Confusion behind the 'greenhouse gas effect' and radiative processes in physics

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Under Construction

To Do: citations, especially mean-free path model | 3 examples (1) M&W 1967, (2) H&S 2000, (3) MFP model

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There is no greenhouse gas effect, GHGE, in physics. There are radiative processes of absorption and emission of infrared radiation by radiatively active gases such as carbon dioxide, CO₂, and water vapour, H₂O, for example.

The idea of a greenhouse gas effect is a fabrication by climate scientists. It preceded any understanding of the physics involved in gaseous radiative processes. It began as something called a 'greenhouse effect', which was a notion that atmospheric gases warmed the surface of earth (by 33°C in the classic case) compared to an imaginary earth with no atmosphere. As such, both the Atmospheric Thermal Effect (ATE), an adiabatic heating effect, and the greenhouse gas effect, GHGE, are both explanations for a 'greenhouse effect'; although the ATE is 80°C, not just 33°C.

Today the greenhouse effect has mutated from its original meaning. It now means only the greenhouse gas effect, GHGE. Anyone wanting to talk about an Atmospheric Thermal Effect is treated like a heretic, banned, and metaphorically sacrificed. I won't talk further about the ATE because I want to look at the conflict between different visions and understandings of the role of gaseous radiative processes in climatology.

Physics - radiative gases

CO₂, but mostly H₂O, strongly absorb and emit infrared photons, due to their molecular electrical dipole. It's a zero sum game, CO₂ molecules, for example, absorb exactly as much as they emit. When CO₂ absorbs a photon of suitable frequency its energy state becomes excited moving from E(normal) to E(excited). CO₂ absorbs and emits in 2 bands centred around 4µm and 15µm. Any radiation outside these bands it 'ignored'. More precisely CO₂ behaves as a non-radiative gas like nitrogen, N₂, when interacting with such. For example, it can still scatter the radiation.

In thermalisation a radiatively excited molecule such as CO₂, with energy E(excited), collides with another molecule such as nitrogen, CO₂'s energy decays from E(excited) to E(normal). The lost energy [ E(excited) - E(normal) ] is transferred to the kinetic energy of the nitrogen molecule. Kinetic energy is generally regarded as the energy giving rise to temperature. So it looks like the nitrogen got 'warmer'. Except it's an equilibrium process. It goes the other way too. A N₂ molecule can collide with CO₂ to transfer some of its kinetic energy to CO₂ to excite the CO₂ energy state from E(normal) to E(excited). The CO₂ may then immediately emit a photon to de-excite from E(excited) to E(normal) again. Not heat is 'trapped'.

The only warming that can happen here is an effect of radiation density. In the case of GHG / non-GHG mixture, such as earth's atmosphere, the absorption/emission processes decrease the photons' mean free path to space and so increase the radiation energy density of the gas as compared to the non-GHG case (for example: an imaginary atmosphere without CO₂ or H₂O vapour.

So it just looks like I've admitted the greenhouse gas effect!

Not so fast. In physics, we'd model the effect of this with a statistical model to calculate this warming due to the average decrease in the mean free path to space of photons. Such models have been written. They are not welcome in climatology. Much like the ATE any scientist touting such a model will be treated as a heretic, banned, and metaphorically sacrificed; but only if they raise the issue in climatology circles. In physic circles it's perfectly OK to model legitimate physics.

These mean free path to space models of radiative atmospheric gases give no dramatic warming by more CO₂ in the atmosphere; even when the models are biased with all assumptions in favour of more warming!

Climatology - Greenhouse gas effect

In the 1950s Gilbert Plass began to model a greenhouse gas effect in terms of the behaviour of radiative gases in the atmosphere. Modellers picked up on his conjectures and they worked in a cul-de-sac journals. They read each others' work. Other scientists ignored them. By 1967, they'd made a model they were happy with (Manabe and Wetherald, 1967). With the popularity of the greenhouse gas effect after 1988 the work continued and reached a new milestone in 2000 with Held and Soden's paper. These are the two papers behind all greenhouse gas model calculations. Anything not in this tradition, but sometimes papers in the tradition, are 'heresy' and 'denialism'.