From the journal Nature, March 16:
As geopolitical tensions rise in nuclear-armed states, scientists are modelling the global impact of nuclear war.
It all starts in 2025, as tensions between India and Pakistan escalate over the contested region of Kashmir. When a terrorist attacks a site in India, that country sends tanks rolling across the border with Pakistan. As a show of force against the invading army, Pakistan decides to detonate several small nuclear bombs.
The next day, India sets off its own atomic explosions and within days, the nations begin bombing dozens of military targets and then hundreds of cities. Tens of millions of people die in the blasts.
That horrifying scenario is just the beginning. Smoke from the incinerated cities rises high into the atmosphere, wrapping the planet in a blanket of soot that blocks the Sun’s rays. The planet plunges into a deep chill. For years, crops wither from California to China. Famine sets in around the globe.
This grim vision of a possible future comes from the latest studies about how nuclear war could alter world climate. They build on long-standing work about a ‘nuclear winter’ — severe global cooling that researchers predict would follow a major nuclear war, such as thousands of bombs flying between the United States and Russia. But much smaller nuclear conflicts, which are more likely to occur, could also have devastating effects around the world.
This week, researchers report that an India–Pakistan nuclear war could lead to crops failing in dozens of countries — devastating food supplies for more than one billion people1. Other research reveals that a nuclear winter would dramatically alter the chemistry of the oceans, and probably decimate coral reefs and other marine ecosystems2. These results spring from the most comprehensive effort yet to understand how a nuclear conflict would affect the entire Earth system, from the oceans to the atmosphere, to creatures on land and in the sea.
Scientists want to understand these matters because the nuclear menace is growing. From North Korea to Iran, nations are building up their nuclear capabilities. And some, including the United States, are withdrawing from arms-control efforts. Knowing the possible environmental consequences of a nuclear conflict can help policymakers to assess the threat, says Seth Baum, executive director of the Global Catastrophic Risk Institute in New York City, who has studied the risks of triggering a nuclear winter. “Fleshing out the details of ways in which it can be bad is valuable for helping inform decisions,” he says.
Cold-war forecasts
Nuclear-winter studies arose during the cold war, as the United States and the Soviet Union stockpiled tens of thousands of nuclear warheads in preparation for all-out assaults. Alarmed by leaders’ bellicose rhetoric, scientists in the 1980s began running simulations on how nuclear war might change the planet after the initial horrific deaths from the blasts3,4. Researchers including the US planetary scientist and communicator Carl Sagan described how smoke from incinerated cities would block sunlight and plunge much of the planet into a deep freeze lasting for months, even in summer4. Later studies tempered the forecasts somewhat, finding slightly less-dramatic cooling5. Still, Soviet leader Mikail Gorbachev cited nuclear winter as one factor that prompted him to work towards drawing down the country’s nuclear arsenals.
After the Soviet Union collapsed in 1991, the world’s stockpiles of nuclear weapons continued to drop. But with many thousands of warheads still in existence, and with more nations becoming nuclear powers, some researchers have argued that nuclear war — and a nuclear winter — remain a threat. They have shifted to studying the consequences of nuclear wars that would be smaller than an all-out US–Soviet annihilation....MUCH MORE
