Scientists back wide seaweed farming, working on emissions absorption data
4m ago

New modelling points to seaweed aquaculture as a promising piece of the climate puzzle, estimating that today’s roughly 3.5 million hectares of farms are already removing between 0.35 and 7.0 million tonnes of carbon dioxide each year. If cultivation widened to about 68 million hectares by mid-century, the annual drawdown could climb to around 57.6 million tonnes of CO₂—while also delivering benefits to coastal ecosystems and economies. Researchers caution, however, that these figures are projections and must be verified through large-scale field measurements.

How seaweed helps store carbon

Seaweed aquaculture, or algae farming, raises fast-growing marine plants that capture CO₂ through photosynthesis and turn it into biomass. Unlike many terrestrial carbon strategies, seaweed requires no freshwater and virtually no land, and can be deployed in coastal waters at scale. Some of the carbon in harvested seaweed is locked into long-lived products, while a share of unharvested or residual biomass sinks to the seabed, where decomposition and particle export can move carbon into longer-term storage.

The new analysis highlights an additional, often overlooked pathway: chemical changes in seafloor sediments beneath farms. As seaweed-derived organic matter settles, it fuels microbial reactions—such as aerobic respiration and sulphate reduction—that generate alkalinity. Higher alkalinity boosts the ocean’s capacity to neutralize acidity and store carbon in stable dissolved inorganic forms, effectively bolstering long-term sequestration beyond the immediate plant biomass.

Co-benefits for coasts and communities

Beyond climate mitigation, seaweed farms can improve water quality by absorbing excess nitrogen and phosphorus from runoff, helping to curb harmful algal blooms and local acidification. Farm structures and the canopy they create can also provide habitat for marine life, supporting biodiversity.

Economically, expanding seaweed cultivation offers new income streams, particularly where fisheries are under stress. Harvested seaweed feeds growing markets for foods, pharmaceuticals, bioplastics and biofertilisers, creating value chains that can anchor jobs in coastal regions.

What the models reveal

To gauge how much carbon could be locked away, the research team applied a sediment diagenetic model to simulate the interplay among organic matter, minerals and key chemical cycles beneath farms, including those of sulphur and iron. They ran 1,000 stochastic simulations to capture environmental variability—factoring in oxygen levels, sedimentation rates and organic matter flux, among other uncertainties.

Across scenarios, alkalinity fluxes from sediments increased markedly, ranging from tens to several hundreds of micromoles per square centimetre per year depending on local conditions. This enhancement substantially strengthens the ocean’s long-term carbon storage potential. At the farm scale, estimated removals span from roughly 0.1 to more than 2 tonnes of CO₂ per hectare annually, with performance highly site-specific.

Pathways to scale—and the evidence still needed

Folding seaweed aquaculture into carbon crediting systems could draw investment and speed deployment, but rigorous measurement, reporting and verification will be essential. Key questions remain about sequestration durability, environmental trade-offs and how outcomes vary by location, species and farming method.

Priority research needs include multi-year field trials, independent validation of sequestration rates, and comprehensive life-cycle assessments that account for cultivation, processing, transport and end uses. Clear safeguards and local engagement will be vital to ensure farms are sited responsibly, avoid conflicts with other ocean uses and deliver benefits to nearby communities and ecosystems.

A nature-based lever with promise

Taken together, the modelling indicates that seaweed aquaculture could make a measurable contribution to climate mitigation while supporting coastal resilience. Realizing that potential will require expanding farms in the right places, building markets for seaweed-based products, and—crucially—closing the gap between promising projections and verified, durable carbon storage in the ocean.