In London, a startup is making a plastic substitute out of seaweed. In Australia and Hawaii, others are racing to grow seaweed that, when fed to livestock, can cut methane excretion. Researchers are studying just how much carbon dioxide can be sequestered by seaweed farms as investors eye them as a new source of carbon credits for polluters to offset their greenhouse gas emissions.

Then there is South Korea. It is one of the most established seaweed-growing countries in the world, and farmers are struggling to keep up with growing export demand. What was mainly a relatively small Asian industry is now coveted by the West. Far beyond South Korea, new farms have cropped up in Maine, the Faeroe Islands, Australia, and even the North Sea. Globally, seaweed production has grown by nearly 75% in the past decade.

However, David Koweek, chief scientist for Ocean Visions, a consortium of research organizations studying ocean-based interventions for the climate crisis, said: "Seaweed protagonists believe seaweed is a cure for everything, that seaweed is a magical panacea for climate problems. Seaweed antagonists think seaweed is completely overhyped."