Expert opinions regarding the concept of blue carbon in seaweed systems

Abstract

A collection of expert opinions critically evaluates the role of seaweed in blue carbon strategies for climate change mitigation. While the concept of fast-growing seaweed to capture atmospheric carbon is appealing, the experts largely agree that its potential for direct, long-term carbon sequestration is currently overstated and faces significant challenges. One primary limitation is that most farmed seaweed is used for food or other products that quickly decompose, releasing the captured carbon back into the atmosphere. Additionally, only a small fraction of seaweed biomass is sequestered in long-term storage sinks like deep-sea sediments. Furthermore, the process of monitoring, reporting, and verification for seaweed-based carbon dioxide removal is complex and currently lacks accurate tools. More importantly, quantifying the net climate benefit is complicated by life cycle emissions from farming and processing, which can offset carbon gains. Some experts suggest a more viable climate benefit lies in using seaweed to reduce emissions by substituting for products with higher carbon footprints. Socio-economic initiatives like the blue carbon crediting scheme in Japan show a path forward, where credits are purchased to support local communities and conservation, suggesting value beyond pure carbon offsetting. The consensus is that while seaweed farming offers substantial benefits for food security and coastal ecosystems, its most realistic contribution to climate action is through indirect emission reduction, not large-scale carbon removal. A rigorous, science-based approach is essential to avoid hype and ensure sustainable development.