Economic and biophysical limits to seaweed-based climate solutions

Abstract

Net-zero greenhouse gas 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 $560/tCO2 on average, while using farmed seaweed for products that avoid a gigaton of CO2-equivalent greenhouse gas (GHG) emissions annually could return a profit of $30/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 and seaweed products can displace products with substantial embodied non-CO2 GHG emissions. Moreover, the gigaton-scale climate benefits we model would require farming vary large areas (>100,000 km2)—a >40-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.

Quantifying baseline costs and cataloging potential optimization strategies for kelp aquaculture carbon dioxide removal

“…Global models of kelp CDR approaches have been valuable tools to evaluate scalability and costs over large geographic regions (Froehlich et al, 2019;DeAngelo et al, 2022). However, due to complexities associated with choice of species, site-specific factors, and cultivation strategies, we contend that more granular regional analyses can help identify pathways for cost reductions that would not otherwise be apparent in global analyses.…”

“…Previous efforts to explore the climate change mitigation potential of macroalgae farming have included using raw materials for the production of biofuels (Michalak, 2018;Osman et al, 2020), nutrient management (Racine et al, 2021), and as a supplement within livestock feed to reduce methane emissions (Roque et al, 2021). Early-stage research is also being conducted to evaluate the potential of growing and then intentionally sinking large quantities of macroalgae in the deep ocean, locking the C incorporated within macroalgae biomass away from atmospheric exchange (DeAngelo et al, 2022;Froehlich et al, 2019;Gaines et al, 2019;NASEM, 2021;Peters, 2020).…”

“…There are still considerable questions regarding the environmental, biological, geological, and, perhaps most importantly, economic feasibility of kelp aquaculture-based CDR (DeAngelo et al, 2022;Hurd et al, 2022;Troell et al, 2022). To satisfy the requirements of the IPCC, ~10 Gt of CO 2 eq will need to be removed each year by mid-century.…”

“…While the upper end of this range is far greater than current market prices, the ability to potentially sequester CO 2 at a price point of under $100 tCO 2 eq -1 warrants further study. Global production models offer valuable insights into the potential of this novel concept (DeAngelo et al, 2022). However, seaweed production cost estimates can vary widely by region, species, and husbandry method (van den Burg et al, 2016).…”

Quantifying baseline costs and cataloging potential optimization strategies for kelp aquaculture carbon dioxide removal

“…Previous efforts to explore the climate change mitigation potential of macroalgae farming have included using raw materials for the production of biofuels (Michalak, 2018;Osman et al, 2020), nutrient management (Racine et al, 2021), and as a supplement within livestock feed to reduce methane emissions (Roque et al, 2021). Early-stage research is also being conducted to evaluate the potential of growing and then intentionally sinking large quantities of macroalgae in the deep ocean, potentially locking the C incorporated within macroalgae biomass away from atmospheric exchange (DeAngelo et al, 2022;Froehlich et al, 2019;Gaines et al, 2019;NASEM, 2021;Peters, 2020).…”