The effects of having less water

[Blackhawk748]

Now, I know water is a hell of a heat sink and all that, but what would happen if a planet had, say, only about 30-40% of its surface area as water? Would it just bake? The hell does this do to weather systems?

[Radar]

Now, I know water is a hell of a heat sink and all that, but what would happen if a planet had, say, only about 30-40% of its surface area as water? Would it just bake? The hell does this do to weather systems?

Assuming that nothing else is changed (rotation, revolution, inclination angle, etc.), it would mean overall higher daily and seasonal temperature differences. So in far more places the climate would resemble the middle of Asia: extreme cold during winter, extreme heat during summer. Would the spread of temperature be even larger than there? Not sure really as the planet itself would get the same amount of heat (barring changes in albedo) and thousands of kilometers away for any decent sea you do not get that stabilizing effect on Earth either.

What would change for sure is that there would be far less rain due to significantly lower evaporation. So I would expect way more desserts around such a planet unless the local life developed some truly hardcore survival methods. Since the air would be that much drier, the average global temperature might be lower than on Earth as water vapor is a greenhouse gas (again, assuming that nothing else is changed).

Additionally, I would probably expect the seas to be somewhat more salty than on Earth without all that fresh water being mixed in constantly.

[Mechalich]

This sort of thing is highly variable, as it depends on both the total amount of water and the distribution. Consider that the percentage of Earth's surface area that is water varies significantly depending on the amount of water locked up in ice, with there being significantly less land surface if there's no ice - as it was during the Cretaceous - and significantly more if there's tons of ice - as there was during the last glacial maximum. Topography also matters, there's a big difference between reduced surface water coverage with mostly shallow seas compared to reduced coverage with mostly deep basins (most of Earth's water is buried under several kilometers of...more water).

Consequently, a world with 30-40% surface water could have several states. It could be a cold, icy tundra planet, or a dry, mostly desert planet, or a humid mostly rainy planet.

[Blackhawk748]

My general thought process was going for a cold arid planet. Basically, think a standard Western backdrop, but instead of it being hot, its cold.

Was just curious as to how to do that and I thought "Hey, less water does that" and then I realized there's like a million knock on effects of that. Oon top of the fact that I wanted the water that was available to be in either large lakes or small shallow seas.

[veti]

Oon top of the fact that I wanted the water that was available to be in either large lakes or small shallow seas.

That suggests a mostly-but-not-completely flat geography. Hills and mountains means streams and ponds, so we can't be having with those. No continental drift, no vulcanism. What does that imply about geology?

I guess we're drifting from "the effects of having less water" now to the question of "why is there less water, and what other implications does that have?"

Edit: Hydrogen, as far as I know, is the most abundant element in the universe, can't imagine there being very much less of that; and if there's a lot less oxygen, that will make the planet unfriendly to humans (which, I'm guessing although you haven't said as much, is not your intention). Left to themselves, hydrogen (reactive) and oxygen (insanely reactive) will bond together very easily. So what's stopping them?

[Mechalich]

My general thought process was going for a cold arid planet. Basically, think a standard Western backdrop, but instead of it being hot, its cold.

Was just curious as to how to do that and I thought "Hey, less water does that" and then I realized there's like a million knock on effects of that. Oon top of the fact that I wanted the water that was available to be in either large lakes or small shallow seas.

I'd suggest, for such a scenario going with Earth as the grip of an ice age comes to an end. It will still be colder than normal, and more arid, but retreating ice sheets leave flattened continents that have yet to rebound and their meltwater produces glacial lakes that can rise to the level of 'shallow seas.' Glacial Lake Agassiz, was massive, larger in area than all of the present-day Great Lakes combined and was by no means unique. For an alternate example, 80,000 years ago, what is now central Russia and Kazakhstan looked like this.

Note that you'd have deviations from the 'standard Western' backdrop because Western Europe's environmental conditions are actually fairly unique due to the Med and North Sea. I'd look more towards more continental European territories, Russia, Poland, etc., as a model. In particular there would be a sustained conflict between the more southerly wetter areas with forests and viable cropland and a vast pastoralist mammoth steppe zone before you reached tundra/ice sheets in the north.