Sunday Q & A appears in this section weekly. Readers are invited to send in questions about national or international affairs; those selected will be answered by Times correspondents who specialize in those issues. Information about submitting questions appears below.

Q. Recent talks between India and Pakistan bring up the question of possible use of nuclear weapons. If there were, say, 2 to 20 atomic explosions in that part of the world, aside from the disastrous consequences at the point of detonation, what would be the likely effects on other continents?

A. James Glanz, a science correspondent for The Times, responds:

By breaking a taboo that has existed for more than half a century, a nuclear exchange of that magnitude would make the world an infinitely more dangerous place and lead to consequences no one could foresee. With millions dead by blast, fire and radiation poisoning on the Indian subcontinent, civilizations there could collapse into chaos, potentially destabilizing governments around the globe.

The physical effects outside the region would be the least of the world's worries — assuming the horrific situation did not spark nuclear war elsewhere. Before 1963, when a treaty banned the testing of nuclear weapons in the atmosphere, radioactive strontium, a fission byproduct, wafted around the globe and generated international outrage. Closer to the explosions, a radioactive isotope of iodine rained from the sky onto plants eaten by cows and goats, which then produced radioactive milk. Those distressing episodes would be replayed in the wake of a nuclear war between India and Pakistan.

The global economic consequences of such a disaster are incalculable. The world would somehow have to intervene to help more than a billion people whose governments had neglected their interests in the most repugnant way imaginable.

Finally, the United States and other Western countries would rightly fear that the end of the nuclear taboo would mean an increase in proliferation, possibly leading to an era in which nuclear terrorism became a credible threat. The effect of a shadow that dark on humanity's fortunes is beyond reckoning.
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