Fewer nuclear weapons could make the world less safe

Tony Schwartz, ghostwriter of Donald Trump’s 1987 book “The Art of the Deal,” issued a dire warning about the man he worked for: “I genuinely believe that if Trump wins and gets the nuclear codes there is an excellent possibility it will lead to the end of civilization.”

Whether Schwartz is exaggerating, talk of nuclear war is more common these days. With tensions rising with China and Russia, it’s a good time to revisit a grim topic that many thought had vanished with the end of the Cold War.

First, the good news: Humanity is no longer in danger of extinction. Nuclear weapon stockpiles in the U.S. and Russia have declined since the late 1980s, when the two superpowers had about 64,000 nukes between them. Now, it’s down to fewer than 10,000. Of those, only a subset are actively deployed and available at a moment’s notice.

So if for some awful reason a full nuclear exchange took place between the U.S. and Russia, it would involve at most about 3,000 weapons. Some of those would probably be destroyed on the ground by “counterforce” strikes against submarines and missile silos, a few would be taken out by missile defenses and some would simply fail to explode because of decayed trigger mechanisms and fissile cores.

That level of nuclear destruction would wipe the U.S. and Russia off the map, cause global crop failures, send worldwide cancer rates soaring and kill hundreds of millions – or billions – of people. Horrible as that would be, we are no longer facing a world-ending apocalypse.

That’s cold comfort for the U.S. and Russia, whose populations would be devastated in a nuclear exchange. World leaders must always think carefully about how to minimize the chances of that happening.

Economic theory can help. Nuclear warfare was one of the first applications of game theory – mathematical models of how parties interact strategically. One idea to emerge from game theory was the concept of mutually assured destruction – in particular, the importance of second-strike capability. Under these scenarios, both sides understand they’ll lose in any conflict. In other words, if initiating a nuclear attack guarantees your country’s destruction, there’s never an incentive to start a war. As the military computer in the 1983 movie “WarGames” put it, the only way to win is not to play.

Paradoxically, this means there’s a danger to having too few nukes. If stockpiles decline to the point that one side thinks it can wipe out the other with a first strike and suffer an acceptable level of retaliatory damage, the situation destabilizes. Each side has an incentive to risk an attack. Improvements in the U.S. ability to track nuclear-armed submarines contribute to this danger, since that raises the tantalizing possibility of destroying the enemy’s second-strike capability in a surprise assault.

What about the danger of an unsteady hand on the nuclear button?

One game theory scenario features the so-called “madman theory” the idea that if the leader of a nuclear-equipped country acts a little crazy, the opposing superpowers will be reluctant to do anything to provoke an irrational leader, tipping him into launching a total war. This idea, which makes sense in some models, induced U.S. leaders such as Richard Nixon to play up their own aggressiveness during the Cold War in order to deter Soviet conventional attacks.

In a world of smaller nuclear stockpiles, a borderline madman is much more dangerous. When the temptation of a potential first-strike victory exists, an unstable president might not need a severe provocation to push the big red button. An erratic president might throw the dice and try to eliminate America’s enemies – with disastrous results for all mankind.

If the danger in the 1980s was far too many weapons, the danger in the 21st century might be the U.S. and Russia having too few. Though President Barack Obama’s recent speech in Hiroshima, calling for the abolition of nuclear weapons, makes for good optics, pursuing that policy might remove the strongest protection against nuclear war. Meanwhile, shrunken nuclear stockpiles should make us a little more fearful of ever electing a president who might think launching a first strike is anything less than madness.

Noah Smith teaches finance at Stony Brook University; he wrote this for Bloomberg View.