I was wondering if having a water world would make a planet more hot or cold? Also would it change the atmosphere and make that warmer or cooler? The planet is smaller then earth (not by to much), has no tilt, has large tectonic plates, a thicker atmosphere, and it's around a k type star I don't have the math down for how close but basically the same distance as earth would be to its sun. I heard water is a greenhouse gas but I wanted my planet to be cooler so I wanna make sure if I can keep it that way or have to change something
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$\begingroup$ Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking. $\endgroup$Community– Community Bot2026-03-19 06:48:17 +00:00Commented Mar 19 at 6:48
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5$\begingroup$ There are many questions asking about water worlds, please check them. At the same time, give some more details and narrow down the scope of the post. We, per help center, take only 1 question per post. $\endgroup$L.Dutch– L.Dutch ♦2026-03-19 06:49:44 +00:00Commented Mar 19 at 6:49
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1$\begingroup$ Depends how deep the water is $\endgroup$Kilisi– Kilisi2026-03-19 12:16:15 +00:00Commented Mar 19 at 12:16
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$\begingroup$ Hi, Doodle. I feel that this question is a misunderstanding of the science. I'd be tempted to answer this question, "any temperature you want it, based on how close it is to the star." The temperature of a planet is almost entirely based on energy received from the star. It can be adjusted by clouds and atmospheric composition, but this question doesn't ask about those. I would suggest researching global warming for a better foundation. $\endgroup$Robert Rapplean– Robert Rapplean2026-03-19 15:13:35 +00:00Commented Mar 19 at 15:13
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$\begingroup$ The problem with the tectonic plates is that they tend to move. Thus, the climate keeps changing over geological time frames. Your story can be put anywhere within a huge range of temperatures. $\endgroup$David R– David R2026-03-20 14:32:35 +00:00Commented Mar 20 at 14:32
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2 Answers
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It's a more reflective surface- so it throws more light and infrared back into space. Even more so as ice. Then again water-vapor is a potent greenhouse gas, so if it gets hot, it gets really Venus-like hot.
I would argue that a waterworld has a thinner climate-saddle. The zone where the world is actually a nice inhabitable world, is smaller, the chance to become an iceball or a hothouse is actually bigger, once an event starts the process.
If a asteroid impact hits large shelves of drifting methanhydrate, a waterworld may go Venus hot within a short time span. Should it freeze over though (do a Europe) it would be locked into this ever after. Volcanoes and such having very little effect, once they are several kilometers down.
I wonder what would happen on an eye planet waterworld. Massive glaciers drifting into tropics. The ice half could, over long times, even grow a bald spot, revealing the planet's surface where glaciers don't flow, and snow does not fall.
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The water world with more land mass is going to be warmer than the water world with less land mass. (source)
I think an entirely water world would be a snowball world (if it were otherwise Earth-like) with no land to warm things up.
But I think the distribution of land matters quite a bit. I can think of 4 major configurations worth discussing:
If you make a big supercontinent like Pangea then the world would be hot and dry because oceanic influence cant reach into the interior of the continent. There would be extreme differences in climate between oceanic regions, costal regions, and deep interior regions with intensely dry deserts despite two thirds of the world being a giant ocean.
If you make an equatorial belt with land concentrated around the equator then the planet would be significantly hotter because without oceans at the equator the sun would bake the ground and push heat toward the poles by wind.
But if you only make land at the poles, then sunlight shines with a lower angle of incidence on the polar landmasses, reducing its heating effect and the world would be much cooler than otherwise. The warming effects of land may be diminished furthermore by them being covered in ice caps (like Antarctica).
I think if you make an archipelago (many small islands) the climate would be "just right" because the moderating effects of the ocean are everywhere and there are small amounts of land at all latitudes to warm things up.
