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Say I've got a creature with a 15 to 20 degrees Fahrenheit higher body temperature than a human. (Trying to figure out what a good temperature for this creature would be. Not good with number estimates so I'm unsure of what exact temperature I need for this particular creature.)

Would it be less vulnerable to a cold environment because its body is warmer, or more vulnerable because said cold environment's temperature is farther away from its normal body temperature?

What would the temperature feel like to a human touching its skin? At this body temperature would it's blood make steam when exposed to earth's air?(I'm hoping not. That would get to much attention since he's trying to blend in.)

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    $\begingroup$ the temprature matters less than the ability to maintain the temprature, that said it is easier to maintain a lower temprature. $\endgroup$ – John Oct 31 '19 at 21:38
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    $\begingroup$ 15 to 20 degrees of Farenheit or Celsius? (20 deg. F. difference is about 12 deg C) $\endgroup$ – Suma Nov 1 '19 at 9:21
  • $\begingroup$ What are you referring to when you say "unsure what I need"? Are you just looking for a critter that will have steam rising off it? $\endgroup$ – puppetsock Nov 1 '19 at 16:15
  • $\begingroup$ Assuming it's warm-blooded? Also remember that Humans operate at 37.5 C internally, but our skin does not become that hot to the touch. I think the biggest challenge is taking on enough fuel to keep the heat generating, and having enough insulation to keep it there. With appropriate insulation, humans do fairly well at under 0 degrees, but not so well over 40 C. Being too hot makes us sweat, as as water is essential for life, sweating it away means we need to take on board more (+ salts minerals etc). An animal would want it's skin to be that of ambient temperature - otherwise it loses heat. $\endgroup$ – Smock Nov 1 '19 at 16:29
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You are such a creature. The skin of your face can be exposed to 0 Celsius when you are 37C. That's almost 40C difference.

What happens is you got skin and fat. Also clothes. What happens when sea mammals swim in cold water?

They use a combo of fur and fat to insulate themselves.

The other stuff is the same as you touching a lizard. Feels cold but it doesn't hurt.

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  • $\begingroup$ I think you are confusing stuff. Your skin might be exposed to 0 degrees but will not instantly be 0 degrees, as evidenced by the blood not instantly freezing. The skin and fur is a good point, but I dont think it was in the original question's scope. $\endgroup$ – Demigan Oct 31 '19 at 22:03
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    $\begingroup$ In scope as per "At this body temperature would it's blood make steam when exposed to earth's air?" $\endgroup$ – Gustavo Oct 31 '19 at 22:46
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    $\begingroup$ If your skin reaches 0 C, you have frostbite. $\endgroup$ – Trevor Nov 1 '19 at 16:25
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    $\begingroup$ Trevor, your skin won't be at 0, your are irradiating heat. What is at 0 degrees is the air in contact with your skin. $\endgroup$ – Gustavo Nov 1 '19 at 17:21
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    $\begingroup$ @Gustavo Although if you were dead in Antarctica your skin would very likely be at 0 degrees. $\endgroup$ – Q Paul Nov 1 '19 at 23:42
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Your body works on a lot of chemistry and enzymes. These are mostly built with about the same optimum temperature, in our bodies 37° celsius. Hypothermia occurs when the temperature goes so far off this ideal temperature that these enzymes break down or stop and chemical reactions stop functioning properly.

Your hotter creature can be assumed to have similar degree difference before his processes grind to a halt as a human, which would be 2 degrees lower than the ideal temperature if I read this source correctly.

This would count for your hotter creature too. As you mentioned, because the difference in body temperature to background temperature is higher the warmer creature would lose heat faster if they have the same skin type, surface area, and amount of clothing, and reach hypothermia faster. Additionally, the higher base temperature would take more energy to maintain causing the hotter creature to lose its energy reserves and fail to keep his temperature up.

*note, this is for the core temperature. There are lots of processes that can handle larger differences. Your hands are often colder than 10 degrees in winter for extended periods of time and don't die off instantly. It is processes like heart, liver, kidney and brain function which don’t handle low temperatures.

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    $\begingroup$ That's Celsius, from the name of the Swedish scientist Anders Celsius. $\endgroup$ – AlexP Oct 31 '19 at 23:44
  • $\begingroup$ @AlexP and I learn something each day! (I also forget 2 things) $\endgroup$ – Demigan Nov 1 '19 at 20:27
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Birds

Chickens have a body temperature averaging around 42 C / 107 F - that's about ten degrees higher than humans. Some birds like the sombre hummingbird can reach as high as 113 F (about 15 degrees higher than humans - as cited by this study).

Warm Blooded Creatures

As @Gustavo and @Demigan point point out in their answers, warm blooded creatures can adapt to external temperature changes by generating heat automatically to counteract the cold. Furthermore, mammals have really good insulation properties (skin, fat). It should be noted that smaller creatures (birds, cats, etc) tend to have higher heart rates and respiration (breath faster), while larger creatures have slower heart rates and respiration. This likely is a factor in ideal body temperature as the faster the heart rate the more heat generated.

The key is to get heat out of you (sweat, breathing) when temperatures rise and generate heat within you when temperatures fall. In creatures with no sweat glands (like dogs), panting becomes the only method of heat dissipation and makes them more susceptible to danger at higher temperatures - not to mention their fur prevents heat loss more than less hairy animals (like humans).

So if your creature is warm-blooded, their heart rate, respiration, and sweat mechanisms would have a delayed kick-in at higher temperatures, but would kick in faster as temperatures fall.

Extreme Temperatures

A bit of an aside, but some animals can survive in extreme temperatures. This is a fascinating article by National Geographic which overviews how this works in some animals; it's an enlightening read which might give you ideas.

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  • $\begingroup$ The study you linked is unfortunately behind a paywall but these temperatures seem very high to me. A human being would have some severe long term consequences from a body temperature of 42 Celsius and would be quite dead at a body temperature of 45C (=113F). AFAIK this is due to proteins in the body just falling apart, (similar to the change when boiling an egg) so this does apply more or less to all animals. $\endgroup$ – quarague Nov 1 '19 at 9:57
  • $\begingroup$ @quarague There's an article I talk about on another question which shows cell death in humans coming around 41C; I don't think this was from proteins falling apart though. There's also an issue of timing (how long you stay at a temperature). $\endgroup$ – cegfault Nov 1 '19 at 12:17
  • $\begingroup$ I'm not a biologist, I was just very surprised at these body temperatures because I thought that the principles that make these particular temperatures deadly to humans are not specific to humans but instead apply to all higher life forms (on earth). $\endgroup$ – quarague Nov 1 '19 at 12:41

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