Re: world with less air pressure - survivable?

On 26 nov, 16:07, Brian Davis <brda...@xxxxxxxx> wrote:
On Nov 25, 2:48 pm, mn_mn <alexwilliamruss...@xxxxxxxxx> wrote:

How could loss of air happen?

See a response lower in the thread. In short, I don't think it could,
in any short-term (less than evolutionary timescale) fashion.


I think earth has only a small greenhouse effect so less air might not
mean temperatures change much.

Earth's greenhouse effect is about 33 K. so without an atmosphere,
picture where you live roughly 33 deg-C (60 deg-F) colder. Yeah, I
think there's an important effect here :). The thing is the greenhouse
effect is closely tied up with a large number of things - including
composition, but also the atmospheric temperature gradient. To first
order the temperature gradient wouldn't change

To the next order, it would.

, but the height of the
ozone layer (and thus the tropopause and stratopause) certainly would,
changing things significantly. A thinner atmosphere would certainly
effect it, likely make the global temperature drop...

Actually, global temperature should rise because of lower air density.
At the surface of ocean, the air is warm, saturated with water (100%
relative humidity) and its absolute humidity is given by the vapour
pressure of water.

Now, the atmospheric temperature gradient near surface is low. It is
low because of wet adiabat: as the air rises and cools, some of the
water rains out, and the latent heat slows down the adiabatic cooling
of nitrogen and oxygen.

As the air rises higher, the temperature gradient increases. Going up
into colder air, the water vapour pressure drops, and so does the
mixing ratio of water. The relative humidity stays at 100 %, and as
the air goes further up the remaining water continues to rain and snow
out, but there are ever smaller quantities of water left to release
its latent heat and slow down the adiabatic cooling of nitrogen and
oxygen.

Now decrease the amount of nitrogen and oxygen.
The relative humidity at sea level is unchanged. So is the absolute
humidity/water vapour pressure at sea level, at first.

But the mixing ratio of water has increased. Thus the adiabatic
gradient drops.
There is less nitrogen and oxygen that the latent heat of rain has to
warm.

Which means that the temperature at each level above sea level rises
dramatically. And the saturation water vapour pressure in upper airs
also rises.

Thus, there is more water vapour in total between sea surface and
outer space, on account of the warmer and moister upper atmosphere.
And the stronger greenhouse effect causes the ocean to get even
warmer...

but it's going
to be tricky to work out in detail.

Less air also means less conduction and convection to lose
heat to space.

...and conversely more radiation to loose heat to space (conduction
and convection actually don't loose *any* heat to space. Think about
it). Less air means more efficient radiative transfer, period.

Storms with less air are less destructive.

Not really. You seem to be assuming the storms would have the same
airspeeds, which again may or may not be true.

Would air be drier?

Why would it? The potential amount of water vapor in the air is set by
the temperature - nothing else. Density and pressure don't enter into
it. So if you want to talk about the global moisture, you need to talk
in terms of energy balances (a 2nd-order effect) not pressures.

Overall I would guess we could lose 1/3 of atmosphere without major
changes, 1/2 of atmosphere and biosphere keeps producing some oxygen,
and 8/10 of atmosphere would mean people live in spacesuit and grow
foot in pressurized greenhouses unless they want ocean algae,

I'm guessing you could drop it to 50% and life would handle it just
fine. Mass extinctions certainly, but if you change any of the basic
parameters by anything like this that's likely to happen.

and below 10% the water even in algae and bacteria would boil so only
minor bacteria deep in ocean survive.

...and if you drop the global pressure so low you start evaporating
the oceans, the atmospheric pressure starts to go up (with a higher
percentage of water vapor in the mix). Depending on the surface
temperature, that might end up being rather high.

Or what if people by spacecraft or maybe a stargate drain the oceans,
can ocean-drained planet survive?

Let's see... can a world without water support water-based life? I'm
just guessing here...

Draining most of the ocean would not need to mean removing all water
and making Earth as dry as Venus.

What would happen to Earth´s climate if the stockpile of liquid water
were decreased so that it only covers 7% of surface, not 71+ ?
.

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