Potential of Land‐Neutral Negative Emissions Through Biochar Sequestration.

Negative emissions (NE) are under discussion as elements of mitigation strategies aiming to achieve the climate targets of the Paris Agreement. However, biomass‐based NE technologies such as bioenergy with carbon capture and storage (BECCS) require vast land areas in order to meet the targets projected by climate economic optimization models, thereby competing with food production and ecosystem protection. Here we assess feasible NE contributions of alternative, more sustainable pyrogenic carbon capture and storage (PyCCS) based on land‐neutral biomass production using biochar‐mediated yield increases to maintain calorie production while realizing net CO2 extraction from the atmosphere. Simulations with a biosphere model indicate that such a land‐ and calorie‐neutral PyCCS approach could sequester 0.44–2.62 Gt CO2 yr−1 depending on the assumed biochar‐mediated yield increase achievable on (sub‐)tropical cropland (15%, 20% and 30%, respectively). Cumulatively, by the end of the century, 33–201 Gt CO2 could be sustainably supplied by such an approach, equaling 6%–35% of the NE demand projected for trajectories likely to limit climate warming to 2°C or lower. Furthermore, additional areas dedicated to BECCS in integrated assessment scenarios could instead be used to increase global calorie production (by 2%–16%), or spared for nature protection (up to ∼ 100 Mha). Thus, land‐ and calorie‐neutral PyCCS may, within limits, contribute to lessening the additional land use pressure of biomass‐based NE technologies. Plain Language Summary: We assessed a land‐ and calorie‐neutral approach to pyrogenic carbon capture and storage (LCN‐PyCCS) as a supply‐driven, bottom‐up approach to large‐scale carbon dioxide removal. LCN‐PyCCS relies on the process of biomass pyrolysis, where biomass carbon is transferred into the more stable biochar that can be used as soil amendment enhancing the soil properties and storing carbon in the soil. The approach is based on land‐neutral biomass production using biochar‐mediated yield increases to maintain calorie production while realizing net CO2 extraction from the atmosphere. In our analysis building on process‐based simulations of biomass growth we find a potential of 0.44–2.62 Gt CO2 yr−1 depending on the yield increase achievable. Furthermore, this approach could substitute negative emissions from other, less sustainable, biomass‐based negative emission technologies. Assuming that this could free biomass plantations, we evaluated the potential of alternative uses of this land, showing potential increased calorie production of 2%–16% or land sparing for nature protection of up to ∼100 Mha. Key Points: Land‐ and calorie‐neutral pyrogenic carbon capture and storage can provide negative emissions of 0.44–2.62 Gt CO2 yr−1 depending on yield increase achievedCumulated until 2100, this amounts to 6%–35% of the negative emission demand in integrated assessment scenarios of climate stabilizationLand not required compared to alternative deployment of bioenergy with carbon capture and storage could be used for increasing food production or nature restoration [ABSTRACT FROM AUTHOR]