Economic and biophysical limits to seaweed farming for climate change mitigation

Abstract

Net-zero greenhouse gas (GHG) emissions targets are driving interest in opportunities for biomass-based negative emissions and bioenergy, including from marine sources such as seaweed. Yet the biophysical and economic limits to farming seaweed at scales relevant to the global carbon budget have not been assessed in detail. We use coupled seaweed growth and technoeconomic models to estimate the costs of global seaweed production and related climate benefits, systematically testing the relative importance of model parameters. Under our most optimistic assumptions, sinking farmed seaweed to the deep sea to sequester a gigaton of CO2 per year costs as little as US$480 per tCO2 on average, while using farmed seaweed for products that avoid a gigaton of CO2-equivalent GHG emissions annually could return a profit of $50 per tCO2-eq. However, these costs depend on low farming costs, high seaweed yields, and assumptions that almost all carbon in seaweed is removed from the atmosphere (that is, competition between phytoplankton and seaweed is negligible) and that seaweed products can displace products with substantial embodied non-CO2 GHG emissions. Moreover, the gigaton-scale climate benefits we model would require farming very large areas (>90,000 km2)—a >30-fold increase in the area currently farmed. Our results therefore suggest that seaweed-based climate benefits may be feasible, but targeted research and demonstrations are needed to further reduce economic and biophysical uncertainties.

Seaweed biogeochemistry: Global assessment of C:N and C:P ratios and implications for ocean afforestation

“…The large range of C:N across species underscores the relevance of selecting potentially carbon‐efficient species for Ocean Afforestation. However, the choice of species for Ocean Afforestation is constrained by the ability to culture them and the ability of the species to grow in often oligotrophic pelagic habitats to which they may not be adapted (DeAngelo et al, 2023). For example, for the 10 species with the highest C:N and C:P (Figure 5), except some species of Sargassum , cultivation techniques have not yet been developed or are in their infancy (Buschmann et al, 2017; Kelly, 2020).…”

“…They are therefore not considered to be limited by iron or other trace metals. In the case of Ocean Afforestation, however, floating platforms with seaweed growing on them may be deployed in the open ocean (de Ramon N'Yeurt et al, 2012; DeAngelo et al, 2023; Wu et al, 2023). In such cases, iron and other trace metals can limit photosynthetic carbon fixation of phytoplankton (Moore et al, 2013), which are adapted to these limiting conditions.…”

Climate benefits of seaweed farming: estimating regional carbon emission and sequestration pathways

“…By this we mean that the success of CDR strategies will depend very much on local environmental and ecological suitability, as well as local production costs and supply chains, community buy-in, and good governance [58] . We therefore advise caution in relying on global models and parameters [5,22,73,74] to assess local feasibility, as these are unlikely to provide the accuracy necessary to answer essential ecological, economic, and certification questions. To advance assessments of feasibility, we need to transfer such models and their parameterization to local social-ecological contexts.…”

The influences of the advancement of green technology on agricultural CO2 release reduction: A case of Chinese agricultural industry

“…This "pioneer revolution" had hardly begun in 1850, yet had reached on peak within the twentieth century, which massively changed the way of producing food and fiber (Sarkar et al, 2021). The change was almost synchronous worldwide and must have led to the release of substantial quantities of CO 2 into the atmosphere (DeAngelo et al, 2022). Moreover, the sector is liable for CO 2 outputs from using natural organisms (mostly woods and natural forest ecologies) to land and as non-carbon emissions from crop and animal operations at the farm gate (Karimi Alavijeh et al, 2022), which is responsible for 24% of greenhouse gases emissions in the world (Yurtkuran, 2021).…”