Brian Burt

Existing global seaweed forests can capture nearly 200 million tons of CO2 a year while also giving a $500 billion boost in ecosystem services to industries including fishing. Expanding them is an excellent investment, said von Herzen, both financially and environmentally.

And using biostimulants can boost the climate benefit even more, both by reducing nitrous oxide emissions and by cutting the CO2 emissions that come both from making artificial fertilizers and from shipping them to farmers. California is already outpacing the rest of the country in reducing fossil fuel emissions. Kelp would help the state meet its target of reaching net-zero emissions by 2045, at least five years sooner than the Paris Agreement’s goal of 2050.

Seaweeds currently grow across nearly 1 percent of the world’s temperate coastal ocean waters. Getting back to pre-industrial levels of about 2 percent would be revolutionary. Von Herzen is focusing on specific species, which grow three times faster than other kelp. He said they could remove enough carbon to equal all emissions from global aviation—all flights using jet fuels everywhere in the world.

What’s more, studies show that kelp forests give off biogenic aerosols—tiny airborne particles that come from living things—that help clouds form. Coastal cloud cover reflects sunlight back into space. In its absence, the seas and soils are hotter, which also heats the air. There is more evaporation, and there are longer periods without rain. The ground becomes drier, making coastal woodlands more susceptible to wildfire. “We can keep California cooler and keep it from burning,” von Herzen said. “This can be done not in the distant future, but within the next ten years.” That’s because kelp can expand its coverage by 18 inches per day. Some giant kelp grow at a daily rate of two feet.