‘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

On Heat, the Laws of Thermodynamics and the Atmospheric Warming Effect

On average, Earth’s solar-heated global surface is warmer than the Moon’s by as much as 90 degrees Celsius! This is in spite of the fact that the mean solar flux – evened out globally and across the diurnal cycle – absorbed by the latter is almost 80% more intense than the one absorbed by the former.

The Earth’s global surface, absorbing on average 165 W/m2 from the Sun, has a mean temperature of ~288K (+15°C).

The Moon’s global surface, absorbing on average 295 W/m2 from the Sun, has a mean temperature of >200K (-75°C).

A pure solar radiative equilibrium for each of the two bodies (according to the Stefan-Boltzmann equation: Q = σT4, assuming emissivity (ε) = 1) would provide them with maximum steady-state mean global temps of 232K (-41°C) and 269K (-4°C) respectively.

As you can well gather from this, the Earth’s surface is 56 degrees warmer than its ideal solar radiative equilibrium temperature, while the lunar surface is at least 70 degrees colder than its ideal solar radiative equilibrium temperature. That’s a spread of no less than 126 degrees! On average …

Still, these two celestial bodies are at exactly the same distance from the Sun: 1AU.

So what could possibly account for this astounding difference between such close neighbours?

Very simple: The Earth has an atmosphere. The Moon doesn’t. Continue reading