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It's circa 1950, world war three is imminent. Suddenly, the world becomes coated in snow. Temperatures plummet, resulting in a winter with no foreseeable end.

Could humans survive, if so, for how long?

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closed as too broad by Mołot, L.Dutch, rek, RonJohn, JBH Apr 17 '18 at 17:13

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    $\begingroup$ Perpetual winter ≠ sustained human life. Choose one, and in the mean time see meta, there is a recent meta question about questions to make impossible things. Highly related to "high concept" issue. $\endgroup$ – Mołot Apr 17 '18 at 15:35
  • $\begingroup$ "The Snowball Earth hypothesis proposes that Earth surface's became entirely or nearly entirely frozen at least once, sometime earlier than 650 Mya (million years ago). Proponents of the hypothesis argue that it best explains sedimentary deposits generally regarded as of glacial origin at tropical palaeolatitudes and other enigmatic features in the geological record." (Wikipedia) $\endgroup$ – AlexP Apr 17 '18 at 15:39
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    $\begingroup$ @Mołot I wouldn't regard this concept as beyond plausibility, given people have survived in Siberia and northern Alaska for a prolonged period of time. Certainly a temperature less harsh than in the aforementioned environments is a reasonable notion. $\endgroup$ – Lutro Apr 17 '18 at 15:52
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    $\begingroup$ People can survive of the tundra like the Inuit, but the tundra is not in a state of constant winter. Antarctica is (most of it). $\endgroup$ – Vincent Apr 17 '18 at 16:00
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    $\begingroup$ @Mołot Inuit people have survived by using animals as food sources, therefore it could still be a viable source of nourishment, even if only for a short time. Winter is still a relative concept, within Australia for example, it rarely reaches sub zero temperatures on the outskirts where most civilization exists, I never stated that food could not be grown here where the temperature permits it and betransported elsewhere. $\endgroup$ – Lutro Apr 17 '18 at 16:06
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Since nuclear fallout and volcanic eruptions are ruled out, that takes away the most likely options. The only others I can think of involve outer space. The first one is that some sort of asteroid knocked into us, like with the dinosaurs. It knocks up a whole chain of natural disasters, although this is similar to nuclear fallout, which you don't want.

The second option is that a huge asteroid sailed past us, and I'm not sure if this would work, but it pulled us out of our normal gravitational orbit. You would have to see how much further the Earth would have to be to freeze up. Mars is the closest planet to us, and it's only around 33 million miles away, and it's frozen, so that might be an idea.

The third is if something weird and catastrophic happened with the sun. Of course, I think most of the options include the sun expanding until it swallows the Earth. But say it compacted, or failed, or something like that, then everything would probably get a lot colder. Hope this helps.

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  • $\begingroup$ The huge asteroid idea won't work. A rogue planet the size Jupiter or Saturn passing through our solar system could change the Earth's orbit, but it would only be able to make Earth's orbit more eccentric. You'd need a second event in order to make Earth's orbit circular again. $\endgroup$ – Rob Watts Apr 17 '18 at 16:36
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There are plausible ways to create Snowball Earth without nuclear war or massive volcanic eruptions, but most don't happen quickly.

1. Loss of Greenhouse Effect

If the CO2 in the Earth's atmosphere drops substantially, you can get a runaway snowball effect where permanent snow fields form and reflect more sunlight lowering the temperature further and forming more permanent snow, etc. As I recall, the Snowball Earth hypotheses blames the loss of CO2 on it being used up weathering newly-exposed rock.

The resultant ice-covered Earth lasts for a very long time -- what is believed to have ended Snowball Earth is the release of enough CO2 by volcanoes to rebuild the greenhouse effect.

But this is a very slow process -- probably taking hundreds of thousand of years, at least, to get to Snowball Earth.

2. Bombardment from Space

This could be very quick, but would work by basically the same mechanism as nukes and volcanoes, so I'm assuming you reject bombardment, also.

3. Loss of Solar Energy

Basically, something happening which dims sunlight. There are a number of possibilities:

3a. Man-made objects like mirrors in orbit which deliberately divert a percent or two of sunlight. An anti-global warming scenario gone bad.

3b. Dimming of the Sun by natural causes. It's difficult to see what they might be, but the Maunder Minimum lowered the Earth's mean temperature by nearly a degree centigrade for a hundred years. While I don't for a second believe that it could happen -- there's just no evidence of it ever happening -- it doesn't do huge violence to what we know to imagine solar output dropping by a couple percent.

3c. A Dark Cloud getting in the way. Imagine the Solar System passing through an especially dense interstellar dust cloud that absorbs a couple percent of the sun's light. I don't know if they get that dense, nor do I know how long the dimming would last.

3d. A nuclear waste dump on the Moon explodes, sending the Moon out of orbit and moving the Earth to a somewhat larger orbit with diminished...oh, never mind!

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