FROM OUT OF NOWHERE there’s a huge explosion, with a mushroom cloud climbing to the sky. Quick, launch the nukes before we lose them all!

What? It was only an asteroid strike? Oops. Sorry.

Not such a surprising scenario; strikes like this are observed every few years, usually in the many empty places of the Earth (the North Pacific, and the South Atlantic, to pick a couple in the past twenty years that happened to be seen from aircraft). And they look a lot like nuclear detonations: big fireball, mushroom cloud, etc. Since there are so many more empty places than populated places on earth — most of ’em way out to sea — that’s usually where it happens. But not always. It would be bad if one hit somewhere near India or Pakistan now, for example. And one hit in Kazakhstan in the 1940s. (Good thing it wasn’t 20 years later — or 60 years later).

There are some technical things you can do (the U.S., and probably Russia, and maybe some other countries — but not Pakistan or India, probably — have the capability to tell the difference in near-real-time, or close enough to avoid accidentally launching in response to a nonexistent attack). But when you’ve got a lot of people sitting on nuclear weapons, with enemies close by so that you have only a few minutes instead of the 15-20 minutes of the Cold War era to react, you’ve got a recipe for accidental war.