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One of my ideas is a dragon that breathes ice, through liquid CO2, stored in special glands and released through pressure, and cooling. It would gain this large amount of required CO2 from eating chalk and natural metabolism. Would it have to be cold-blooded to maintain its cold temperature? Or would it being warm-blooded affect it? It is a large predator, and it could be somewhere in between, similar to dinosaurs. Would it be able to be cold-blooded, especially if it lives in a freezing environment?

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    $\begingroup$ You know how a refrigeration system works right? to get or keep something cold inside it means you're pumping a lot of heat out of it into the surrounding tissues, chances are good your dragons are going to need some way to keep the rest of their body cooler so they don't overheat, big ears or a sail fin like some dinosaurs to act as a thermal dump they can pump warmer blood through to radiate away the excess heat, at a guess (of the knee jerk variety) they'll need a high metabolism of some sort, because they'll be burning energy to keep that organ cold enough to hold liquid CO2. $\endgroup$
    – Pelinore
    Feb 19 at 20:35
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    $\begingroup$ cold blooded means it cannot regulate its body temperature internally and must seek out a heat source usually the Sun and in your particular case those flaming stones fired from the trebuchets... $\endgroup$
    – user6760
    Feb 20 at 2:48
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    $\begingroup$ There's a creature called a bombardier beetle. It does something similar to shoot hot water. $\endgroup$
    – David
    Feb 20 at 6:49
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    $\begingroup$ To liquify the CO₂ you'd need to increase the pressure (Gay-Lussac's law). This would lead to an increase in temperature (ΔT) equivalent to the ΔT reduction in temperature achieved. You're not reducing temperature, you're moving it. You can't obliterate energy. Our dragon would be extremely hot on the outsides! Also, you don't need to replenish CO₂ unless it leaks; you've described a refrigerant - you don't replace the refrigerant gas in your fridge right? It's a closed loop. [NB. Plus CO₂ makes an appalling refrigerant; because it sublimates (turns into a solid with no liquid stage)]. $\endgroup$
    – Rab
    Feb 20 at 8:24
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    $\begingroup$ @David I believe the bombardier beetle holds two chemicals seperate until needed then brings them together to fire (and a chemical reaction causes them to get hot). It isn't constantly holding them hot (or cold) $\endgroup$ Feb 20 at 14:27

2 Answers 2

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Warm and cold blooded are colloquial terms that really refer to thermo-regulation vs no thermo-regulation. Nothing inherent about warm or cold, just that in real life all examples are thermo-regulating to a warm temperature. There are no examples of organisms in the real world that are refrigerators. Not thermo-regulating in a cold environment implies activity levels that are dependent on temeprature though. Most notably, lack of activity when it is cold, although fish can be active in cold water.

That said, technically liquid CO2 doesn't really line up with a dragon that lives in Earthly freezing temperatures since liquid CO2 is so cold that Earthly freezing temperatures would be considered warm.

Not really a problem though. That just means that your dragon's gland really is a refrigerator: Using energy to thermoregulate the gland by moving heat out of it and dumping it to the surrounding "warmer" temperature. And in that sense, the colder the ambient temperature, the easier it would be. This probably means the rest of your dragon is actually quite warm as it consumes energy to maintain the refrigeration moves the heat from the gland into the rest of its body, which is just as well so it isn't always just lazing around from lack of metabolism.

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  • $\begingroup$ So to clarify, it would be better for it to be warm-blooded than cold-blooded? $\endgroup$ Feb 19 at 19:08
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    $\begingroup$ @ScoutPaige Yes, you need thermo-regulation since CO2 is significantly colder than the ambient will ever be. $\endgroup$
    – DKNguyen
    Feb 19 at 19:09
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    $\begingroup$ Liquid CO2 is not necessarily terribly cold, it just has to be at least moderately high pressure. Below 5.1 atmospheres, there is literally no temperature at which CO2 is liquid. $\endgroup$
    – Jay McEh
    Feb 19 at 20:35
  • $\begingroup$ We thermo-regulate to cool down too using sweat. "Warm" is just a relative term anyway $\endgroup$
    – Cullub
    Feb 20 at 19:39
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    $\begingroup$ @Cullub I guess sweating is part of homeostatis $\endgroup$
    – DKNguyen
    Feb 20 at 20:29
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Your question essentially appears to be "is it easier to keep something cold when you're not surrounding it in a substance that produces heat", which: yes. As to whether or not something can be cold-blooded (ie, not producing much heat through its own metabolic processes) while living in a cold environment, and that is certainly possible as long as its basic chemistry is sufficiently different. Cold blooded icefish have a variety of adaptations to permit functioning in extreme cold:

...antifreeze running through its opalescent white blood... [the] lack of red blood cells means icefish blood is particularly thin, making it easier to circulate in the cold...researchers also found that fish had an excess of genes responsible for creating proteins to keep it from freezing as it ingests ice crystals from the surrounding water

This is about as far as real world animals can get, and anything capable of "breathing ice" will need basic cellular chemistry that deviates drastically from anything on earth. Like, different basic building blocks than the stuff shared by everything from humans and dinosaurs all the way through mushrooms and deep sea vent tube worms and e. coli bacteria. Which is fine; you're making your own world, after all.

What will be trickier is that liquid CO2, which we'll grant your unearthly metabolism is able to create, is a far cry from "breathing ice". Assuming a vaguely earth-like environment, CO2 can only be liquid under fairly high pressure (5.2 atmospheres), so even if your icy dragon has pressure tank bladders internally, the second it starts to breathe it you no longer have liquid CO2. You have a rapidly expanding gas, which may or may not be useful as a weapon but is absolutely a tremendously effective method of propulsion, that unfortunately is pushing the head of your dragon in a direction it probably doesn't want to go. At snout-petting range this sudden expansion of very cold gas would be quite unpleasant and potentially fatal, assuming a large dragon and a good flow rate. At more than a few meters of range, it's a chilly breeze that will refresh the onlookers being entertained by watching a dragon being launched backwards by its own invisible rocket belching. Expanding gases aren't like streams of liquid, and will spread out very quickly in every direction. To have any force at range would require a force at point of origin that is literally the strength of a bomb, since bombs are definitionally things that generate very rapidly expanding gases. Do recall that the point of origin for this expanding gas is inside the throat and skull of your dragon, so some caution is advised.

Even liquid nitrogen isn't really much like breathing ice. I've recreationally splashed myself and friends with liquid nitrogen. As with many activities undertaken by adolescent idiots, it's absolutely fine right up until it very, very much is not, so please do not try this at home. But due to a fun phenomenon known as the Leidenfrost effect, a brief dousing of liquid nitrogen will actually result in less cooling than being splashed with the same amount of ice water.

If you truly want a cold-based breath weapon, you need to get into extremely exotic chemistry like supposing some sort of violently endothermic chemical reaction, spraying two separate chemicals that when they combine absorb a great deal of heat from their environment. There are real-world chemicals that do this on a small scale, such as ammonium chloride and barium hydroxide. But for complicated reasons that go deeper into thermodynamics than I'm comfortable swimming, we don't really expect to see actual chemicals that do this in a dramatic way. So you'll need some unobtanium if you want to stay in a supposedly scientific frame.

A final alternative for a cold-based breath weapon is exotic physics: some means of manipulating energy fields in a way that reduces the vibration of atoms within the area of effect. In our universe, that reduction the energy of one system means the energy has to go somewhere else, so it could be a way that the dragons "eat" the heat from their targets to keep themselves warm, assuming that's something they want. But this kind of field manipulation is so deep into Star Trek technobabble that it might as well be magic.

Sadly, absolutely none of these will produce the icy blast we're used to seeing in comics. If you want that solid blast of ice, your dragon has to vomit every single ounce of that up as water first. And since unlike gases, water doesn't compress, that means your dragon is a giant waddling sloshing reptilian water balloon that can presumably immobilize its prey through laughter and doesn't need all the fancy science to freeze them as well.

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