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January-February 2010

Could farm-friendly ‘biochar’ suck up a fifth of the world’s carbon emissions?

Brad Badelt

Biochar.

The Claim

Proponents believe that biochar—a fine charcoal produced when biomass is burned without oxygen—could dramatically cut our carbon emissions while improving soil productivity.

The Investigation

Here’s how it works: When organic matter decomposes, it releases carbon back into the atmosphere. This naturally occurring breakdown contributes a whopping 220 gigatonnes of carbon dioxide to the atmosphere every year, or nearly 10 times the emissions from fossil fuels.

If that same organic material were to undergo pyrolysis—combustion without oxygen—most of the carbon would be “locked in” as a solid, or biochar, and would remain in a stable form for hundreds or even thousands of years. The other byproducts of pyrolysis— oils and methane—could be captured and used as environmentally friendly fuels.

Biochar expert Johannes Lehmann of Cornell University suggests that carbon emissions could be reduced by between one and two gigatonnes a year through biochar, or roughly 20 percent of the annual emissions from burning fossil fuels.

While it might seem like the latest miracle cure for climate change, biochar was used centuries ago by Amazonian farmers, who burned manure, crop residue, and bones in primitive kilns to produce dark, fertile soil.

Because of biochar’s potential agricultural benefits, “there’s a strong economic incentive for it,“ says Kevin Aschim, interim chair for the Canadian Biochar Initiative, who adds that the cost of producing biochar is relatively low: likely half that of sequestering carbon underground.

So what’s the catch? Right now, it’s basically a lack of research. “Biochar holds a lot of promise,” Aschim concedes, “but there’s a lot of demonstration work that has to be done to prove that it can work.” For instance, the agricultural benefits of biochar work best in nutrient-starved, acidic soils typically found near the equator, like those in the Amazon. Canadian soils are more varied and may not benefit from the addition of biochar.

The Verdict

Biochar is a promising tool for reducing greenhouse gases but it’s by no means a climate-change panacea. In fact, the best usage may be as a soil amendment for developing countries that currently rely on slash-and-burn agriculture.

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