A critical review of the life cycle climate impact in seaweed value chains to support carbon accounting and blue carbon financing

Seaweed is often touted as a blue economy resource with climate benefits. Several calls are made to scale the industry up and to use blue carbon financing to create additional incentives for the sector to expand. But how much of a climate crisis panacea is seaweed, and under which conditions can climate benefits be realized? The article reviews the literature on climate impacts from seaweed value chains and proposes a cradle-to-grave structure for carbon accounting in seaweed value chains. While the literature points towards several ways in which climate benefits can be generated, the evidence base for net negative emissions across the value chain is not robust enough to suggest seaweed value chains, by default, are a climate solution. Instead, climate effects depend on the specific production setup, product choice and the fate of the product on the market. Climate benefits can only be claimed by tracking blue carbon flows across whole life cycles and over time. Knowledge gaps relate to effects at sea, the role of temporarily locking carbon into products and the effects of introducing this resource to the market. Blue carbon financing should be directed only to setups proven to lead to additional and permanent carbon storage. •A life cycle perspective is needed to understand climate effects of seaweed.•Carbon storage and system boundaries are key in climate impact calculations.•A carbon accounting framework for the seaweed sector is presented.•Key knowledge gaps remain around ecosystem effects at sea.•Blue carbon financing should be directed only to ventures with proven positive impact.