In a recent post Claes Johnson attempts to answer the following question from Roy Spencer:

*How does the surface 'know' how opaque the atmosphere is before it 'decides' at what rate it should emit IR?*

There is one point which I would like to make here which seem to have escaped many GHE-skeptics. In a previous post I constructed a simple radiation model, which does not necessarily come close to the real situation, but which nevertheless highlights something important. In the model in question no part of the system 'knows' what goes on anywhere else, the only things each part knows is its own temperature and absorptivity. The model also contains 'backradiation'. Moreover, the 'backradiation'

*taken alone*does in fact slow down the rate of cooling in the system. The question is now:*Does the model reproduce anything like the greenhouse effect?*The answer is:*It doesn't.*In the model the temperature lapse rate flattens as the absorptivity/emmisivity increases with the consequence that the system cools, which is a clear deviation from the so called GHE.The reason for this is probably the following: The amount of backradition can never exceed the radiation that at the same time is lost to outer space. Thus the backradiation cannot trap energy in the system since it is always associated with an 'out-radiation' that is equally big.

The real difference with the GHE and reality is thus probably much more subtle than both Roy and Claes wants it to appear. To be honest, I have not quite understood the supposed mechanism of GHE although I have tried, but maybe I will succeed in the future to completely disentagle the mathematical structure of it. I very much encourage the mathematically inclined audience to also make such an attempt, since the present 'wordy' discussion on 'backradition' has not managed to clear the confusion.

My

*suspicion*though is that the greenhouse effect is based on a mechanism of**reflection**rather than**absorption-thermalization-thermal reemission**. Hence it is formally more akin to radiation pressure, but that remains to be clarified. Good luck.