I have a nuclear post-apocalypse that isn't 100% depressing. It's only 95% so. /s

I was contemplating an origin story of a solar flare doing some rather nasty things to circuitry related to nuclear launches, or nuclear launch detection equipment. I was curious from an answer by LSerni at Would it be feasible for a series of coronal mass ejections (CME) from the sun to cause E1 EMP damage to electronics on Earth?

So: how likely would a solar flare cause a nuclear winter? (Possibly this nearly happened during heightened tensions of the cold war, I could not find examples).

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    $\begingroup$ I would have to say almost zero. I don't design nuclear launch technology, but if I did, I'd design it to be hardened against CMEs and flares, and I'd also build it to failsafe (no launch on power loss) rather than a de facto dead man's switch. But then, that's thinking with the priority of not needlessly killing people rather than the priority of ensuring enemy destruction so perhaps I hold the minority view. $\endgroup$
    – Tim B II
    Commented Mar 15, 2019 at 4:39
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    $\begingroup$ Are you going for a realistic approach or just a believable approach. I believe that almost all military equipment would be protected from surges caused by EMP so you will probably burn all the circuitry instead of setting off a bomb with an EMP. Nukes are also often stored in very protected locations with lots of material and metal between them and the surface reducing the effectiveness of an emp. $\endgroup$
    – Shadowzee
    Commented Mar 15, 2019 at 4:42
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    $\begingroup$ The only armed missiles are kept in launch silos, either underground or underwater, that, by definition, are protected from EMP smaller than what would wipe out most life on the surface anyway. The rest of the warheads are kept in underground bunkers, that (presumably) have the same levels of protection. Possibly, there is a non-zero chance of a warhead in transport being affected, but that, by itself, would not create a worldwide nuclear winter $\endgroup$
    – nzaman
    Commented Mar 15, 2019 at 5:17
  • $\begingroup$ If the solar flare took out backup power to pump so that the trapped water vapour becomes highly compressed... $\endgroup$
    – user6760
    Commented Mar 15, 2019 at 6:33
  • $\begingroup$ A supermassive mass coronal ejection will damage communication satellites and may cause some damage to the power grid and electric equipment connected to the power grid. ("May" because it is almost certain that preventive measures will be taken by taking the grid offline before Earth gets hit; such events do not come by surprise.) It cannot cause any damage to electronic devices which are not connected to the grid and do not have large antennas. $\endgroup$
    – AlexP
    Commented Mar 15, 2019 at 9:18

4 Answers 4


As a general principle, all space-based hardware is "hardened" against radiation, at least in the sense that someone will have run the math on the probability of a radiation event causing undesired behaviors such as single event upsets. Informally, everything that goes into space is @&#$ expensive, and is used in situations where people really don't want anything to go wrong. It warrants taking the extra time to check for such occurrences.

As for military hardware that remains on the ground, as a general rule it tends to be more robust to extreme environments than normal equipment. For instance, MIL SPEC integrated circuits often has extreme temperature ranges specified which normal corporate customers find no need for. They cost a pretty penny because of this!

So the real question is not whether an event could cause a mishaps for these systems. The real question is, if an event of sufficient magnitude occurred to disrupt these systems... what else went wrong?

I would expect an event which permanently disables military hardware, with their extreme requirements, would have far reaching implications for the States that might be firing the nuclear weapons in the first place. Trying to win a nuclear war after such civil devistation would be like trying to finish winning a correspondence game of chess immediately after being knifed in the back or having a large boulder fall on you. It isn't a game nations like to play.

Which leaves the question of whether a nuclear device could go off without intent. The general answer is probably the most resounding "no" you can get short of when the LHC announces that they are 99.9999% positive they have discovered something. These are not unstable devices. Nuclear fuses are designed to be markedly reliable to a level of pathological fervor that most of us humans don't fully comprehend. Consider, as an example, the first nuclear bomb dropped, and its safeguards.

  • The bomb was not fully built at takeoff. The cordite charge that would drive the projectile rings of uranium towards the target rings (causing the nuclear explosion) was not even installed until after the plane was already in the air. (This appears to be the choice of the weaponeer, not necessarily a design choice)
  • The bomb had a physical cutoff preventing power from going to the charge's detonators unless an arming plug was installed. These plug were about 1 inch in diameter and dumb as can be, by design. The armed plug had wires bridging the gaps between the pins to complete the circuit. The safe plug (installed to keep the socket clear of debris and to make sure nothing could accidentally touch the pins and bridge the circuit) simply had no wires. Even then, there wasn't one plug but three. All three arm plugs had to be installed for the bomb to work. This was done on approach to the target by climbing into the bomb bay and physically swapping them out.
  • There was a 15 second timer, which ensured no fusing event could possibly occur until 15 seconds after drop (defined when the electrical plugs connecting the bomb to the plane were physically puled by the bomb dropping). This ensured that any false positives which could occur in the later fusing steps could not possibly set the bomb off. Again, dumb as possible, by design. (no solar event was going to stop either of these first two steps, short of the sun expanding to swallow the earth 4 billion years from now).
  • There were two redundant radar altimiters measuring the altitude of the bomb. These had the actual control over the firing switch which actually sent the charge to the cordite.
  • These radar altimiters weren't even trusted. There was a barometric fuse added as well, which measured air pressure and would not let the altimiters fire the bomb until it was satisfied.

And this was all features applied during the heat of a world war. Modern weapons have safety features constructed over decades. Modern nuclear weapons do not go off unless someone wants them to.

Which brings me to the one caveat to the whole "it can't happen" argument. Some nations, such as the UK, have a "fail deadly" nuclear arsenal. Unlike the US, which strictly limits the authority to fire its estimated 4,018 nuclear weapons to the president and only the president (considered "fail safe"), the UK took a different approach. They have a smaller arsenal (estimated to be 120-215 weapons, depending on which stat you look at), primarily in the form of nuclear tipped Trident missiles to be fired from their four Vanguard submarines. They, as a policy, keep at least one at sea at all times. Unlike the fail safe arsenal of the US, which explicitly withholds some of the launch keys until the president gives them out, the fail deadly arsenal of the UK stores those keys on-board the Vanguard submarines when they are on duty. Each captain is given an envelope, the letters of last resort, instructing them what to do with these keys should they lose communications with the British government.

These letters of last resort are handwritten by the prime minister them self, after the prime minister is briefed on precisely what damage a Trident missile can do. They are then sealed in a nested double safe onboard the submarine, and never opened unless needed. At the end of a tour, or if a prime minister retires, they are brought back, unopened, and summarily destroyed such that only the prime minister themselves ever knows the content of the letter.

What is written in these letters, is of course secret, but it has been publicly revealed that there are four known options for a captain of a Vanguard:

  • Retaliate with nuclear weapons
  • Do not retaliate
  • Place your submarine under the command of an ally (the US and Australia have been publicly listed as possibilities)
  • Use your own judgement

From this, it is clear that there is a possibility that these letters of last resort could lead to an individual being given the authority to exercise judgement, so thus could indeed intend to launch a nuclear weapon. No nuclear safeguard is designed to stop an authorized individual from consciously launching a weapon, so if an event wrecked nuclear defenses and the letters of last resort were written in a particular way, Vanguard subs could launch (this probably implies that the solar event looked like a nuclear attack). They typically carry 48 weapons, and current estimates suggest 100 firestorms are needed for nuclear winter, so two such subs would both have to be given letters which lead them to fire their entire arsenal.

So the final question would be, which nations have fail-deadly arsenals, and whose defenses might need to be negated to cause a nuclear winter. That is a more complicated policy. While the UK publicly acknowledges its fail deadly arsenal, as a deterrence policy, its not popular to admit that's your approach. Russia has the Dead Hand system, which was designed as a fail deadly system. Most sources state that it is not active, only activated in emergencies, and its exact details are not all public, but it could be a sufficient piece of the puzzle.

After writing all of this, I have to reflect on your 95% depressing nuclear post-apocalypse. If I may quote Douglas Adams:

What to do if you find yourself stuck in a crack in the ground underneath a giant boulder you can't move, with no hope of rescue. Consider how lucky you are that life has been good to you so far. Alternatively, if life hasn't been good to you so far, which given your current circumstances seems more likely, consider how lucky you are that it won't be troubling you much longer.


how likely would a solar flare cause a nuclear winter?

Unlikely, bordering the impossibility.

A nuclear winter is defined as

the severe and prolonged global climatic cooling effect hypothesized to occur after widespread firestorms following a nuclear war. The hypothesis is based on the fact that such fires can inject soot into the stratosphere, where it can block some direct sunlight from reaching the surface of the Earth. It is speculated that the resulting cooling would lead to widespread crop failure and famine.

A solar flare cannot directly inject soot into the stratosphere, nor can indirectly: nukes are designed to explode only when a large set of events happen with the proper order and timing. It's already unlikely that one nuke will explode because of the induced currents generated by a solar flare. To have an unlikely event happen on hundreds of nukes further reduce the likelihood of such an event.

  • $\begingroup$ I would add that nuclear early warning systems have many layers and single detection didn't cause nuclear war in many accidents. And yep, those systems are intedned as EMP resistant. P.S. I suppose my comment is too small for separate answer. I would be grateful if you integrate it to your answer $\endgroup$
    – ADS
    Commented Mar 15, 2019 at 6:31

It would probably effect sattalites, effecting targeting capabilities. Most nuclear defenses I know are laser or shooting another rocket to intercept, both I assume to be damaged by emp. But icbms are by nature emp protected to ensure they withstand the emp from an enemy nuke to retaliate. But in that scenario you would still have gps, you would not from a Coranol ejection

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    $\begingroup$ ICBMs do not rely on GPS... For the obvious reason that it is extremely unlikely that in case of war the belligerant powers will somehow forget to turn off GPS / Glonass / Beidou etc. $\endgroup$
    – AlexP
    Commented Mar 15, 2019 at 9:13

By itself, I'd say the odds are basically 0. The USA designed their nuclear weapons to have EM resistant shielding on them so they couldn't be deactivated by the enemy. However it's quite possible that the CME could be mistaken for a High Altitude Nuclear Explosion.

The USA and USSR both discovered and experimented with these in the late 50's and early 60's. You nuke the ionosphere and it creates a large EMP that knocks out satellites within a significant radius. A significant enough CME could produce a nearly identical result.

Now suppose this happened at a time of some significant tension like the Cuban Missile Crisis. It would be quite reasonable that either party could mistake this as the enemy taking out their launch detection satellites as a prelude to an all out nuclear strike. One itchy trigger finger later and you have your nuclear winter.


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