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.
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
Lately there’s been a bit of back-and-forth discussion going on on the so-called ‘Gravito-Thermal Effect’ (GTE) at a few notable climate blogs, like The Hockey Schtick, Tallbloke’s Talkshop, Clive Best and even Judith Curry’s Climate Etc. (in fact, this is where the lengthiest discussion thread on the subject is to be found).
To me the whole thing appears to arise from a fundamental misunderstanding of the adiabatic process (see the end of the post).
Something called the ‘Loschmidt Effect’, after a proposal in the 1870s by the Austrian scientist Josef Loschmidt, seems to lie at the heart of the GTE argument. Tallbloke brought it out from relative obscurity in a post in early 2012. A quote from a textbook describes the proposed effect as follows: Continue reading
‘Climate ScienceTM’ (represented and promoted by the IPCC) has so corrupted ordinary people’s way of thinking, that in order to demonstrate why there is no ‘atmospheric radiative greenhouse effect’ (rGHE), you have to start all the way from scratch. You have to step completely outside the framework of their concocted ‘mental model’ within which they shape their arguments.
‘Climate ScienceTM’ is afflicted with a dual case of monomania, two major fixations that they cannot and will not drop under any circumstances.
The first one is a complete linear trend line mania. They are unable to look at a data time series and not mentally project one onto it. The data – and especially the variation in it – basically doesn’t matter. Only the straight trend line plastered across it, from the one end to the other, does.
The second one, of direct relevance to this post, is their peculiar obsession with radiative flux intensities and their perceived direct correlation with the surface temperature of objects, expressed by the purely radiative Stefan-Boltzmann relationship. They clearly misinterpret and hence stretch the applicability of this law in the real world far beyond its actual justified range of operation, but absolutely refuse to recognise it. They worship (and use) it as sanctified truth.
Basically, they see the world in terms of radiation first and last. Everything in their world is in the end determined and controlled by thermal radiation. When it comes down to it, according to the warmists, you can simply scrape away everything else and just look at instantaneous radiative emission fluxes and directly know surface temperatures. As if we all lived in Max Planck’s conceptually pure radiative universe.
‘Climate ScienceTM’ thinks (or promotes the idea) that the temperature of any object – even real-world objects on Earth – is determined strictly by its radiative energy output (its emission flux), likewise that this final temperature is known and fixed even from the onset of heating, simply by the instantaneous intensity of its radiative energy input (the absorbed flux) minus convective loss (!).
In other words, if you only know the total (added) intensity of the instantaneous radiative energy flux input to the surface of an object and you are at the same time able to determine its energy loss through convection per unit of time, you will be able to tell its final temperature, no actual thermo-measurement required. Or, turn it around, if you know the temperature of an object, you instantly know the intensity of its radiative energy output, regardless of any simultaneous convective loss of energy.
(Well, you also need to know its surface emissivity/absorptivity, but according to ‘Climate ScienceTM’ most relevant real-world materials (like soil, rock, water, vegetation) possess emissivities close to unity anyway, and so can be approximated as (convecting) black bodies …!) 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