Dr. Jeff Masters ·

Above: A Pakistani civil society activist sings a peace song as others carry placards during a peace rally in Islamabad on February 28, 2019. Pakistan said on February 28 it will release a captured Indian pilot in a 'peace gesture', taking a step towards rapprochement as clashes between the nuclear-armed rivals ignited fears of a disastrous conflict. Image credit: AAMIR QURESHI/AFP/Getty Images.

As nuclear-armed India and Pakistan engage in military clashes over the disputed Kashmir region, consider that a “limited” nuclear war between them is capable of causing a catastrophic global nuclear winter that could kill two billion people. The inevitable wars and diseases that would break out could kill hundreds of millions more.

A 2008 paper by Brian Toon of the University of Colorado, Alan Robock of Rutgers University, and Rich Turco of UCLA, "Environmental Consequences of Nuclear War", concluded that a war between India and Pakistan using fifty Hiroshima-sized weapons with 15-kiloton yield on each country, exploded on cities, would immediately kill or injure about forty-five million people. However, the final toll would be global and astronomically higher, according to recent research.

Figure 1. A mushroom cloud of fire and smoke rises 40,000 feet in two minutes after a hydrogen bomb explosion at Eniwetok Atoll in the Pacific in 1952. (Photo by Three Lions/Getty Images).

The most recent study of the environmental aftermath of a nuclear conflict, Mills et al. 2014, Multidecadal global cooling and unprecedented ozone loss following a regional nuclear conflict, used an Earth system climate model including atmospheric chemistry, ocean dynamics, and interactive sea ice and land components, to investigate a limited nuclear war where each side detonates fifty 15-kiloton weapons over urban areas—less than half of the existing arsenals of the approximately 140 warheads each that India and Pakistan have. These urban explosions were assumed to start 100 firestorms. Firestorms are self-feeding fires that suck air into themselves and generate immense columns of rising smoke which lofts into the stratosphere, where it spreads globally. The model predicted the smoke would block enough sunlight for the Earth to experience the coldest temperatures since the last ice age, thousands of years ago.

Figure 2. Change in surface temperature for (a) June to August and (b) December to February. Values are 5-year seasonal averages for years 2 – 6 after a nuclear war between India and Pakistan. Image credit: Mills et al. 2014, Multidecadal global cooling and unprecedented ozone loss following a regional nuclear conflict, Earth’s Future (American Geophysical Union).

Since it does not rain in the stratosphere, the smoke would stay aloft for years, and surface temperatures would stay depressed for more than twenty-five years, due to thermal inertia from the cooled ocean waters and to extra reflection of sunlight back to space by expanded sea ice. The effects would be similar to what happened after the greatest volcanic eruption in historic times, the 1815 Tambora eruption in Indonesia. This cooling from this eruption triggered the infamous Year Without a Summer in 1816 in the Northern Hemisphere, when killing frosts disrupted agriculture every month of the summer in New England, creating terrible hardship. Exceptionally cold and wet weather in Europe triggered widespread harvest failures, resulting in famine and economic collapse. However, the cooling effect of that eruption only lasted about a year. Cooling from a limited nuclear exchange would cause 5 - 10 consecutive "Years Without a Summer", and more than a decade of significantly reduced crop yields. Killing frosts would reduce growing seasons by ten to forty days per year for five years at mid-latitudes. Global precipitation would fall 6% during the first five years, and be reduced by 4.5% ten years later, resulting in a crippling increase in regional droughts. Over the Asian monsoon region, including the Middle East, the Indian subcontinent, and Southeast Asia, annual rainfall would fall by 20% - 80%, so that even the “winner” of the nuclear war between India and Pakistan would experience devasting famine due to the failure of the life-giving monsoon rains.

An added global calamity would result from the intense heating of the stratosphere by 30°C (54°F), due to absorption of sunlight by the smoke there. In the hot stratosphere, ozone would be destroyed by chemical reactions, causing global ozone losses of 20 - 50 percent over populated areas. UV light would increase by 30 - 80 percent over midlatitudes, suggesting widespread damage to human health, agriculture, and terrestrial and aquatic ecosystems beyond what the cold temperatures and drought would wreak.

The cold temperatures and increased drought might reduce global grain production by 20 percent for the five years after the war, and 10 - 15 percent for the following five years, said Toon et al., 2017. Helfand (2013) estimated that two billion people who are now only marginally fed might die from starvation and disease in the aftermath of a nuclear conflict between India and Pakistan, due to the cold weather and drought. The inevitable wars and diseases that would break out would likely kill hundreds of millions more.

The insanity of global nuclear war

It is sobering to realize that the nuclear weapons used in the study represented less than 0.7% of the world's total nuclear arsenal of about 14,500 warheads. A larger-scale global nuclear war would have much more severe environmental impacts. In the 1980s and early 1990s, a series of scientific papers published by Soviet and Western scientists (including prominent scientists Dr. Carl Sagan, host of the PBS "Cosmos" TV series, and Nobel Prize winner Paul Crutzen) laid out the dire consequences on global climate of a major nuclear exchange between the U.S. and Soviet Union. The nuclear explosions would send massive clouds of dust high into the stratosphere, blocking so much sunlight that a nuclear winter would result, they said. Global temperatures would plunge 20°C to 40°C for months and remain 2 - 6°C lower for 1 - 3 years. Up to 70% of the Earth's protective stratospheric ozone layer would be destroyed, allowing huge doses of ultraviolet light to reach the surface. This UV light would kill much of the marine life that forms the basis of the food chain, resulting in the collapse of fisheries and the starvation of the people and animals that depend on it. The UV light would also blind huge numbers of animals, who would then wander sightless and starve. The cold and dust would create widespread crop failures and global famine, killing billions of people who did not die in the nuclear explosions.

The nuclear winter papers were widely credited with helping lead to the nuclear arms reduction treaties of the 1990s, as it was clear that we risked catastrophic global climate change in the event of a full-scale nuclear war. But even a limited nuclear war between India and Pakistan is a catastrophic threat to Earth's climate. I urge India and Pakistan to seek a peaceful solution to their dispute. Pakistan said on February 28 it will release a captured Indian pilot in a 'peace gesture', and that is a hopeful sign. There is nothing more important than preventing nuclear war.