Ships play a major role in global trade—but they’re also a big source of carbon emissions.
In fact, the shipping industry is responsible for nearly 3% of all greenhouse gases released into the atmosphere.
Finding ways to reduce this pollution is tough, especially for long-distance ocean travel.
But now, scientists have come up with a surprisingly simple solution: use limestone and seawater to trap carbon dioxide (CO₂) before it enters the air.
Researchers from the University of Southern California (USC) and Caltech, along with a startup company called Calcarea, have created a new system that could be installed directly on ships.
This system, described in the journal Science Advances, has the potential to cut a ship’s carbon emissions by up to 50%.
The idea is based on a natural process that already happens in the ocean. When CO₂ dissolves in seawater, it makes the water slightly acidic.
In nature, this acidic water sometimes reacts with limestone, turning the CO₂ into a harmless compound called bicarbonate, which is found naturally in ocean water.
The new shipboard system copies this process—but speeds it up and controls it so it works on moving ships.
Here’s how it works: As a ship travels through the ocean, it pumps seawater onboard. Then, CO₂ from the ship’s engine exhaust is mixed into the water. This makes the water more acidic, just like in nature.
That acidic water is then passed through a container filled with crushed limestone. The CO₂ reacts with the limestone and turns into bicarbonate. Finally, the treated water, now safe and CO₂-free, is returned to the ocean.
William Berelson, a professor at USC and one of the lead researchers, said the beauty of the system is in its simplicity. “We’re using a process the ocean already uses to absorb CO₂—but doing it on ships, where it can make a real impact,” he said.
The team tested the process in the lab, measuring how much CO₂ could be removed under different conditions.
Their results matched their predictions, giving them confidence to plan larger versions that could be used on real ships.
They also ran computer simulations to study how the bicarbonate-rich water would affect the ocean if it were discharged over time. In one test, they modeled a ship sailing between China and Los Angeles for 10 years, releasing treated water along the way. The results showed almost no change in ocean pH, suggesting the process is environmentally safe.
Calcarea, the company helping to bring this idea to life, is now working with commercial shipping companies to test the system on actual vessels. They’ve already partnered with Lomar Labs, the innovation arm of Lomar Shipping, to help move the technology from the lab into real-world use.
According to Jess Adkins, Caltech professor and CEO of Calcarea, the goal is to make the system easy to install on existing ships. “We’ve designed it to scale,” he said. “This could be a practical tool for cutting emissions across entire fleets.”
If adopted widely, this system could help the shipping industry become much greener—without needing brand-new ships or expensive fuel changes. It’s a promising example of how science and nature can work together to tackle climate change.
Source: University of Southern California.
