Large global variations in the carbon dioxide removal potential of seaweed farming due to biophysical constraints

Estimates suggest that over 4 gigatons per year of carbon dioxide
(Gt-CO2/year) be removed from the atmosphere by 2050 to meet international
climate goals. One strategy for carbon dioxide removal is seaweed farming,
however, its global potential remains highly uncertain. Here, we apply a
dynamic seaweed growth model that includes growth-limiting mechanisms,
such as nitrate supply, to estimate the global potential yield of four
types of seaweed. We estimate that harvesting 1 Gt/year of seaweed carbon
would require farming over 1 million km2 of the most productive exclusive
economic zones, located in the equatorial Pacific. We estimate cultivation
area would need to be tripled to attain an additional 1 Gt/year of
harvested carbon, indicating dramatic reductions in carbon harvest
efficiency beyond the most productive waters. Improving the accuracy of
annual harvest yield estimates requires better understanding of
biophysical constraints and seaweed loss rates, such as disease, grazing,
and wave erosion.