Scrutinizing the feasibility of land-based CDR potentials under socio-ecological constraints

99% of current anthropogenic carbon dioxide removals (CDR) happen on land, and land-based CDR such as re/afforestation or bioenergy with carbon capture and storage (BECCS) will likely play important roles on our way to net-zero/net-negative emissions while more novel methods need to be scaled up. However, the partly large estimates of the potentials of land-based CDR require a reality check, as obstacles to their implementation and non-negligible side-effects on society and ecosystems have not been comprehensively considered so far. Here, we present key results from an interdisciplinary project that scrutinized the feasibility of land-based CDR potentials at the national level of Germany and at global level applying a holistic approach to socio-ecological constraints.

Investigating the potentials for land-based CDR in Germany under different socio-economic scenarios shows that even optimistic scenarios that include extensive economic, lifestyle and dietary changes fall short of meeting both food demands and CDR requirements in line with the national LULUCF sector target. To implement CDR on a relevant scale, extensive land management and land use transitions in particular through afforestation of agricultural land are required. However, interviews with relevant stakeholders reveal diverse and extensive barriers in this regard, such as land use conflicts, changes to the landscape, knowledge gaps, limited human and financial resources and legal restrictions. Uncertainty about the political and economic future are also major obstacles, as afforestation needs a considerable investment of time before leading to economic viability. This highlights the need to assess not only the feasibility of CDR measures, but also their desirability.

Limited CDR potentials at national level draw the attention to compensating residual emissions through CDR in other parts of the world. However, CDR faces different but similarly severe constraints on global level: We not only find global land-use scenarios to be conflicting with key biodiversity areas, but [1]  implementation and persistence of land-based CDR faces severe challenges by a range of socioeconomic limitations, particularly in the Global South. We find that economic and technological factors such as poverty, costs, and infrastructures are the primary constraints for successful re/afforestation across the globe, with institutional factors also being important. This provides insights into key levers for up-scaling CDR.

When comparing land-based CDR methods, as needed to inform the design of CDR portfolios, we find a lack of consistent specification of assumptions and targets in the literature. We find that the efficiency of BECCS and its advantages over conventional methods like forest-based CDR in terms of carbon storage depends strongly on the timing not just of its implementation, but even more on the world’s capacities to deliver efficient CCS. On short term, we find that re/afforestation is the more efficient CDR method across a range of vegetation models. For a complete picture, we propose to compare CDR efficiency in terms of several measures: area required, time needed to break even, and the levels of CCS and fossil-fuel substitution. Future studies should deliver explicit information on the assumed CCS and fossil-fuel substitution, which proved a major source of sensitivity of CDR estimates.