Why verifying ocean carbon removal is harder than it sounds
The biggest credibility problem with carbon offsets is that it's often unclear whether the claimed carbon removal actually happened. Ocean-based methods face this same challenge, but with added complexity. For seaweed-based approaches, the key issue is that simply growing seaweed does not automatically mean CO2 has been removed from the atmosphere. One study explains that to claim carbon removal, you must prove that the CO2 fixed by seaweed photosynthesis leads to a net drawdown of CO2 from the atmosphere via air-sea equilibrium, a process that operates on timescales of weeks to years depending on the ecosystem [1]. This means that even if seaweed stores carbon in biomass or sediments, you cannot count it as removal unless you can quantify and verify that atmospheric CO2 actually decreased as a result [1]. Another study reinforces this by stating that effective implementation of ocean alkalinity enhancement and macroalgae-based strategies requires rigorous monitoring, reporting, and verification (MRV) frameworks to ensure quantifiable efficacy and environmental integrity [2].
Governance and public trust are make-or-break for credibility
Even if the science of ocean carbon removal improves, credibility will depend on strong governance and public acceptance. One policy-focused study argues that governance frameworks are needed urgently to ensure that the potential contribution from coastal and ocean systems to climate change mitigation can be evaluated properly and implemented safely [3]. The same study warns that coastal and ocean systems cannot be relied upon to deliver significant carbon dioxide removal until further knowledge of specific management options is acquired and evaluated [3]. Public perceptions also matter: a survey of people in British Columbia and Washington state found that comfort with ocean-based methods varied widely—coastal restoration was viewed favorably, while ocean alkalinity enhancement and ocean fertilization caused discomfort [5]. The study notes that perceived severity of climate change predicted greater comfort with all approaches, but beliefs about marine environments being 'fragile' or 'manageable' also shaped views [5]. This suggests that credibility is not just about science but also about aligning with public values.
Can new technology and monitoring solve the credibility gap?
Emerging technologies like electrochemical direct ocean capture (eDOC) may offer more verifiable pathways, but they are still early-stage. One study highlights advancements in eDOC, which uses pH swing mechanisms to capture CO2 directly from seawater, potentially allowing for more precise measurement of carbon removed [6]. However, this approach is not yet deployed at scale. Another study emphasizes that the ocean's natural carbon cycle already absorbs about 25% of anthropogenic CO2 emissions, but this leads to ocean acidification and reduces the ocean's future ability to take up CO2 [4]. This means that any ocean-based method must account for the ocean's changing chemistry and buffering capacity. The bottom line: without transparent, independent verification and adaptive governance, ocean-based carbon removal risks the same credibility problems as traditional offsets—but with the right frameworks, it could offer a more trustworthy path.
About These Sources
This answer is built on 6 peer-reviewed studies — published from 2022 to 2026, 2 from 2024 or later, 5 in Q1 journals, collectively cited 306 times — selected as the most relevant from 6 studies that passed quality screening, drawn from 41 papers retrieved from a database of over 500 million.
Sources used in this answer
Air‐sea carbon dioxide equilibrium: Will it be possible to use seaweeds for carbon removal offsets?
Quantifying air-sea CO2 equilibrium is the critical step needed to verify carbon dioxide removal by seaweed, and this process operates on timescales of weeks to years, making verification difficult.
Ocean Carbon Dioxide Removal and Storage
Effective implementation of ocean alkalinity enhancement and macroalgae-based strategies requires rigorous monitoring, reporting, and verification (MRV) frameworks to ensure quantifiable efficacy and environmental integrity.
Can coastal and marine carbon dioxide removal help to close the emissions gap? Scientific, legal, economic, and governance considerations
Governance frameworks are needed urgently for coastal and marine carbon dioxide removal, and these systems cannot be relied upon for significant removal until further knowledge is acquired and evaluated.
The Ocean Carbon Cycle
The ocean absorbs about 25% of anthropogenic CO2 emissions, but this leads to ocean acidification and reduces the ocean's future ability to take up CO2.
Public evaluations of four approaches to ocean-based carbon dioxide removal
A survey in British Columbia and Washington state found that public comfort varies by method: high for coastal restoration, some discomfort for ocean alkalinity enhancement and ocean fertilization, and that perceived climate urgency predicts greater comfort.
Direct ocean capture: the emergence of electrochemical processes for oceanic carbon removal
Electrochemical direct ocean capture (eDOC) using pH swing mechanisms is an emerging negative emission technology that may offer more verifiable carbon removal, but it is still in early development.