A nuclear war would disrupt the global climate so badly that billions of people could starve to death, according to what experts are calling the most expansive modeling to date of so-called nuclear winter. Although the exact effects remain uncertain, the findings underscore the dangers of nuclear war and offer vital insights about how to prepare for other global disasters, researchers say.
The study comes as Russia’s invasion of Ukraine has put the world in “one of the top three most worrisome time periods” for the threat of nuclear war, says Seth Baum, executive director of the Global Catastrophic Risk Institute—behind only the 1962 Cuban Missile Crisis and the 1983 Able Archer incident, when the Soviet Union mistook a NATO military exercise for a real attack. “It’s a continued reminder that [nuclear war] is really terrible.”
Scientists have long known massive explosions can throw enough dust, ash, and soot into the air to affect the global climate. In 1815, Mount Tambora in what’s now Indonesia unleashed the largest known volcanic eruption in history. In the following months, its ash rose and spread worldwide, blocking enough sunlight to produce “the year without a summer”—a cold spell in 1816 that resulted in massive crop failures and famine across the globe.
For decades, scientists have warned a similar catastrophe could follow a nuclear war, as fires ignited by hundreds or thousands of nuclear explosions would release millions of tons of soot, blocking sunlight and inducing global environmental effects. Worries about climate effects of nuclear warfare emerged soon after World War II, and studies took off during the Cold War.
Over the past decade, two pioneers of nuclear winter studies, Alan Robock and Brian Toon, have assembled a cross-disciplinary team of scientists to take the calculations further. They turned to the same climate models that underlie global warming studies—but used the models to simulate global cooling instead. “Now, we have the computational capacity to simulate these kinds of things in a sophisticated way,” says Jonas Jägermeyr, a climate change scientist, crop modeler, and team member at NASA and Columbia University.
In new the study, out today in Nature Food, the team has attempted to quantify the potential impact of nuclear war on the global food supply by coupling the climate models with simulations of global food production. A previous analysis, led by Jägermeyr in 2020, showed that even a small regional nuclear war between India and Pakistan could result in global crop shortages. The new study includes six nuclear war scenarios and incorporates models of fisheries as well as farming to get a broader picture of the impact.
The researchers estimated that the various nuclear exchanges would inject between 5 million and 150 million tons of soot into the atmosphere. They simulated the resulting changes in sunlight, temperature, and precipitation, which they then fed to the crop and fishery models. By tracing the reductions in corn, rice, soybean, wheat, and fish harvests, the team estimated the total loss in calories. From there, they calculated how many people would go hungry—assuming international food trade would cease and resources would be distributed optimally in each country.
A few years after a nuclear war between the United States, its allies, and Russia, the global average calories produced would drop by about 90%—leaving an estimated 5 billion dead from the famine, the researchers report. A worst-case war between India and Pakistan could drop calorie production to 50% and cause 2 billion deaths. The team tried to simulate the impact of food-saving emergency strategies, such as converting livestock feed and household waste to food. But in the larger war scenarios, those efforts did little to save lives.
Baum urges caution in interpreting the estimates. Although the climate models are “excellent,” he says, there’s too much uncertainty in how humanity would react to such a global catastrophe to get an accurate read on the death toll. Still, the study “makes a very worthy contribution” to envisioning these scenarios, he adds.
Lili Xia, a climate scientist at Rutgers University, New Brunswick, and lead author on the paper, agrees there’s lots of room to improve the models—including factoring in the effects of soot on ultraviolet radiation and surface ozone and implementing more effective food management techniques. Rather than aiming to forecast exactly how the food catastrophe might play out, she says her group wanted to understand the level of risk humanity faces.
The nightmarish prospects have already inspired others to look for ways to fight the hypothetical famine. David Denkenberger, who co-founded the nonprofit Alliance to Feed the Earth in Disasters, is exploring ideas including scaling up “resilient foods” such as seaweed, repurposing paper factories to produce sugar, converting natural gas into protein with bacteria, and relocating crops to account for an altered climate. He and his research associate Morgan Rivers think those approaches could dramatically increase the amount of food available to humans. “Even if [a substitute] doesn’t taste as good as sweet corn, it’s better than starving,” he says.
Such thought exercises can also help humanity prepare for the effects of climate change and other disasters, Denkenberger adds. “It’s not just nuclear winter; resilience helps us with a lot of other catastrophes … such as a supervolcanic eruption.”
Still, the obvious takeaway for all these scientists is that nuclear war should be avoided at all costs, Rivers says. “Their analysis is showing something really critical to transmit: that nuclear winter is really, really bad.”
Source: Science Mag