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