Using the Ocean’s Power to Fight Climate Change
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Can the ocean help save the planet?
Covering 70% of the Earth's surface, the ocean already acts as a giant carbon sink, removing about a quarter of the carbon dioxide produced each year by human activity, scientists estimate. Atmospheric carbon is absorbed through the physical mixing of air and water at the surface and with chemical reactions below that involve photosynthesis by marine plankton. Once the carbon enters the ocean, it can be safely locked up in the deep sea for hundreds or thousands of years, research has shown.
Scientists say it may not be enough to switch to renewable energy, drive electric vehicles and move to low-carbon manufacturing to avoid the most dangerous impacts of climate change. To meet international climate goals, it's also necessary to remove 10 gigatons of atmospheric CO2 every year between now and 2050, according to a 2019 report by the National Academy of Sciences.
Some strategies are already under way, such as technologies aimed at sucking carbon dioxide directly from the air, agricultural techniques for storing carbon in soils, and changes in how forests are managed. Now, some researchers are looking at how the ocean could soak up additional carbon -- and what the benefits and risks would be.
"We seriously need to figure out how to remove some CO2, and it's already becoming pretty clear that you can't do it all on land," says David Keller, a senior scientist at the Geomar Helmholtz Centre for Ocean Research Kiel in Germany. "The ocean plays a major role in the carbon cycle, and that's where most of the carbon is stored anyway. I think it just makes natural sense to look there. Of course, we don't want to mess up the ocean."
Ideas for ocean-aided carbon removal include dumping tons of iron filings in the ocean as a nutrient to promote plankton growth -- something that has been done more than a dozen times on a small scale. Other proposals involve building huge offshore kelp farms or restoring coastal ecosystems.
Whether such techniques can be effective and safe, especially on a large scale, remains to be seen. Scientists and entrepreneurs say ocean carbon removal needs more research as well as a sustainable economic model.
Experts convened in 2021 by the National Academies of Science, Engineering and Medicine identified six ocean carbon removal technologies that might make a dent in atmospheric carbon dioxide. The report recommended a $125 million research program to better understand the challenges, including potential economic and social effects, and estimated it would take $1.3 billion to translate these ideas into scalable demonstration projects.
Meanwhile, some entrepreneurs have already been testing their own ideas for employing the ocean to remove carbon. Here's a sampling:
San Francisco-based Project Vesta says it is readying an experiment on a Caribbean island later this year to add a carbon-absorbing mineral to seawater to act as a kind of massive antacid tablet. Boosting alkalinity causes a series of chemical reactions that convert dissolved CO2 in the seawater into stable bicarbonate and carbonate molecules, which in turn causes the ocean to absorb more CO2 from the air.
Project Vesta plans to grind a green mineral called olivine into sand-like particles and spread it along the beach of a cove on the island, which it declined to name. As waves and currents dissolve the olivine, it is expected to create a series of chemical reactions that allow the ocean to capture CO2 from the air. A second bay on the island will serve as a control site. "We do change the ocean chemistry, but we do it in a very gradual way," Project Vesta CEO Tom Green says.
Meanwhile, Canadian startup Planetary Technologies plans to use nickel-mine waste, or tailings, to make an alkaline material that can be added to the ocean. The tailings are used in a process with electrical current to split water into hydrogen and oxygen and produce a byproduct called mineral hydroxide. Added to seawater, the hydroxide raises the alkalinity and captures more CO2 from the air, the firm says. The idea is to add the compound to existing industrial outfalls that lead to the ocean.
Researchers led by Geomar devised an experiment using large clear cylinders to measure how adding various alkaline minerals to seawater helps reduce CO2. The first phase took place off the coast of Grand Canary Island in the fall. The second part is planned for May in a Norwegian fjord. Early results show that the ocean chemistry must be carefully monitored to make sure the carbon is properly absorbed. If the alkalinity gets too high, a chemical precipitate forms, which can be toxic to ocean plankton.
Floating Kelp Farm
Aquaculture startup Running Tide proposes a flotilla of basketball-size buoys that support fronds of the macroalgae kelp underneath. As the kelp grows, it would absorb CO2 from the ocean. Once the kelp plant gets too big and heavy, it would sink to the bottom, dragging with it the carbon it has absorbed.
"It just hits the mud and then some of it gets eaten, becomes part of the ecosystem down there," says Running Tide CEO Marty Odlin, a former commercial fisherman who has an engineering degree from Dartmouth.
The recent National Academies study notes that too much decomposing kelp on the seafloor could cause "dead zones" of low-oxygen water that could harm marine life, while too much floating kelp could rob the surface layer of nutrients that supply other marine organisms.
Carbon Burial at Sea
What if you could grab CO2 from the air and bury it in the volcanic rock beneath the seafloor? That's the idea behind Solid Carbon, a Victoria, B.C.-based consortium that includes U.S. and Canadian scientists.
Floating platforms equipped with direct air capture machines would pipe the CO2 gas into basalt formations that lie 350 feet below the seafloor. The basalt would absorb the carbon dioxide and turn it into rock. Solid Carbon plans a demonstration project in 2024 at Cascadia Basin, about 130 miles off the coast of British Columbia.
Marine experts warn that any buried CO2 needs to be monitored to make sure it doesn't escape from the formation and bubble up into the ocean.