By Melissa Leach, James Fairhead and James Fraser

Introduction: Biochar refers to the carbon-rich product that results when biomass – from wood or leaves to manure or crop residues – is burned under oxygen-deprived conditions and then buried in the ground. Yet around this apparently simple practice extraordinary levels of technological optimism and debate are emerging amidst the imperatives for global climate change mitigation and associated carbon markets. Burying biochar offers the promise of long-term sequestration of carbon, part of a suite of ‘biogenic’ approaches to climate geo-engineering that now attract the interest of scientists, policymakers and companies alike. Because its production and burial might also enhance soil fertility and thus food security, and can generate bio-energy and improving women’s health through reduced-smoke woodstoves – biochar is rapidly being promoted as a ‘multiple win’ technology for small farmers in Africa and beyond. Meanwhile, biochar-related businesses are multiplying rapidly, given rich if uncertain rewards promised by emerging global carbon markets. At the same time, critiques are emerging that question this promise and point to the dangers inherent in certain styles of biochar development.