Nuclear war could bring more than global famine, radioactive fallout, and unrelenting winter—it could also kick off the most intense, longest El Niño the world’s ever seen. New research presented at the Ocean Sciences Meeting last month in San Diego suggests that global cooling from a nuclear conflict would disrupt normal atmospheric circulation, leading to a persistent, severe response in the Pacific Ocean similar to an El Niño.
“Hopefully, this will never happen,” said coauthor and assistant professor Samantha Stevenson from the University of California, Santa Barbara. “The idea behind the project is to demonstrate just how catastrophic this would be.”
“A Pretty Big Hammer”
The researchers tested the reactions of Earth’s atmosphere and ocean to a nuclear war using a climate model from the National Center for Atmospheric Research. Although the climate model doesn’t have a “nuclear war” setting, the researchers added varying amounts of black carbon to the model’s atmosphere over 1 week to simulate different nuclear war scenarios. (Past research has suggested that massive explosions and burning cities would inject tiny pieces of charred ash and soot high into the atmosphere, where they would remain for years and cool Earth.)
Each nuclear war scenario they tested provoked a cascade of changes to the world’s largest ocean basin, the Pacific. Trade winds, responsible for aiding sailors across the high seas, would reverse direction. The height of the sea surface on either side of the Pacific Ocean would recalibrate, bringing slightly more water to South America’s shores than Australia’s, for instance, a complete reversal of today’s ocean. Without the normal sea surface shape, upwelling along the equator would turn off, halting the delivery of nutrient-rich water that marine life depends on. In the most severe case, downwelling would kick off along the equator, a total reversal of ocean circulation.
“This is a pretty big hammer you’re hitting the climate system with, so we figured it would do something,” Stevenson said. “But looking at it was pretty shocking….It was beyond what I had thought about as a possibility.”
The changes brought to the ocean and atmosphere look very close to an El Niño event, said Stevenson. The index commonly used to assess the El Niño–Southern Oscillation cycle, the Southern Oscillation Index, dips five standard deviations away from the norm for the most severe case. “We’re calling it a nuclear Niño, because it looks like an El Niño, but it lasts for 7 or 8 years,” Stevenson said.
The severity of the response depends on just how much humans decide to explode. If the United States and Russia, for instance, unleash their massive arsenals, the resulting El Niño could last 7 to 8 years. In less destructive cases, like a conflict between India and Pakistan (in which the belligerents’ arsenals are smaller in number and have lower payloads), the El Niño would last between approximately 1 and 5 years, depending on how many weapons they use.
First author and graduate student at Rutgers University Joshua Coupe said that future work will look into the physical mechanisms that instigate the nuclear Niño. The qualitative answer so far points to air circulation over Southeast Asia as the culprit. Typically, big updrafts over the water near Malaysia, Papua New Guinea, and the Philippines drive an atmospheric loop over the Pacific called the Walker Circulation, but nuclear winter shuts it off. “It’s the first mechanism that we see at play,” Coupe said. “In the future we’d like to conduct sensitivity tests.”
“I’ve never seen this kind of research before,” said oceanographer Christopher Wolfe from Stony Brook University in Stony Brook, N.Y., who was not involved in the research. “I can see it inspiring more work into the climatological consequences of large-scale conflict.”
Halting upwelling in the equatorial Pacific “is kind of impressive, because it’s the basic state of the ocean,” Wolfe said. “We should be worried about what all the changes to the ocean will do to people.”
The latest study also tested the impact of nuclear war on the base of the marine food web, photosynthesizing phytoplankton, in the tropical Pacific. “It seems in the event where this enormous nuclear war happens, it would be very difficult to produce food in the ocean, based on these results,” Coupe said. Less light during nuclear winters means that less phytoplankton can grow, dropping their uptake of carbon by about a third in the most severe case. “The numbers that we see are pretty grim.”
The latest research was funded by a grant given to Rutgers University from the Open Philanthropy Project, a foundation started by Facebook cofounder Dustin Moskovitz, to study the ecological and social costs of nuclear war. “I hope that by providing more details about what could happen to the climate in the aftermath, that it will add to the deterrents of using these ever,” Coupe said.
—Jenessa Duncombe (@jrdscience), Staff Writer