The Congo vs. Sahara-Sahel once more

OK, so commenter “Norman” asked me at Roy Spencer’s blog to clarify my position on whether a “more IR active atmosphere” would necessarily produce a higher average annual surface temperature at the bottom of that atmosphere. His inquiry in full:

Kristian

Then you would also agree that increasing GHG in the atmopshere (the quantity makes a difference since it decreases the heat out) will lead to the end result of a warmer surface?

Good. That is what the basic point is all about.

Does the amount of GHG in the atmosphere change the equilibrium temperature of the Earth’s surface?

In your other writings you have states some GHG is necessary but the quantity does not matter. what is your current understanding?

More GHG warmer surface?
Less GHG cooler surface?
Or No change once a certain amount is present?
If in both cases the solar flux to surface remains the same.

So what do we mean by a “more IR active atmosphere”? Well, a proponent of the AGW idea (that of the anthropogenically “enhanced GHE”), like Norman here, would simply say: more “GHGs”. But what does this actually entail? It would lead to an atmospheric column that is more opaque (that is, less transparent) to outgoing surface IR. The idea is that the so-called “GHGs”, the IR active gases (and clouds, mind you), would absorb it more strongly, sort of “capture it” on its way out, and reradiate it in ALL directions, not just the upward one, thus diminishing the net flux of IR moving away from the surface and in the direction of space. And what is this net flux of outgoing IR from the surface? It’s the surface radiant HEAT loss, its Qout(LW).

So Norman’s central claim is this one: “(…) increasing GHG in the atmopshere (the quantity makes a difference since it decreases the heat out) will lead to the end result of a warmer surface (…)”

Well, will it? What does empirically based data from the real Earth system have to say about it?

We return to Africa. Continue reading