Seaweeds help fight climate change

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

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 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.

They found that raising macroalgae in just 0.001 percent of seaweed-growing waters worldwide and then burying it at sea could offset the entire carbon emissions of the rapidly growing global aquaculture industry, which supplies half of the world’s seafood. Altogether, 18.5 million square miles of the ocean is suitable for seaweed cultivation, the study concluded.

Beyond seaweed’s potential to counteract acidification and deoxygenation, absorb excess nutrients and provide habitat for marine life in at least 77 countries, seaweed can be processed into biofuel. And research has shown that adding seaweed to livestock feed can reduce potent methane emissions from the burps of cows and other grazing livestock—a significant source of global greenhouse gases—by as much as 70 percent. Seaweed can also be used as an agricultural soil supplement, replacing petroleum-based fertilizers.

“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.

Getting the international carbon credit bean counters to accept seaweed as a legitimate source of greenhouse gas reduction is one of the bigger challenges.

“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.” (National Geographic)

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