How would you know if a nuclear war started?
With the Russians getting cocky and the Chinese itching to sow their expansionist oats, I'm starting to have The Day After dreams again. I live about two hours from a primary target; if a nuclear exchange took place one morning while I was at the office, what signs would let me know that something horrible had happened, and in what order would they take place?
It would have been easy to read this question as merely a dark but diverting hypothetical until, oh, about the time the results started rolling in on election night. In January we'll hand the nuclear codes over to a guy who's said he's OK with an Asian nuke race and who couldn't explain the nuclear triad if you drew him a picture. Meanwhile his autocratic idol Vladimir Putin has just previewed a new fall line of ICBMs that TASS says can flatten Texas in record time. We can only hope some sage advisor will steer the president-elect back toward the conventional wisdom on using nuclear weaponry, namely “Don’t.” Me, I'm already nostalgic for the days when civilization seemed less likely to end with a bang than a whimper.
But let’s press on. I take it you’re asking about the whole enchilada here: not some piddly North Korean warhead with just enough oomph to cross the Pacific, but a full-on thermonuclear conflict like Reagan used to joke about. For old times’ sake, we'll assume our adversaries are the Russians and that their plan is, as in the ’80s, to achieve maximum devastation by detonating a one-megaton warhead about a mile and a half above the target — which (working from your two-hours figure) we’ll say is a population center a little more than 100 miles away from where you'll be watching the show.
Taking some of the zing out of this scenario is the existence of the Wireless Emergency Alert system, which in a high-stakes situation enables the White House to send out a geographically-targeted heads-up via the cell network. Assuming the scary new Russian missiles are still trackable by radar, and that @realDonaldTrump doesn't tweet the news first (“BIG mistake from loser Russians. Launching nukes? Sad!”), you’d become aware of the incoming warhead when the official POTUS-issued message showed up on your phone.
So let’s further imagine you're off the grid when the missiles are launched. If you'd gone camping for the weekend and weren’t getting any signal, how soon would you begin to suspect there might be a lot less civilization for you to eventually return to?
Well, from 110 miles out, anything less than around 8,000 feet up — i.e., about a mile and a half off the ground — would be hidden by the curvature of the earth, meaning you might or might not see a flash right at the horizon. (Ideally you wouldn’t be looking with binoculars, or your retinas could get zapped.) You’d be at the very edge of the range covered by a tech-disabling electromagnetic pulse (discussed here a few years back when EMP was the terror du jour for ninnies like Newt Gingrich); if you were in a running car, the dash lights would maybe flicker a bit. So you might have a feeling something big was going on, but you wouldn't be able to tell just what.
The next few seconds would clear up any ambiguity. A fireball would rapidly expand to a diameter of maybe 6,000 feet, continuing to grow as it rose into the air from the point of detonation — clearly visible above the horizon, in other words. Within a minute or so, a miles-high cloud of hot gases, water vapor, and atomized debris would form and begin to flatten into the characteristic mushroom shape, confronting even the most optimistic of viewers with the severity of the situation.
What would make the experience particularly eerie, though, is that none of the effects of the blast would reach you. At ground zero, the drastic change in air pressure would level buildings, and winds of hundreds of miles per hour would flay human flesh already scorched by third-degree radiation burns. But the blast wave and associated winds would peter out within 15 miles or so, sound waves would probably be damped down beyond detection en route, and an aerial explosion wouldn’t trigger any kind of tremor you might feel out in your neck of the woods. The apocalypse you'd witness would be still and silent.
The big question is: what do you do next? You can't stay out in the wild forever (depending on prevailing winds at various altitudes, fallout could be drifting your way within 16 hours in any case), and there’s no imagining the chaos that awaits you back in town. The human aftermath would likely hit your area hard, with busloads of refugees from the ruined city taxing medical and social services. And that’s not even to mention the long-term effects of radiation, or the skies darkening with soot in an early hint of the possible nuclear winter to come. Sweet dreams, Chris.