A simple argument is put forth against the idea that the radiative properties of an atmosphere somehow serve as the CAUSE of elevated steady-state planetary surface temps. Continue reading
Be sure to read Part 1 first, now …
DEFINING THE rGHE THROUGH THE ERL.
How is the rGHE defined in the most basic way? If you have a planet with a massive atmosphere, the strength of its “greenhouse effect” is defined as the difference between its apparent planetary temperature in space and the physical mean global temperature of its actual, solid surface. The planet’s apparent temperature in space is derived simply from its average radiant flux to space, not from any real measured temperature. It is assumed that the planet is in relative radiative equilibrium with its sun, so is – over a certain cycle – radiating out the same total amount of energy as it absorbs.
If we apply this definition to Venus, we find that the strength of its rGHE is [737-232=] 505 K. Earth’s is [288-255=] 33 K.
The averaged planetary flux to space is conceptually seen as originating from a hypothetical blackbody “surface” or ‘radiating level’ somewhere inside the planetary system, tied specifically to a calculated emission temperature. This level can be viewed as the ‘average depth of upward radiation’ or the ‘apparent emitting surface’ of the planet as seen from space. Normally it is termed the ERL (‘effective radiating level’) or EEH (‘effective emission height’).
The idea behind the ERL is pretty straightforward, but does it accord with reality? The apparent planetary temperature of Venus in space is 231-232K, based on its average radiant flux, 163 W/m2. Likewise, Earth’s apparent planetary temperature in space is 255K, from its mean flux of 239 W/m2. In both of these cases, the planetary output is assumed to match its input (from the Sun), so one ‘simple’ method one could use to derive the apparent temperature of a planet is by taking the TSI (“solar constant”) at the planet’s (or moon’s) particular distance from the Sun, and multiply it with 1 – α, its estimated global (Bond) albedo, a number that’s always <1, finally dividing by 4 to cover the whole spherical surface. Determining the average global albedo is clearly the main challenge when going by this method. The most common value provided for Venus is 0.75, for Earth 0.296.
But does the resulting value really say anything about the actual planetary temperature? If the planet absorbs a mean radiant flux (net SW) below its ToA, then how this flux affects the overall system temperature very much depends on the system’s total bulk heat capacity. If it is large, the flux will have little effect, if it’s small, the flux will have a bigger effect.
And so finally we have reached the stage where we will explain why the atmospheric insulating effect is inherently a ‘massive’ one and not a ‘radiative’ one. The answer is quite intriguing, maybe even a bit surprising to some, the solution rather subtle in many respects. I have settled for two posts, but could probably have written several, considering the bewildering amount of different aspects in some way or other pertaining to this whole issue.
I hope you can bear with me on what might seem like a rather repetitive style of writing in this first post. I have only done so in a humble attempt to punch through the basic idea presented, which might at first come off as a novel or unfamiliar one to most people.
The second post is more lengthy, gradually winding its way towards the final resolution. When reading it, always bear this first one in mind.
I will most likely at some point publish a (strongly) condensed version of these posts. However, their content and interconnected nature might take time to digest.
OK. Let’s begin …
TO NECESSITATE > TO ENABLE > TO CAUSE
In his ‘Physics Today’ feature article of January 2011, “Infrared radiation and planetary temperature”, Raymond T. Pierrehumbert stated the following about the proposed rGHE surface warming mechanism:
“An atmospheric greenhouse gas enables a planet to radiate at a temperature lower than the ground’s, if there is cold air aloft. It therefore causes the surface temperature in balance with a given amount of absorbed solar radiation to be higher than would be the case if the atmosphere were transparent to IR. Adding more greenhouse gas to the atmosphere makes higher, more tenuous, formerly transparent portions of the atmosphere opaque to IR and thus increases the difference between the ground temperature and the radiating temperature. The result, once the system comes into equilibrium, is surface warming.”
This is a most interesting quote, one that reveals a central misconception lying at the heart of the rGHE and AGW hypotheses. In order to get his message across, Pierrehumbert employs two quite specific terms – “enable” and “cause” – as if they were almost interchangeable. They are not. Read the two highlighted sentences once more. “An atmospheric ‘GHG’ enables a planet to radiate at a temperature lower than the ground’s, if there is cold air aloft. It therefore causes the surface temperature to be higher than would be the case if the atmosphere were transparent to IR.”
How did he get from “enables” to “therefore causes”?
He seems to forget that there’s crucially a third term that needs to be included before this chain is complete and one is able to see the whole picture, and that term is “necessitate”.
Something necessitates an effect, but cannot cause the effect before it is enabled to do so.
I will explain … Continue reading
If there were no atmosphere on top of our solar-heated terrestrial surface, then Earth’s mean global surface temperature would likely be about 80 degrees lower than what it actually is (209 rather than 289K). And this would be in spite of the fact that in this case the solar heat input to the global surface would be almost 80% larger on average (296 rather than 165 W/m2).
Much of this cooling of the mean would simply come as a result of greatly amplified temperature swings between day and night and between the seasons. The larger the planetary surface temperature amplitudes in space and time, the lower the mean global planetary surface temperature needs to be to maintain dynamic radiative equilibrium with the Sun. This is why the Moon is so cold.
So we need to get this straight: The Earth’s surface would be a much colder place without an atmosphere on top of it. Even with much more solar heat absorbed. There is no escaping this. The lunar surface is about 90K colder than ours, on average.
SO WHAT DOES OUR ATMOSPHERE DO?
The short answer: It insulates the solar-heated surface.
Well, so how does it do this?
Mainly in four ways, three of which concern suppressing the effectiveness of convective cooling of the surface at a certain temperature.
Why is this important? Why convective cooling?
Consider a hypothetical single-room house. Continue reading
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
This could hopefully be a nice learning experience as part of our ongoing discussion on ‘how to heat a planetary surface’.
I went over to Joseph Postma’s site to see how they treat the whole sphere/shell problem there, having learned that some commenter had linked to my last post on the subject on one of his threads, evidently leading to the appearance soon after of a couple of climateofsophistry.com regulars on this blog.
What I found quite frankly appalled me.
It is just as much a cultic echo chamber as any warmist site I’ve ever visited. They live firmly and tightly packed inside their little pink bubble, completely detached from reality, but keep patting each other on the back, congratulating themselves whenever more elaborate ways are found to consolidate and entrench the cult’s profoundly absurd ideas about the world, loudly and indiscriminately thrashing everyone not agreeing with them, calling them idiots, criminals and the like. Anyone who dares question the dogma is immediately and summarily labelled a ‘sophist’. The cult leader, Postma himself, is of course first in line, the worst of the lot, a person with clear megalomaniacal tendencies, whose modus operandi when it comes to meeting a challenge consistently revolves around twisting the opponent’s every word, nitpicking on irrelevant semantic details to evade major points being made, constantly ‘misunderstanding’ opposing arguments, thus creating the opportunity to divert and build straw men to tear down, all of it sprinkled with a nice dose of mockery and verbal abuse.
Following are a couple of exchanges from Postma’s blog exemplifying precisely what I mean, highlighting the blinkered, confused nature of Postma’s world view, plus his aggressive rhetorical tactics employed whenever he needs to escape rational – but obviously uncomfortable – counter-arguments threatening to trap and expose him, keeping his flock’s cognitive dissonance safely at bay: Continue reading
“Bryan needs no introduction on this blog, but if we were to introduce him it would be as the fearless champion of Gerlich and Tscheuschner.”
And the challenge appears to be a return to the ‘Steel Greenhouse’, a setup that is meant to convey in the simplest possible way the basic mechanism behind ‘atmospheric radiative greenhouse warming’ of the surface of the Earth.
The challenge goes as follows: Continue reading
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