Colder with increasing altitude.

[haruspex]

So you would prefer the explanation that radiative equilibrium, moderated by convection (where the adiabatic cooling comes in), is the "cause" of the decreasing temperature with altitude?

Not sure it's necessary to specify equilibrium, but yes, the primary cause is atmospheric absorption/reradiation.

 

[D H]

If I asked you what caused sand dunes in the desert you wouldn't say it was the angle of repose; you'd say it was the wind.

Saying that the angle of repose is responsible for sand dunes is exactly what you have done by saying that greenhouse gases are the cause of the lapse rate.

Take away the sand and you don't get sand dunes. Take away the 99% of the dry atmosphere that is transparent to thermal IR and you don't get anything like our atmosphere.

To say that one specific thing is the cause of a complex process is fallacious reasoning.

 

[haruspex]

Saying that the angle of repose is responsible for sand dunes is exactly what you have done by saying that greenhouse gases are the cause of the lapse rate.

I didn't say GHGs cause the lapse rate, and that wasn't the original question.

The analogy runs like this:
Q1. Why do sand dunes form?
A1. The wind blows sand uphill.
Q2. What stops them getting really steep?
A2. Gravity
Q3. Why doesn't gravity flatten them out?
A3. The angle of repose.

Q1. Why does it tend to get colder as you go higher?
A1. Because the Earth is a source of radiation that GHGs trap and release
Q2. If I do the maths on that, the temperature gradient would be much steeper than it is.
A2. Convection tends to move excess heat upwards
Q3. Why doesn't convection bring it back to uniform?
A3. Because of adiabatic cooling.

To say that one specific thing is the cause of a complex process is fallacious reasoning.

The lapse rate, i.e. the specific gradient observed, is certainly a result of the whole shebang. I won't object violently to giving that answer also to the question as posed, but I certainly object to giving adiabatic cooling as the main or only explanation. There would be a cooling with altitude without convection and adiabatic cooling; but without some primary cause such as GHGs or diurnal variation there would be no convection, no adiabatic cooling, and no temperature drop with altitude.

 

[olivermsun]

Not sure it's necessary to specify equilibrium, but yes, the primary cause is atmospheric absorption/reradiation.

That seems fair.

 

[Ken G]

It's always hard to specify a "cause" of anything, it somewhat depends on the logic being used. But my perspective is, greenhouse gases "try to" cause the temperature to fall at high altitude (or more correctly, be warm at low altitude), and then the temperature gradient they "try" to cause is too steep to be stable, so convection sets the actual gradient. But radiation and thermal equilibrium is what sets the ball rolling, so that does kind of sound like a cause, and indeed convection is not a cause of it being colder at altitude, it is a cause of it not being even colder than it is at altitude (hence it should be thought of as a warming effect). Thus I would say, in agreement with haruspex, that the greenhouse effect "causes" the temperature to be higher at low altitude, but it is convection that determines the actual gradient. Shall we mince words thusly, or just agree with D_H that a complex process is best understood by the process itself, rather than any labels we might tend to hang on it? The labels "cause" and "effect" are surprisingly vague in physics, as they mean something rather different in an equilibrium process than they do in a time varying process (in the latter, they have to do with time ordering, whereas in the former, they have more to do with "if I had the power, what would I achieve the greatest impact by changing").