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Global Warming
Please Smoke
An ancient method for enriching soil could help curb climate change.

Josiah Hunt sticks his nose into a steaming pile of compost baking at 150 degrees in the morning sun on Hawaii’s Big Island. But this is no ordinary compost. Mixed into the horse manure and guava-tree chips is an ecofriendly charcoal called biochar.

Hunt is investigating how biochar can help boost crop growth on nearby farms. In addition to reducing the need for fertilizer (by locking in nutrients), the substance, made by burning biomass at high heat in low-oxygen conditions, may act as a carbon sink, slowing climate change. Soils that ancient Amazonians stocked with charcoal—perhaps to increase fertility—have trapped carbon for a millennium, studies show.

In the past 150 years activities like logging and plowing have released 78 billion tons of carbon dioxide from soil (half by burning fossil fuels). Increasingly, countries are considering schemes to put CO2 in the ground—primarily by capturing it at power plants and injecting it into deep geological formations. “Out of sheer desperation people are focusing on geological sequestration,” says Debbie Reed, head of the International Biochar Initiative. “But biochar is low tech, low cost, and has ancillary benefits that won’t go unrecognized much longer.”

Biochar retains up to 70 per-cent of the carbon that burning or decaying would emit, and could lock up a couple billion tons of carbon a year, says Johannes Lehmann, a Cornell University biochar researcher. “You’re slowing down the release of CO2 by one to two orders of magnitude.” 

At the Copenhagen climate talks last year, 20 nations agreed to fund agricultural mitigation, including biochar. Here the USDA is increasing biochar funding from $90 million to $130 million over the next four years, and Congress is considering bills that would offer financial incentives for biochar.

Yet the energy needed to make and transport the charcoal might outweigh carbon savings, so some suggest producing it locally. Another concern is feedstocks: Biomass from forests and crops is problematic because neither would net a CO2 reduction, and waste materials like sewage can create toxic byproducts.

The hurdles aren’t stopping Hunt from rotating his compost pile. He’d like to go big-time commercial if he and others prove that biochar truly works.

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