India, Pakistan and the Threat of Nuclear Winter

As we approach the 80th anniversary of the August 1945 nuclear bombings of Hiroshima and Nagasaki, Pakistan and India have given us a timely reminder of how lucky we’ve been — and how soon our luck could run out.

On May 7, India launched missiles at what it called terrorist bases inside Pakistan, saying they were retaliation for the deaths of 25 Indian tourists in April. Pakistan, denying all knowledge of who killed the tourists, responded by shooting down five Indian jet fighters and a drone.

The rights and wrongs of the quarrel hardly matter; the question is how to get back to a routine level of hostility. The two countries have fought four wars since Pakistan was created by the partition of India as the British departed after the Second World War. Low-grade border clashes filled in the intervals between wars. Both countries developed nuclear weapons — India tested its first atomic bomb in 1974, Pakistan in 1998 — the better to deter each other from an all-out war.

Deterrence works until it doesn’t, and both sides seem keenly aware of how easily events could drag them into an inferno. We have happily forgotten the threat of nuclear weapons since the fall of the Soviet Union in 1991, but the world lived in fear of them from Hiroshima in 1945 to the late 1980s. I cannot recall a more serious threat to humanity since the Cuban missile crisis of October 1962.

In 2019, the Bulletin of the Atomic Scientists published an article by a group of researchers led by Alan Robock, a climatologist and professor at Rutgers University who advocates for nuclear disarmament. It features a scenario in which a conventional war between India and Pakistan might break out — in 2025.

The scenario starts with a terrorist attack (against the Indian Parliament, not against tourists in Kashmir). Each side is assumed to have about 250 atomic bombs ranging from five to 100 kilotons each (a kiloton is equivalent to the explosive impact of 1,000 tons of TNT). The Indian army invades both Pakistan and Kashmir, which is nominally under joint Pakistan-India administration.

To halt the invasion, Pakistani generals launch 10 tactical atomic bombs of five kilotons each against India’s tank columns. The next day, it fires another 15; the Indian army responds with 20 strategic weapons over the Pakistani garrison at Bahawalpur as well as over airfields and nuclear weapons depots.

Researchers predicted millions of deaths

And so it goes, with each side raising the stakes by hitting the other side’s military bases in major cities. By the fifth day Pakistan has used up all its nuclear weapons while India holds on to 100 bombs to deter any possible attack from China.

“The direct effects of the nuclear exchange,” the researchers wrote, “would be horrible; our group... estimated that 50 to 125 million people would die, depending on whether weapons used had yields of 15, 50, or 100 kilotons.”

That death toll is just the beginning. In their 2019 modelling, the researchers estimated that the nuclear exchange, by burning target cities, lifts at least 16 million tons of black carbon into the upper atmosphere. Bigger bombs would hurl even more black carbon. Warmed by sunlight, the carbon rises north and east into the stratosphere, where it remains for years.

As the carbon spreads around the Northern Hemisphere, it blocks sunlight and the world begins to cool down; assuming the war has been fought in May, with 50-kiloton weapons, the researchers estimate that by 2028 the average sea-surface temperature has fallen by 5 C. Eurasia and North America see the average land surface temperature fall by 5 to 15 C.

Presumably the war also adds to carbon dioxide emissions, so temperatures would rise sharply as carbon eventually leaves the stratosphere.

The prospect of famine

The researchers concluded: “Based on these results, any of the India-Pakistan nuclear cases we posit clearly would cause large reductions in agriculture and food shortages. Depending on whether people hoard food or share, there could be famine for millions or billions of people — even for the smaller amounts of smoke in the scenarios presented here.”

Researchers first predicted such outcomes in 1983 when the concept of “nuclear winter” emerged from scenarios of nuclear exchanges between the Soviet bloc and the NATO countries. The authors of those scenarios included many of the 2019 team, as well as the late Carl Sagan. With 36 more years of further research, the 2019 paper carries great plausibility.

But is it plausible that such a war would ever be fought? We should bear in mind that India is now the most populous country in the world, with a population estimated at 1.4 billion. India has a US$3.57-trillion GDP and a military of 1.45 million troops.

Pakistan is comparatively smaller, with a population of 248 million, a GDP of US$338 billion and combined military-paramilitary forces of 1.5 million.

In conventional war, victory goes to the country that can afford the economic and human costs of attritional warfare. In those terms, India is sure to be the victor. Still, such a war would be immensely disruptive to countries all over the world, which is why the United States and other nations have exerted immense pressure on India and Pakistan in their four previous wars.

This time, however, U.S. President Donald Trump has behaved like a helpless bystander. Historian Heather Cox Richardson quoted him as saying: “It’s a shame. We just heard about it, just as we were walking in the doors of the Oval.... No, I just hope it ends very quickly.”

A strategy of desperation

“Very quickly” is the way to win a war when you’re outmatched. In both world wars, Germany relied on surprise and speed to overcome numerically larger enemies. Japan did the same in the Second World War. It’s a strategy of desperation, as both Germany and Japan learned to their sorrow.

Still, Pakistan’s generals might gamble that a sudden nuclear attack on India’s key military and transportation centres could stun the Indian government into a ceasefire and then a peace treaty.

The generals would have even better reasons if they knew that India was planning a first strike despite its stated policy not to do so. In that case, Pakistan might decide to launch its weapons on the principle of “use them or lose them.”

And of course India, suspecting a surprise attack from Pakistan, might make the same decision.

The generals on both sides, however, must be aware of the environmental and climate consequences of a nuclear exchange. It might cool off the subcontinent for a few years, but not for long. With the return of high temperatures due to carbon emissions, vast regions of both countries would be uninhabitable for generations if not millennia.

Part of the current conflict is due to India’s scrapping of the Indus Waters Treaty, which supports 80 per cent of Pakistan’s irrigated farmland. According to a recent article in the Pakistani newspaper Dawn, “The flows of the Indus, Jhelum, and Chenab are the backbone of our agriculture, our cities, our energy system. At this moment, we simply do not have a substitute for these waters.”

And as an article in the Indian journal Business Standard explained, “About 93 per cent of Indus water is used for irrigation, supporting crops like wheat, rice, sugarcane, and cotton. Any reduction or stoppage in river flows would threaten food security, lower crop yields, and could trigger widespread shortages.”

Those problems would not be solved by war and will certainly be aggravated by climate change. India, Pakistan, the Persian Gulf countries and China all face the prospect of temperature and humidity increases that will turn their farmlands into uninhabitable deserts.

Far from fighting wars, India, Pakistan and their neighbours should be working together now to heatproof the subcontinent. A nuclear winter is not the way to do it.