http://thebulletin.org/deterrence-without-nuclear-winter8083

Deterrence, without nuclear winter
Seth Baum
03/09/2015

The biggest danger posed by today’s large nuclear arsenals is nuclear winter. One or two nuclear strikes could wreak devastating destruction on a few regions, but would not destroy human civilization as a whole. The roughly 16,300 nuclear weapons that currently exist, though, are more than enough to cause nuclear winter, which, through extreme cold conditions, ultraviolet radiation, and crop failures, could threaten the whole of humanity. If we fail to avoid nuclear winter, we could all die, or we could see civilization collapse, never to return.

That makes avoiding nuclear winter paramount. But the world’s major powers, in particular the United States and Russia, have long argued that their large nuclear arsenals are required for deterrence. Deterrence means threatening another party with some sort of harm in order to persuade it not to do something. In this case, it means threatening massive nuclear retaliation to dissuade another country from launching an attack itself. If two countries were to follow through on their threats of nuclear retaliation, mutual destruction would be assured. That deters both sides from starting a war. But nuclear deterrence can fail, as demonstrated during events like the Cuban missile crisis, when there have been escalations towards nuclear war. (Martin Hellman, Ward Wilson, and others have documented such events.)

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How significantly do arsenals need to be cut to avoid nuclear winter? They don’t need to be reduced to zero, but the short answer is that nobody knows. Humanity’s ability to survive massive nuclear attacks is not well-studied. One recent study found that two billion people—nearly a third of humanity—could be at risk of starvation from a nuclear war involving just 100 weapons. The actual death toll could be even larger, because this study only looked at starvation. Secondary effects such as pandemics and violence could kill even more.

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Deterrence doesn’t have to rely on large arsenals of nuclear weapons, or even on nuclear weapons at all. A range of candidate weapons could conceivably achieve the same goal without risking global catastrophe.

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