Even a Small Nuclear War Could Trigger a Global Apocalypse

Stipulated: A nuclear war would be real bad. But, like, how bad, exactly? What if it wasn’t all-out, the United States and Russia throwing thousands of warheads at each other , but instead something more limited? Longtime adversaries India and Pakistan have a couple hundred bombs each, tops, according to the best intelligence. Obviously it’d still be a localized nightmare —radiation, flattened cities, death. But whether a regional, so-called limited exchange could have global ecological consequences is a question on which nuclear strategy is disconcertingly quiet.
Climate science, though, is not. “I don’t like the term exchange,” says Alan Robock, a climate resesarcher at Rutgers who’s been studying nukes for three decades. “It’s jargon that nuclear war planners use to not think about the horror they’re planning.” Robock and a few colleagues have, for years, been running the numbers on what scientists in the 1980s called “nuclear winter,” the idea that multiple nuclear detonations would send enough dust, soot, and smoke into the atmosphere to literally block out the sun. With the end of the Cold War, fears of the world ending in both fire and ice faded, but reports of the demise of that demise may have been premature. Not only does President Trump seem to have a somewhat cavalier attitude toward the deployment of nuclear weapons and their wider accessibility, and not only are nuclear treaties crumbling around the world, but those two adjacent South Asian countries I mentioned have nuclear arsenals, and they’ve gone to war with each other before.
In 2007, Robock’s group tried to do the math. They approximated India and Pakistan’s arsenals at the time and imagined a war involving 100 Hiroshima-sized nuclear bombs—15 kilotons—over cities. The results were literally chilling: up to 5 million tons of carbon pumped into the atmosphere as smoke and soot, where climate models predicted it would remain for a decade. In just the first year that’d chop up to 20 days off the growing season in much of the northern hemisphere, resulting in global famines like the one in 1815, the “year without a summer” that followed the volcanic eruption of Mt. Tambora.Not everyone bought it. In 2018 a team at Los Alamos National Laboratory—where they make, among other things, nuclear weapons—published a more detailed model of both the climate and the fires that’d produce all that carbon, and came to a different conclusion. Sure, that “limited exchange” would put about 4 million tons of carbon into the air, they said, but it wouldn’t stay there. No nuclear winter. We’re saved! Well, not the millions of people who’d die in the conflict, but still.
But now Robock’s back, and his news is not good. India and Pakistan, he says, “have more weapons and they’re more powerful. And they’re the only two countries that have this upward trend.” So for an article in the journal Science Advances this week, his people built a new scenario, something more intense, with about 100 bombs launched by both sides, aimed directly at cities. In that part of the world, those cities are denser, which means more people with more stuff—some percentage of which turns to carbon particles when it burns. And they ran the numbers on carbon again. “There would be between 16 and 37 million tons,” Robock says. “If India and Pakistan had a war, it would be a much larger potential for climate change.” The solutions to that cold equation: 50 to 125 million people dead in the first week. A reduction of as much as 35 percent in sunlight reaching Earth’s surface, translating to a decrease in temperature of up to 5 degrees Celsius, with rainfall decreasing between 15 and 30 percent globally … and the amount of food produced by an equal amount. That’s worldwide famine for a decade.