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I'm coming up with an alternate world that is far more balanced when it comes to the surface area. Real life Earth is 71% ocean and 29% land. Astronomers speculate that Earth got its big oceans by being hit by water comets from outer space billions of years ago.

Let's say that far less water comets hit Earth in a different universe. As a result, sea levels are hundreds of meters lower in this alternate Earth than it is in real life. What would be the climatic effects on land if the world had smaller oceans? Remember that lower sea levels in this scenario were caused by there just being less water to begin with, not by an ice age. I'm also mainly focusing on how land climates are changed by less ocean water. Assume that all of Earth's freshwater lakes and rivers are still around. With the exception of underwater mountains, almost all of the new land in this half-and-half Earth would be along the existing coastlines of real life Earth.

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    $\begingroup$ How many "hundreds of meters"? Two hundred meters lower is one thing, nine hundred meters lower is a very different thing, For example, if the level of the ocean is 900 meters lower, then the entire Mediterranean Sea vanishes -- it has a massive water deficit, and if the ocean level is below the Strait of Gibraltar then the Mediterranean evaporates in a very short time. $\endgroup$
    – AlexP
    Aug 13, 2022 at 22:47
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    $\begingroup$ Hello Rhymehouse. I'm loathe to close this question, so I'm hoping to convince you to ask a much (much) more specific question. Climate is quite literally the most complicated aspect of world design. Thousands of variables affect it and it's not helped that we have really just one data point: Earth. That means you're asking a speculative, hypothetical question that's forbidden by the help center. Frankly, the only practical guess (and it's an outrageous guess) is, "not that much different, other than more and larger deserts." That being a guess, anything more specific is an outright lie. $\endgroup$
    – JBH
    Aug 14, 2022 at 1:40
  • $\begingroup$ In your ponderings when you edit, don't forget how much our world has been shaped (literally in terms of the landscape, flora/fauna, cities etc.) by human habitation - which will be different in your world. Where I live used to be marshland for a radius of many kilometres, the rivers flowed with fish. Not so now, it's covered in urban sprawl and there are few fish. How the Hoover Dam changed the landscape both up and down stream. $\endgroup$ Aug 14, 2022 at 4:05

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Earth is about70 percent ocean and about 30 percent land. If the sea level is lowered enough, all the contiental shelves will be exposed, and there will be a few percent more dryland.

And then then lowering the sea level will not do much to increas the land ara, because continents will never come close to 50 percent of the surface of Earth. Musch less than 50 percent of the surface of Earth is continental rock towering about the sea beds.

It is hard to tell exactly from the maps in this comic strip, https://what-if.xkcd.com/53/ but it looks like about 50 % of the earth's surface would be dry land if the water level dropped tosme level between the three kililometer drop map and the five kilometer drop map.

That would drastically reduce the amount of water on Earth, causing extreme climate change.

I think that the more reasonable way to design an imaginary planet with about 50 percent land surface would be to have a somewhat different geology causing much more o rmuch larger continental land masses to form. With more high continents, the world could have a much water as Earth, but the oceans would be smaller and deeper. Much of the lower parts of the continents would be submerge, but the dry land would be enough for about 50 percent of the world's surface to be dry land.

Since the moving crustal plates of the Earth are forced deep underground and melted into magma at many of their junctions with other plates, and are being created at other places, I find it easy to believe Earth might have had higher or lower percentages of continental crust in the past and might have higher or lower percentage in the future. And another planet with different geology coud easily be 50 percent continental crust at some points in its hsitory while having about as much surface water as Earth.

I'm not certain that making your world an alternate univese version of Earth would work. You need a geological opinion for that. I note that water deep underground is supposed to be a lubricrant for plate techtonics, so an alternate Earth with less water might have slower moving crustal plates or no plate techtonics at all. If crustal plates move slower on your world maybe you could find a map of a past era where Earth had 50 percent of its surface contental plates instead of 30 percent. But since plates get dissolved as they plunge under other plates, I don't think there is any record of destroyed continental plates.

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I don't think this is a bad question for worldbuilding, I wouldn't close it. We need a topological map of the Earth, so we can roughly measure land area exposed if we drop 100 meters, 200 meters, etc. Exactly how far do we need to drop to move from 29% land mass to 50% land mass? Most of the islands can probably be ignored, the big continents are enough to consider, and we can estimate the "average" coast lines using 100 km straight lines on the coasts and topological lines. This "cartoonish" version of the coast lines would make the computations of land area much easier.

Then once you decide on how many meters of sea level we need to ditch to get to 50% land mass, use the actual topological line at that level for your coastlines; so they look natural.

To make any plausible guess at the climate zones, we need at least a rough map of the final coastlines.

I know this is not a full answer, it is just advice on how to conduct your research.

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