By deploying modern computers and modern cli¬mate models, the two of us and our colleagues have shown that not only were the ideas of the 1980s correct but the effects would last for at least 10 years, much longer than previously thought. And by doing calculations that assess decades of time, only now possible with fast, current computers, and by including in our cal¬culations the oceans and the entire atmosphere— also only now possible—we have found that the smoke from even a regional war would be heat¬ed and lofted by the sun and remain suspended in the upper atmosphere for years, continuing to block sunlight and to cool the earth.
India and Pakistan, which together have more than 100 nuclear weapons, may be the most worrisome adversaries capable of a regional nu¬clear conflict today. But other countries besides the U.S. and Russia (which have thousands) are well endowed: China, France and the U.K. have hundreds of nuclear warheads; Israel has more than 80, North Korea has about 10 and Iran may well be trying to make its own. In 2004 this situation prompted one of us (Toon) and later Rich Turco of the University of California, Los Angeles, both veterans of the 1980s investiga¬tions, to begin evaluating what the global envi¬ronmental effects of a regional nuclear war would be and to take as our test case an engage¬ment between India and Pakistan.
The latest estimates by David Albright of the Institute for Science and International Security and by Robert S. Norris of the Natural Resourc¬es Defense Council are that India has 50 to 60 assembled weapons (with enough plutonium for 100) and that Pakistan has 60 weapons. Both countries continue to increase their arsenals. In¬dian and Pakistani nuclear weapons tests indi¬cate that the yield of the warheads would be sim¬ilar to the 15-kiloton explosive yield (equivalent to 15,000 tons of TNT) of the bomb the U.S. used on Hiroshima.
Toon and Turco, along with Charles Bardeen, now at the National Center for Atmospheric Re¬search, modeled what would happen if 50 Hiro¬shima-size bombs were dropped across the high¬est population-density targets in Pakistan and if 50 similar bombs were also dropped across In¬dia. Some people maintain that nuclear weapons would be used in only a measured way. But in the wake of chaos, fear and broken communications that would occur once a nuclear war began, we doubt leaders would limit attacks in any rational manner. This likelihood is particularly true for Pakistan, which is small and could be quickly overrun in a conventional conflict. Peter R. La¬voy of the Naval Postgraduate School, for exam¬ple, has analyzed the ways in which a conflict be¬tween India and Pakistan might occur and ar¬gues that Pakistan could face a decision to use all its nuclear arsenal quickly before India swamps its military bases with traditional forces.
Obviously, we hope the number of nuclear targets in any future war will be zero, but policy makers and voters should know what is possible. Toon and Turco found that more than 20 million people in the two countries could die from the blasts, fires and radioactivity—a horrible slaugh¬ter. But the investigators were shocked to discover that a tremendous amount of smoke would be generated, given the megacities in the two coun-tries, assuming each fire would burn the same area that actually did burn in Hiroshima and as¬suming an amount of burnable material per per¬son based on various studies. They calculated that the 50 bombs exploded in Pakistan would produce three teragrams of smoke, and the 50 bombs hitting India would generate four (one teragram equals a million metric tons).
Satellite observations of actual forest fires have shown that smoke can be lofted up through the troposphere (the bottom layer of the atmosphere) and sometimes then into the lower stratosphere (the layer just above, extending to about 30 miles). Toon and Turco also did some “back of the en¬velope” calculations of the possible climate im¬pact of the smoke should it enter the stratosphere. The large magnitude of such effects made them realize they needed help from a climate modeler.
It turned out that one of us (Robock) was already working with Luke Oman, now at the NASA Goddard Space Flight Center, who was finishing his Ph.D. at Rutgers University on the climatic effects of volcanic eruptions, and with Georgiy L. Stenchikov, also at Rutgers and an author of the first Russian work on nuclear winter. They developed a climate model that could be used fairly easily for the nuclear blast calculations.
Robock and his colleagues, being conserva¬tive, put five teragrams of smoke into their mod¬eled upper troposphere over India and Pakistan on an imaginary May 15. The model calculated how winds would blow the smoke around the world and how the smoke particles would settle out from the atmosphere. The smoke covered all the continents within two weeks. The black, sooty smoke absorbed sunlight, warmed and rose into the stratosphere. Rain never falls there, so the air is never cleansed by precipitation; par¬ticles very slowly settle out by falling, with air resisting them. Soot particles are small, with an average diameter of only 0.1 micron (μm), and so drift down very slowly. They also rise during the daytime as they are heated by the sun, re¬peatedly delaying their elimination. The calcu¬lations showed that the smoke would reach far higher into the upper stratosphere than the sul¬fate particles that are produced by episodic vol¬canic eruptions. Sulfate particles are transparent and absorb much less sunlight than soot and are also bigger, typically 0.5 μm. The volcanic par¬ticles remain airborne for about two years, but smoke from nuclear fires would last a decade.
Source of Information : Scientific American January 2010
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