ISLAMABAD – The concept of nuclear winter—a years-long planetary freezebrought on by airborne soot generated by nuclear bombs—has been around fordecades. But such speculations have been based largely onback-of-the-envelope calculations involving a total war between Russia andthe United States.
Now, a new multinational study incorporating the latest models of globalclimate, crop production and trade examines the possible effects of a lessgargantuan but perhaps more likely exchange between two longtimenuclear-armed enemies: India and Pakistan.
It suggests that even a limited war between the two would causeunprecedented planet-wide food shortages and probable starvation lastingmore than a decade. The study appears this week in the journal *Proceedingsof the National Academy of Sciences*.
Of an estimated 14,000 nuclear warheads worldwide, close to 95 percentbelong to the United States and Russia. India and Pakistan are thought tohave about 150 each. The study examines the potential effects if they wereto each set off 50 Hiroshima-size bombs—less than 1 percent of theestimated world arsenal.
In addition to direct death and destruction, the authors say thatfirestorms following the bombings would launch some 5 million tons of soottoward the stratosphere.
There, it would spread globally and remain, absorbing sunlight and loweringglobal mean temperatures by about 1.8 degrees C (3.25 F) for at least fiveyears. The scientists project that this would in turn cause production ofthe world’s four main cereal crops—maize, wheat, soybeans and rice—toplummet an average 11 percent over that period, with tapering effectslasting another five to 10 years.
“Even this regional, limited war would have devastating indirectimplications worldwide,” said Jonas Jägermeyr, a postdoctoral scientist atthe NASA Goddard Institute for Space Studies who led the study. “It wouldexceed the largest famine in documented history.”
According to the study, crops would be hardest hit in the northerlybreadbasket regions of the United States, Canada, Europe, Russia and China.But paradoxically, southerly regions would suffer much more hunger. That isbecause many developed nations in the north produce huge surpluses, whichare largely exported to nations in the Global South that are barely able tofeed themselves.
If these surpluses were to dry up, the effects would ripple out through theglobal trade system. The authors estimate that some 70 largely poorcountries with a cumulative population of 1.3 billion people would then seefood supplies drop more than 20 percent.
Some adverse effects on crops would come from shifts in precipitation andsolar radiation, but the great majority would stem from drops intemperature, according to the study. Crops would suffer most in countriesnorth of 30 degrees simply because temperatures there are lower and growingseasons shorter to begin with.
Even modest declines in growing-season warmth could leave crops strugglingto mature, and susceptible to deadly cold snaps. As a result, harvests ofmaize, the world’s main cereal crop, could drop by nearly 20 percent in theUnited States, and an astonishing 50 percent in Russia. Wheat and soybeans,the second and third most important cereals, would also see steep declines.
In southerly latitudes, rice might not suffer as badly, and coolertemperatures might even increase maize harvests in parts of South Americaand Africa. But this would do little to offset the much larger declines inother regions, according to the study.
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Since many developed countries produce surpluses for export, their excessproduction and reserves might tide them over for at least a few yearsbefore shortages set in. But this would come at the expense
of countries in the Global South. Developed nations almost certainly wouldimpose export bans in order to protect their own populations, and by yearfour or five, many nations that today already struggle with malnutritionwould see catastrophic drops in food availability. Among those the authorslist as the hardest hit: Somalia, Niger, Rwanda, Honduras, Syria, Yemen andBangladesh.
If nuclear weapons continue to exist, “they can be used with tragicconsequences for the world,” said study coauthor Alan Robock, aclimatologist at Rutgers University who has long studied the potentialeffects of nuclear war. “As horrible as the direct effects of nuclearweapons would be, more people could die outside the target areas due tofamine.”
Previously, Jägermeyr has studied the potential effects of global warmingon agriculture, which most scientists agree will suffer badly. But, hesaid, a sudden nuclear-caused cooling would hit food systems far worse.And, looking backward, the the effects on food availability would be fourtimes worse than any previously recorded global agriculture upsets causedby droughts, floods, or volcanic eruptions, he said.
The study might be erring on the conservative side. For one, India andPakistan may well have bombs far bigger than the ones the scientists use intheir assumptions.
For another, the study leaves India and Pakistan themselves out of the cropanalyses, in order to avoid mixing up the direct effects of a war with theindirect ones. That aside, Jägermeyr said that one could reasonably assumethat food production in the remnants of the two countries would dropessentially to zero. The scientists also did not factor in the possibleeffects of radioactive fallout, nor the probability that floating sootwould cause the stratosphere to heat up at the same time the surface wascooling. This would in turn cause stratospheric ozone to dissipate, andsimilar to the effects of now-banned refrigerants, this would admit moreultraviolet rays to the earth’s surface, damaging humans and agricultureeven more.
Much attention has been focused recently on North Korea’s nuclear program,and the potential for Iran or other countries to start up their ownarsenals. But many experts have long regarded Pakistan and India as themost dangerous players, because of their history of near-continuousconflict over territory and other issues. India tested its first nuclearweapon in 1974, and when Pakistan followed in 1998, the stakes grew. Thetwo countries have already had four full-scale conventional wars, in 1947,1965, 1971 and 1999, along with many substantial skirmishes in between.Recently, tensions over the disputed region of Kashmir have flared again.
“We’re not saying a nuclear conflict is around the corner. But it isimportant to understand what could happen,” said Jägermeyr.
The paper was coauthored by a total of 19 scientists from five countries,including three others from Goddard, which is affiliated with ColumbiaUniversity’s Earth Institute: Michael Puma, Alison Heslin and CynthiaRosenzweig. Jägermeyr also has affiliations with the University of Chicagoand Potsdam Institute for Climate Impact Research.
