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This question was prompted by my answer to Under what conditions does heating a backpacking tent artificially make objective sense?. In my answer, I mention the possibility of hiking across Antarctica during the winter to experience the harshest cold that our planet has to offer.

You are on this Antarctic winter hiking trip, and you are chasing the cold. You know that the record cold is approximately -135F (-95C), and you are expecting you probably will encounter close to that, and you need to prepare for the possibility of a new record being set so you want to be safe down to a few degrees below that in case of emergency.

To assist in keeping safe, you build a snow cave. Though emergency snow caves are often not done correctly, let us assume that you did construct one correctly on this trip (ie: top of door below inner floor to trap heat, properly placed ventilation, doorway plugged up, etc.)

Normally, I hear people say that a good snow cave can keep the inner temperature at a pleasant freezing (32F, 0C) temperature even if the air outdoors is crazy cold. Would this still hold true at -140 degrees? At what point is it just so freaking cold that even a snow cave cannot be kept warm?

The amount of snow that is insulating you does obviously matter. Let's say you dig into a small embankment, so part of it is more than a few feet thick. For the front of it where you dug into the bank and had to then patch up the front of your cave, I would personally assume a few inches at most, as I have read about safety concerns of cave-ins when people craft thick walls. If you are not concerned about such a cave in danger, then feel free to assume thicker if that is truly what you would do.

Assume that there is a modest wind. Enough that heat does not linger well around objects, but not enough to worry about the integrity of the snow cave.

So, what is the minimum temperature at which a properly constructed snow cave can no longer be expected to maintain a constant 32F/0C temperature without artificial heating?

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    Some thoughts on a theoretical answer... Snow has an R value of around 1 per inch (depending on how compressed and the water content). Assuming your tunnel is 8 feet long, that is an R value of 96 (which is pretty dang high), but to get an accurate estimate of the R value you would need to factor in the door. I believe they stay at 0C because it takes a ton of energy/heat to melt snow. If the inside starts at -135 F, I am not sure you could survive long enough to warm it up.
    – StrongBad
    Jun 26, 2018 at 22:20
  • @StrongBad Took HVAC training long ago, but that is very rusty after this time .Yes, I think that's why temp maintains: insulation state changes. I agree with your last sentence, though the record low is a point in time, a point that is probably after the cave was built. I suppose I could flesh the scenario out more, but I'm not sure that would help much. Maybe I'll add more assumptions (eg: assume the temperature was only -40 when the cave was constructed, or that you provided some initial external heat but want to maintain the temp with body heat, or something... I'll think about it).
    – Loduwijk
    Jun 26, 2018 at 22:30

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TLDR: -148 °F including windchill has been survived inside of a snowcave.

I went looking for cases of people surviving extremely low temperatures while inside a snow caves, and it looks like the record is held by the climbers who did the first winter ascent on Denali.

On February 28, 1967, Dave Johnston, Art Davidson, and Ray Genet became the first climbers to stand on Mt. McKinley’s 20,322-foot summit in winter. On the descent, the weather turned, and they dug a tiny snow cave above 18,000 feet and hung on for six days and nights, barely able to sit up in what they wondered would be an icy grave. The windchill dropped temperatures as low as -148 Fahrenheit, and their teammates lower on the mountain assumed the worst.

After six days, the men were able to descend – just barely. Davidson’s account of the climb and descent, Minus 148 Degrees, was published in 1970 and instantly became a mountaineering classic. In 2013, the 100th anniversary of the first ascent of Mt. McKinley, Mountaineers Books published an anniversary edition of Minus 148 Degrees with a new prologue and afterword updated with details of more recent winter attempts on McKinley.

Climber Art Davidson on the 1st Winter Ascent of Denali, Adventure, and Surviving ‘Minus 148 Degrees’

The full story is in the book, Minus 148 Degrees

While that at least means that -148 ° F is survivable by some people, other people have frozen to death inside snowcaves at much higher temperatures.

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  • The 1986 incident in your "frozen to death" link is the Oregon Episcopal School incident, which involved extremely inexperienced climbers with improper cotton clothing. I suspect that the cotton was the reason for their deaths rather than the snow cave not working.
    – Qudit
    Jun 27, 2018 at 6:00
  • @Qudit And, if I remember correctly, 2 or 3 of the people inside the snow cave survived in that incident. Though many more died.
    – Loduwijk
    Jun 27, 2018 at 13:30
  • @Qudit I had read about that incident recently on a mountaineering safety site. Many of the examples given were to point out the mistakes that people made, but I don't recall if there were mistakes in their snow cave. I would not be surprised, as I would think a large group of bodies would have warmed the cave reasonably well, but maybe not if they were already too cold and had no insulation against the cave walls themselves.
    – Loduwijk
    Jun 27, 2018 at 13:32
  • @Aaron It sounds like another problem was that the cave was not properly constructed (too small) for so many climbers. Between that and the clothing, it is not surprising that they died. I suspect that with proper gear and a proper cave, they would have been fine. They decided to climb when a storm was predicted with inexperienced climbers in the party though, so they clearly had no clue what they were doing.
    – Qudit
    Jun 27, 2018 at 15:23
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    No wind, no windchill. Being protected from wind inside a cave with ambient temperatures of -45C and 90km/h winds outside is very, very different from being inside a cave with ambient air temperatures of -95C. In fact, windchill only (largely) applies to exposed skin. Actual cold temperatures are much worse than windchill temperatures because they are actually colder and also impact conduction losses through insulation (ie: your coat, boots, etc).
    – J...
    Jun 29, 2018 at 11:31

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