Floating offshore farms should increase production of seaweed

IN MANY PLACES where seaweed used to thrive, often growing in vast “forests”, it is disappearing. The cause is global warming, which, by heating the ocean’s upper layer, reduces its density through thermal expansion—thus making it more buoyant. That extra buoyancy means it is less likely to mix with cooler, denser and more nutrient-rich waters below. This is bad for the marine environment in general. More specifically, it is bad for commercial seaweed farming, a business with revenues of (depending on whom you ask) between $6bn and $40bn a year.

The algae involved, particularly kelp, are popular in Asian cuisine. They are also used as fertiliser, and are processed into carrageenan, a natural binder and emulsifier employed in foods, cosmetics and drugs. Most are grown either on the seabed or on ropes attached to it (see picture above). But some are cultivated on small floating platforms.