In addition to its economic benefits, the role of seaweed farming as an important purveyor of ecosystem services is being increasingly recognized. A scientific narrative advocating for the large-scale expansion of the seaweed aquaculture industry in recognition of the relatively high removal rates of atmospheric carbon dioxide (CO2) during biomass growout has recently been articulated. As a climate solution, the idea has catalyzed investment from the private sector on projects aimed at the development of ‘carbon negative’ seaweed products such as food, feed, extracts and fertilizers. Nevertheless, a scientific consensus on the true potential of seaweed farming as a Carbon Dioxide Removal (CDR) solution is yet to emerge as uncertainties regarding the permanence of carbon storage in culture facilities are still being resolved.
To improve our understanding of the CDR potential of seaweed aquaculture, a meta-analysis of Life Cycle Assessments (LCA) and carbon sequestration models published during 2013-2022 was conducted to arrive at standardized estimates of the Global Warming Potential (GWP) of the activity. The analysis revealed that while substantial CDR can be achieved though dissolved and particulate carbon exported to sediments and the deep sea, benefits are much more apparent if substitution of fossil fuel products (gas, fertilizers) is embedded into the LCAs. Non-parametric tests indicated that removal through both pathways potentially exceed the emissions associated with culture activities (Figure 1). Although the CDR potential of seaweed aquaculture was confirmed by the meta-analysis, updated assessments are recommended to further reduce the variability in the estimates of positive emissions and removal rates.