Even if countries keep their promises to cut emissions, global warming will exceed the ability of many ecosystems to withstand it safely. That reality has pushed scientists, governments and a growing number of startups to explore ways to remove carbon dioxide from the atmosphere or, at least, temporarily offset its effects. But these interventions carry risks, especially for the ocean, the world’s largest carbon sink and the foundation of global food security.
A team that spent decades studying the oceans and climate analyzed how different interventions could affect marine ecosystems, for better or worse, and where more research is needed before anyone tries them at scale. The conclusion: some strategies are less risky than others, but none is free of consequences.
Two very different paths
Interventions fall into two broad categories. The first is carbon dioxide removal (CDR), which attacks the root of the problem by pulling carbon from the air. The ocean already absorbs nearly a third of human emissions each year and has an enormous capacity to hold more. Biological methods capture carbon through photosynthesis in algae and plants: iron fertilization and seaweed farming boost that growth, though much of the carbon returns to the atmosphere when the biomass decomposes.
The second category, solar radiation modification, works like sunscreen: it does not remove carbon, but injects tiny particles that reflect sunlight and could reduce heat waves and coral bleaching, mimicking the cooling that follows major volcanic eruptions. It is fast, but only masks the problem while CO2 keeps rising.
Where the risk to marine life lies
Drawing more carbon dioxide into the ocean can worsen acidification, which already weakens oyster shells and harms corals and plankton, the base of the food chain. Biological methods also depend on nutrients: fertilizing the surface in one area can suffocate the waters below it or damage fisheries thousands of miles away by depleting nutrients that currents would carry to productive zones. Shifts in plankton composition ripple through the entire food web and end up affecting fisheries that millions of people rely on.
The least dangerous options
Of all the methods analyzed, electrochemical ocean alkalinity enhancement carried the lowest direct risk, though it is not harmless: it uses an electric current to split seawater into an alkaline stream and an acidic one, and requires safely neutralizing or disposing of the acid. Other relatively low-risk options include adding carbonate minerals to seawater and sinking land plants into deep, low-oxygen waters for long-term storage. All still need more study before any real-world scale.
A window that will not stay open
Commercialization is already advancing: investor-backed startups sell marine carbon credits to companies such as Stripe and British Airways, while global emissions keep climbing. The authors warn that pressure to deploy these techniques quickly, without understanding the risks, may grow as climate damage worsens. They call for transparent research that can rule out harmful options and verify the promising ones. It may be that no intervention is safe enough to deploy at scale, but that decision, they say, should be guided by evidence, not by fear, markets or ideology.
Reporting: Anne Silva / Amazonia Mag. Source: study by researchers at NILU and the Norwegian University of Science and Technology.