What consequences would a nuclear war between Israel and Iran, or between Pakistan and India, have for the world's climate? Scientists have now created a computer model of what might happen. The results are alarming -- even for experts.
Pakistani missile test (2005): A nuclear war in India and Pakistan would devastate both countries and spur massive climate change.
Researchers based at four separate US universities have used modern climate models to calculate the damage the smoke from burning cities, the pollution of the atmosphere and the radioactive fallout caused by a small-scale nuclear war in the region would entail. The scientists assumed a nuclear clash involving a total of 100 nuclear weapons, each of them with an explosive force equivalent to 15 kilotons of TNT -- roughly the power of the bomb dropped on Hiroshima.
Led by Owen Toon from the University of Colorado in Boulder, one of the teams started by calculating the damage caused by the nuclear explosions in cities and the consequent release of dust particles into the atmosphere. Five million tons of dust would enter the atmosphere, Toon and his colleagues write in the professional journal Atmospheric Chemistry and Physics Discussions.
Catastrophic Climate Anomalies
A second group of scientists, led by Alan Robock from Rutgers University in New Jersey, then went on to feed this information into their climate computer. "A cooling of several degrees occurs over large areas of North America and Eurasia," the study that describes the results of the simulation claims. Robock points out the areas concerned contain most grain-growing regions on the continents. The result is reminiscent of calculations on the possibility of a nuclear winter made during the 1980s and 1990s. The study also points out that "large climactic effects would occur in regions far removed from the target areas or the countries involved in the conflict."
A comparable, if much smaller catastrophe has already occurred in modern times: When Indonesia's Tambora Vulcano erupted in 1815, releasing enormous amounts of ash and gas into the atmosphere, temperatures in Europe and North America dropped significantly. The so-called "Year Without a Summer" saw cold temperatures and frost ravaging harvests. Famine followed in many countries.
But the results of Tambora's eruption were limited mainly to the year 1816 -- unlike those of a regional nuclear war, which could last as long as 10 years. If 100 nuclear weapons with an explosive force of 15 kilotons each were used, Robock says, it could spur "climate changes exceeding changes experienced in recorded history."
Small but lethal
The scientists themselves weren't expecting such results. Given the relatively small number of weapons and their low explosive yield, the global results are remarkably serious, the report concludes. "Such small weapons are very effective at killing people and causing smoke which can alter climate and ozone," Robock told SPIEGEL ONLINE. Detonated in the center of a major city, a small nuclear bomb could cause up to 100 times as many deaths and 100 times more smoke per kiloton of explosive force than a weapon with a larger explosive force.
The approach used by Toon and Robock goes back to the theory of a "nuclear winter," developed by Carl Sagan with four of his colleagues in 1983 in order to assess the consequences of a nuclear war between the United States and the Soviet Union. The nuclear ice age would kill 90 percent of the world's population, Sagan chillingly predicted. Toon says that 100 Hiroshima-size nuclear weapons wouldn't cause a nuclear winter. But the climate and the ozone layer would change in a devastating way: "Our work shows the entire world would be impacted, possibly severely."
Climate expert Steve Ghan, who did not participate in the studies, has tentatively criticized their results. He claims they exaggerate the role of smoke and soot. But he argues that they are still important because they shed light on the incalculable risk involved in the use of nuclear weapons.
20 Million Dead in India and Pakistan
The question remains whether the scenario chosen by Toon and Robock -- the use of a total of 100 nuclear weapons -- is plausible. In their academic articles, the scientists quote estimates according to which Pakistan has about 52 and India about 85 nuclear weapons. The explosive force of these weapons is probably relatively low, since the technology used is based on nuclear fission and since it's difficult to develop an explosive force greater than that of 20 kilotons of TNT on this basis. Thermonuclear or "high yield" weapons have far greater explosive force, but they're also much more complex. "It is not plausible that countries such as India and Pakistan currently have high yield weapons," says Toon.
If these two states were to attack each other with nuclear weapons, more than 20 million people would die immediately, according to Toon's estimate. "A war between India and Pakistan with 100 weapons could kill half as many people as died in World War II," he says. But would the two states really use a total of 100 weapons all at once? "That's not very plausible," says Gebhard Geiger, an expert for international security at the German Institute for International and Security Affairs in Berlin. Robock has a simple reply: "In the first nuclear war, the entire planetary arsenal was used."
But it was never the intention of Toon and Robock to develop the most realistic regional nuclear war possible. They simply wanted to simulate the results of such a clash for the climate. "To do that, you need solid assumptions that you can base your calculations on," Geiger says. In this sense, he believes the US scientists have delivered "new, independent and first-rate work."
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