International shipping moves 80% of global trade and accounts for about 3% of the world’s carbon emissions, but right now, it’s not on course to meet its climate targets.

A year ago, the International Maritime Organization — the UN agency that regulates shipping — tightened emission targets for the shipping industry, aligning it with other industries aiming to achieve net zero emissions by 2050. But low-emission fuels like methanol, hydrogen and ammonia are not becoming available fast enough.

Now, Jess Adkins, a chemical oceanographer from the California Institute of Technology (Caltech) thinks he can lend a hand by equipping cargo ships with reactors capable of turning the carbon dioxide (CO2) emitted from burning fuel into ocean salts, which he says will keep it locked away for 100,000 years.

The process is similar to what’s already naturally happening in the oceans. “This is a reaction that the planet has been running for billions of years,” said Adkins, who founded Calcarea, a startup that is designing and testing the reactors.

“If we can just speed it up, we have a shot at a safe and permanent way of storing CO2.”

Natural, but faster

Seawater naturally absorbs about a third of the CO2 emitted into the atmosphere, making the water more acidic and causing it to dissolve calcium carbonate, which is abundant in the ocean. “Calcium carbonate is what coral skeletons, shells and all the things that make up most of the sediments at the bottom of the ocean are made of,” said Adkins.

The dissolved calcium carbonate then reacts with the CO2 in the water to form bicarbonate salts, locking the CO2 away. “There are already 38,000 gigatons (38 trillion tons) of bicarbonate in the ocean right now,” Adkins added.

Calcarea wants to mimic this natural process by funneling the ship’s exhaust fumes to a reactor in the ship’s hull, where the fumes are vigorously mixed with seawater and limestone — a type of rock mostly made of calcium carbonate, and a common ingredient in concrete. The CO2 in the exhaust fumes reacts with the mixture, creating salty water that locks the CO2 away in the form of bicarbonate salts. Adkins says that with a full-scale reactor, he aims to capture and store about half of a ship’s CO2 emissions.

In the natural world, the reaction takes over 10,000 years, according to Adkins, but in Calcarea’s reactors it takes about a minute, he said. This is achieved by bringing the CO2 and the limestone into intimate contact with each other.

The salty water that’s created is simply released into the ocean, where it poses no threat to marine life or to the seawater’s chemical balance, according to Adkins. He added that the company is also looking into adding a pre-filter to the system to get rid of other pollutants from the exhaust that might get mixed into the water, such as particulates and unburnt fuel, as well as other contaminants.

After two years of working on the project, in January 2023 he spun the company out of Caltech, where he is still a professor, albeit on leave. He was joined by three co-founders: Caltech undergraduate Melissa Gutierrez, engineer Pierre Forin, and University of Southern California (USC) professor and geochemist Will Berelson.

They raised $3.5 million in funding and focused on the shipping industry. “The beautiful part is that the ship is a natural water pump,” Adkins said, noting that the system requires water to be constantly moving around for the reaction between the various elements to happen, something that is provided naturally by a ship’s movement.