Seaweed farming is not a scalable climate solution, research warns
Preserving existing kelp forests is far more effective and cheaper than industrial aquaculture efforts.
Seaweed cultivation is not a scalable solution for climate change because the carbon released by dying kelp forests far outweighs the amount sequestered by farming. Research led by Karen Filbee-Dexter of the University of Western Australia argues that the priority must shift from restoration to the preservation of existing ecosystems.
The study highlights a stark imbalance between natural loss and human intervention. While seaweeds absorb approximately 3.7 billion tonnes of CO2 annually, only a small fraction is sequestered as "blue carbon" in the deep sea. Currently, approximately 60% of global kelp forests are in decline due to warming waters, releasing an estimated 14 million tonnes of CO2 per year. In contrast, a 70-hectare restoration project in Norway drew down only about 50,000 tonnes annually, illustrating the inefficiency of active cultivation compared to the scale of natural collapse.
The failure of industrial aquaculture
For years, kelp has been marketed as a "natural climate solution," sparking a wave of government-backed plans and private startups. However, practical application has struggled. The U.S. carbon removal startup Running Tide shut down last year after facing difficulties growing kelp in the open ocean.
Beyond the struggle to grow seaweed, operational costs often negate environmental benefits. A study published earlier this year found that 9 out of 11 seaweed farms actually emitted more CO2 than they sequestered. These emissions stem from operational requirements, including the use of plastic lines and boat fuel, suggesting that industrial-scale aquaculture may be carbon-positive rather than carbon-negative.
The case for conservation
The research suggests that the current focus on "growing" new solutions is a costly mistake. Preserving existing kelp ecosystems is at least eight times cheaper per hectare than attempting to restore them. Despite this cost-efficiency, only 2% of global kelp forests are currently located within protected areas.
"Instead of asking how much carbon we can remove with seaweeds, we should be asking how much carbon we can stop from being released as these ecosystems are damaged by climate change," said Karen Filbee-Dexter.
Industry implications
If policymakers and corporations continue to rely on seaweed cultivation as a primary carbon offset strategy, they risk pursuing a "false hope" that could delay the essential phase-out of fossil fuels. The collapse of natural sinks is currently outpacing the ability of humans to create artificial ones, making conservation the only viable high-impact strategy.
What remains
While the scalability of farming is under fire, some experts believe blue carbon still plays a role in the broader climate puzzle. Pamela Walsh of Queen’s University Belfast noted that while blue carbon is part of the solution, the critical remaining challenge is how that sequestration is determined and validated. Future efforts will likely focus on whether protected areas can be expanded quickly enough to stem the 14-million-tonne annual leak of CO2 from dying forests.