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How do sea levels impact air pressure on Mount Everest?
April 11, 2014 7:42 AM   Subscribe

As the sea level rises and falls, how does that impact air pressure on Mount Everest?

Climbers on Mount Everest typically use bottled oxygen because of the low air pressure that reduces the amount of oxygen in the bloodstream. If the oceans rose, would it become easier to oxygenate your blood at high altitudes? And if the sea level dipped, would it become harder?

These are the things that keep me up until 3am, staring at a dark ceiling and mustering my inconceivably small amount of meteorological and climatological knowledge.
posted by burnfirewalls to Science & Nature (13 answers total)
 
Air pressure has to do with how much air is above you, not how much air is below you. So exact height of "sea level" isn't relevant.
posted by i_am_a_fiesta at 7:46 AM on April 11


Everest is 29,000 feet tall. The kinds of rise in sea level we're facing with climate change are in the single-digit range. Six feet of ocean rise, for example, is plenty to cause massive problems for human settlements which tend to be located right by major bodies of water, but the mountains won't even notice it.
posted by Tomorrowful at 7:49 AM on April 11 [4 favorites]


As a thought experiment, lets say that all of the antarctic ice melted and the oceans rose by twenty meters. What impact would that have on the density of the atmosphere (no matter how small) with the interaction of earth's gravity?
posted by burnfirewalls at 8:20 AM on April 11


You say "no matter how small," but the thing is, you're talking about changes that would be absolutely immeasurably tiny. Twenty meters is nothing compared to the height of Everest or the atmosphere.

As for gravity, it changes nothing. Gravity has nothing to do with density - it's about how much mass there is, not how it's arranged. You could instantly crush the Earth into a ball one foot on a side, and the moon's orbit around it would be totally unchanged.
posted by Tomorrowful at 8:32 AM on April 11


I would argue that you would actually reduce the air pressure at the top of Everest with sea level rise.

The biggest factor in sea level rise is due to moving ice from the continents to the oceans. If you just moved all of the ice from the continents to the oceans as floating icebergs, sea level would rise as expected, but it wouldn't change the air pressure at all because the earth would have exactly the same volume as before. You've just moved ice from one place to another. So to a first approximation, sea level rise does nothing to air pressure. The volume of the earth which displaces air is unchanged.

But if you then melt the ice, it does reduce its volume by about 9%. This reduces by a tiny amount the average diameter of the earth that displaces the air so there will be less air at 29,000 feet. The change is tiny because the volume of ice is small compared to the total volume of the earth.

This ignores the counteracting effect of expansion of water due to a temperature increase, but if you consider melting of all of the ice, the decrease in ice volume is much bigger than the increase due to water expansion.
posted by JackFlash at 9:46 AM on April 11 [4 favorites]


I think the OP is asking, wouldn't the rise in sea level "push up" (displace) the air, thereby increasing the amount of air above you? The OP is not asking about gravity at all, and of course it wouldn't change gravity.

OP, to answer you question, I would think not. That ice is already "pushing up" the air where ever it is now. The Earth's volume isn't changing.

Actually, it might even decrease since water is one of the few compounds that becomes less voluminous when going from solid to liquid, (because of ice's crystal structure). In the other direction, since it would be warmer it would gain some volume there, but the former effect is more powerful, which is why frost/thaw creates cracks in materials over time.

Twenty meters is nothing compared to the height of Everest or the atmosphere.

The tinest speck of dust in the most distant part of universe has a gravitational effect on you. The OP isn't asking about how measurable it is, just if it's there.
posted by spaltavian at 9:49 AM on April 11 [1 favorite]


But, another factor is that melting the ice caps is going to put more water vapor into the air, (a) because a lot of water is unlocked from its previously frozen state, and (b) because there going to be more open water from which evaporation occurs. An atmosphere that is more humid because of all this evaporation is going to be denser, on average, which would tend to increase its pressure from top to bottom.
posted by beagle at 9:52 AM on April 11 [1 favorite]


Good point, beagle.
posted by spaltavian at 9:53 AM on April 11


The addition of water vapor doesn't increase air density. It reduces it. That is because a molecule of H2O weighs less than a molecule of N2 or O2.
posted by JackFlash at 9:56 AM on April 11


Normal changes in weather cause the atmospheric pressure to change by up to about 3%, approximately the same as a 1000 foot change in elevation.

A change of a hundred feet in sea level (huge) would therefore change the pressure by less than that already caused by weather.
posted by phliar at 10:28 AM on April 11


If you link sea level rise and fall to the melting or growth of glaciers, then there is another factor to consider: isostasy. The model for earth structure states that the outer most layer called the crust is "floating" on a more dense layer below called the mantle. So when weight is added to the crust, it causes the crust to depress or "float lower" in a sense, like a bunch of people climbing into a boat causes the boat to float lower. Conversely, removing weight from the crust does the opposite. It would cause the crust to "bob up" or "float higher". So, if all the glacial ice on Earth were to melt, sea level would indeed rise. But the removal of ice from the continents would cause the crust (which includes mountains of course) to rebound--meaning an increase in elevation. This is formally called post-glacial rebound. This increase in elevation would mean lower air pressure at the top of a mountain compared to the pre-rebound state. But that rebound takes time because the viscosity of the mantle is not like water. For example, parts of Scandinavia are still rising from the melt off of the glaciers 10-15 thousand years ago. The highest rebound rates are in northern Sweden at almost 1 cm/year.
posted by Seymour Zamboni at 11:23 AM on April 11


The addition of water vapor doesn't increase air density. It reduces it. That is because a molecule of H2O weighs less than a molecule of N2 or O2.

OK, but the H2O is not actually replacing any of the N2, O2 or other gases in the atmosphere. So it is going to add to the total mass of the atmosphere. Wouldn't adding mass to the atmosphere tend to increase the pressure at all altitudes?
posted by beagle at 11:28 AM on April 11


An atmosphere that is more humid because of all this evaporation is going to be denser, on average, which would tend to increase its pressure from top to bottom.

Whether or not the more humid airmass is denser is going to be strongly dependent on temperature as well. And if you are getting this extra water by melting all the glaciers, an overall warmer atmosphere is implied.
posted by Seymour Zamboni at 11:33 AM on April 11


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