What needs to be changed in the human body to adapt it to the cold conditions of the tundra?

Question

A person who is not dressed for the weather may develop hypothermia in the cold. This word is called a state when a person's internal temperature drops below 35 degrees. The dangers of its development are most susceptible to the elderly and people under the influence of alcohol.

Hypothermia is mild (when the temperature drops to 32-35 degrees), moderate (28-32 degrees) and severe (below 28 degrees).

On average, the temperature of a person's body in the cold drops by about 1-2 degrees in 30-40 minutes.

With a mild degree of hypothermia, when the internal temperature drops to 35 degrees, severe tremors begin, and reactions slow down.

After another hour or so, the body temperature will be 34-33 degrees. The person no longer trembles, because the body has practically no energy left, the poor man who finds himself in the cold begins to lose his memory and reason.

After the body temperature drops below 33-32 degrees, a state of apathy sets in, and then a stupor. In this state, a person from the outside looks lifeless: the skin becomes pale and cold, arms and legs stop bending, breathing and other life processes slow down. But a person can still be saved.

When the internal temperature drops to below 25 degrees, blood circulation and respiration stop and the person dies from hypothermia.

And here I became interested in what I needed to change in the body of my genetically modified people so that they could be without clothes for a long time at temperatures below - 20-30 ° C, and for several hours at temperatures below - 45 ° C, which can be seen in Antarctica and the Arctic?

Note: These superhumans must not be covered in hair.

Answer 1

In reality you can't

they have to be covered in some kind of insulation you choices for mammals are fur or clothes, (blubber does not work well on land).

The only other option is for them to be eating hundreds of thousands of kilocalories a day and converting it in to heat. But that will never believably happen, insulation is too easy to evolve, and food is too hard to find in the artic and this is likely pushing the limits of what is physiologically possible for energy conversion in biology.

Humans require around 2400 calories per day but only 1000 calories of that is used on thermoregulation.

Under laboratory conditions a human can consume as many as 4 times as many calories as baseline while shivering at -3C

so to start at -3degrees your creatures are consuming 9600 calories (or 8200 calories for thermoregulation)

we have to extrapolate from there, but changing temprature is multiplicative in the heat loss equation so we can assume a temprature 27 degrees lower requires 27 times as much energy to maintain. (8200 X 27) plus 1400 So your creature is consuming AT LEAST 222,800 calories per day. If it is windy or or wet much more calories are needed.

to give you an idea this is what that many calories are. Assuming they are not cooking their food, that is close to eating an entire cow every two day (500,000 calories). They would have to spend most of their waking time eating.

source source 2 Source 3 Source 4

Answer 2

Arctic Life

It is a well-established fact, that a heavily overweight person not only has a better Volume-to-Surface ratio, making them favorable under Bergmann's rule for a colder climate, just as well as taller specimens. However, we also know that animals in these climate rely on a denser, longer fur coat in conjunction with insulating fat to keep the body core warm but the surface as cold as possible. Polar bears are one of the most effective setups - Such as this thermal image shows:

Humans are rather hairy...

By nature, humans have hair on the head, but they also have androgenic hair on arms (especially lower), legs, and pubic areas. Most males also on the face and some males on the chest. The amount of these hairs is varying highly between individual specimens, but even low haired specimens have a thin, downy, almost invisible amount of haires there. There's a heat map of where this androgenic hair tends to appear:

Hairless humans?

So, OP established, that the heroes can't have any hair. No hair means, that our heroes suffer from alopecia areata universalis, the loss of all body hair. This condition can be a result of radiation poisoning, genetic factors, and possibly an autoimmune disorder. So, our heroes have no insulation outside of their skin. How could they stay active longer without adding insulating layers?

Blubber-Humans?

Let's start with the insulating factor that can easily be added to humans: fat, or rather blubber.

Taking the condition literally, there is only one suborder we can take a look at to guesstimate what our heroes need to stand against the low temperature for long times: Cetacea, as all other mammals have hairs. Only Whales and dolphins do not have any hairs and pores, and instead, insulate their body with blubber alone.

They too follow Bergmann's law and by living exclusively in the water have made sure that their surroundings will be at worst -2°C under the antarctic ice shelf, while the vast majority of deep ocean water is 0-3°C. Pretty stable, and relevant for all but the warm water species. Most large whale species (Orca, Blue Whale, etc) spend a long amount of time in these areas, and their blubber can be up to almost a foot thick - only to insulate the 37°C core against 0°C and some moments to minutes against the arctic air! This picture documents an Orca specimen with about 10 inches of blubber, which was analyzed for its chemical contents:

The loss of thermal energy through a surface is $P = \frac{k A\, \Delta T }{d}$, where d is the thickness, A the surface area, and k a material constant. To insulate with the same effectiveness - and keep P constant - against twice the temperature difference $\Delta T$ at -37°C, you can, as a rule of thumb, double the thickness of the same material. That's about 2 feet of fat all over.

Taking a skinny estimate of a human gives us an oval cross-section of 2 by 1 feet as a base. Adding the 2 feet blubber, this would turn them into a 6 feet wide, five feet deep blob. That's the level of obesity a human being has at about 600 lbs, and those humans are immobile.

Conclusion: IMPOSSIBLE.

Answer 3

Simple really. They need to be able to extrude insulation, then when no longer needed they can shed it.

You denied hair. But fur evolved with just about exactly this as the the selection factor. Critters that could tolerate cold could move away from the equator.

But if not fur, then they emit a gel from their pores. This then forms a foam, then stiffens to something like foam rubber. Many 10's of thousands of little pockets of air form a very good insulation. Flexible and tough. And when they no longer need it they can shed it off and leave it. Probably a few pounds, maybe a few 10's of pounds, would be enough for one adult to be toasty and comfortable quite far below freezing. If it gets colder they can extrude more, thickening it from the inside. If the current layer gets damaged, they can just extrude another layer.

Possibly the extrusion process is started by the skin surface being cold.

With some mods it could be made into flaps that would allow rapid adjustment. You really don't want to be sweating at -40C. Maybe it does not stick to strategic parts of their anatomy, allowing that part to be kept tight when it is cold, and opened a bit when not as cold. A nice flap to cover the face when needed. Possibly it would be thicker over areas with additional challenge, such as the feet, the hands, and the head and neck.

If you could get a consistency comparable to Styrofoam, you get quite good insulation. Extruded polystyrene provides an R-factor of about 5 per inch, compared to sheep's wool which produces something like 3.6 per inch. So a 2 inch thick coating of this material would produce much better insulation than 2 inches of wool.