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Abstract:
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.
