More than 10,000 tonnes of waste wood have been sunk into the Atlantic Ocean in an effort to remove carbon dioxide from the atmosphere. The US-based company behind the effort, Running Tide, says the carbon within the wood, which would otherwise have been burned, won鈥檛 be circulated out of the deep ocean for hundreds or even millions of years.
This effort is the largest yet among a growing slate of start-ups aiming to lock up CO2 on the seafloor from the atmosphere, but external researchers say it is an open question whether this approach to CO2 removal is effective, especially at the vastly larger scale required to have an appreciable impact on climate change.
Running Tide鈥檚 carbon-removal system involves deploying large numbers of hockey puck-sized buoys made from waste wood on the sea surface. They float around for two weeks before filling with water and sinking, taking the carbon they contain to the bottom of the sea.
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The company has attempted this on 16 occasions since May this year and has completed the first delivery of carbon credits generated by the wood in the buoys: 275 tonnes of carbon purchased by Canadian e-commerce company Shopify at $250 a tonne. Shopify has made commitments to purchase carbon removals before the technologies involved are fully proven, in order to grow the sector.
叠耻迟听 at the University of California, Santa Barbara, says there are major uncertainties regarding the durability of carbon storage in the deep ocean and its effects on marine ecosystems. 鈥淥ur ambition to do this is far outstripping what our scientific knowledge is.鈥�
In addition to the wooden buoys, Running Tide is experimenting with other ways to remove carbon. These include coating the buoys in limestone, which increases the alkalinity of seawater as it dissolves and should help convert more CO2 absorbed in the ocean into a more stable form.
The firm is also testing methods of seeding buoys with seaweed so it will grow in the open ocean, then sink along with the buoys. This distinguishes Running Tide from companies aiming to grow seaweed near the shore, then sink it in the deep ocean, an approach that would require enormous areas of ocean. One found that farming enough seaweed to remove a billion tonnes of carbon would require 1 million square kilometres of the most productive ocean.
Running Tide has extensive documentation on how it uses high-tech buoys and computer models to , as well as . But the company 鈥� and 鈥� has been criticised for moving forwards too quickly.
鈥淭hey are collaborating with science, but at the same time they are selling this message that it is working, and they are selling the credits,鈥� says at the Institute of Marine Sciences in Spain. She says more transparent data and more research are needed to know how much carbon is being removed, for how long and how such projects affect marine ecosystems over time.
at Running Tide acknowledges there are uncertainties involved, but says this is why tests at a relatively small scale are needed. 鈥淚 think the work we are doing is helping to advance the science,鈥� he says. 鈥淭he faster we can figure out which of these systems works or does not work, the better.鈥�
