Over on the suggestions page, talkshop contributor ‘mydogsgotnonose’ has posted an interesting synopsis of his understanding of constraints on the co2 greenhouse effect. I think this is worth discussing, so I’m putting it here as a post in its own right.
Limits on the Co2 Greenhouse Effect
MDGNN – June 2012
There is probably no net CO2-AGW. If you look at Nasif Nahle’s work, it could even be slightly negative. Basically, the assumption by the IPCC that all the absorbed Infra Red radiation (IR) is directly thermalised is wrong.
The basis of this is two-fold. One is empirical.
This link shows that >200 ppmV [CO2] there is no increase in absorptivity/emissivity [assuming Kirchhoff's law at equilibrium]. These data are routinely used in furnace design and are correct in that they work.
Furthermore, the experiments were done using a heated/cooled container and there are good theoretical reasons that the real process is absorption then pseudo-scattering to give indirect
direct thermalisation at the walls of the container, so the real process is the effectiveness of the CO2 at scattering energy to the container walls and vice versa.
The theoretical reason is that there is no direct process for transfer of absorbed quanta in GHG molecules by multiple collisions to symmetrical N2 and O2 as apparently claimed in climate science.. Also the Principle of Indistinguishability means that molecules have no memory so Local Thermal Equilibrium (LTE) is restored once an already excited molecule emits the same quantum: no direct thermalisation. This is kinetic selection in that the energy is transferred by multiple pseudo-scattering events as if the GHGs were a heat transfer medium, only stopping when the quantum is absorbed/thermalised at a heterogeneous interface, or heads off to space.
In the atmosphere, the ‘container’ is clouds and bare aerosols giving the impression of direct thermalisation. Nahle has shown theoretically from partial molar specific heat data [implying a container] that the apparent absorptivity slightly decreases as [CO2] rises.
This reference is an interesting discussion where the conclusion is the IR is pseudo-scattered, also possibly by resonance emission of existing excited molecules:
The ultimate arbiter is the experimental data of Hottel and Leckner. Clouds are grey bodies because the absorbed band specific IR is thermalised over many more wavelengths, so again making a very different heat transfer problem than the IPCC claims. Thus cloud under surfaces will emit specular IR
light in the atmospheric window back to the Earth whose energy will have originally been partly CO2 specific. On the contrary, there will also be transfer in the other direction so it probably cancels out.
Basically, the IPCC has got it completely wrong in that they fail to realise that the Tyndall and PET bottle experiments are driven by the container and the pressure rise at constant volume. There may be some direct thermalisation but Nahle’s recently reported Mylar balloon experiment showed no detectable thermalisation:
A key rider to this discussion is that as the atmosphere thins and has fewer clouds, the IR emitted by clouds and warm air will preferentially escape to space because as it is pseudo-scattered, it is selected to escape UP. This means that as height increases, the emissivity DOWN tends to zero.
Thus the Schwarzchild two-stream approximation cannot be applied at Top of Atmosphere ( TOA) and emissivity DOWN will be <<absorptivity DOWN above the cloud level.
At Bottom of Atmosphere (BOA), the boundary condition is that only the net IR UP is important in that the rest of the heat transfer is conduction and convection, the total being 160 W/m^2. In effect the emissivity of the earth’s surface is <<1 and radiative flux only exceeds [conductive plus convective] flux at ~100 °C [see McAdams’ Heat Transfer for example. Thus the IPCC claim that there is a radiative equilibrium between a ‘blackbody’ surface in equilibrium and ‘blackbody’ air is completely wrong.
At TOA there is zero DOWN IR. At BOA, UP IR = 63 W/m^2 [data from the Trenberth cartoon**] and it is claimed that 40W/m^2 of this goes through the atmospheric window. Let’s assume this is correct. The net result is that the climate models artificially increase heat in the system by a factor of [240+333-240]/240 = 1.39 and the IR bit by a factor of [23 +(333-240)]/23 = 5.04. This shifts the calculation to IR dominance whereas the real atmosphere is dominated by convective processes; thus the incorrect model is the origin of the unphysical positive feedback.
In summary: thermalisation is indirect and because the scattering of IR from the Earth’s surface asymptotes at ~200 ppmv [CO2], there can be no net CO2-(A)GW in the post ice age World.
I’ll add to this something Ned Nikolov said in email which is relevant and adds some background on the way radiated energy is distributed in the atmosphere:
IR radiation emitted to space by the Earth-atmosphere system equals
the SW solar radiation absorbed by the system, which is about 238.3 W
m-2 (the 240 W m-2 value is based on the old solar constant). It is
also true that the atmosphere emits IR radiation in all directions.
However, the atmosphere is not vertically homogeneous in terms of
pressure and density. There is a huge pressure/density gradient between
the surface and the stratosphere. The LW atmospheric flux measured at
the surface originates virtually 100% within a 1km layer adjacent to the
surface. The outgoing LW flux observed from space originates primarily
in the top layers of the troposphere, which are much colder and also
lower density and thermal emissivity compared to the bottom layers. On
average, the vertical temperature gradient (lapse rate) is caused by the
pressure gradient. Lower layers in the troposphere have higher pressure
and higher temperature (as well as higher thermal emissivity) compared
to higher layers, which results in a larger IR down-welling flux (back
radiation) at the surface than at higher levels in the atmosphere.
The difference between outgoing and down-welling IR flux is always
negative and its absolute value increases with altitude – it’s about 43
W m-2 at the surface and reaches 238 W m-2 at the top of the atmosphere.
[edits 6th June 2012, see comment. –Tim]