Seaweed ‘forests’ can help fight climate change

Scientists are looking for ways to farm seafood as an effective way of fighting global warming. Farming seaweed and then sinking the mature plants tot the bottom of the ocean could accomplish this.

BY TODD WOODY

As the Amazon burns, there’s growing interest in cultivating forests that absorb planet-warming carbon emissions, but that are fireproof. That’s because these forests are underwater.

An increasing body of research is documenting the potential of seaweed farming to counter climate change as deforestation decimates rainforests and other crucial carbon sinks. Fast-growing oceanic jungles of kelp and other macroalgae are highly efficient at storing carbon. Seaweed also ameliorates acidification, deoxygenation, and other marine impacts of global warming that threaten the biodiversity of the seas and the source of food and livelihoods for hundreds of millions of people.

“Seaweed is finally having its moment in the spotlight,” says Halley Froehlich, a marine scientist at the University of California, Santa Barbara.n She is the lead author of a new study that for the first time quantifies the global capacity of large-scale seaweed farming to offset terrestrial carbon emissions and maps areas of the ocean suitable for macroalgae cultivation.

Farming seaweed in just 3.8 percent of the federal waters off the California coast—that’s 0.065 percent of the global ocean suitable for growing macroalgae—could neutralize emissions from the state’s $50 billion agriculture industry, according to the paper published Thursday in the journal Current Biology.

Seaweed is currently grown on a small scale for use in food, medicines, and beauty products. The scientists, however, propose the establishment of industrial-size farms to grow seaweed to maturity, harvest it, and then sink it in the deep ocean where the captured carbon dioxide would be entombed for hundreds to thousands of years.

Carlos Duarte, a leading seaweed scientist at the Red Sea Research Center in Saudi Arabia, attended a presentation on the paper’s findings in April. “The new study adds to previous research and global estimates … to point at seaweed aquaculture as a major avenue to mitigate climate change,” he writes in an email, noting that he had not reviewed the final paper. “My opinion is that the estimates are very conservative and the potential is much higher, if the crop is maintained properly.”

“The math shows you that seaweed can be a very effective tool to fight climate change, but it has to be validated by the market,” says Scotty Schmidt, chief executive of Primary Ocean, a Los Angeles company working on a United States government-funded project to develop technologies to deploy large-scale seaweed farms. “Farming seaweed just for carbon sequestration is not a viable business case at this time as there’s barely a carbon market that’s willing to accept seaweed offset credits,” he says.

Primary Ocean’s strategy is to extract material from seaweed that can be sold for agricultural use. If a profit could be made from those sales and carbon credits were available, the company could then sequester the macroalgae waste, Schmidt says.

“The science and the demand is already there; the bottleneck is a catalyzer that makes the production meet the demand,” says Duarte. “Specifically we need carbon credit protocols that can be used to claim carbon credits from seaweed aquaculture and also regulatory environments that facilitate concessions and licenses for seaweed aquaculture.”

Despite a long coastline suitable for seaweed cultivation, the U.S. has almost no offshore aquaculture operations. China and other Asian nations that produce most of the world’s farmed seaweed are expected to take the lead in establishing macroalgae as a source of “blue carbon.”

Seaweed ‘forests’ can help fight climate change

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