Isn’t it funny that the ‘domino effect’ of teleconnections works with everything except the Medieval Warming Period…?

in Re to Barry E Finch, 24 Jun 2026 at 8:56 PM,

https://www.realclimate.org/index.php/archives/2026/06/unforced-variations-june-2026/#comment-849390

Dear Barry,

For dioxygen molecules, transitions between their rotational energy states are inactive in microwave radiation spectrum, because the selection rule for such radiation absorption / emission requires a permanent dipole moment of the respective molecule (which is zero in O2).

For the same reason, also carbon dioxide does not absorb / emit radiation at microwave frequencies (except when its molecules occur in vibrational excited states that make it asymmetric), while water does, irrespective of the vibrational state of its molecules.

Greetings
Tomáš

Ray Ladbury,
You describe stuff that I haven’t ever considered but which seemingly contradict my understanding of he radiative mechanisms found in the atmosphere. (I’ve never found a good authoritative explanation of such mechanisms so support for the following is sans reference.)
The problem sentence is “High in the atmosphere, collision rates are lower, and radiative relaxation dominates.”

In my understanding of it, the vast majority of IR shooting round within (& out of) the atmosphere result from GHG excitation due to collision. In the lower atmosphere, This domination results from the relaxation time, the time for an excited GHG to emit a photon, being measured in hundredths of a second while impacts which can transfer the energy of that excitation into atmospheric kinetic energy occur every few microsecond. Very few ‘excitations’ can thus survive long enough to emit a photon. At the same time, these massively numerous impacts set loads of GHG molecules into the excited state, far more than are excited by absorption, and it is this large population of excited GHG molecules which result in the vast majority of emitted photons. Thus the collisions are the thing exciting the GHGs and rate-of-collisions is a temperature-thing.

What I have never considered is the impact of altitude on that mechanism. But that said, I’d be surprised if by the tropopause a 70% drop in density + 80% drop in pressure would be enough to allow radiative excitation to dominate.
And I don’t think sympathetic emissions (relaxation prompted by a passing photon) would be enough either.

There seems to be a lot of wordage (33 comments, 7,500 words) generated by an objection from Barry E Finch to a comment by Martin Smith on a different thread, objection which to me didn’t seem warranted.
The crux of the objection eventually emerges and that objection is to the existence of back-radiation. Given back-radiation is easily measured, denying its existence is a very tricky position to adopt. Barry E Finch has gone so far as to tell us that “climate scientists such as our hosts have messed up big time” in this regard!!!
The error I see generating this ‘back radiation is a myth’ nonsense is summed up by consideration of the argument that back-radiation should be half the upward surface radiation (roughly) because the other half is not back-radiation but front(?)/upward/outward radiation.

Because re-emission occurs in all directions, roughly half of the energy is directed back toward the Earth’s surface … But the energy budget shows 396 w/m**2 going up and half of that energy is 198 w/m**2 going down, but they show 345 w/m**2 back radiation so they added 147 w/m**2. Where’s this magical non-existent energy coming from?!!! They almost doubled the real warming to make it sound scarier! It’s all a big hoax!”

If there were some “big hoax” in operation here and back radiation was “magical non-existent energy,”, the measurement of said back radiation would constitute a proof that magic was real!!!
Of course, the emissions from the surface can only go ‘up’. The other missing half of surface radiation is 12,000 km away on the other side of the planet!!! The Stefan–Boltzmann curve is a spherical-thing not just a flat-surface thing.

But eventually, no matter how many times the energy is passed around in collisions, it leaves the atmosphere, up or down, as an infrared photon. Yes?

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https://diff.wiki/index.php/Differences_between_Portable_Air_Conditioner_and_Window_Air_Conditioner

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I think the split-unit heat pump is much more efficient. I got one last year. I run it most of the time from May through August to keep my bedroom below 21C at night. I can say I don’t notice the difference in my electricity bill. When I sit outside on the balcony, where the external unit sits, I can barely hear it.

JCM summarizes his comments: “In summary: I propose that worrying too much about surface atmospheric radiative exchange may be barking up the wrong tree if the idea is to learn about how climate works.”

MS: But my purpose in this exchange, mainly with Barry, has been to improve my understanding of the mechanics of the GHE, to develop a better mechanistic explanation for what happens when we add CO2 to the atmosphere. I’m not a physicist, nor am I a mathematician, although I got an MS in math 50 years ago. I have neither the time nor the physics and math to understand the physics math of the GHE the way climate scientists and other physicists understand it. I need a correct, simplified, mechanistic explanation using photons, molecules, kinetic energy, and words like ground, ocean, re-emit, and back radiation.

My need probably applies to 99% of the human race.

chris,
Without getting too far into the weeds, the Columbia Climate press release you link-to does not itself get into the weeds. The abstract of the paywalled paper Cohen et al (2026) ‘Stratospheric cooling and amplification of radiative forcing with rising carbon dioxide is not as understandable as the abstract/full preprint account (HERE). The preprint abstract runs:-

The cooling of the stratosphere in response to increasing CO2 concentration has long been recognized as a “fingerprint” of human effects on climate. However, the radiative mechanisms that control this cooling, particularly its magnitude and vertical structure, remain unclear. Using idealized models of spectroscopy and radiative transfer, we demonstrate that the sensitivity of stratospheric temperature to CO2 concentration is mainly driven by the distribution of mass absorption coefficients in the primary CO2 band and modulated by the emission of water vapor and ozone in other parts of the spectrum. These spectral mechanisms explain why the stratosphere cools more aloft than it does below, why each doubling of CO2 yields roughly zero to eight Kelvin of cooling across the depth of the stratosphere, and why stratospheric cooling increases the radiative forcing of CO2 by about 75%.

This is all about the ‘why’ of the already-known-&-quantified stratospheric cooling. It’s about the stratospheric cooling mechanism kicked-off by increased CO2 and modulated by the impact of that cooling on O3 & H2O levels in the stratosphere. It’s not about surface global warming. The climate Forcing from GHG-changes is measured at the tropopause below the stratosphere. Because of stratospheric ‘effects’ across the tropopause, the climate Forcing is adjusted for a stratosphere in equilibrium with that Forcing (IRF → ERF). The “study explains” the cooling. It does not ‘explain’ how this “warms the Earth below”.

CO2 molecules in Earth’s troposphere manufacture (by colliding with other molecules) something like 100,000 times as many photons in 1 second as all the photons heading up from the surface in 1 second. I’m not bothering to format or tidy up this spread sheet I made 2 years ago. It’s based on Solar flux absorbed but then I thought it’s better to compare with surface flux to explain to bods in the other Forum (not RealClimate) where I’ve been providing this sort of stuff. Obviously, the CO2 molecules in Earth’s troposphere that manufacture (by colliding with other molecules) ~100,000 times as many photons in 1 second as all the photons heading up from the surface in 1 second also absorb ~100,000 times as many photons in 1 second as all the photons heading up from the surface in 1 second, Obviously they absorb a tad less like 99,999.8 for every 100,000.0 with the other 0.2 being the CO2 part of downwelling into surface and upwelling into (or through) stratosphere. The surface exchanges photons with only the lowest 25 to 100 m of atmosphere with a clear sky (clouds from any height emit to the surface 8-9 & 10-13 microns that gases don’t absorb).

Mantissa decimal
exponent
6,022 20 Molecules in 1 Mole of a gas Avogadro’s number = 6.0221 x 10**23 molecules / mole
423 0 ppmv CO2
10,300 3 Grammes/m**2 mass of air
510,072 9 Earth’s area in m**2
5,253,742 15 Total mass of atmosphere in Grammes
182,422 15 Total Moles of atmosphere
77,164 12 Total Moles of CO2 in atmosphere
464,691 35 Total Molecules of CO2 in atmosphere
371,753 35 Total Molecules of CO2 in troposphere
650 -3 Seconds per photon emitted per molecule
71,491 36 Photons emitted per second in atmosphere
57,193 36 Photons emitted per second in troposphere
122,927 12 Solar SWR absorbed by Earth Joules/second
2,838 -22 Solar SWR average Joules per photon at 700 nm
43,315 31 Solar SWR photons absorbed per second
165,050 0 CO2 molecules in the atmosphere emission in units of a set of Solar SWR photons that Earth absorbs
132,040 0 CO2 molecules in the troposphere emission in units of a set of Solar SWR photons that Earth absorbs
Earth absorbs 4.3 x 10**35 photons per second of Solar (which is 99.7% of what heats the ecosphere).
So all CO2 molecules in the troposphere emit 131,000 times as many photons as the Sun’s photons that Earth absorbs.