Nuclear war would launch a global climate catastrophe

With ongoing tensions between India and Pakistan raising concerns about the possibility of nuclear conflict, even as neither country is likely to initiate without significant provocation, researchers have evaluated both the direct fatalities and global climate anomalies that would result if nuclear war did break out. The researchers evaluated this scenario for the year 2025.

Fatalities could reach 50 to 125 million people if Pakistan attacked urban targets in 2025 with 150-kiloton nuclear weapons and if India attacked with 100-kiloton nuclear weapons.

Smoke from burning cities would release 16 to 36 teragrams of black carbon into the atmosphere, blocking out sunlight, cooling the global surface by 2-5°Celcius, reducing precipitation by 15 to 30%, and diminishing the rate at which plants store energy as biomass (net primary productivity) by 15 to 30% on land and by 5 to 15% in oceans.

Together, these calamites would threaten mass starvation. Toon et al. were motivated to study such a scenario because India and Pakistan share a long history of military clashes and are currently engaged in a nuclear arms race–each nation may currently possess 140 to 150 warheads and could expand to 200 to 250 by 2025, raising concerns that a conventional war between them could turn nuclear.

Toon et al. developed a simplified war scenario based on advice from military and policy experts. Although Pakistan attacks first in this scenario, the researchers do not think Pakistan would be more likely than India to initiate conflict. They expect the results would be similar in both cases.

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Toon et al. calculated the quantity of smoke lofted to the upper troposphere and lower stratosphere using a recent population database and observations of fire ignition area from Hiroshima. They conducted climate and net primary productivity simulations using a model similar to one used to simulate the climate following the asteroid impact that killed the dinosaurs.

In a related editorial, Science Advances Deputy Editor Kip Hodges highlights how, unlike in the days of the Cold War, when only a few countries were capable of starting a nuclear war, nine countries now possess a total of nearly 14,000 nuclear warheads. With respect to India and Pakistan, the deteriorating relationship between these neighboring countries puts south Asia–and the rest of the world–at risk.

As the new research from Toon et al. shows, nuclear war between India and Pakistan creates not just a regional but a global disaster. The scientific case against the use of nuclear weapons in any capacity is clear, Hodges emphasizes, even if their limited use remains a subject of political debate.