Even as renewable energy and zero-emissions transportation scale up and the rest of the global economy slowly decarbonizes, it’s likely that the world will still need to suck an enormous amount of carbon dioxide out of the atmosphere to tackle climate change—10 billion metric tons per year by the middle of the century, by one estimate. Some startups are turning to machines that suck CO2 directly from the air. Others are betting on trees. But a team of scientists from the University of California, Los Angeles, is turning to the ocean instead.
The researchers took inspiration from seashells, which are formed from the carbon dioxide that naturally dissolves in the ocean. “We were thinking, What would be one of the best ways for us to start trapping CO2?” says Dante Simonetti, an assistant professor of chemical and biomolecular engineering at the UCLA Samueli School of Engineering. “And we all thought about, well, what about the formation of seashells? This is a reaction that happens naturally and a reaction that we had all studied in previous projects. So we started thinking, How can we leverage that at a scale where it will start affecting atmospheric CO2 levels?”
Because the ocean and the atmosphere are in a state of equilibrium, if CO2 is taken out of the water the ocean will then pull more from the air. In a lab, the scientists started testing new technology that could speed up the process of turning carbon dioxide into minerals. The seawater the machine pulls in goes through a mesh that gives the water an electric charge. That triggers chemical reactions that combine dissolved CO2 with calcium and magnesium in the water, creating limestone and magnesite. These materials—essentially ground-up seashells—can either be disposed of on land or released back into the ocean. The seawater can also flow back into the ocean, where it can absorb more CO2.
The process has some advantages compared to other carbon-removal technology, including the fact that seawater already naturally takes up CO2 at a high concentration, 150 times the level in air. “We don’t have to expend any energy for that to happen, and we get a very concentrated medium to work with,” Simonetti says. “If we compare that to direct air capture, direct air capture requires a tremendous amount of energy to take the CO2 out of the air and to concentrate it into something that can then be stored.” Without using so much energy, the new process can be less expensive than direct air capture. It also produces hydrogen as a by-product, which can be used to help run the equipment or sold as fuel.
The technology also permanently sequesters CO2, something that doesn’t necessarily happen in other processes. If a power plant captures carbon dioxide at its smokestacks or a direct air capture plant pulls it out of the air, the CO2 might be turned into fuel that’s burned or plastic that’s later incinerated, releasing the CO2; if it’s injected underground, there’s a danger that it might later leak. Trees that are planted or protected to capture CO2 might be lost to disease or in forest fires. But the minerals created through the new process offer permanent storage without the need for additional steps.
“We’re talking about geological time, millions of years,” Simonetti says. “If we’re looking at a direct air capture system, you’re still left with a gas and that has to be compressed. And that has to be stored somewhere, where you have to expend energy to get it into that formation, whether it’s underground or in some other form of sequestered state. Then you will have to monitor the site to make sure there’s no leakage. . . . Our process doesn’t have any of those complications.”
Stripe, the tech company that began paying for carbon removal two years ago—instead of more typical carbon offsets—recently announced that it would purchase CO2 removal from the team, which has spun the technology into a new company called Seachange. The next step will be to transfer the tech from the lab to a demonstration site where the scientists can get real-world performance data. They’ll also work with other experts to ensure that the process doesn’t have any negative impact on the marine environment. When the technology begins to roll out, it will have to happen at a large scale: Capturing 10 billion metric tons of CO2 each year would take 1,800 of the devices.