SINKING SEAWEED

An ambitious strategy aims to cool the planet by dumping farmed seaweed on the sea floor. Will it work?

29 AUG 2024 12:40 PM ET
BY WARREN CORNWALL

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Davis is there to study the potential benefits and risks of a controversial idea: growing seaweed to fight climate change. The concept has generated enthusiasm among entrepreneurs, philanthropists, and some scientists. They envision vast seaweed farms floating in the open ocean, where plants such as kelp would be grown and then sunk thousands of meters to the ocean floor, entombing the carbon for centuries.

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Companies looking to feed the growing market for carbon credits have hatched a variety of strategies. One now-defunct company proposed seeding buoys with kelp spores, then setting the buoys adrift and letting them sink. Another company plans to grow and sink enormous tracts of sargassum, a tropical seaweed. Yet another says it will harvest kelp from underwater farms, then turn the biomass into the equivalent of charcoal that can be used to fertilize agricultural fields.

But the strategy faces daunting, unanswered questions about how much carbon it might actually sequester, potential ecological effects, and whether coastal seaweed can thrive in the open ocean. In 2022, a National Academies of Sciences, Engineering, and Medicine committee recommended pouring $235 million into studying this approach to carbon capture. Another group of scientists upped the ante to $1 billion.

Meanwhile, some ocean scientists have called for a moratorium on the practice. It is unlikely to work as promised, they say, and threatens to upend ocean ecosystems. “I think it’s nonsense,” says Catriona Hurd, a seaweed carbon physiologist at the University of Tasmania and lead author of a March letter in the journal One Earth calling for a ban. “I just don’t believe it’s going to have any effect on the climate.”

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