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There is one question that has been bothering me sometimes the last couple of years that I want to share.

There are two statements that I believe are true. A) snow's natural color is white B) snow of white color melts under sun the slowest.

This, to me, seems like something that cannot be a coincidence, but rather some sort of result of an evolutionary process of the snow crystal, but that sounds silly because it is not a living organism. Anyway, I can't seem to resolve this paradox.

To motivate this a little better, I would guess that if snow were a shade even a little darker than white, the ice caps probably would've already melted,because from what I know, white snow reflects something like 99,...% of light, and even a small increase in relative light absorption will increase heat absorbed by many times.

Hope this makes sense

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  • $\begingroup$ @bowlofred thanks, that's an interesting question and answer. However, my dissatisfaction caused by apparent coincidental existence of snow masses on the earth with the fact that they're white, remains. (if the snow wasn't white, all of it would melt) $\endgroup$ Nov 29, 2021 at 23:26
  • $\begingroup$ Regarding your last comment, are you asking why it doesn't snow other chemicals, and asking whether the explanation for this is because they would all change phase before they hit the earths surface, due to the wavelengths they absorb? (I ask this bearing in mind that you think the linked question isn't a dupe). $\endgroup$
    – user400188
    Nov 29, 2021 at 23:55
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    $\begingroup$ @NickTheDick The universe is full of such coincidences that have nothing to do with evolution or some design. They just ARE. This is not even the most mindblowing coincidence. Consider that ALL matter are heavier as solid than as liquid so ALL solid things sink in their liquid form (eg: solid gold sinks in liquid gold). BUT water is an exception. Solid water (ice) floats on water. This coincidentally means that water forms its own insulation layer when cold (the ice on top slows down the heat loss of water below it). Without this fact all water everywhere should be solid ice or vapor $\endgroup$
    – slebetman
    Nov 30, 2021 at 7:14

2 Answers 2

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Individual snow-flakes, just like pure ice, are pretty much transparent (see picture for example) - so almost all the light hitting one is transmitted, a littel is reflected (dependent on the angle of incidence of the light), and a tiny bit is absorbed.

But snow consists of millions of snow-flakes all jumbled up together, so when sun-light hits it, the light reflects/refracts/transmits randomly through/from a flake, and then through a neighbouring flake, and then another one... and so on. So the light follows a more or less random path through the snow. Some of that light will be transmitted deeper and deeper into the snow-bed and eventually be absorbed, but much of it will eventually be going in the right direction that it passes back out of the surface of the snow-bed (and perhaps to your eye).

The result of this is that the light that emerges from the snow will be fairly diffuse in direction but (as absorption is so small) will have almost the same spectral information as the original light. And as sun-light is more or less white, that is the 'colour' you will see from the snow.

If you add to the snow, a material that absorbs light in some part of the spectrum, then the light that escapes back to your eye will also show absorption in that frequency range. Hence the infamous 'yellow snow'.

If you took pure snow into a room and lit it with filtered light, say red or green, then the snow would simalarly look red or green.

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Sunlight is made up all of the colors. Sunlight is also known as white light. White color is a mixture of all the colors. As sunlight hits on the snow, it is it's natural property of reflecting all of the sunlight, and not absorbing any colors. As it has reflects most of the colors, it has basically reflected back white light itself! Therefore it appears white!

Also, yes, if snow had a darker color, it would lead to faster melting of ice, as it would absorb more heat.

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