Please use this identifier to cite or link to this item: https://hdl.handle.net/10419/302101 
Year of Publication: 
2024
Citation: 
[Journal:] Environmental Research Letters [ISSN:] 1748-9326 [Volume:] 19 [Issue:] 7 [Article No.:] 074067 [Publisher:] IOP Publishing [Place:] Bristol [Year:] 2024 [Pages:] 1-9
Publisher: 
IOP Publishing, Bristol
Abstract: 
Ocean alkalinity enhancement (OAE) deliberately modifies the chemistry of the surface ocean to enhance the uptake of atmospheric CO 2 . The chemical efficiency of OAE (the amount of CO 2 sequestered per unit of alkalinity added) depends, among other factors, on the background state of the surface ocean, which will significantly change until the end of this century and beyond. Here, we investigate the consequences of such changes for the long-term efficiency of OAE. We show, using idealized and scenario simulations with an Earth system model, that under doubling (quadrupling) of pre-industrial atmospheric CO 2 concentrations, the simulated mean efficiency of OAE increases by about 18% (29%) from 0.76 to 0.90 (0.98). We find that only half of this effect can be explained by changes in the sensitivity of CO 2 sequestration to alkalinity addition itself. The remainder is due to the larger portion of anthropogenic emissions taken up by a high-alkalinity ocean. Importantly, both effects are reversed if atmospheric CO 2 concentrations were to decline due to large-scale deployment of land-based (or alternative ocean-based) carbon dioxide removal (CDR) methods. By considering an overshoot pathway that relies on large amounts of land-based CDR, we demonstrate that OAE efficiency indeed shows a strong decline after atmospheric CO 2 concentrations have peaked. Our results suggest that the assumption of a constant, present-day chemical efficiency of OAE in integrated assessment modeling and carbon credit assignments could lead to economically inefficient OAE implementation pathways.
Subjects: 
carbon dioxide removal
ocean alkalinity enhancement
efficiency of CDR
path dependency
Persistent Identifier of the first edition: 
Creative Commons License: 
cc-by Logo
Document Type: 
Article
Document Version: 
Published Version






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