Biochar projects for mitigating climate change: an investigation of critical methodology issues for carbon accounting

Biochar is a potential tool in our fight against climate change, driven by its high carbon stability and supported by its roles in bioenergy and soil fertility. We consider methodology aspects of biochar systems used for carbon management and investigate the criteria for establishing additionality, baselines, permanence, leakage, system drivers, measurement, verification, economics and development for successful standalone projects and carbon offsets. We find that explicitly designing a biochar system around 'true wastes' as feedstocks combined with safe system drivers could minimize unwanted land-use impacts and leakage. Applying baselines of biomass decomposition rather than total soil carbon is effective and supports a longer crediting period than is currently standard. With biochar production introduced into bioenergy systems, under a renewable biomass scenario, the change in emissions increases with higher fuel use, instead of decreasing. Biochars may have mean residence times of over 1000 years, but can be accounted for more effectively using a recalcitrant and labile fraction.