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Study finds that the ocean could never fully recover if a nuclear war were to break out 

Scientists have a good idea of what would happen after a nuclear war on land: Soot would fill the atmosphere and block the sun, leading to worldwide crop failures and famine. But, until recently, they’ve understood less about how nuclear weapon detonation would affect the oceans, which cover more than 70% of the Earth’s surface.

A recent study in the journal AGU Advances helps fill in the gaps: Nuclear war would wreak havoc on the world’s oceans, causing them to cool rapidly and become choked with sea ice. Ocean marine life would die out, and marine ecosystems would take decades—possibly even longer—to recover. 

“This research suggests that the consequences of nuclear conflict can be quite dire,” says Nicole Lovenduski, one of the paper’s authors and a University of Colorado Boulder associate professor in the Department of Atmospheric and Oceanic Sciences (ATOC) and the Institute of Arctic and Alpine Research (INSTAAR). 

Top of page: A mushroom-shaped cloud and water column rise above Bikini Atoll from the underwater Baker nuclear explosion of July 25, 1946. Radioactive sea spray caused extensive contamination. Photo by Bill Gustafson. Above: Nicole Lovenduski's research focusses on marine carbon cycle, ocean climate variability and change and ocean modeling.

“Because the ocean moves slowly, when you change or perturb the ocean, it takes a long time to recover back to its initial state. The ocean would be affected for decades to hundreds or thousands of years, depending on the process. And in our experiments, it really never recovered,” she says.

There are about 13,000 total nuclear weapons around the world under the control of nine nations. While a few thousand weapons are waiting to be dismantled, the United States and Russia each have roughly 4,000 deployed or spare weapons—90 percent of all active nuclear weapons—while other countries have much smaller arsenals. 

India and Pakistan each have 150; China, Britain and France have roughly 200 each; Israel has 100; and North Korea has an unknown number, according to Brian Toon, one of the paper’s authors and a professor at ATOC and the Laboratory for Atmospheric and Space Physics (LASP).

To understand what might happen to the oceans after nuclear detonation, scientists ran a series of simulations that modeled major nuclear conflicts, such as what could occur between the United States and Russia, as well as smaller wars, such as those between nations like India and Pakistan. 

No matter the location or magnitude of the war, the researchers found that soot would quickly clog the stratosphere, preventing sunlight from reaching the oceans’ surface for roughly a decade. 

“Once soot gets up there, there are very few natural processes by which it can leave, so it hangs out there for a while,” Lovenduski says. “It gets mixed all around and forms a cloud of soot around the Earth, which leads to a cooling of the climate system.”

After a nuclear war between the United States and Russia, they project that global average surface temperatures at sea and on land would decline by 10 degrees Celsius (18 degrees Fahrenheit) in the three years after the conflict, triggering what researchers have called a nuclear winter. 

Ocean temperatures would also drop dramatically, creating a new “ocean state for the lifetime of many organisms, including humans” long after the conflict ends, the researchers write. The colder temperatures would allow sea ice to proliferate, which would block shipping routes and major ports.

“We find an extension of sea ice even in a simulation of what you might consider a regional or smaller nuclear conflict,” Lovenduski says. “Even a small conflict can have large consequences for the climate system.”

The sunlight-blocking soot cloud would also make it difficult, if not impossible, for phytoplankton to photosynthesize and stay alive. Since phytoplankton, also known as microalgae, form the basis of the marine food chain; their demise would set in motion a chain reaction that would likely devastate fish and other marine wildlife populations.

On land, scientists predict that nuclear conflict would lead to disastrous crop failures. And if the world’s population had hoped to replace those crops by turning to the oceans for food, they likely wouldn’t find much to eat there, either.

“If the algae go, everything else goes, too,” Lovenduski says. “The ocean essentially starves as a result of these nuclear conflicts.”

Other takeaways

Scientists from a dozen institutions around the world collaborated on this project. And although they began their work long before Russia invaded Ukraine in February 2022, the timing of the paper’s publication amid the heightened threat of nuclear war has generated increased interest in their work.

“Certainly, our study came out at a time when a lot of people are thinking more about the threat of nuclear conflict than they have in the recent past, so it’s very timely, unfortunately,” Lovenduski says. “The fact that our project is becoming more relevant is depressing and terrifying.”

The scientists hope their nuclear war projections never become reality, but, in the meantime, they’re using this line of research as an opportunity to learn more about the ripple effects of other potentially damaging events. For instance, what would happen after a massive volcanic eruption, which would also send sunlight-blocking materials and chemicals into the stratosphere? 

The findings are also helpful for considering one proposed solution to climate change: Artificial cooling of the planet.

“There’s a lot of talk about geoengineering the climate because we made it warmer, so why don’t we fix it by making it cooler?” she says. “Some of those geoengineering solutions are in line with this kind of simulation, where you loft aerosols into the stratosphere to cool the planet. This gives us an understanding of how the Earth system might respond to these types of manmade cooling events.”

They also hope their paper raises awareness among the general population that any nuclear conflict, even a relatively small one, could have calamitous worldwide consequences.

“Even if there is a small, regional nuclear conflict far away from you, you can also be affected,” she says. “People are coming to realize how interconnected our global society is, especially after the pandemic, and even a small conflict that occurs on one day can have huge implications for the entire Earth system for centuries to come.”