[Subjectivist]

From time to time I come across the air pressure theory of climate change. The logic based version of the theory goes like this, greenhouse gasses like methane, carbon dioxide and water vapor are expressed in terms of their percentage of the total atmosphere in parts per million by volume. Therefore if the Earth's atmosphere was thicker the percentage or parts per million could be exactly the same but in absolute terms the amount could be substatially different. For example water vapor on average is 900,000 parts per million, far less in deserts and at the poles, much more at the equator. If sea level air pressure were 500 millibars the amount of water vapor would still be the same, but he total number of molecules would only be half a much so the effect would be half as strong, and conversly 2000 millibars would be twice as many molecules and twice the effect.

Scientists believe that the air pressure has been slowly falling for the entire existance of the Earth and during the Dinosaur era the pressure was 110% to 200% of what it is today. The problem is almost impossible to resolve because there is no way to directly measure past air pressure, and proxy measurements are strongly argued by both pro and con sides because what effect higher pressure has on geological chemistry is strongly debated.

[rollin]

April Fools?

[Subjectivist]

April Fools?

Not at all.

An earlier article in Chemical Innovation (1) showed that if you believe that biology’s mouse-to-elephant curve also applies to the flying creatures of the past, and if you also trust aerodynamic theory (which applies equally to flying insects, birds, and airplanes), then the giant flying creatures of the dinosaur age could only fly if the atmospheric pressure was much higher than it is now: at least 3.7–5.0 bar.

If this is so, it raises several interesting questions. For example, how did the atmosphere get to that pressure 100–65 million years ago (Mya)? What was the pressure before that? And how did it drop down to today’s 1 bar? Although we have no definite answers to these questions, let us put forth reasonable possible explanations.


Figure 1. Three possible alternatives for the atmospheric pressure early in Earth’s lifetime, given that it was at ~5 bar, ~100 Mya. What was the air pressure for the 97% of Earth’s life before the age of dinosaurs? We have three possible alternatives, as shown in Figure 1.

The pressure could have been at 1 bar throughout Earth’s earlier life, risen to 4–5 bar ~100 Mya (just at the time when the giant fliers needed it), and then returned to 1 bar (curve A).
The pressure could have been ~4–5 bar from Earth’s beginning, 4600 Mya; and ~65 Mya, it could have begun to come down to today’s 1 bar (curve B).
The atmosphere could have started at higher pressure and then decreased continuously through Earth’s life to ~4–5 bar ~100 Mya and down to 1 bar today (curve C).
The third alternative seems to be the most reasonable, so let us pursue it. We will also look into the composition of Earth’s atmosphere, but we will first discuss Earth’s surface and see how it affects the atmosphere.

.
From http://pubs.acs.org/subscribe/archive/c ... learn.html

[rollin]

Earth's atmosphere at 90 Bar, mostly CO2, would have been far too hot for the water vapor to condense and thus start the removal of the CO2 as the "paper" states.

Very high atmospheric pressures on the 3 to 5 bar level (denser atmosphere) would have changed the size of lungs and gills dramatically, making them much smaller than present. Plants would needed far less stomata than presently needed. I have never come across any evidence of that, it would be a hugely significant difference. Any evidence of that?

[ROCKMAN]

rollin - I see abundant evidence every time I look in a mirror. Oh...wait...I thought it said "Thin Hair..."

[rollin]

Damn, me too. Thanks for the laugh Rockman.

Would the thin air hypothesis actually mean things were better in the good ole days?

[Outcast_Searcher]

First, correlation isn't causation.

Venus, the mother of all greenhouse gas planets in our solar system, has a surface pressure over 90 times that of earth. With an extimated mass, size, and surface gravity at about 90% that of earth, that certainly doesn't seem to be the cause. Yet the surface temperature will melt lead. It's actually hotter than Mercury's hot side. Science says the cause is the composition of it's highly greenhouse gas' atmosphere.

Second, are we to then speculate that the well established pattern of ice ages is caused by atmospheric pressure changes?

Third, the atmosphere has changed tremendously over earth's history. Early on, it didn't have much oxygen. Lots of water (rain, forming oceans) and oxygen built up before widespread life was established.

...

This has the feel of the "bad" science the AGW denialist camp uses to try to claim there is no such thing as AGW. Searching on Google for "atmospheric pressure and climate change" the hits I got were related to the obvious fact that atmospheric pressure is closely correlated with short term WEATHER, and a few on seasonal weather impacts (like the Polar Vortex and the cold winter we had).

By now we should all know that short term weather patterns are NOT significantly correlated with long term climate change (including the hysterical media when there is a bad storm -- they're just as wrong as the AGW denialists when they do this).

[ROCKMAN]

Yep: between PO and AGW you just want to cry some times but that sh*t gets old after a while. Humor isn't always where you find it...sometimes you just have to make it up for the slimmest of reasons.

[Subjectivist]

Earth's atmosphere at 90 Bar, mostly CO2, would have been far too hot for the water vapor to condense and thus start the removal of the CO2 as the "paper" states.

Very high atmospheric pressures on the 3 to 5 bar level (denser atmosphere) would have changed the size of lungs and gills dramatically, making them much smaller than present. Plants would needed far less stomata than presently needed. I have never come across any evidence of that, it would be a hugely significant difference. Any evidence of that?

Actually there is a fair amount of evidence from two different records, fossilized leaves from eons ago do have far fewer stomata than earlier leaves. Second effect, insects in the Carbonatious epoch were very large includin dragon flies with a 1 meter wing span and ants the size of your hand. The gill comment doesn't make any sense to me, water breathers shouldn't show much change o fish in high altitude lakes would exhibit much larger gill structures than fish near sea level lakes. The argument of the paper I cited is that ancient land animals exhibit a different mass ratio than modern animals, one possible explanation of the different ratio is greater air pressure, but it is not the only possible answer.

[rollin]

This is amazing -from the "Earth's atmosphere before the age of dinosaurs"

"Figure 5 verifies the earlier statement that the present oceans are relatively young because they contain limestone not older than 200 million years. On the other hand, the continental landmasses are much older because, 100–65 Mya, the oceans and the atmosphere shared the free CO2 equally. Consequently, the pressure of CO2 in the atmosphere was ~8–10 bar in the age of the flying creatures (Figure 6)."

Do they know what they are saying? The earth's atmosphere had 20,000 times the amount of CO2 in it during the coal age!! Absolutely amazing that proteins could exist at those temperatures. This is a whole new kind of science!
Actually an old one - it's called Snake Oil.

[Tanada]

This is amazing -from the "Earth's atmosphere before the age of dinosaurs"

"Figure 5 verifies the earlier statement that the present oceans are relatively young because they contain limestone not older than 200 million years. On the other hand, the continental landmasses are much older because, 100–65 Mya, the oceans and the atmosphere shared the free CO2 equally. Consequently, the pressure of CO2 in the atmosphere was ~8–10 bar in the age of the flying creatures (Figure 6)."

Do they know what they are saying? The earth's atmosphere had 20,000 times the amount of CO2 in it during the coal age!! Absolutely amazing that proteins could exist at those temperatures. This is a whole new kind of science!
Actually an old one - it's called Snake Oil.

I only skimmed the citation so I didn't get as far as figure 6. I do know that for a long time the fact that Venus has 93 Bar of atmosphere has been seen as evidence that the Earth could have had a much thicker atmosphere than it presently does, but I do not recall actually reading a reputable source quoting anything like 8-10 Bar of CO2. On the other hand I have seen claims that total gasses added up to 3-5 BAR and that during the Carboniferous age there was also a 29-32% O2 ratio in the atmosphere, so not only were giant insects able to fly much easier, the O2 content was higher making it easier for them to absorb enough oxygen to support much larger body mass despite their primitive breathing organs.

As far as I recall from Earth Science class a very long time ago the primitive Earth atmosphere before the arrival of cyano-bacteria and photosynthesis was about 1 Bar CO2 and 2 Bar Nitrogen, but that was around 3 Billion years ago. In the intervening time two thirds of the Atmosphere has escaped for varied reasons, or been converted into Water in the oceans. The way I remember it the Aurora at the poles is a very slow influx of electrically charged Hydrogen from the Sun/Solar Wind. A little of that hydrogen gets combined with a little of the Atmospheric Oxygen when conditions are just right and eventually falls to the surface as water vapor. At the same time some Methane rises up into the Stratosphere where it is broken down by Ozone into Water Vapor and Carbon Dioxide and the water vapor sometimes breaks down into free hydrogen and free oxygen with the hydrogen escaping into space. The two processes are supposed to be in near perfect balance, but with a little to much one way or the other the sea level undergoes a very long term change.

By the way, it is the partial pressure of Oxygen that matters, if someone puts you in a diving chamber and increases the pressure so you experience 3 Bar with 7% Oxygen and 93% Helium you will breathe just fine, the partial pressure of Oxygen is the same as it is at 1 Bar of 21% Oxygen. Very deep technical divers use this fact, they do not use Nitrogen because it can cause Nitrogen Narcosis aka the raptures of the Deep, they use Helium. Humans can't handle too much Nitrogen or too much CO2, either one will make you have a narcotic like reaction and eventually lead to death. If you had a time machine and went back to an Era with 8 BAR CO2 you would die pretty quickly even if the temperature was perfectly comfortable and the partial pressure of Oxygen was the same as it is today. Astronauts use pure Oxygen but 1 Bar of that will kill you too, and it starts by making you blind, so they use it at about 350 Millibars of pressure, a little higher than the partial pressure on Earth but not extremely so.

[sparky]

.
the past atmosphere of the Earth is a complex subject ,
certainly there is a constant losse to space , there is an input , mostly from ice meteorites and comets
but on the whole it seems there has been a net losse

first there was the poisonning of the atmosphere with the by product Oxygene
Iron deposit in Western Australia show a massive reaction with Iron ,other minerals also were affected
oxides are everywhere

large quantity of CO2 got fixed into carbonate rocks , that's chalk and marble , in some place the deposits are miles thick
the CO2 fixed in coal ,natural gas and oil are of course now being released as a gas

there is the issue of the sun evolution , the main theory is that the Solar irradiance has been slowly increasing

and last but not least , the Earth rotation is slowing down , this is important ,
a fast spinning planet has less temperature variation ,

I'm not quite sure how all this tie together but it would seems the Earth was warm and moist for very long period
for the last ten millions years we seems to have cyclical instability with warm and cold periods alternating rapidly
( in control theory it's called an unstable harmonic response )
that's when a feedback loop has trouble balancing two oposite effect

[rollin]

Here is an interesting article on life and the evolution of Earth's atmosphere

http://www.amnh.org/learn/pd/earth/pdf/ ... sphere.pdf

[Subjectivist]

Here is an interesting article on life and the evolution of Earth's atmosphere

http://www.amnh.org/learn/pd/earth/pdf/ ... sphere.pdf

Interesting link, thanks for posting.

In case it wasn't clear, I am not saying thinning of the atmosphere explains how we got where we are. Quite the contrary if fact, what I am saying is greenhouse gas concentrations are a function of atmospheric density. Talking only about concentration completly ignores all the other factors that influence climate. CO2 amplifies the amount of water vapor in the air by warming it a little, thus strongly impacting the greenhouse effect. At the same time air density also influences water vapor totals because denser air holds more water vapor so it is also warmer than the current air. People traveling to the shore of the Caspian or Dead Seas are at higher air pressure and the air is consequently warmer than it would be at sea level in the same location. Temperature record from Haifa and the Dead Sea shore only a few dozen km apart show these effects, just like weather changes climbing any mountain.

[Tanada]

Interesting.
https://en.wikipedia.org/wiki/Dead_Sea#Climate
https://en.wikipedia.org/wiki/Haifa#Climate

To get all the way down to the Dead Sea from Haifa by car is 275 km, I am sure a direct as the crow flies is about half that from looking at an old topographical map.
Climate variability, the Dead Sea yearly average high is 30.40C/86.70F, yearly average low 21.90C/71.40F
Climate variability the port Haifa yearly average high is 24.76C/76.57F, yearly average low 15.94C/60.69F

They are not right next to each other, but the main effect is clearly much more warm and stable temperatures 1,000+ feet below mean sea level.

[sparky]

.
When calculating a gas mixure partial pressure response to heat ,
the formula is to calculate each gas independently then sum the parts

IE if there is a lot of CO2 it would be calculated as one CO2 atmosphere ,
then Nitrogen , then Oxygen ...etc..etc

So you are right , it matter , but as an absolute quantity of molecules not as a percentage as such

[Subjectivist]

[img]http://www.asc-csa.gc.ca/images/educateurs/ressources/scisat/trop2-trans-e.jpg
[/img]
http://www.asc-csa.gc.ca/images/educate ... rans-e.jpg

This graph shows how pressure decreases with altitude. Wikipedia says that the temperature drops on average 6.5C for every kilometer altitude increase.
http://en.wikipedia.org/wiki/Lapse_rate

For the lower part of the pressure curve the rate of change is 10% per kilometer of altitude change. My math isn't the best thing about me but that hints to me that 2 Bar of pressure would be like decreasing altitude 10 kilometers by going into a super deep mine, and at that depth the temperature change due only to pressure would be 65 C higher than at the surface. If that is correct then the Dinosaurs should all have been cooked by slow roasting so I Think I must have messed something up. Any help in understanding this effect would be greatly appreciated.

[sparky]

.
The pressure does not create the temperature
by itself it is just neutral , temperature must be gained from something , then re-emitted

As a though experiment think of a well insulated maze ,
mice come in , then come out ,
the time spend inside depend on the " density "of the maze
the more time spend , the more mice inside the more effort to get out
would increase the temperature inside

I know it's a bit silly , but gas density of the atmospheric maze does not heat up anything by itself
Total solar irradiance , internal planetary heat and the odd meteorite crash are the input
radiative cooling is the output

[Subjectivist]

.
The pressure does not create the temperature
by itself it is just neutral , temperature must be gained from something , then re-emitted

As a though experiment think of a well insulated maze ,
mice come in , then come out ,
the time spend inside depend on the " density "of the maze
the more time spend , the more mice inside the more effort to get out
would increase the temperature inside

I know it's a bit silly , but gas density of the atmospheric maze does not heat up anything by itself
Total solar irradiance , internal planetary heat and the odd meteorite crash are the input
radiative cooling is the output

So how much difference would 2 Bar of pressure make in surface temperature?

[rollin]

Air density 2.7 billion years ago limited to less than twice modern levels by fossil raindrop imprints

"According to the ‘Faint Young Sun’ paradox, during the late
Archaean eon a Sun approximately 20% dimmer warmed the early
Earth such that it had liquid water and a clement climate1.
Explanations for this phenomenon have invoked a denser atmosphere
that provided warmth by nitrogen pressure broadening1 or
enhanced greenhouse gas concentrations2. Such solutions are
allowed by geochemical studies and numerical investigations that
place approximate concentration limits on Archaean atmospheric
gases, includingmethane, carbon dioxide and oxygen2–7. But no field
data constraining ground-level air density and barometric pressure
have been reported, leaving the plausibility of these various hypotheses
in doubt. Here we show that raindrop imprints in tuffs of the
Ventersdorp Supergroup, SouthAfrica, constrain surface air density
2.7 billion years ago to less than twice modern levels. We interpret
the raindrop fossils using experiments in which water droplets of
known size fall at terminal velocity into fresh and weathered volcanic
ash, thus defining a relationship between imprint size and raindrop
impact momentum. Fragmentation following raindrop flattening
limits raindrop size to amaximum value independent of air density,
whereas raindrop terminal velocity varies as the inverse of the square
root of air density. If the Archaean raindrops reached the modern
maximum measured size, air density must have been less than
2.3 kgm23, compared to today’s 1.2 kgm23, but because such drops
rarely occur, air density was more probably below 1.3 kgm23. The
upper estimate for air density renders the pressure broadening
explanation1 possible, but it is improbable under the likely lower
estimates. Our results also disallow the extreme CO2 levels required
for hot Archaean climates8."

http://faculty.washington.edu/dcatling/ ... _Suppl.pdf