Sea Change

Last year, a ship just off the coast of Massachusetts pumped thousands of gallons of red liquid into the ocean. A trail of scarlet fluid spread out behind the vessel. Anyone watching might have wondered: Was a beverage company getting rid of expired fruit juice? Were polluters dumping chemical waste?

The reality was nothing so scandalous—but it was unusual. The red liquid was part of an experiment. Its goal was to test whether changing the chemistry of seawater could help cool the planet.

Right now, the experiment’s results look promising. But there’s a long way to go before this method of altering the oceans to counteract climate change could be deployed on a global scale. Here’s what the investigation has revealed so far about how Earth’s oceans and climate are connected.

Last year, a ship was sailing off the coast of Massachusetts. It pumped thousands of gallons of red liquid into the ocean. The scarlet fluid spread out behind the ship. It was a puzzling sight. Was a beverage company getting rid of old fruit juice? Were polluters dumping chemical waste?

The real story wasn’t that shocking, but it was unusual. The red liquid was part of an experiment. It changed the chemistry of seawater. The goal was to see if this could help cool the planet.

Right now, the experiment’s results look promising. The idea is to alter the oceans to fight climate change. But there’s a lot to do before this method could be used worldwide. Here’s what the study has revealed about the connection between Earth’s oceans and climate so far.

Industries and people around the world burn fossil fuels—like coal, oil, and natural gas—for energy. This causes climate change by releasing heat-trapping greenhouse gases, such as carbon dioxide (CO₂), into the atmosphere.

To fight climate change, says geochemist Adam Subhas, “the number one thing we can do is reduce emissions” of greenhouse gases by switching to renewable energy (see “Renewable Energy Revolution,” Science World, April 13, 2026). Subhas studies ocean chemistry at Woods Hole Oceanographic Institution in Massachusetts. Today the carbon dioxide in Earth’s atmosphere is at its highest level in 800,000 years. That’s causing climate change to accelerate so quickly that a shift to renewable energy may no longer be enough. Recent reports from the Intergovernmental Panel on Climate Change and other scientific institutions stress the need for additional solutions. “To avoid putting ourselves in a dangerous place with the climate, we need a way to trap carbon and store it away from the atmosphere,” explains Subhas. That’s where the ocean comes in.

Currently, about a third of the CO₂ humans produce stays in the atmosphere, absorbing heat and raising average temperatures. Another third is taken up by plants on land. The ocean soaks up the last third—which helps regulate temperatures on Earth (see “The Carbon Cycle,” below).

But the absorption of all that CO₂ comes at a cost to marine ecosystems. Carbon dioxide reacts with water to form an acid, says Subhas. Acids are substances that tend to eat away at other materials. The addition of extra CO₂ “is acidifying the ocean,” he explains. Increasingly acidic waters can make it harder for animals such as corals and mollusks to build their hard outer skeletons and shells, which they need to survive. These organisms provide vital habitat and food for other creatures. Some are important food sources for people too. Their decline impacts the entire ocean ecosystem.

Today Earth’s oceans are about 30 percent more acidic than they were 200 years ago. As the amount of CO₂ in the ocean increases, the water absorbs the gas more slowly from the atmosphere. But Subhas and other climate experts think there could be a solution to help the oceans safely store more carbon: adding chemicals to reduce the water’s acidity.

Industries and people around the world burn fossil fuels for energy. These fuels include coal, oil, and natural gas. When they burn, they release greenhouse gases like carbon dioxide (CO₂). These gases trap heat in the atmosphere and cause climate change.

How can we fight climate change? Geochemist Adam Subhas says that “the number one thing we can do is reduce emissions” of greenhouse gases. That means switching to renewable energy (see “Renewable Energy Revolution,” Science World, April 13, 2026). Subhas studies ocean chemistry at Woods Hole Oceanographic Institution in Massachusetts. Today the carbon dioxide in Earth’s atmosphere is at its highest level in 800,000 years. As a result, climate change is quickly speeding up. Now a shift to renewable energy may not be enough. Recently, the Intergovernmental Panel on Climate Change and other scientific institutions released reports. They stress the need for more solutions. “To avoid putting ourselves in a dangerous place with the climate, we need a way to trap carbon and store it away from the atmosphere,” explains Subhas. That’s where the ocean comes in.

Right now, about a third of the CO₂ from human activities stays in the atmosphere. It absorbs heat and raises average temperatures. Plants on land take up another third. The ocean soaks up the last third. This helps control temperatures on Earth (see “The Carbon Cycle”). 

But all of that extra CO₂ causes problems for marine life. Carbon dioxide reacts with water to form an acid, says Subhas. Acids tend to eat away at other materials. Adding more CO₂ “is acidifying the ocean,” he explains. When waters become more acidic, it’s harder for animals to build hard outer skeletons and shells. Animals like corals and mollusks need these to survive. These organisms provide vital habitat and food for other creatures. Some are important food sources for people too. Their decline affects the entire ocean ecosystem.

Earth’s oceans are about 30 percent more acidic today than 200 years ago. As more CO₂ enters the ocean, the water absorbs the gas more slowly from the atmosphere. Is there a way to help the oceans safely store more carbon? Subhas and other climate experts hope so. Their idea is to add chemicals to reduce the water’s acidity.

During the 2025 experiment at sea, Subhas and colleagues pumped more than 61,000 liters (16,000 gallons) of sodium hydroxide (NaOH) into the water. That’s enough to fill a typical aboveground swimming pool. Sodium hydroxide, also called lye, is a base—the chemical opposite of an acid. Adding a base increases seawater’s alkalinity, or ability to resist becoming more acidic when acids are introduced. Under more alkaline conditions, CO₂ reacts with seawater to create stable substances that remain in the water for tens of thousands of years—where they can’t warm the planet. Also, with higher alkalinity, some organisms may more easily use carbon from CO₂ to build their shells. When they die, they sink to the ocean floor. Carbon in fallen shells can stay locked in ocean sediments for millions of years.

To track the sodium hydroxide, the researchers mixed a nontoxic red dye into it. Another ship and a group of underwater robots followed nearby as the liquid flowed into the ocean. Over the next four days, the researchers took samples from the dyed alkaline seawater and surrounding untreated seawater. “We can confidently say CO₂ absorption increased,” says Subhas. The team also studied the effects of the alkaline treatment on sea life. They saw no signs of harm in samples of plankton, young fish, and baby lobsters they collected.

Subhas and his colleagues performed the 2025 experiment at sea. They pumped more than 61,000 liters (16,000 gallons) of sodium hydroxide (NaOH) into the water. That would fill an average aboveground swimming pool. Sodium hydroxide is also called lye. It’s a base—the chemical opposite of an acid. Adding a base increases seawater’s alkalinity. That’s its ability to resist becoming more acidic when acids are added. When seawater is more alkaline, CO₂ reacts with it to create stable substances. They remain in the water for tens of thousands of years, so they can’t warm the planet. Higher alkalinity could also help some organisms. They may more easily use carbon from CO₂ to build their shells. When they die, they sink to the ocean floor. Carbon in fallen shells can stay locked in ocean sediments for millions of years.

The researchers mixed a nontoxic red dye into the sodium hydroxide to track it. The liquid flowed into the ocean. Another ship and underwater robots followed nearby. For four days, the researchers took samples from the dyed alkaline seawater and surrounding untreated seawater. “We can confidently say CO₂ absorption increased,” says Subhas. The team also studied the effects of the alkaline treatment on sea life. They collected samples of plankton, young fish, and baby lobsters. And they saw no signs of harm.

For Subhas and his colleagues, this test was just a first step. There’s still a lot to learn about whether it’s safe to increase ocean alkalinity across large areas and long time spans. “One of the uncertainties is how different species—and entire ecosystems—will respond,” says Nina Bednaršek, a biological oceanographer with the Jožef Stefan Institute in Slovenia. She and colleagues have analyzed the effects of increasing alkalinity on dozens of marine species. While some do well, others show sensitivity to changes.

Subhas notes that even if tweaking ocean chemistry turns out to be safe and effective, collecting, transporting, and releasing enough of any alkaline substance to make a difference would take a lot of energy. Scientists would need to make sure there’s still a benefit for the climate after accounting for all of that.

Despite these concerns, Bednaršek thinks it’s important to keep investigating ocean alkalinity additions. “Climate change itself is already causing significant harm to marine ecosystems,” she says—so doing nothing is risky too.

Whether or not people ultimately try to change ocean chemistry, Subhas says it’s important to appreciate everything Earth’s seas provide for humanity. “The next time you’re at the beach, be thankful for all the work the ocean does for us and our climate,” he says.

This test was just a first step for Subhas and his colleagues. Big questions remain. Is it safe to increase ocean alkalinity across large areas and long time spans? “One of the uncertainties is how different species—and entire ecosystems—will respond,” says Nina Bednaršek. She’s a biological oceanographer with the Jožef Stefan Institute in Slovenia. She and her colleagues have studied the effects on dozens of marine species. When alkalinity increases, some do well. But others are sensitive to changes.

Subhas notes another concern. It might turn out to be safe and effective to alter ocean chemistry. But people would have to collect, transport, and release enough of the alkaline substances to make a difference. That would take a lot of energy. After all of that, would there still be a benefit for the climate? Scientists would have to make sure. 

Bednaršek still thinks we should keep studying ocean alkalinity additions. “Climate change itself is already causing significant harm to marine ecosystems,” she says. So doing nothing is risky too.

We don’t know if people will eventually try to change ocean chemistry. But no matter what, Subhas says it’s important to appreciate Earth’s seas. They provide so much for humans. “The next time you’re at the beach, be thankful for all the work the ocean does for us and our climate,” he says.