6 ms·

It's interesting that many/most organisms are more sensitive to heat than cold. Cattle, dogs and whatnot usually enjoy room temperature, 20C-25C... like us. At

It's interesting that many/most organisms are more sensitive to heat than cold. Cattle, dogs and whatnot usually enjoy room temperature, 20C-25C... like us. At 30-35, may will start to struggle. At 40-45, deaths start. Even heat adapted desert species need shade, burrows and such to survive 40+ temps. Meanwhile, life at cold temperatures goes on. A lot of animals can adapt to a temperate 0C-20C conditions, and colder. Humans adapted and thrived, like many/most megafauna to pretty cold conditions. The far north has been inhabited by people for half a million years. You can get a lot further from comfort and still make it in the cold. Heat is deadly.

codewritero 4y ago
It wasn’t that long ago that an article making the exact opposite point was at the top of this site.
- dalbasal 4y ago
  got link?
  - codewritero 4y ago
    Can’t find it. The title was along the lines of global warming might result in a net increase in usable land.
    - schoen 4y ago
      Well, it might! It might also be necessary for many people to migrate to cooler areas than where they currently live.
    - kjs3 4y ago
      How is "land which is too cold to use now might be useable on a warmer world" and "human beings aren't as tolerant to higher heat as we once thought" the 'exact opposite' of each other?
    - namlem 4y ago
      While I suspect this is probably not true, it is plausible due to the fact that there is a lot of land in the northernmost regions of the world.
krzat 4y ago
Well it's easier to make fire than a fridge.
- wongarsu 4y ago
  And you can insulate from cold with fat, but insulating against heat is difficult because you have to get rid of the waste heat from muscles and other body functions somehow.
tialaramex 4y ago
Almost (?) all life runs off chemical reactions that are temperature sensitive and produce heat. In a closed system these reactions stop, they are able to continue (and so life continues) only within a context where the heat is lost. You can adjust the gradient so as to change the rate of heat loss, you can grow fur, shunt blood flow away from outer surfaces - or the reverse. Humans have clothes and even buildings to do this even more. Say you're losing 10K per hour and producing 5K per hour, if you cut the gradient to 50% you break even and your temperature remains viable indefinitely. But that only works when you're losing heat. If you can't lose heat, this doesn't help. You will die.
323 4y ago
A body can burn energy to create heat. But it can't burn energy to remove heat. That's a fundamental asymmetry. Maybe it's also the reason why body core temperature is close to environment maximum temperature - since you can't really decrease your temperature you might as well learn to live at the upper extreme.
- chaorace 4y ago
  Indeed, it's why sweat was such an evolutionary leap for humankind. Our species didn't necessarily invent the sweat gland, but we certainly did become the sweatiest of the Great Apes -- by an order of magnitude in some measures. I wonder how much of the species' worldwide dominance can be attributed to the evolutionary diceroll that placed our ancestors in subsaharan Africa? Could we have survived in Egypt, Mesopotamia, or India without sweat?
  - dalbasal 4y ago
    In the sweatiest of those places, our sweaty strategy is imperfect. Sweating works well in dry climates, not as well in humid ones. In high enough humidity, the sweat doesn't evaporate, doesn't cool you, and the whole system becomes a moist, messy loop. In dry, hot climates sweating works well, but increases our water consumption... these are the habitats where water is often scarce. Tradeoffs.
    - Tagbert 4y ago
      And it was evolved for the African savanna which is relatively dry. We already had enhanced sweating by the time we moved into more humid locales.
    - acoard 4y ago
      Are there better natural responses to heat that we see in mammals? I know sweating isn't perfect, for the reasons you mentioned, but do we see nature evolving any better solutions at a mammalian level? My armchair understanding is sweating is a natural marvel with nothing else like it seen in creatures as large as us. That it truly is a differentiator between humans and other animals (or mammals at least). Sweating is the foundation of humans ability to engage in long-distance endurance running which is one of our unique features, also called persistence hunting[0]. You can easily draw a line between this sweating and our ability to travel large distances and hunt the way we did, which in turn can be connected to humanity's success as a species on earth. [0] https://en.wikipedia.org/wiki/Persistence_hunting https://en.wikipedia.org/wiki/Persistence_hunting
amelius 4y ago
Makes sense, given that people often store biological specimens at -80C, not at +50C.
swayvil 4y ago
You see it working outside (building fences or whatever). You can work all day in the cold but heat cuts your day in half. It drains your energy.
jcranmer 4y ago
The human body needs to maintain core body temperature at 37°C. Whenever we extract energy from our food to do stuff, some of that energy gets dumped into heat. If we assume (just for round numbers) that we eat 2000 Calories/day, and that 10% of that energy is heat, then that's 200 Calories/day of heat that needs to be dumped into our environment. Abusing units somewhat, if a human being is 100 kg of mostly water, that's 2°C/day of heat. If we didn't dump that heat, in a day, core body temperature rises to 39°C and we get heatstroke. Heat naturally flows from hot to cold at a rate proportional to the difference in temperature. If we're fully passively cooled at an environmental temperature 25°C at a rate of 2°C/day, then at 1°C, we'd be passively cooled at 6°C/day. However, we can also modulate heat flow by introducing some thermally nonconductive layers--or, in layman's terms, put on a sweater. When it's cold, all you have to do is slow down the rate of heat flow. But hotter temps are more difficult. We can't take off thermal insulators or modulate the main thermal barrier between core body temperature and the outside world (i.e., skin). At 31°C, passive cooling is down to 1°C/day, and we need to turn to active cooling. Sweating is the main mechanism for humans: it takes heat for liquid water to become water vapor, and this heat is drawn from your skin surface, cooling it (this kind of allows heat to move from a colder to a hotter environment, unlike passive cooling). At 37°C, there's no longer any passive cooling, and active cooling needs to handle 2°C/day. But hotter than that, and things get worse: the environment is now passively warming you up. By 43°C, that's now 3°C/day of heat that needs to shed, and 49°C ups it to 4°C/day. At some point, you're going to overwhelm the ability of active cooling to cool you down, and the passive heating is still going to warm you up even if you shut down metabolism. Even worse is if sweating isn't effective at cooling down--at high humidities, the sweat won't evaporate and the cooling effect won't happen. (This also illustrates why heat-and-humidity can be deadly even at below-body-temperature environments.) This analysis was purely done for humans, but it's pretty similar for most organisms, just with different set points for core body temperature and active cooling mechanisms. Fundamentally, extreme cold is "easy" to handle--just slow down heat loss; extreme heat requires developing ways of pumping heat from a hot reservoir to a cold reservoir, which thermodynamics does not look kindly on.
racl101 4y ago
You can put on a sweater to sleep on a very cold night. But you can't take off your skin to sleep on a very hot night.
dorgo 4y ago
I don't see how a naked human can survice 0C for long. Maybe our gear and technology is better suited for cold temperatures. All in all I would say the temperature tolerance is the same in both directions.
- warble 4y ago
  0C is pretty cold, but the Yaghan indians seemed to handle it, or close to it, basically naked: https://www.ancientpages.com/2016/09/19/mystery-yaghan-people-first-true-discoverers-america/ https://www.ancientpages.com/2016/09/19/mystery-yaghan-peopl...

codewritero 4y ago

It wasn’t that long ago that an article making the exact opposite point was at the top of this site.

dalbasal 4y ago
got link?
- codewritero 4y ago
  Can’t find it. The title was along the lines of global warming might result in a net increase in usable land.
  - schoen 4y ago
    Well, it might! It might also be necessary for many people to migrate to cooler areas than where they currently live.
  - kjs3 4y ago
    How is "land which is too cold to use now might be useable on a warmer world" and "human beings aren't as tolerant to higher heat as we once thought" the 'exact opposite' of each other?
  - namlem 4y ago
    While I suspect this is probably not true, it is plausible due to the fact that there is a lot of land in the northernmost regions of the world.

krzat 4y ago

Well it's easier to make fire than a fridge.

wongarsu 4y ago
And you can insulate from cold with fat, but insulating against heat is difficult because you have to get rid of the waste heat from muscles and other body functions somehow.

tialaramex 4y ago

Almost (?) all life runs off chemical reactions that are temperature sensitive and produce heat. In a closed system these reactions stop, they are able to continue (and so life continues) only within a context where the heat is lost. You can adjust the gradient so as to change the rate of heat loss, you can grow fur, shunt blood flow away from outer surfaces - or the reverse. Humans have clothes and even buildings to do this even more. Say you're losing 10K per hour and producing 5K per hour, if you cut the gradient to 50% you break even and your temperature remains viable indefinitely. But that only works when you're losing heat. If you can't lose heat, this doesn't help. You will die.

323 4y ago

A body can burn energy to create heat. But it can't burn energy to remove heat. That's a fundamental asymmetry. Maybe it's also the reason why body core temperature is close to environment maximum temperature - since you can't really decrease your temperature you might as well learn to live at the upper extreme.

chaorace 4y ago
Indeed, it's why sweat was such an evolutionary leap for humankind. Our species didn't necessarily invent the sweat gland, but we certainly did become the sweatiest of the Great Apes -- by an order of magnitude in some measures. I wonder how much of the species' worldwide dominance can be attributed to the evolutionary diceroll that placed our ancestors in subsaharan Africa? Could we have survived in Egypt, Mesopotamia, or India without sweat?
- dalbasal 4y ago
  In the sweatiest of those places, our sweaty strategy is imperfect. Sweating works well in dry climates, not as well in humid ones. In high enough humidity, the sweat doesn't evaporate, doesn't cool you, and the whole system becomes a moist, messy loop. In dry, hot climates sweating works well, but increases our water consumption... these are the habitats where water is often scarce. Tradeoffs.
  - Tagbert 4y ago
    And it was evolved for the African savanna which is relatively dry. We already had enhanced sweating by the time we moved into more humid locales.
  - acoard 4y ago
    Are there better natural responses to heat that we see in mammals? I know sweating isn't perfect, for the reasons you mentioned, but do we see nature evolving any better solutions at a mammalian level? My armchair understanding is sweating is a natural marvel with nothing else like it seen in creatures as large as us. That it truly is a differentiator between humans and other animals (or mammals at least). Sweating is the foundation of humans ability to engage in long-distance endurance running which is one of our unique features, also called persistence hunting[0]. You can easily draw a line between this sweating and our ability to travel large distances and hunt the way we did, which in turn can be connected to humanity's success as a species on earth. [0] https://en.wikipedia.org/wiki/Persistence_hunting https://en.wikipedia.org/wiki/Persistence_hunting

amelius 4y ago

Makes sense, given that people often store biological specimens at -80C, not at +50C.

swayvil 4y ago

You see it working outside (building fences or whatever). You can work all day in the cold but heat cuts your day in half. It drains your energy.

jcranmer 4y ago

The human body needs to maintain core body temperature at 37°C. Whenever we extract energy from our food to do stuff, some of that energy gets dumped into heat. If we assume (just for round numbers) that we eat 2000 Calories/day, and that 10% of that energy is heat, then that's 200 Calories/day of heat that needs to be dumped into our environment. Abusing units somewhat, if a human being is 100 kg of mostly water, that's 2°C/day of heat. If we didn't dump that heat, in a day, core body temperature rises to 39°C and we get heatstroke. Heat naturally flows from hot to cold at a rate proportional to the difference in temperature. If we're fully passively cooled at an environmental temperature 25°C at a rate of 2°C/day, then at 1°C, we'd be passively cooled at 6°C/day. However, we can also modulate heat flow by introducing some thermally nonconductive layers--or, in layman's terms, put on a sweater. When it's cold, all you have to do is slow down the rate of heat flow. But hotter temps are more difficult. We can't take off thermal insulators or modulate the main thermal barrier between core body temperature and the outside world (i.e., skin). At 31°C, passive cooling is down to 1°C/day, and we need to turn to active cooling. Sweating is the main mechanism for humans: it takes heat for liquid water to become water vapor, and this heat is drawn from your skin surface, cooling it (this kind of allows heat to move from a colder to a hotter environment, unlike passive cooling). At 37°C, there's no longer any passive cooling, and active cooling needs to handle 2°C/day. But hotter than that, and things get worse: the environment is now passively warming you up. By 43°C, that's now 3°C/day of heat that needs to shed, and 49°C ups it to 4°C/day. At some point, you're going to overwhelm the ability of active cooling to cool you down, and the passive heating is still going to warm you up even if you shut down metabolism. Even worse is if sweating isn't effective at cooling down--at high humidities, the sweat won't evaporate and the cooling effect won't happen. (This also illustrates why heat-and-humidity can be deadly even at below-body-temperature environments.) This analysis was purely done for humans, but it's pretty similar for most organisms, just with different set points for core body temperature and active cooling mechanisms. Fundamentally, extreme cold is "easy" to handle--just slow down heat loss; extreme heat requires developing ways of pumping heat from a hot reservoir to a cold reservoir, which thermodynamics does not look kindly on.

racl101 4y ago

You can put on a sweater to sleep on a very cold night. But you can't take off your skin to sleep on a very hot night.

dorgo 4y ago

I don't see how a naked human can survice 0C for long. Maybe our gear and technology is better suited for cold temperatures. All in all I would say the temperature tolerance is the same in both directions.

warble 4y ago
0C is pretty cold, but the Yaghan indians seemed to handle it, or close to it, basically naked: https://www.ancientpages.com/2016/09/19/mystery-yaghan-people-first-true-discoverers-america/ https://www.ancientpages.com/2016/09/19/mystery-yaghan-peopl...