Target Atmospheric CO2: Where Should Humanity Aim?
James E. Hansen, NASA Goddard Institute for Space Studies, and colleagues mention biochar in a report, “Target Atmospheric CO2: Where Should Humanity Aim?”:
Carbon sequestration in soil also has significant potential. Biochar, produced in pyrolysis of residues from crops, forestry, and animal wastes, can be used to restore soil fertility while storing carbon for centuries to millennia. Biochar helps soil retain nutrients and fertilizers, reducing emissions of GHGs such as N2O. Replacing slash-and-burn agriculture with slash-and-char and use of agricultural and forestry wastes for biochar production could provide a CO2 drawdown of ~8 ppm or more in half a century.
The full report can be found here: www.columbia.edu/~jeh1/2008/TargetCO2_20080407.pdf