that biochar along highways helped sponge up stormwater, a climate-resiliency strategy as the risk of flooding increases.

Eventually, Minneapolis' plant could sell carbon-offset credits to companies that want to meet net-zero targets, Doten added. In 2019, biochar was listed for the first time on a voluntary carbon marketplace in Finland, followed by another listing in 2020, according to the International Biochar Initiative.

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