In the thread about crossing the oceans with bridges, someone suggested emptying the oceans, which inspires my question. Suppose all the oceans, seas, etc. were magically emptied of water. I would think that the air would immediately sink onto those spaces to fill the sudden vacuum, and we would be left at relative Everest-like altitudes. And unless you happen to live right next to an ocean or very deep lake and can start hiking down the the bottom, you’re screwed.
Leaving aside the question of us all dying of thirst, how what would happen to atmospheric pressure at typical altitudes most people live at? Oh, fuck that, let’s talk about where I live at – the upper Midwest. Would temperature also drop drastically?
Need answer fast! There’s a sale going on at the Burlington Coat Factory!
The average depth of the ocean is 12,430 feet, and covers 72% of the Earth’s surface, so everywhere would become effectively about 8,950 feet higher in elevation. That’s a first-order figure, and there’d be effects that depended on the actual topography, but it should still be around 9,000 feet.
Survivable for people below one or two thousand feet in elevation, I’d think, to make it to lower elevations, even if they aren’t near a shore.
I don’t know if it would work out that way. Since three quarters of the world’s surface is under sea level, a correspondingly large proportion of the atmosphere would also sink to below that level. And the atmospheric pressure at heights above (the former) sea level may be substantially lower than the linear distance would suggest.
If the former sea level is now 9,000 feet above the average surface height, but there is 3 or 4 times the surface area at the bottom, why wouldn’t the 9,000 feet pressure be similar to what the pressure is today at 18,000 feet, or 27,000 feet, or even 36,000 feet?
We are (or maybe I) are thinking about this too much in terms of height and not enough in terms of volume. What is the volume of the world’s water? If you then removed that volume from the world’s atmosphere by moving it into the space formerly occupied by water, how much volume would be left above (the former) sea level?
Of course, this wouldn’t be a linear conversion either, as air is compressible as water is not. Atmospheric pressure at the bottom of the (former) ocean would be higher than pressure at sea level now because it would have several more miles of atmosphere pressing down from above.
Assume the atmosphere is a slab of XYZ square miles (total surface of the earth). Assume the ocean is a pyramid such that the base has the number of square miles the ocean has. And the pyramid has a base width to height ratio such that the average height of the pyramid is average depth of the ocean.
Use that info to figure out how much of todays atmosphere can “drain” into the ocean basin.
I’m too lazy to do the actual math but that would be my first start.
The volume of the hydrosphere is 310 million cu. mi. The volume of the atmosphere below 2 miles above current sea level is about 400 miilion cu. mi. That’s enough to see that the atmosphere at current sea level will have dropped to that of areas thousands of feet higher in elevation. People in Denver, Mexico City, and other elevated locations may die of apoxia. Numerous people below those altitudes will have difficult breathing. All uncontained water rapidly evaporates, so everybody will be very thirsty.
I’ll kick the ball in a somewhat answerward direction. It looks like the volume of (i) the oceans is 1.3 billion cubic kms and (ii) the atmosphere is 4.2 billion cubic kms (although there’s a lot of complications with each of these numbers, as explained in the cites below).
The quick answer seems to be that we’d all get about 31% higher than we are right now (i.e., 1.3/4.2). Multiply that by the thickness of the earth’s atmosphere to see how many feet we’d gain. I’m pretty sure that means we’re screwed.
Ok, this is kinda interesting. Less than an hour ago I looked for “ask the scientist” websites, and submitted this particular question to two different sites:
I’m stunned that I’ve already received a reply from an earth scientist named Ken Rubin at the University of Hawaii. His answer was this:
I cannot figure out why air pressure would not drop significantly. Then again, he clearly didn’t spend a ton of time doing calculations on this.
I really hope the other site (run by the US Geological Survey) also responds so I can compare answers.
Ken hasn’t even spent much time thinking about this. That, or he misunderstands the question.
At the VERY least, if the average ocean depth is 4 km, somebody at what used to be at sea level will be about 4 km higher atmospheric pressure wise after the ocean is gone. And probably more like 2 to 4 times that depending on what ratio floats your back of the envelope boat.
That height is anywhere from “man, its kinda hard to breath” to “pass out almost immediately”. And thats for folks starting at sea level.
Dunno if his answer is right or not, but his response doesn’t suggest to me that he didn’t understand the question I was asking.
The only way his response makes sense to me is if he doesn’t consider the pressure difference between sea level and 12,000 feet to be much of a change. Though it seems to me it would be a substantially bigger difference than that, since there is so much more area of ocean basin than there is of today’s landmass.
I’m thinking he is thinking the atmospheric pressure at the average elevation that WAS 4km below sea level before the sea left would be about what the atmospheric pressure was at sea level when there was a sea.
And as a first think about it for a momen WAG I’d say that would roughly be true.
While off the top of my head I’d agree with most of what he said, a few things bother me.
Where is this 20 percent coming from. Seems to me thats the about the LEAST it could be.
Also a few points. IIRC the FAA requires supplemental oxygen above 10,000? feet so there’s one data point for how high starts to be a problem.
Also, I know someone who was at about 10,000 feet to snow ski. They went a few thousand feet higher and needed oxygen and had to go back down. So, thats another data point.
Then, there was a Top Gear Episode where the guys tried and failed to drive over about a 16k pass. They couldn’t take the thin air. So thats yet another data point.
So, my WAG is 1. Its gonna be a bit more than a 12 thousand foot equivalent gain. 2. Without allowing much time for aclimation, even people at what was sea level are gonna be hurting a bit. 3 People who started out at a significant altitude are gonna be screwed.
Well, I personally have strolled around in the Rockies above 10,000 feet, and while I was a but short of breath, I’m reasonably confident it wasn’t life threatening.
Which 20%? In the first email he says 20% less O2 then there is at today’s sea level. In the second he says the atmosphere column would be about 20% lowered, in altitude I think.