The global economy relies on sending goods around the world. But shipping carries a heavy carbon burden. The maritime industry is responsible for 3% of the world’s carbon emissions. If growth rates continue, shipping could produce about 10% of global carbon emissions by 2050.
Shipping, like flying, is also extremely challenging to decarbonize. Scientists have now developed a new technology that mimics the ocean’s natural carbon dioxide-trapping process to cut shipping emissions by half. The system would sit aboard a sea vessel, converting carbon dioxide from ship exhaust into bicarbonates. The bicarbonate-rich water could then be released back into the sea, where they naturally exist and remain stable for tens of thousands of years.
“What’s beautiful about this is how simple it is,” said William Berelson, a professor of earth sciences at the University of Southern California (USC) in a press release. Berelson and Jess Adkins, a professor of geological and planetary sciences the California Institute of Technology (Caltech), led the work published in Science Advances.
The shipping industry is trying to become greener by testing the use of batteries and of sustainable hydrogen or ammonia fuels. But these technologies remain expensive, and the fuels don’t always come from clean sources.
Until clean fuels become reality, it is necessary to reduce the carbon dioxide that ships emit. So the USC and Caltech team devised a route to speed up a natural mechanism. Oceans absorb significant amounts of carbon dioxide from the atmosphere naturally. When carbon dioxide reacts with water, it forms carbonic acid. The acid is unstable and splits to form stable bicarbonate ions.
In the researchers’ system, ship exhaust mixes with seawater that is pumped onboard. The carbon dioxide reacts with water to form acid. The water then passes over a bed of limestone, where the acid reacts with limestone to form bicarbonates. The treated water with bicarbonates can be released back into the ocean.
Small-scale tests of the chemical reactions in the laboratory show that the system works as predicted. The researchers also ran computer simulations to analyze what would happen when the bicarbonate-rich water is released into the ocean. The models considered a ship traveling back and forth between China and Los Angeles continuously over a 10-year period. The results showed that the discharged water affected ocean pH and chemistry by less than 1.4%, while reducing carbon dioxide emissions by 50%.
Adkins is co-founder and CEO of startup Calcarea, which is now in talks with commercial shippers to test the technology.
Source: Sijia Dong et al. Potential of CO2 sequestration through accelerated weathering of limestone on ships. Sci. Adv., 2025.
Photo by Ian Simmonds on Unsplash
