The main plank of the standard theory of the flow of energy in Earth’s climate system is the notion that energy leaving the surface is partly recycled by radiatively active gases, GHG’s, in the atmosphere as ‘downwelling long-wave radiation’, DLR, which warms the surface of the planet relative to the temperature it would have without an atmosphere.
The basic idea is that the surface temperature has to rise in order to be radiating at such a temperature that the radiatively active ‘greenhouse gases’ at cold, high altitude in the atmosphere are able to emit the same amount of energy back out into space as arrives from the Sun, which in the end, along with other radiatively active object in the air such dust particles and cloud droplets, they must. The basic scheme is nicely typified in this diagram by Willis Eschenbach, in his 2009 article on WUWT, entitled ‘The Steel Greenhouse’. (though Willis uses the idea of an internally heated planet with a steel shell to simplify the concept) The diagram shows the difference between a planet with no ‘shell’ (top), and a planet with a radiatively active shell (bottom).
“In order to maintain its thermal equilibrium, the whole system must still radiate 235 W/m2 out to space. To do this, the steel shell must warm until it is radiating at 235 watts per square metre. Of course, since a shell has an inside and an outside, it will also radiate 235 watts inward to the planet. The planet is now being heated by 235 W/m2 of energy from the interior, and 235 W/m2 from the shell. This will warm the planetary surface until it reaches a temperature of 470 watts per square metre. In vacuum conditions as described, this would be a perfect greenhouse, with no losses of any kind. Figure 1 shows how it works.”
In his article. Willis then develops the idea that his model is analogous to the real Earth and its atmosphere.
But there are problems.
Firstly, the real situation is that the ‘shell’, the portion of the atmosphere doing most of the radiating, is colder than the surface. This is a simple observational truth. Cooler things don’t warm warmer things, as the second law of thermodynamics tells us, though they can slow the rate of cooling of the warmer thing.
Secondly, radiation from the atmosphere only penetrates around 0.07um into the ocean surface. Much less than the thickness of a human hair. This will mean that since a relatively high amount of energy is being absorbed in a layer only a small number of molecules deep, the principle effect will be to promote evaporation, which cools the ocean rather than warming it. This leads me to believe that DLR doesn’t warm the ocean, or even slow its rate of cooling. It’s a big problem for the standard theory if so, because the ocean covers around 3/4 of the planet. For DLR to lift the Earth’s surface temperature to what it is, from the temperature it would be without an atmosphere or ocean (you can’t lose one and keep the other), by warming the ground and air is not possible, and contrary to observation. The near surface air and the ground are on average cooler than the ocean surface by 3C globally. Hitherto, theorists have got around this problem by denying it exists, or just ignoring it. In a discussion on this issue, Willis tried to get around it by saying that wind ruffling the water surface will mix the DLR heated water down into the ocean. The problem with that idea is that wind promotes evaporation too, and the effect is exponentially amplified as wind increases.
So if downwelling radiation from ‘greenhouse gases’ can’t be doing the job of keeping Earth’s surface much warmer than it would be without an atmosphere or ocean, what else could?
Energy from the sun in the form of short-wave radiation has no trouble penetrating deep into the upper 100m of the ocean, a three dimensional matrix, transferring heat into the water. But because water re-radiates long-wave radiation, which can’t travel more than a few nanometres before being re-absorbed, the only way for energy to escape is from the surface, a two dimensional plane. The the near surface air, into which the ocean has to lose energy, principally by evaporation, is only a few degrees cooler on average which makes the job tougher. The only way the ocean can get rid of enough energy fast enough to approach equilibrium, is to keep gathering solar energy until it is at a temperature which enables it to do that effectively. The ocean ‘traps heat’. But the rate of evaporation is set by the surface pressure, which limits the energy releasing ability of the ocean.
By this analysis, the ‘greenhouse effect’ is primarily taking place in the ocean, not in the air. Rather than Earthly energy having a tough time getting past the greenhouse gatekeeping gasbags, it is long-wave converted solar energy that is having a tough time escaping from the oceans, due to the pressure they are under.
I’ve stolen the steel greenhouse and tossed it in the ocean. Sorry Willis.
If this is correct, then the atmospheric mass is the key quantity, not the amount of GHG’s by volume within that mass. This is because atmospheric mass determines the surface pressure brought about by the force of gravity acting on it, and thus the rate of oceanic evaporation. We can further see that if that is the case, the higher value for radiation measured near the surface compared to the value at high altitude is more a consequence of its emission from higher density, warmer near surface air, rather than the cause of that higher temperature. The cold, radiatively active gases and particles fulfill the role of cooling the planet by radiating energy back to space from high altitude, which maintains overall radiative balance. Could it be that cause and effect has been fundamentally confused by an overemphasis on modeling the apparently most easily calculable quantity – radiation?
Has facility has been confused with causality?