As we count down to the 4th International Conference on Carbon Dioxide Removal in Milano, we are hosting a series of discussions on the research that will be shaping our sessions this June.
This research evaluates the real-world scalability and long-term carbon removal potential of Ocean Alkalinity Enhancement by combining industrial growth constraints with climate and Earth system modelling. The authors show that, despite its promise, OAE is unlikely to contribute significantly to global carbon removal targets before the second half of the century, with deployment limited by industrial scaling rates, geographic constraints, and delayed atmospheric impacts.
Full Abstract: The Scalability and Carbon Removal Potential of Ocean Alkalinity Enhancement
Connor Mack, Ryan Hanna, Daniela Faggiani-Dias, David Victor
Most studies on economy-wide deep decarbonization find the need for widespread carbon dioxide removal (CDR) to meet climate goals, typically projecting deployment needs of 5–10 Gt CO₂ yr⁻¹ by 2050. However, almost none of those studies pay attention to the real-world industrial scalability of such novel technologies. We look to address this gap by assessing the scalability of ocean alkalinity enhancement (OAE) using an integrated modeling framework that constrains scaling rates based on historical data from analogous marine industries—offshore wind, desalination, and industrial aquaculture. Respecting these empirically derived growth rate limits, we model the diffusion of OAE technologies, coupled to geophysical models of alkalinity injection, air-sea gas equilibration, and Earth system climate emulators. Our results show that OAE’s impact by mid-century may be limited. Under central model scenarios, the OAE industry reaches the 1 Gt CO₂ yr⁻¹ benchmark only in the early 2060s, with a second gigatonne achievable by the early 2070s. By 2100, we find a global removal potential of 0.64–2.7 Gt CO₂ yr⁻¹ (15th–85th percentile), with cumulative removals totaling approximately 90 Gt CO₂. This represents only 8–28% of the cumulative CDR required in typical 1.5–2°C overshoot scenarios. Furthermore, due to the lag in the atmospheric response to carbon balance changes, the impact of OAE on atmospheric concentrations by 2100 is modest (0.08–0.23 ppm reduction). We also identify a key tension in the political geography of deployment. Deployment is modeled across three modes: a small group of motivated first movers (Europe only), a larger coalition of developed economies with track records of capital-heavy climate investment (OECD), and deployment along coastlines worldwide (Global). While early investment will likely stem from highly motivated countries in Europe and the OECD, their combined potential never exceeds 1 Gt CO₂ yr⁻¹ under central model scenarios. Conversely, roughly 75% of the global OAE potential lies in non-OECD waters. For major emitters like China and the United States, domestic OAE potential can offset only 0–5% of current emissions, whereas some less industrialized nations possess OAE removal capacities that exceed their current levels of CO2 emissions, suggesting a future role for an international trading system of OAE credits. Our findings show that while OAE may achieve gigatonne-scale removals, its contribution will likely be limited to the latter half of the century, with minimal impacts on the global carbon balance by 2050. The integrated modeling framework presented in this study is applicable to any CDR approach and has previously been used to evaluate direct air capture and soil carbon storage. Future applications of this modeling framework across a broader range of CDR techniques can help develop more realistic portfolios of carbon removal feasibility for the next generation of integrated assessment models.
If Ocean Alkalinity Enhancement may not scale fast enough to meaningfully contribute to 2050 climate targets, how should policymakers balance investment between long term OAE deployment and other carbon removal approaches that could deliver nearer term climate impacts?