Climate Change Means You Breathe More Oxygen on Summits

[timisimaginary]

well, i see science is back. that didn't take long.

[Iguru]

Helicopters perform better in winter than summer because air is denser in winter than summer. Density is directly proportional to pressure and indirectly proportional to temperature.

I digress. In terms of the planet and atmospherically, in winter, air has less energy, increased density and sits closer to the earth. So at some height, there would be less molecules of it overall because I assume there is approximately a finite amount of air on the planet. In summer, it has more energy, lower density and therefore more molecules available higher in the atmosphere. Thereby increasing the availability of Os at higher altitudes, DESPITE the fact that density is in fact lower at lower altitude with higher temps and lower pressures.

Does that make sense? Question mark because I'm really not sure and trying to understand it from a thermodynamics background.

Not sure the relative humidity analogy applies here.

Yes, that makes sense. I think I understand the idea that the original article is trying to convey now.

[Conor]

but, it doesn't mean anything about the number of molecules of O2 in a given volume of air at a given pressure. The counter example I would offer is the varying dew point and the amount of of water (in a gas state) air can hold. absolute humidity goes up with temp and the air can hold more water. And water is lighter than air (comparing the same phase), reducing the density of the air and making it seem (for aircraft) that they are taking off at a higher altitude. But nothing to do with the amount of O2 in the air unless you want to make assumptions....which may or may not hold true.

Hmm... I don't follow. Are you using humidity as a metaphor for relative oxygen?? The relative amount of O2 in the air does not change. The partial pressure of oxygen is always the same in air. Pressure of air is reduced at altitude so you have less to breathe. It has nothing to do with the relative amount of oxygen in the air.

Helicopters perform better in winter than summer because air is denser in winter than summer. Density is directly proportional to pressure and indirectly proportional to temperature.

...

Not sure the relative humidity analogy applies here.

I wasn't offering an analogy, rather a counter example of how O2 concentration can vary independent of density. aircraft has better takeoff/landing performance in more dense air (I have a commercial pilot certificate), but it has nothing to do with the amount of oxygen in the air.

an infinite set of possibilities exists to make up a given density (pressure, temp and molecular composition). Another example would be the oxygen concentrations at the poles.

[timewarp01]

Hmm... I don't follow. Are you using humidity as a metaphor for relative oxygen?? The relative amount of O2 in the air does not change. The partial pressure of oxygen is always the same in air. Pressure of air is reduced at altitude so you have less to breathe. It has nothing to do with the relative amount of oxygen in the air.

The partial pressure of all the constituent gases is lower in humid air than in dry air, because in humid air water vapor contributes its own partial pressure. If you have two parcels of air at the same temperature, volume, and pressure, but one is humid and the other is dry, the humid one will be lighter, less dense (in terms of mass, not molecule number), and have less oxygen. Each parcel will have the same ratio of nitrogen to oxygen, but the ratio of oxygen or nitrogen to the total of the other gases is lower in the humid parcel.

[Jorts]

I wasn't offering an analogy, rather a counter example of how O2 concentration can vary independent of density. aircraft has better takeoff/landing performance in more dense air (I have a commercial pilot certificate), but it has nothing to do with the amount of oxygen in the air.

an infinite set of possibilities exists to make up a given density (pressure, temp and molecular composition). Another example would be the oxygen concentrations at the poles.

The partial pressure of all the constituent gases is lower in humid air than in dry air, because in humid air water vapor contributes its own partial pressure. If you have two parcels of air at the same temperature, volume, and pressure, but one is humid and the other is dry, the humid one will be lighter, less dense (in terms of mass, not molecule number), and have less oxygen. Each parcel will have the same ratio of nitrogen to oxygen, but the ratio of oxygen or nitrogen to the total of the other gases is lower in the humid parcel.

Alright, that clarifies that humidity thing. Thanks. I was just trying to grasp it conceptually more broadly not taking variables like humidity into account. Guess the really interesting takeaway to me here is:

At sea level, on a hot summer day, air pressure and density are lower than they would be on a really cold winter day.
Whereas, at some threshold altitude, air pressure and density are actually higher on that same hot summer day than they would be on that cold winter day.

Because as the study states, "[warmer temperatures] causes air pressure to fall less rapidly with height."

That concept is new to me and I find it fascinating. Thanks OP.

[martinleroux]

...as the study states, "[warmer temperatures] causes air pressure to fall less rapidly with height."

This is often noticeable when using a barometric altimeter. Here in Colorado, if it's a warm summer day then in my experience barometric altimeters tend underestimate elevation gain by roughly 50-100' for every 1,000' of ascent, even if they're calibrated when you start. In winter or early spring they tend to overestimate, although not to the same extent.

[Jon Frohlich]

As a lifelong asthmatic I support more oxygen on summits.

[pvnisher]

I just came here for #thescience.

[XterraRob]

Just get a lung transplant from one of the Sherpas in Nepal, that's what I did.

#TheFutureIsNow

[Burkart]

I just came here for #thescience.

Ask and you shall receive! Missed the first round, so I might as well beat the dead horse now that it's been dragged back out.

At sea level, on a hot summer day, air pressure and density are lower than they would be on a really cold winter day.
Whereas, at some threshold altitude, air pressure and density are actually higher on that same hot summer day than they would be on that cold winter day.

Because as the study states, "[warmer temperatures] causes air pressure to fall less rapidly with height."

I think there's some confusion in this thread about the relationship between temperature and pressure. You were on the right track referencing the ideal gas law: PV = NkT. Since n/V is proportional to density (keep in mind that N and mass are always constant for a parcel in an adiabatic process), we could rewrite the equation as P/rho = T*constant, which contradicts your first statement above - pressure and density vary inversely, so density must increase relative to pressure if you drop the temperature. In my opinion, it's easier to stick with volume, since volume already contains all the necessary information and adding density muddies things by making the math less intuitive.

So, is a parcel of air at sea level on a hot summer day likely to be lower in pressure*volume than a comparable parcel on a cold day? If you double the temperature of the parcel, you have increased the rms velocity of the constituent molecules by 50%, which means you have increased both the number of collisions with the imaginary edge of your parcel and the impulse of these collisions by 50%. Since P = Force/Area, this means you have also doubled your pressure, assuming rigid walls. Thus, hotter air in an ideal gas will always have a higher pressure or a higher volume. With this in mind, meteorological terms like adiabatic heating (the heating of a parcel that results from an adiabatic increase in pressure) and adiabatic cooling (the cooling of a parcel that results from an adiabatic decrease in pressure) make more sense.

Iguru referred to the stack effect as evidence that hotter air has lower pressure, but the low pressure at the base of a fire is really just a vacuum that results from a hot, high pressure air parcel chasing parcels of even lower pressure air above. This is the initial stage of convection, which occurs when the Rayleigh number exceeds a critical value (typically as a result of a large temperature differential against the gradient of the gravitational field). This is actually a pretty intriguing phenomenon and I can describe an idealized model to clarify it, if you'd like. The important thing to remember, though, is that hot air rises only in a gravitational field; a hot parcel of gas floating in deep space would simply expand outward due to its higher pressure.

Long story short, the scientific article linked by OP is correct: increase the temperature evenly across the earth, expect an increase in air pressure across the board (things are never distributed evenly, of course, and the air is not truly an ideal gas, but, hey, the only perfect model of the world is the world itself). The pop article is wrong, though, because the journalist doesn't understand the relationship between density, pressure, and temperature.

[mikefromcraig]

So the article is referencing an over 3.5 degree Fahrenheit temperature increase. That's 100 years away. We will all be dead and gone by then and people will be climbing mountains virtually.

[Wentzl]

Who decided electric cars are good for the planet?