“The industry is getting ahead of the science,” says Isabella Arzeno-Soltero, a postdoctoral scholar at Stanford University, who worked on the project. “Our immediate goal was to see if, given optimal conditions, we can actually achieve the scales of carbon harvests that people are talking about. And the answer is no, not really.”
Seaweed pulls carbon dioxide from the atmosphere through photosynthesis, and then a significant amount is sequestered—potentially for millennia—when the plant matter eventually sinks down into the ocean depths. The idea is that it could be grown and then intentionally sunk to lock away that carbon long enough to ease the pressure on the climate.
Arzeno-Soltero and her colleagues at the University of California, Irvine, used a software model to estimate how much seaweed, of four different types, could be grown in oceans around the world.
The model considered things like the seaweed’s nitrate uptake (which is essential for growth), the water temperature, the sun’s intensity, and height of the sea’s waves, using global ocean data gathered from past years, while accounting for current farming practices. The researchers performed more than 1,000 seaweed growth and harvest simulations for each of the seaweed types, which they said represented the “optimistic upper bounds” for seaweed production.
For example, the new estimates assumed that farming space could be found within the most productive waters for seaweed in the equatorial Pacific, around 200 nautical miles off the coast. In less productive locations, growing enough seaweed to reach climate targets would be even more challenging: three times as much space would have to be devoted to seaweed farming to sequester the same amount of carbon.