Hi All,
I have a question about how or if our atmosphere might thicken assuming any predictions about Global Warming.
This is not a discussion on whether it happens or not or how fast it happens.
If the surface or the earth heats, I assume so would the atmosphere. Heat should expand our atmosphere making it thicker at higher altitudes. Am I wrong?
If so, would it make it easier to climb mountains like Everest?
Thanks,
Steve
The best I’ve found for the coefficient of volumetric expansion for air is 3.7 x 10[sup]-3[/sup] K[sup]-1[/sup]. If we just multiply that by Everest’s elevation of 29,029 ft (8,848 m) we get about 110 feet (33 m) per 1.6ºF (1ºC) of warming.
The death zone starts at 26,000 ft (8,000 m), so a hundred feet would only be a little help.
Tricky. In the simplest model, more or less an exponential atmosphere, you’d expect the density to fall at the lowest altitudes as the average temperature increased, and to rise at the higher altitudes. The atmosphere does indeed get “thicker” – meaning the distance from bottom to “top” (however we define that) gets greater. But because the total amount of air can’t change, that means increases in density at some altitudes must be compensated for by decreases at others. Indeed, on average the density has to decrease if the total volume increases. Everest is kind of smack in the middle, I’d say, not low enough to believe the density would clearly decrease, and not high enough to say it would clearly increase.
And that leaves out the fact that the actual atmosphere has substantial deviations from the simplest model, particularly with respect to temperature, which strongly affects how the density translates to pressure.
I interpret the OP’s use of “thicker” to mean “more dense”, not “taller”.
Well, if that’s what he means, I’m sure you could be the first to attest that warmer air is less dense. Hot air balloons aside, is it not actually sufficient sometimes to affect aircraft takeoff performance? I read somewhere that early 747s, with somewhat underpowered engines, had quite the takeoff roll if fully loaded and the day was really hot.
See, I interpreted it to mean “less dense”, which would cause it to expand and become “taller”, aka “thicker”.
I suspect the OP was thinking PV=nRT and if it got hotter the pressure would rise. And that pressure and “thicker” were the same idea.
The obvious flaws in that thinking being that the atmosphere isn’t inside a closed container of fixed size, and that density & pressure are two different things.
Agree it was a badly thought out and poorly worded question. Obviously our OP, though well-meaning, is past the edge of his physics.
Everybody “knows” it’s hard to climb Everest because the air is so “thin”. Lots and lots of pop science articles & nature shows say that. And he says he wonders whether GW would make climbing Everest easier because it would thicken the air up there.
Or at least that’s how I parsed it.
I hope he’ll come back so we can confuse each other some more! 
The op is kinda in “assume a spherical cow” territory by only looking at the expansion of gases due to temperture.
Another thing that needs to be considered is water vapor. Water vapor generally isn’t considered to be a greenhouse gas even though it factors into the greenhouse effect because the amount of water vapor that the air can hold depends on the temperature. If you throw a bunch of water vapor into the air, all it does is condenses out somewhere else.
However, in this case the OP is changing the temperature, which means that the amount of water vapor in the air will also increase. This will likely have a significant effect on the atmosphere’s thickness per the OP.
How all of this wll play out in the atmosphere and what other things will come into play are beyond my knowledge of global atmospheric physics.
Uh… I hate to correct a respected and very smart SDMBer, but water is a critical greenhouse gas in Earth’s atmosphere. It’s just not the one anthropogenic activity is directly increasing.
[Quote=NASA]
Water vapor is known to be Earth’s most abundant greenhouse gas, but the extent of its contribution to global warming has been debated. Using recent NASA satellite data, researchers have estimated more precisely than ever the heat-trapping effect of water in the air, **validating the role of the gas as a critical component of climate change.
**
Andrew Dessler and colleagues from Texas A&M University in College Station confirmed that the heat-amplifying effect of water vapor is potent enough to double the climate warming caused by increased levels of carbon dioxide in the atmosphere.
[/quote]
From http://www.nasa.gov/topics/earth/features/vapor_warming.html, emphasis added
In AGW, it’s not the primary lever. CO[sub]2[/sub] is. But water vapor comes along, and when it does, it makes the warming even worse.
ORBIT DECAY PREDICTION SENSITIVITY TO SOLAR FLUX VARIATIONS
Satellite orbits decay faster when solar max heats, and expands, the upper atmosphere.
As for global warming’s effects on atmosphere: PV=nRT
Actually, engineer_comp_geek is correct in the context in which he made that statement, and you’re really just nitpicking. How one characterizes the role of water vapor depends on the context of the discussion. What he said was (emphasis mine):
Water vapor generally isn’t considered to be a greenhouse gas even though it factors into the greenhouse effect because the amount of water vapor that the air can hold depends on the temperature. If you throw a bunch of water vapor into the air, all it does is condenses out somewhere else.
However, in this case the OP is changing the temperature, which means that the amount of water vapor in the air will also increase.
Water vapor is physically a greenhouse gas in that it absorbs and re-emits longwave radiation, but it isn’t counted among greenhouse gases when adding up GHG forcings. For instance, you won’t find tropospheric water vapor on a chart like this. There is a very small component of stratospheric water vapor there (that’s the “H[sub]2[/sub]O[sup]str[/sup]” item), and that’s because this is an unusual case of water vapor resulting from oxidization of anthropogenic methane, making this water vapor uniquely a forcing rather than a feedback. But water vapor in the troposphere – the elephant in the room – is strictly a feedback, and a fairly direct consequence of temperature. So it’s never included on forcing charts, and simply regarded as an amplifier of GHG forcings. Climate models, of course, have to carefully compute the effects of water vapor feedback.
If one wanted to guard against this sort of nitpick, the original statement could be rephrased as “Water vapor isn’t counted among greenhouse gas climate forcings even though it factors into the greenhouse effect because the amount of water vapor that the air can hold depends on the temperature …”
I believe pressure at the surface would remain the same, so that any increase in temperature would increase volume. What I don’t know is whether the death zone is defined by pressure or by density.
