‘To heat a planetary surface’ for dummies; Part 4

I rounded off Part 3 of this series by suggesting the following:

Next up: How do you heat a planetary surface, then? If not by the Earth’s own thermal radiation, a result of its temperature rather than a cause of it … How does the atmosphere insulate the surface?”

Not so. This will have to wait a bit still. Next post, perhaps. I will rather try to clarify my stance on the whole ‘bidirectional flow’ concept thing, seeing how this topic has a tendency of stirring up both emotions and misconceptions.

There is quite a bit of confusion surrounding the whole issue of electromagnetic radiation, the Stefan-Boltzmann Law and the thermodynamic concept of ‘energy transfer’.

I will try to explain why there can be no such thing as a bidirectional energy transfer between two objects radiating at each other. Yes, they are radiating at each other! Radiation goes in all directions. Continue reading

‘To heat a planetary surface’ for dummies; Part 3

We’re still discussing Willis Eschenbach’s ‘Steel Greenhouse’.

How come the warming EFFECT of putting the shell around the sphere is real but Eschenbach’s “back radiation” EXPLANATION of how it comes about is wrong?

Simply put, it’s because the effect doesn’t violate the 2nd Law of Thermodynamics, but the explanation does.

In Part 1 and Part 2 we established some fairly basic principles of thermodynamics that we can now put to use in analysing Eschenbach’s explanation of why and how the radiating central sphere needs to warm with the steel shell surrounding it:

“In order to maintain its thermal equilibrium, the whole system must still [after the steel shell is placed around the sphere] 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.”

The first part of this paragraph simply describes the necessary conditions for reaching a new dynamic equilibrium upon putting the steel shell up around the radiating sphere. Nothing mysterious about it at all.

But then (in the bolded part) Eschenbach starts ‘explaining’ how he sees this new state of dynamic equilibrium to be accomplished.

And this is where any connection to basic, ordinary physics – and hence, to the real world – appears to be lost.

Let’s parse what he’s saying: Continue reading