Dynamic assessment of biochar soil carbon climate change impacts

Biochar is receiving increasing political attention as a scalable and relevant climate change mitigation tool. With this growing focus comes a growing need for more accurate assessments of biochar climate change impact potentials. The mechanism of biochar soil carbon climate change mitigation is the time offsetting of emissions through decreased soil carbon decay. Therefore, temporally dynamic modelling is necessary to accurately assess these impacts. In this study, the 100-year evolution of soil carbon following soil application of biochar, residual straw and agricultural biogas digestate is modelled considering uncertainty related to biochar stability and environmental variability. From soil carbon modelling, dynamic climate change impacts are determined for biochar, straw and digestate per unit carbon added to soil for use in life cycle assessment. The developed methods are showcased in impact assessments of biochar at two levels of systems perspective. Results show that the developed dynamic modelling methods improve the accuracy of soil carbon climate change impact assessment. By disregarding short-term soil carbon storage, static modelling underestimates the impacts of non-pyrolyzed biomass soil carbon by a factor of two to three. Biochar is shown to provide a significant net climate benefit through increased soil carbon storage. In a large-scale implementation scenario, it is shown that biochar can contribute beneficially towards the Paris agreement 2100 temperature target, but also that national emissions accounting methods and short-term political climate targets can become a barrier for political incentives to realize the climate change benefits of biochar.