What they really mean, however, is that they *cannot absorb infrared radiation*, not that the cannot "absorb heat".
Back to the UW course, note that they said conduction of heat & evaporation of water transfer *about twice as much* energy to the atmosphere than IR does.
17/
What's the point?
To answer that, let's look to "Basics of Radio Astronomy", published by NASA's JPL ()
From Chapter 3 ():
"Did you know that any object that contains any heat energy at all emits radiation?"
The GHE is predicated on downward IR causing surface heating.
By these very same premises, then, the non-IR-absorbing 99% of the atmosphere, heated far more by convection, emit IR just like the IR-absorbing part...
and should therefore contribute more to the GHE.
22/
One might ask, do these gases really emit IR?
A user's answer on a physics forum was quite indicative: "Experimentally it is probably very hard to measure these emissions [...] I am not aware of such measurements." ()
Almost four decades since the IPCC was founded, centuries of climate science, all predicated on downwelling IR's effects on surface temps...
... and it is not common common knowledge how much IR nitrogen and oxygen emit & contribute.
One can only speculate why.
24/
One might ask, do nitrogen and oxygen really emit IR due to their temperature? As we said, it's not well-studied - what if they don't? Or only very little?
If that were the case, then 99% of the atmosphere would have *no way to cool down* radiatively.
25/
Any heat uptaken from the Earth's surface, by conduction & convection (which dominate below 12km) would have **no way to be lost to space**.
They would perfectly inhibit such cooling -- and therefore still achieve the purpose of keeping Earth warmer than otherwise.
26/
Nitrogen and oxygen are, in effect, greenhouse gases either way:
By the very tenets of the theory if they emit IR,
and by being near-perfect retainers of heat if they don't.
27/
This thread ends here, but not the journey.
As a hint for what's next, take a look at this particularly illustrative diagram of the one-layer model.
See how the thermal radiation emitted by the surface returns back to the surface to heat it up further?
28/
As you go about your daily life, ask yourself if any objects you interact with behave this way.
If you stand in front of a mirror, does your reflected heat cause you to warm up?
29/
The simple models have a ~50% IR return. Aluminum foil reflects over 90% of IR.
If you step into a foil-lined closet, would you nearly burst into flame as your own body heat reflected off the walls back onto you and heated you up?
30/
Does *anything* you observe in the world heat itself up with its own heat?
A common reply to presenting the fact that the greenhouse effect has never been experimentally proven is that CO2 absorbs IR, or to refer to the works of Foote or Tyndall.
Yet this IR-absorption property *is not* the GHE and *does not* prove it.
🧵A thread...
To grasp this one needs to grasp what the GHE actually is.
Interestingly, the AR6 SYR () defines greenhouse gases, but not the GHE itself!
It provides a hint, though: IR-absorption is a property that *causes* the GHE, thus it is not itself the GHE.