Following up on this question, Would Living Underground during Impact Winter be Ideal, I realized I have more questions.

I was asking about an impact winter that was caused by an asteroid and leads to continuous snowfall and weather conditions that people are unprepared for.

The the answer I received was that underground works fine, but only for small groups and not in the long run. So then my response to that was, if an impact winter is happening, is there really another choice aside from living in a fortress if not underground?

I ask because in my previous question, we see what the benefits/cons are with Kromey's answer for underground shelters. However, living above ground doesn't appear to have too many benefits either. Some examples of this would be:

Above Ground Hazards:

  1. bursting pipes and frozen pipes = no heat/water, possibly flooding a place that will further cause temperature drop and hypothermia
  2. collapsing buildings (poor infrastructure)
  3. limited or no transportation
  4. being stranded to a small area with limited supplies or reach to others
  5. weak defenses for other desperate survivors or looters
  6. No power if utility poles and such fall down, same with communications

I also used this article for some reference. Now this is assuming that an asteroid hit during the start of an already early winter, so there's already a brewing blizzard. Let's say this asteroid happened in the mid-west of the US, and we're focusing on the east by the coasts. Here's what I imagine happening:

The setting of this question (happens in a period of days/2 weeks?)

  1. Some stubborn workaholics will show up to work even if some people stay home and some businesses close, we know it happens even during bad weather.
  2. Transportation is already limited, then the asteroid happens
  3. People panic, before public transportation shuts down it's clogged with city workers trying to get home
  4. Government is advising people to hunker in their homes/businesses until they can figure things out
  5. Transportation shuts down due to worsening weather, those that remain or didn't make the last trains/buses stay in their businesses or homes to wait for help.
  6. Worsening weather begins to cause some of the conditions I listed in the above ground hazard list
  7. Now there's two choices, wait above ground or find better shelter and re-supply. Not to mention if someone is clever enough to realize that the weather is only going to get worse, they'd want to get home or to a more permanent shelter asap.

But with the beginnings of an impact winter, help isn't arriving. No helicopter is going to fly in blizzard conditions and the government has enough to worry about with the midwest of the US hit by the asteroid and wondering how they're going to deal with the new "year without summer".

So now with all of that, I might be exaggerating a bit, but that's the point of fiction - is this the same thing others would envision happening to cities and how they stop functioning?


Also what gives me the impression that an impact winter is bad news and can force humans to seek shelter underground is what's on the Wikipedia page for impact winter as well:

Those on land could possibly be kept alive in underground microclimates, with one such example being the Zbrašov aragonite caves, greenhouses in such underground complexes with fossil or nuclear energy power stations could keep artificial sunlight growing lamps on until the atmosphere began to clear. Those outside that were not killed by the lack of sunlight would most likely be killed or kept dormant by the extreme cold of the impact winter.

See? "Be killed or kept dormant by the extreme cold of the impact winter."

  • $\begingroup$ The snowstorm won't last forever. How long is the winter supposed to last? How cold is it supposed to be ? You said east coast: Maine or Florida ? Maine can handle the snow but not Florida. $\endgroup$
    – Vincent
    Oct 17, 2014 at 19:13
  • $\begingroup$ @Vincent Aiming for New York if that helps. $\endgroup$
    – KaguraRap
    Oct 17, 2014 at 20:49

3 Answers 3


As Tim B points out in his answer, and I pointed out in mine to your original Impact Winter question, the temperatures are only going to drop by about 13 degrees C, or less than 25 degrees F. Yes, it will get cold, but if we're talking early-winter time period here then we're only getting to around usual mid-winter temperatures, or perhaps a bit colder-than-normal mid-winter temperatures.

This year's polar vortex brought colder temperatures, and yet cities didn't collapse into ruin overnight.

Over the short-term period you're talking about, we've seen worse, though of course that doesn't mean it isn't bad -- just because we've seen Category 7 hurricanes doesn't mean a Category 6 is no big deal.

Yes, you'll see some pipes bursting, disrupting water supplies, but in general those will be pretty localized, such as individual homes where the heat's already failed. But cold weather doesn't make buildings fall over -- I'd lose my home every winter if that were the case. I live in Alaska, -40F/C is an annual week-long event (at least), and I've seen -60F/-50C. Lived through it even.

Now, yes, we do build up here for those temperatures. But all that means is that we stuff more fiberglass insulation in our walls, build our windows with 3 panes of glass apiece, and pay a lot more attention to the quality of our weather seals. Fundamentally though we're still using the same materials -- wood, steel, and concrete -- to build our buildings, and even those that have been abandoned and aren't being heated stay standing just as well as yours.

You will see a sharp rise in cars that won't start, and those that do will run "rough" until the engine warms up again. This will not affect cars kept in heated garages (and will be reduced even in enclosed unheated garages), nor will it have any effect on a car once it is warmed up. If you get heavy snowfall (certainly not a given, but possible), though, you'll be in pretty bad shape as cars slide off of roads, leaving motorists stranded; you'll also have people turning off their cars when they get somewhere, only to find later that the car won't start.1

What is going to cause problems for you is the people. A major meteor strike all by itself will send everyone into a panic. If you want to drive this up, have the big meteor be a part of a swarm, and have smaller impacts hitting all over the place, or really play up the smaller pieces that will inevitably break off of it as it punches through the atmosphere and hit up to hundreds of miles away.

The impact winter will add to this panic. Look at the near-panics around this year's polar vortex -- obviously the world didn't end, but lots of people were scared nonetheless.

The big deal with impact winter is that food will become scarce, since we won't be able to grow any. (Well, not without electric grow lights, but we wouldn't be able to scale that up in time to feed everyone.) As people start to figure that out, that will increase the panic.

Now you have riots. And you have bands of thugs intent on making sure they survive, no matter who they have to hurt to get food and supplies they think they need.

These are your real enemies. Widespread social unrest and panicked disorder. If these get too far out of hand, you'll see panicked survivors fleeing the cities to get away from the mobs. That's the real threat for your setting.

Of course, this is about the latitudes you're interested in. Way up here, we would be in trouble from the winter itself -- you take our -60F/-50C winter, and drop it to -85F/-63C, and we are in very serious trouble. You, though? You're fine. Mostly.

As I implied above, if this were to happen in the dead of winter, it could be a lot more devastating. But given the timing you've provided, social order would most likely be restored and people could have prepared for those temperatures by the time they come to pass; again, it will not be pleasant, and there will be deaths from exposure, but it's still not going to cause your buildings to collapse or anything like that.

1 It's not relevant to this question, but if you're curious: Our cars are "winterized", which basically amounts to having installed electric heater pads underneath the battery and the oil pan. When we park, we plug in to the "head bolt heaters" that are liberally available all over the place. A few minutes isn't a big deal, but if you're going to be parked for a couple of hours or more you plug in, or you expect to need a jump from someone who did. Then you run your engine for a bit to let it warm up before you start driving.

  • $\begingroup$ Ah just re-read the end of your comment, so if I aim for the dead of winter, it'll at least increase my chances of weather related havoc. Perhaps I should focus more on the people as you suggested, more mobs less snow. $\endgroup$
    – KaguraRap
    Oct 17, 2014 at 21:24
  • $\begingroup$ @KaguraRap Sure. But you have to come up with some reason for the heat to fail before you get pipes freezing and bursting; even down there you guys have insulation in your buildings, so while it may cost a lot you can keep your homes from freezing. Not going to have any collapse though, I'm afraid. Not unless the rioters start some fires. $\endgroup$
    – Kromey
    Oct 17, 2014 at 21:26
  • $\begingroup$ @KaguraRap On second thought, in the already-below-normal temperatures, you might get cold enough for city water mains to freeze and burst. That's not going to be easy though, there's a lot of water moving through there which will inherently resist freezing, but if you can manage it the loss of water service will be a pretty big deal. $\endgroup$
    – Kromey
    Oct 17, 2014 at 21:28

The thing is an impact winter isn't a snowball earth scenario.

From wikipedia:

These pulverized rock particles would remain in the atmosphere until dry deposition, and due to their size, they would also act as cloud condensation nuclei and would be washed out by wet deposition/precipitation, but even then, about 15% of the sun's radiation might not reach the surface. After the first 20 days, the land temperature might drop quickly, by about 13 Kelvin. After about a year, the temperature could rebound by about 6 K, but by this time about one-third of the Northern Hemisphere might be covered in ice.

So in other words the average temperature would drop by 13 degrees, slowly returning to a drop of 6 degrees over a year and then finally returning to normal a few years after that.

This is enough to turn temperate conditions decidedly unpleasant but not enough to freeze entire continents. So long as people could keep the power on and gas flowing to homes then people would survive, at first. This does give you the first reason not to hole up in caves though, moving south for warmth!

The problem comes when gas supplies fail, and when food starts running low, and when you realize that no new crops will be growing this year. When people start getting cold and tired and hungry. That's when the real trouble comes and how the authorities and survivors handle that is what makes the difference in how many people last and how long they last for.

  • $\begingroup$ This is what confuses me, I keep getting answers that Impact Winter isn't as bad as I think, and at the same time, it can be. Reading theories how it aided in wiping out dinosaurs and seeing games where it is apocalyptic. latimes.com/science/la-sci-impact-winter-20140517-story.html I know it's only a few degrees but those degrees mess everything up, don't they? Especially with the sun blocked out? news.nationalgeographic.com/news/2014/05/… kickstarter.com/projects/mojobones/impact-winter $\endgroup$
    – KaguraRap
    Oct 17, 2014 at 20:53
  • 1
    $\begingroup$ @KaguraRap Ignore the games, they deliberately sensationalize the scenario to provide a "more interesting" setting. It's either not fact-based, or so loosely fact-based as to practically not be. It can be bad, but it was so bad for dinosaurs only because they were cold-blooded and that few degrees was fatal to them; warm-blooded mammals did quite well, as evidenced by the fact that we're here today talking about it! Add to that modern technology and ingenuity, and humanity will weather (heheh) this pretty well. $\endgroup$
    – Kromey
    Oct 17, 2014 at 21:02
  • 2
    $\begingroup$ The main effect of an impact winter is on plants and crops. Essentially you can grow no (or very little) food for 1 to 2 years. $\endgroup$
    – Tim B
    Oct 17, 2014 at 21:05
  • $\begingroup$ That's bad. That's lots of people starving to death or serious rationing. It's greenhouses and tropical farming and hydroponics and stored rations. etc $\endgroup$
    – Tim B
    Oct 17, 2014 at 21:05
  • $\begingroup$ @TimB - do you know roughly how long the cooling trend will take to take hold? I'm under the impression that the initial impact would warm the planet for a while before the effects of prolonged winter set in. Am I wrong with that? $\endgroup$
    – Twelfth
    Oct 17, 2014 at 21:06

The difference between your scenario and the one at the K-T boundary is the asteroid which hit the Earth there was orders of magnitude larger. It is thought some of the ejecta from that impact was literally blown in ballistic paths almost halfway around the Earth and caused large scale fires, for example.

Now if your true aim is to cause a civilization ending apocalypse, your impact could be used to trigger lots of secondary events, such as the unlocking of the San Andreas fault network on the West Coast, triggering the eruption of the Yellowstone super volcano or unlocking the New Madrid fault mid continent. These on top of the already devastating impact of the asteroid strike and a persistent winter would probably stress the Federal and local governments beyond their breaking points.

AS for the impact winter itself; as noted it is livable, although in places where power and other services are disrupted, unprepared people are going to have a very hard time of it. Even preppers will eventually run out of fuel for their generators, so if this happens in November, by February things will be a bit tight.

Your immediate problem is that without transport networks, urban areas will run out of food. Supermarkets will be stripped by panic buying, and there will be no means of bringing new supplies in from the warehouses. This will cause panic, mobs roaming the streets and looting for food and an exodus of people trying to leave the cities, making transportation networks even more stressed (cars abandoned on bridges or tunnels will block these choke points). When the spring rolls around, another issue will emerge; the same factors which caused the impact winter will create a year without summer, causing global crops to fail or be far smaller than normal. Now you have stress on societies all over the world, and the more fragile states will likely slip into anarchy. Depending on how late the impact was and how much ejecta is in the atmosphere, this could persist for several years.

As well, since you specified the United States is the locus of the impact, the effects on global trade markets, security and even political events will be very striking. Look how quickly Iraq collapsed after the Obama administration unilaterally withdrew US troops, creating the power vacuum that allowed ISIS to grow and move in. Now do that globally...

So the immediate effect, while severe for the people involved, is not civilization ending in of itself, but could trigger larger and longer term problems.


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