Ocean Alkalinity Enhancement: A Synthesis of Research on its Climate Mitigation Potential and International Governance Challenges

Deploying carbon dioxide removal (CDR) technologies has been deemed necessary to complement drastic emissions reductions and limit global warming to well below 2°C compared to pre-industrial temperatures by the end of the century (IPCC, 2023). Attention has turned to deploying CDR in marine environments (mCDR) due to the ocean’s natural capacity for sequestering and storing atmospheric carbon dioxide (CO2). Ocean alkalinity enhancement (OAE) is an mCDR approach that aims to increase the ocean’s chemical storage capacity for atmospheric CO2 by adding alkaline materials to its surface to enhance its natural buffering capacity (Kheshgi, 1995; Wang et al., 2023). This scoping review synthesized the academic literature on OAE’s CDR potential, climate mitigation benefits, and the opportunities and challenges associated with the international governance of OAE and mCDR approaches. Earth model scenarios of OAE show different potentials for atmospheric CO2 uptake and storage due to varying model parameters, such as the scale of OAE (e.g., global or regional), the location of OAE, the amount and type of alkaline material added, and the forecasted emissions pathway. Overall, model scenarios of global, regional, and coastal OAE using various natural and synthetic alkaline materials indicate that oceanic uptake and storage of atmospheric CO2 would increase (e.g., Jin & Cao, 2023; Fakhraee et al., 2023). OAE termination scenarios indicate that once OAE ceases after a certain period, the ocean stops taking up CO2 at an enhanced rate; however, the CO2 previously sequestered remains in the marine environment (e.g., Ilyina et al., 2023; Keller et al., 2014). Corresponding with the enhanced oceanic CO2 uptake and reduced atmospheric CO2 concentrations, future projected increases in average global surface air temperature are predicted to decrease under OAE scenarios (e.g., Gonzalez et al., 2018; Sonntag et al., 2018). However, despite OAE’s potential for climate mitigation, numerous knowledge gaps remain regarding its impact on the climate system and the marine environment. Future multi-model research into the effectiveness and feasibility of OAE and its influence on the global climate system and ocean ecology is required (Butenschan et al., 2021; Lenton et al., 2018). mCDR approaches, including OAE, have no legally binding international governance regimes (Bach et al., 2024). However, numerous frameworks likely have implicit roles in mCDR governance due to their connections to the marine environment and climate change, such as the London Protocol, Paris Agreement, United Nations Convention on the Law of the Sea, and Convention on Biological Diversity (Gambardella, 2019; McGee et al., 2018). While research on mCDR approaches is needed to evaluate their effectiveness and impacts, experimental groundwork and deploying OAE and other mCDR techniques are expected to face numerous governance challenges (Gattuso et al., 2021; Sovacool et al., 2022). Substantial challenges for mCDR governance stem from the potential of transboundary harm and the fragmented international law framework for the ocean (Boettcher et al., 2021; Roschel & Neumann, 2023). Further, mCDR research and deployment will likely have low social acceptability due to risks to the marine environment and human well-being (Cox et al., 2021). To address these challenges, transdisciplinary and inclusive research is needed to develop a governance approach that comprehensively assesses mCDR approaches (McGee et al., 2018; Roschel & Neumann, 2023). OAE displays a strong potential for climate mitigation. Future research is needed to assess OAE’s CDR potential under different earth system models and determine OAE’s impact on marine ecosystems and biodiversity (Feng et al., 2017; Jin & Cao, 2023; Lenton et al., 2018). An inclusive and transdisciplinary approach to mCDR governance is required to create an extensive and foresighted framework that addresses the unique challenges and opportunities of mCDR approaches for climate mitigation (Bach et al., 2024; Loomis et al., 2022; McGee et al., 2018).