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

[guyanonymous]

Thanks for the suggestions!

I just want to figure it out enough that it can be there, the event most distant in the past that is dealt with on this planet. It's what happens after it sets the stage that is most important.

I'll likely work on the idea of a massive belt of ice intersecting the planet's orbit long enough for this volume of water to accumulate in the atmosphere, but brief enough to overwhelm the people, killing them all. Muahhaha. Or right, inside voice.

[töff]

It's all rediculously interconnected

I'll sing that hymn with ya, brother!

You want great answers, ask UN Climate Change what they know...

... but not that one

[su_liam]

... but not that one

They probably know as well as anyone.

[Juggernaut1981]

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.

I'm just thinking of the specific heat capacity of water, compared to most other things, and its stupidly large. Water's specific heat is about 4kJ/kg... Iron is 0.4kJK/kg

It just takes a lot more energy to warm up water. So depending on how much you dump in there, how fast, etc, etc, etc you could cause a nice dip in the temperature. I doubt the energy of the asteroids would compensate for the heat capacity of the water.

[Nexis]

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.

Ok how about this.

You say the world is a cold world. This could be the apex of a long growing ice age of the world. Most of the north and South hemispheres are under massive ice sheets, This will bring the sea level down a lot. Our last ice age reduced the sea level well over 300 m. Now the population are gathered mainly along the equatorial belt which has a cold temperate climate at best. This will explain the use of the sea for heat and power. Now you need some thing to happen that is quick but not so sudden, like an impact, that will destroy all things. I propose that the ice is crushing the continental plates together and now one of the mid sea faults fails and splits wide open causing a massive earthquake, tsunamis and volcanic action that cascades along all the major faults spewing forth magma, hot gases and a lot of other nastiness. This quickly heats up the seas and air melting the glaciers very quickly raising the sea level at an alarming rate. As the pressures dissipate the volcanic activity subsides over time but the big melt is unstoppable as the air and sea are warmer and greenhouse gasses are heating up the air. This disaster will take a few years to complete and devastate crops technology and displace and kill lots of people. All the water that was trapped in the ice is now flooding all the lowlands that were once coastline and if the land was low to begin with... Man that was long but fun.

[guyanonymous]

More to think about - I like it, keep the suggestions coming!

And thanks!

[töff]

specific heat capacity of water, compared to most other things, and its stupidly large. Water's specific heat is about 4kJ/kg...takes a lot more energy to warm up water. So depending on how much you dump in there, how fast, etc, etc, etc you could cause a nice dip in the temperature. I doubt the energy of the asteroids would compensate for the heat capacity of the water.

If the ice meteors are "burning up on reentry" to steam in the upper atmosphere, there ain't no reason to worry about this at all.

I smell a stratometeorological thesis here: the caloric limit of net energy gain per the mass of an ice asteroid.

[guyanonymous]

ha....

OK...so even if they average r. was 20m across, I'd still need over a trillion of these things to connect.

BUT...I revisited my spreadsheet where I worked this stuff out....there's actually only a difference of 10% between the volume of ice in Antarctica. etc, and the amount I need. So an event that causes my more substantial ice caps (fitting in with my living-near-the-ocean plan) to form would work.

The trick is to have it happen in a catastrophic (i.e., number of hours) manner. But that much ice, no matter what, isn't going to melt that quickly.

Hmm....

[Coyotemax]

Solar flare-up?

Then again any flare of a magnitude that would melt the polar caps in a matter of hours is likely to incinerate the rest of the surface to a depth of several dozen miles, I imagine

[waldronate]

Assuming an impact speed of roughly 25 miles/sec (roughly 40 000 meters/sec) then the kinetic energy of that beastie will be about 800 000 000 joules / kg (KE = MVV). Assuming the ice starts out at -270C then it takes 1 130 000 joules to heat the ice to 0C, ballpark 330 000 joules of energy to melt it, 418 000 to raise it to boiling, and another 330 000 to turn the ice into steam. That's a grand total of 2 208 000 joules to take a kg of ice from interstellar temperatures to just over boiling. That only leaves about 798 million joules of energy to heat that kg of ice.

It's why ice meteors make an incredibly bright light and a huge shock wave as they are decelerated rapidly. No real worry about cooling things off by dropping rocks from orbit. The big problem is to keep from frying the planet.

A 10cmx10cm column of water weighs 1kg per 10cm. An 800 meter column over that area weighs 8000kg. 8000 * 800MJ (ballpark) gives a delightful stellar-grade plasma if you drop it all at once.