Data for: Economic and biophysical limits to seaweed farming for climate change mitigation

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 $480/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 $50/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 (i.e.,
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.