Air density with a significantly higher sea level

[CMaso]

TL;DR Summary

If Earth's volume of liquid seawater increased to cause sea level to rise significantly (miles), how dense would air be relative to old level?

2 scenarios:
1) Situation in the movie "2012", where volume of ocean water hasn't changed, but worldwide seismic activity has caused massive tidal waves. In one scene, a ship is sailing by Mt. Everest close to its peak. In such a scenario, I believe the air density outside the ship would the same as though it were at 27K ft. above current sea level; i.e., much too thin for anyone who hasn't been spending months acclimating to it (or isn't a Sherpa).

Correct?

2) Situation where volume of Earth's liquid ocean water DOES change (from, say, melting of all polar ice, or introduction of more water from outer space such as ice comets), and this causes average sea level to rise several miles.

How would the air density at the new sea level compare to air density at the old sea level?

I'm thinking, on the one hand, the atmosphere is now further from the Earth's center, so there's less gravity acting on it. But on the other hand, overall volume of atmosphere hasn't changed; all of the air that used to be at the old sea level has just been "pushed up" to the new sea level by the ocean (or most of the air--some would no doubt mix into those extra vertical miles of water). So I'm not sure if air density at the new sea level would be thicker, thinner, or the same as air density at the old sea level.

 

[anorlunda]

The ice has melted before. Sans many new asteroids, the past is an indicator of how much levels could change in the future. That's nowhere near the 8848 meters elevation of Mount Everest.From
https://en.wikipedia.org/wiki/Past_sea_level

 

[CMaso]

The ice has melted before. Sans many new asteroids, the past is an indicator of how much levels could change in the future. That's nowhere near the 8848 meters elevation of Mount Everest.

Thank you, but what I asked is what if (for whatever reason) sea volume increased such that sea levels rose by several miles -- how the air density at the new sea level would compare to air density at the old sea level.

 

[256bits]

Summary:: If Earth's volume of liquid seawater increased to cause sea level to rise significantly (miles), how dense would air be relative to old level?

I'm thinking, on the one hand, the atmosphere is now further from the Earth's center, so there's less gravity acting on it

How much less do you think?

 

[Arjan82]

So let's simplify a bit. Forget about seawater and just consider these cases:

The radius of the Earth increases by 9 kilometers or so (i.e. about the height of the mount Everest) without changing the total mass of the earth, and without changing the total mass of air out of which the atmosphere exists. What would the pressure be at the new 'sea level'?

Although the gravity is indeed a bit less, 9 kilometers on a radius of 6371 kilometers (the radius of the Earth according to Google) is not a lot. The gravitational force changes with $r^2$, so this effect is really small. The surface area of the Earth would be a bit larger, by about a factor of (6371 + 9)^2 / 6371^2 = 1.002, so about 0.2% increase in surface area. This would give the air somewhat more surface area to spread over, but this effect is also rather small. Therefore I think the pressure at the new sea level would be pretty much the same as the old one.

The second scenario is, as I understand, a local but large 'bump' on the surface of the Earth (I didn't see the movie...). But then the same would happen as on the mount Everest, which is also just a big 'bump' on the surface of the Earth :). So the pressure would be much lower. Air will flow towards the lowest elevations and thus away from the higher elevations. Therefore I think you are correct indeed.

 

[Chestermiller]

If, somehow, there was a layer of water 9km thick added to the Earth's surface, what would this amount to in terms of the mass of the earth? What percentage increase would this make in the mass of the earth?

What percentage increase in the radius of the Earth (up to the new water level) would there be, and what would be the new acceleration of gravity at the new water level? What percentage increase in the surface area of the Earth (at the new water level) would there be? If the mass of the atmosphere did not change, what would be the change in the mass of atmosphere per unit area of water surface. How much would the weight per unit area of atmosphere change at the surface? If the temperature profile of the atmosphere did not change, how would that affect the density of atmosphere at the surface?