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Let's say I imagined a world that is as habitable as Earth and has the same oxygen levels, land to ocean ratio and similar average temperature. However it has no clouds at all. How different its climate could be and how would life had evolved on it?

I know that thick and darker clouds have a cooling effect on climate but thin and whiter clouds tend to trap more heat. That is why it is common for cloudy days with white skies in Rio de Janeiro to be almost as hot as a sunny day in the summer.

So I think that since clouds are just water in aerosol form then the climate of my planet would be drier and obviously much sunnier.

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    $\begingroup$ If it has an ocean like Earth does, and it has the same temperature, then it will have clouds. Unless the oceans are made of something other than water and much less volatile. $\endgroup$
    – AlexP
    Commented Nov 1, 2021 at 23:04
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    $\begingroup$ If it had no clouds, then it would have no rain. So it would have no rivers and likely no freshwater. Hard to imagine being as habitable as Earth with no rain. $\endgroup$
    – Priska
    Commented Nov 1, 2021 at 23:30
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    $\begingroup$ (a) You're misusing the reality-check tag. Please either edit your question to make it comply with the tag's wiki or remove it. (b) Your question is insensible as an Earth-like planet (assumes water) with similar land-to-ocean ratio, atmosphere, and temperatures would be required to have clouds. No clouds means the planet isn't using H2O, which means (insofar as we understand life) it's not just uninhabitable, it's inhospitable. $\endgroup$
    – JBH
    Commented Nov 1, 2021 at 23:39
  • $\begingroup$ You would be better off asking HOW a habitable planet like Earth could exist without cloud cover first. There are clouds (but not many) from -30F in Minnesota to 107F in Arizona in my own personal experience, and I doubt you'll get such a world without some preconditions that seriously affect this answer. Arrakis? $\endgroup$
    – DWKraus
    Commented Nov 1, 2021 at 23:45

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Your habitability is nonexistent.

Clouds are formed by water vapour (and other gases, but that's not as important, the big one for this question is water) as it condenses: this is the preparatory step before rain or snow or whatever else comes down, even if the clouds aren't always thick enough to be readily seen. If you don't have clouds, you don't have precipitation. Without precipitation, you don't have a rain cycle, which means underground water suppliers like aquifers won't be refilled; from the direction of your question, the planet has implicitly always been this way, so those aquifers likely don't exist anyways.

Now, without precipitation nor usable groundwater, it means your planet has no access to freshwater supplies. That immediately invalidates basically all land-based life as we know it on Earth, because most creatures can't drink saltwater.

This is also obviously not much of an Earth-like planet at this point, but let's keep going a little farther.

Without clouds, one of the planet's major methods of temperature control vanishes. The lack of precipitation means you have no snow, which means that the ice caps can't effectively replenish themselves in the face of incidental or seasonal melting. They probably won't melt entirely, as even saltwater freezes when it's cold enough, but they're certainly going to be pretty small. There's no defense against a sudden flare of solar activity, nor against the reverse. Ice ages will be a lot more severe.

Without rainfall, inland vegetation is simply impossible within Earth-like constraints: you need water for life, and there isn't any of that inland. You're going to have a very dull brown planet outside the oceans. This leaves the planet entirely reliant on sea life to manage the atmospheric balance of oxygen, nitrogen, CO2, etc. I can't speak with absolute certainty here, but my expectation is that that won't produce a balance like what Earth has now.

Another major point: without rainfall, it means that any water evaporation from the oceans will stay in the atmosphere. This is going to produce a nasty greenhouse gas effect, I would expect, as the atmosphere thickens (higher density) from sheer volume of gas. Atmospheric pressure will rise, which might check the process eventually; temperature and boiling point both rise with higher pressures, so it could in theory reach an equilibrium. In practice, however, that's going to be long past survivable temperatures; if the average temperature of the planet is over 100C, I'm pretty sure that fails the definition of an Earth-like planet.

Conclusion: Don't treat planetary phenomena lightly, nor in isolation, because they're usually very interconnected. You remove one piece, and you're likely to topple the entire system, with catastrophic effects. Secondary implications, like the mess that spilled out above, are not necessarily obvious, but that isn't necessary for them to be extremely nasty.

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Letting aside it's not possible to have no clouds everywhere, anytime, imagine a planet without macroscopic life, with a weather like in or around Abu Dhabi or Doha - incredible hot and sickly sticky humid.

Would you like it?

Speaking for myself, I had better experiences in sauna, at least I could throw a bucket of cold water on my head.

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