An updated version of a technique used by Amazonian Indians hundreds of years ago offers a way to store carbon for hundreds or thousands of years while producing nonfossil fuel-a double whammy for researchers seeking tools for fighting climate change.

Biochar-charcoal produced by heating organic material in the absence of oxygen (O2)-not only contains stable carbon (C), but may also help boost soil fertility.

But the benefits depend on a complex combination of factors that must be controlled to make it economically attractive while ensuring that it is a net greenhouse gas (GHG) sink, rather than a source of emissions, according to an ES&T research article (Environ. Sci. Technol. 2009, DOI 10.1021/es902266r) by Kelli Roberts and colleagues from Cornell University and the University of New South Wales.

While biochar “can play an important role in reducing our greenhouse gas emissions,” Roberts says, the added advantage is that “it’s actually sequestering carbon and not just offsetting emissions.”

The principle behind biochar is straightforward. Pyrolysis of biomass-from grass clippings to cornstalks to pine-beetle-infested forest debris-drives off volatile substances and unstable C, producing gas and oils that can be used for energy and leaving behind stable, C-rich charcoal.

The concept is not new. Amazonian Indians mixed a combination of charcoal and organic matter into the soil to make it more fertile. Scientists believe this terra preta, or “dark earth”, allowed large civilizations to thrive in places where the soil would otherwise have been too poor to produce large harvests. The stability of that C led researchers to investigate biochar for carbon capture and storage (CCS).