How to measure the efficiency of terrestrial carbon dioxide removal methods

Abstract. The climate mitigation potential of terrestrial carbon dioxide removal (tCDR) methods depends critically on the timing and magnitude of their implementation. In our study, we introduce different measures of efficiency to evaluate the carbon removal potential of afforestation/reforestation (AR) and bioenergy with carbon capture and storage (BECCS) under the low-emission scenario SSP1-2.6 and in the same area. We define efficiency as the potential to sequester carbon in the biosphere in a specific area or store carbon in geological reservoirs or woody products within a certain time. In addition to carbon capture and storage (CCS), we consider the effects of fossil fuel substitution (FFS) through the usage of bioenergy for energy production, which increases the efficiency through avoided CO₂ emissions.

These efficiency measures reflect perspectives regarding climate mitigation, carbon sequestration, land availability, spatio-temporal dynamics, and the technological progress in FFS and CCS. We use the land component JSBACH3.2 of the Earth System Model MPI-ESM to calculate the carbon sequestration potential in the biosphere using an updated representation of second-generation bioenergy plants such as Miscanthus. Our spatially explicit modeling results reveal that, depending on FFS and CCS levels, BECCS sequesters 24–158 GtC until 2100, whereas AR sequesters around 53 GtC on a global scale with BECCS having an advantage in the long term. For our specific setup, we find that BECCS has a higher potential in the South American grasslands and Southeast Africa, whereas AR is more suitable in Southeast China. Hence, our results reveal that the efficiency of BECCS to sequester carbon compared to ‘nature-based solutions’ like AR will depend critically on the upscaling of CCS facilities, replacing fossil fuels with bioenergy in the future, the time frame, and the location of tCDR deployment.