I'm trying to figure out what sort of mechanism might...

[guyanonymous]

I'm trying to figure out what sort of mechanism might <within reason> increase water sea levels on a fictional planet by 800m around the globe. In the end, the planet ends up a typical mishmash of climate zones. Most of humanity is destroyed.

That works out to 2.8E+19L of water for my planet. (I'm not worried about salinity levels - though it's something I should think about)

I'm ok with the water slowly,over thousands of years, receding back to "normal" levels, but it's not necessary.

Ideas?

I've thought about meteors (I think those are the ones made out of ice) hitting, etc, but the size involved would destroy the planet. Even if thousands smaller did so, they're still too large.

I'd like the solution to at least be in the realm of plausibility...not something "magical", if that makes any sense.

[töff]

Melted polar caps comes to mind.

So do comets, which can contain a lot of water (ice). You might have one or many comets get disturbed out of stable orbit and crash into your planet.

You might also be more gentle about it, and postulate a big ring of ice particles (such as Saturn's rings) that your planet passes through. Imagine the Asteroid Belt, but smaller and wetter (icier). Again, you'd need an astronomical event to bring your rocky planet into proximity with such a mass of ice particles.

Then there's always artificial hydration. Maybe fish aliens are trying to terraform the planet. Let the alien engineers haul in some water!

[Ascension]

At the extreme edge of plausibility you could have a giant earthquake swallow a whole continent, thereby pushing water levels up. Or you could have some volcano spew out some enormous amount of lava. Neither is all that realistic but it avoids giant craters and fires left over from impacts. My first thought was as Toff says...icy comets.

[guyanonymous]

I'd thought about passing through some sort of ice-asteroid belt, but if most things are burnt up in orbit, does that remaining matter (i.e., H2O and H and O) end up inside or outside of the atmosphere?

If the particles are the size of a loaf of bread vs. the size of a VW bug vs. the size of a movie theatre, does that make a difference to where the matter ends up?

[töff]

Water that "burns up" in the atmosphere recondenses and enters the planet's water cycle.

It's the dinosaur-killer effect you're wanting to avoid ... the transmission of a huge amount of energy into the planet's crust, kicking up dust that obscures the sun, and also causing earthquakes & tsunamis.

If you just say all the ice meteors were no larger than the hippie vans, you'd be fine, and you can dump as much water as you like into the system from space.

[guyanonymous]

At the extreme edge of plausibility you could have a giant earthquake swallow a whole continent, thereby pushing water levels up. Or you could have some volcano spew out some enormous amount of lava. Neither is all that realistic but it avoids giant craters and fires left over from impacts. My first thought was as Toff says...icy comets.

That's why I'm wondering about size of particle and where the residual matter ends up....if everything can burn up in the atmosphere, but the water end up within the atmosphere, I don't have to worry about craters - which, really, I don't want to do, as I've got the planet already designed.

I, obviously, should have mentioned that earlier.

Initially the planet will be fairly cold, with most of the residents located close to the ocean using it's energies to generate heat, food, etc.

There are several billion residents of a fairly old civilization.

Then the "incident" happens.

90% of population killed....water levels risen (covering up most cities)...in subsequent years, starvation, disease, nature's turmoil at massive climate change, kills of most of the rest.

1000 years later, scattered small groups survive, though almost all under 5 people (mostly family groups). They are hunters/gatherers/ and exist at an animalistic level in terms of survival of the strongest.

There's the nutshell of my prehistory - but I want to figure out this event before I move forward.

[guyanonymous]

Water that "burns up" in the atmosphere recondenses and enters the planet's water cycle.

It's the dinosaur-killer effect you're wanting to avoid ... the transmission of a huge amount of energy into the planet's crust, kicking up dust that obscures the sun, and also causing earthquakes & tsunamis.

If you just say all the ice meteors were no larger than the hippie vans, you'd be fine, and you can dump as much water as you like into the system from space.

This would be great!

Would the increase in matter result in an increase in atmospheric pressure?

[Juggernaut1981]

Okay, long list of wierd things that could happen...

Comets come into atmosphere and melt leaving water and tiny dust landing.
Additional water will increase the oceans.
Water takes lots of energy to heat (in chemistry terms) so more water = more energy to maintain temperature = planet cools.
Enough water (e.g. comets landing to cause 800m sea level rise) would eventually accumulate into an ice age if the planet wasn't heated well enough.


So I'm guessing your society will probably still be stuck in the leftovers of an ice age. Atmospheric pressure is more regulated by temperature than things falling from space, but water from space will drop worldwide temperature if there is enough of it... and then change atmospheric pressure...

It's all rediculously interconnected. You want great answers, ask UN Climate Change what they know...

[töff]

Would the increase in matter result in an increase in atmospheric pressure?

If the matter becomes gas in the atmosphere, then yes. Our atmosphere is mostly free nitrogen, about 1/5 free diatomic oxygen, plus tiny little trace gases like argon.

But you can have anything you want in your comets ... just plain water and dirt would be fine, and if they don't bring in any atmospheric gases, then there's no increase in air pressure ... okay, maybe a little, due to the increased water volume ... I'm not really sure, to be honest. I kinda doubt it. Google for "vapor pressure" though. I once tried to figure the vapor pressure for neon on Pluto ~ omg I'm such a geek.

[töff]

Water takes lots of energy to heat (in chemistry terms) so more water = more energy to maintain temperature = planet cools.
Enough water (e.g. comets landing to cause 800m sea level rise) would eventually accumulate into an ice age

I dunno about that. Sure, keep dumping ice on a planet, it'll cool ... but solar energy plus core-produced radioactive heat, I would think, would soon bring back equilibrium.

Plus, the energy of the ice meteors themselves, as they brake into the planet, would ADD to the total energy of the system.

This is not an effect I would worry about unless I thought it was a fun thing to include.