Isn´t this a funny coincidence:
Look at the right graph in each figure, the left figure is the temperature gradient in the atmosphere, and the right picture is a van der waals fluid where the terms of stability is broken. The model of the fluid in the right picture is the exact same function that determines the gradient in the atmospheric fluid.
It is the part of the graph holding the points M to F that is violating the terms for stability, it is said to be a region where other processes supersedes the isotherm. So, my interpretation of the temperature gradient show that the heat flow in the atmosphere behaves like a van der Waal fluid with the action of gravity included.
There has been some talk about perfect fluid in the universe, in relation to dark matter and other problems. Could it be that heat/radiation is what has the behaviour of a fluid? It looks like that on earth anyway.
In any case, the similarity between the heat flow behaviour and the principles that describe vdW-fluids, indicates that there is something else at work than a greenhouse effect.