Chances are good that you’ve never heard of biochar, though you may know of it by its common name: charcoal. Burying partially burned wood may enhance the storage of carbon in soils, helping to mitigate climate change.
It works like this: when plants grow, they accumulate carbon dioxide from the atmosphere, using it to produce woody tissues. When we burn plants, we return carbon dioxide to the atmosphere. But, suppose we only partially burn it, so that some charcoal remains?
Charcoal is more resistant to decomposition than fresh plants. So, if we bury it, it will store carbon in the soil for long periods of time. Meanwhile, we can use some of the energy for heating or other uses that have traditionally relied on fossil fuels.
Biochar has a lot of advocates. Farmers see a way to get paid for storing carbon in their soils. And foresters see it as revenue stream for the leaves and branches that are normally left behind after logging.
Energy released during biochar generation is much less than the energy released by burning an equivalent weight of fossil fuels. So a lot of wood must be consumed. And to be an effective carbon sink, biochar must store more carbon in the soil than if the forest were left to grow to maturity.
Realistically, we know little about the net gain in carbon storage by generating charcoal, or biochar. And while there is no doubt that charcoal decomposes slowly, we should be cautious when we hear how plans for biochar will wean us from fossil fuels.
Photo, taken on October 12, 2007, courtesy of BobSacks via Flickr.