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A few sites I've stumbled across recently....
I am looking for the simplest definition of Greenhouse Effect. I would have thought that would be that the temperature that we experience - the one that meteorological offices give in their forecasts - is higher than it would be without a Greenhouse Effect.
But what I find always includes a description of how the Greenhouse Effect comes about and invariably invokes Greenhouse Gasses 'trapping heat'.
Yet if I look up the definition of, as an example, Coriolis Effect, I get a simple definition without a causative mechanism for it attached.
Could it be that there is a simple definition in both cases but with Greenhouse Effect we need to be directed toward some wobbly interpretation of observations lest we formulate another less wobbly?
Belle Epoque - Yes, I think that the definition of the greenhouse effect is simply that the mean surface temperature of the Earth is higher than it would be if the atmosphere contained no greenhouse gasses. [Overlook the fact that an "average temperature" is physically nonsense with an infinity of possible definitions]
Some time back there was discussion about explanations of the greehouse effect on Judith Curry's website.
She concluded (if I remember correctly) that there are highly simplified explanations but nothing seems ever to have been published at the level of say, 2nd year physics degree course.
There are essentially two complementary explanations/simplified analyses.
[Explanation A] The greenhouse gasses are approximated as a thin shell surrounding the Earth and the Earth is regarded as a black body. I think the following uses this explanation:
[Explanation B] The final radiation back to space of energy that arrived as sunlight is assumed to take place at some altitude, whose height depends on the concentration of GH gasses in the atmosphere.
Below this altitude, IR energy emitted by the surface or by greenhouse gasses is re-absorbed by greenhouse gasses before escaping to space.
Because of the lapse rate, if this altitude is increased (due to increased GH gasses), then the ground level temperature has to increase (because of the lapse rate which is pretty well fixed) to maintain the temperature at which the final radiation back to space occurs at that temperature which results in balance between incoming energy (sunlight) and outgoing energy (infra red emitted to space by the atmosphere). I can't just at the moment put my hand on a reference to Explanation B. There are one or two out there but not so easy to find. ____________________________________________________________________________________
The "greenhouse gasses trap heat" mantra was one of the things that first made me start to think that I ought to find out what this global warming stuff was all about. The faint aroma of bullshit it brought with it got me wanting to learn a more.
Thank you for the effort of finding the [A] link. Again we have what I consider as a wobbly interpretation of observations being used to bolster what should be a simple definition. I say wobbly because there is a repetition of the bi-directional energy exchange between surface and atmosphere always attached to this scenario. That ignores the fact that the exchanges are omni-directional - the atmosphere is aglow with radiation in the infra-red. Considering that that IR is energy that has been converted completely to heat at the surface once, there needs to be another or more comprehensive explanation of what it is actually doing before it is lost entirely.
I think there may be more mileage toward a simple definition in the [B] explanation. Perhaps it will turn up.
Martin A, thank you explaining that!
As a non-physicist, I have noticed that however technical the explanation, reality does not match the theory. Climate Scientists have spent a lot of other people's money, trying to prove they are right, rather than encouraging an open debate about which bits of their only theory might be wrong.
Climate Scientists have had to rely on non-Climate Scientists finding mistakes in their maths and methodology, so clearly they do not understand their own "Science" and are incapable of self-criticism or correction.
I am not sure how people can be qualified in climate science, when I am not sure it even qualifies as a "science" in the first place.
Many businesses, trades etc are prepared to pay for more accurate weather forecasting. I think it would be more fair if Climate Scientists depended on accuracy and reliability to retain employability, in the private sector. Given the amount of taxpayer funding they have already squandered without demonstrable benefit, they can refine or redefine Greenhouse Theory in their own time
Perhaps it will turn up.
Mar 6, 2017 at 1:51 PM | Belle Epoque
Don't expect a Climate Scientist to look.
gc - Entropic man will often come up with such references. If he happens to see this thread, perhaps he might this time. You in there, EM?
The best explanations of physics applied to climate are generally to be found on Science of Doom.
As soon as you hear someone talk about "CO2 trapping heat" [eg a Met Office climate scientist Dr ******* ****** on "My Climate and Me") you know they are talking about a subject they don't understand (a.k.a. "bullshitting")].
Martin A, that is sort of why I accepted Mann's Hockey Stick originally, alleged experts talking about stuff way above my O Level Grade in Physics.
Work has taken me into some interesting environments, trying to work out what went wrong. Bullshysters are more difficult to spot if they genuinely believe what they are saying, because they do not know any better.
It is too late for 97% of Climate Scientists to admit they never worked out for themselves what was wrong with Mann's Hockey Stick. Their repeated failures to prove Mann was right, is sufficient proof to confirm Climate Science is not science based.
Searching "Greenhouse Effect definition” returns these as the first four pearls;
A term used to describe the heating of the atmosphere owing to the presence of carbon dioxide and other gases. Without the presence of these gases, heat from the sun would return to space in the form of infrared radiation.
A phenomenon in which the atmosphere of a planet traps radiation emitted by its sun, caused by gases such as carbon dioxide, water vapor, and methane that allow incoming sunlight to pass through but retain heat radiated back from the planet's surface.
The greenhouse effect is the process by which radiation from a planet's atmosphere warms the planet's surface to a temperature above what it would be without its atmosphere.
The greenhouse effect is the trapping of heat by a layer of gases surrounding the Earth. The heat is trapped by atmospheric gases such as carbon dioxide,
There are many more of the same and so I take it that these align with the 'official' hypothesis.
Martin A has kindly now found Explanation B
which I doubt is 'official'. In fact, one or the other has to be correct, not both. Interpreting that, all averages but...
Radiation is lost to space from above the surface. The temperature of that is what would be the temperature if lost from the surface should there be no greenhouse gasses. Descending down the lapse rate finds an increasing temperature until we experience the full Greenhouse Effect at the bottom of the atmosphere.
OK, pretty simple and I can look up the cause of lapse rate and find it is a gravitational effect. So do I have the simple definition I was hoping for? I think so;
Greenhouse Effect is a temperature augmentation at the bottom of an atmosphere caused by a gravitational field with 'Greenhouse Gases' present. It produces the atmospheric temperature you experience when you step outside, the temperature of tomorrow's weather forecast.
That works: no need to include surfaces, selective radiation directions, trapped radiation/heat, the same radiation warming a surface twice. No need to add any descriptive mechanism to the definition - it stands alone.
Explanation B goes on to describe adding Greenhouse Gasses and their effect. The conclusion is that an increased concentration lifts the height of radiation loss. That is then from a colder temperature and therefore energy is again 'trapped'.
But we already have a mechanism for Greenhouse Effect. It is a temperature profile in the atmosphere caused by Greenhouse Gases and gravity. There is also a relationship between the temperature of the planet and the temperature of space that causes the former to be a constant. More Greenhouse Gases raise the emitting height of that temperature and the lapse rate further augments the bottom of atmosphere temperature.
We do need to understand what all that infra red radiation is doing though. I would make the suggestion that it is the steady-state energy that is supporting/shaping the atmosphere. It is the effect of having Greenhouse Gases not the cause of Greenhouse Effect.
This is as concise as I can find.
greenhouse effectnounthe trapping of the sun's warmth in a planet's lower atmosphere, due to the greater transparency of the atmosphere to visible radiation from the sun than to infrared radiation emitted from the planet's surface.
CO2 doesn't "trap" the heat, it delays it by absorbing and re-radiating it, some towards outer space, some back towards the Earth. if the Sun was switched off the heat Earth would eventually cool to the temperature of the surrounding space.
A simple explanation of the above.
"...the trapping of the sun's warmth..."
Thank you but is that not just another version of the four examples returned by my internet search for a definition. One more of the wobbly definitions that lead us into greater complexity rather than clarity. Whereas the gravity explanation, with the small tweak for additional greenhouse gas, is concise, elegant and apparently sticks within the laws of physics.
@geronimo. The term 'delay' in a dynamic scenario, would be easily replaced by the word 'trapped'. Would it not? You may be familiar with this;
Collision absorption & emission
BE - just a short comment.
one or the other has to be correct, not both.
They are both approximations to the reality so neither is 'correct' in the sense of describing exactly what goes on but also neither is 'incorrect' in the sense of, for example, being inconsistent with the laws of physics or of being contradictory to what really happens.
Belle Epoch: the long-term idea for greenhouses was that the glass would let the sunlight (solar radiation) in, but stop it being re-emitted, thus the greenhouse gets warm. This has since changed, and is considered that the glass merely prevents the heat convecting out, trapping it to warm the tomatoes.
“Greenhouse effect” works on the presumption that what energy falls on the Earth immediately radiates back out to space; thus, without an atmosphere, the Earth would be considerably cooler than it is. The “miracle” of having an atmosphere loaded with “greenhouses gases” means that the energy that the Earth is trying to radiate out to space is “trapped” by the pesky “greenhouse gas” (GHG) molecules, and – ta-daah! – the Earth is warmed.
Others on this site may well be aware that I do not fully subscribe to this idea, as it quite irritatingly ignores that fact that the energy falling onto surfaces will also warm the otherwise useless majority gases of nitrogen and oxygen (which account for over 99% of the atmosphere) by conduction. Convection will then move these pesky molecules away from the surfaces, distributing the heat through the rest of the atmosphere. As these molecules are poor absorbers of the relevant radiation, they are also poor emitters of this radiation, so the heat is kept within the atmosphere, even during hours of darkness; hence the Earth is warmed. Of course, this means that the presence of greenhouse gases is more or less irrelevant to global warming or climate change, which means that all the scaremongering and shovelling shed-loads of money “fighting” climate change is really just a sham – or, as you might have noticed others referring to it, a scam.
CO2 doesn't "trap" the heat, it delays it by absorbing and re-radiating it, some towards outer space, some back towards the Earth. if the Sun was switched off the heat Earth would eventually cool to the temperature of the surrounding space.Mar 6, 2017 at 9:23 PM | Unregistered Commentergeronimo
Yes. Looking at a system in equilibrium and discussing what causes what can be a waste of time - in searching for a chain of cause and effect. The different effects coexist and depend on each other for their existence.
But if you consider the system as a dynamic system, where the Sun is switched on at t = 0, you can then trace how the energy flows as the system warms up, finally to approach equilibrium as t → ∞. Doing a simple analysis like that makes it very clear that anybody who talks about "back radiation warming the Earth" is talking bollocks. It becomes obvious that *all* of the warming is done by the incoming solar radiation, notwithstanding the IR radiation bouncing around, being absorbed and re-emitted, as the energy wends its way back out to space.
The third paragraph of you 10:10 post is as I see the phenomenon. I completely concur.
I disagree with your last paragraph of your 9:49 post. I am sold on the (tweaked by me) gravitational explanation.
Yes, you are probably right, as I see it the omnidirectional IR radiation supports atmospheric volume via temperature. Martin's dismissal of 'back radiation' as GE cause is therefore entirely correct. It is a measurement of something that owes its existence to the GE, not vice versa.
Belle Epoque - I am not sure why you should disagree with my third 9:49 paragraph. Clearly the lapse rate explanation is closer to the reality than the "thin shell surrounding a block body" model. But the latter does provide a model for how greenhouse gases prevent radiation from the Earth's surface directly exiting to space, and so require the surface temperature to be higher to achieve incoming/outgoing balance, even if it's only a crude model.
Question: Would the lapse rate exist in the absence of greenhouse gases, so that the the only way the atmosphere could cool would be by coming into contact with cold areas of the surface? Years ago I studied, and I think I understood, the gas laws but I would not want now to have to give a detailed explanation or do a calculation of the lapse rate in the presence/absence of atmospheric radiation.
I think a few years back I read Feynman's explanation of it [in Lectures on Physics] but my recollection is very hazy now.
"Traps Heat"? The atmosphere 'traps heat' to about the same extent as the walls of my house 'trap heat'. Admittedly each joule of the energy that enters via my electricity meter stays in the house for a short time before escaping to the outside world but the energy I pay for is - sad to say - not 'trapped' in the normal sense of the word.
trap verb Prevent from escaping. Catch (something) somewhere so it cannot be freed. (COD)
You could define the greenhouse effect as "a process which increases the temperature of the troposphere".
That removes any mention of cause. Unfortunately it also fails to distinguish the greenhouse effect from Insolation, convection, cloud cover, wind, radiation and other mechanisms which warm the troposphere.
You might get away with a cause-free definition for the Coriolis effect since that has only one cause, though "a tendency for winds to change direction" feels unsatisfying without some indication of why it happens. A minimum definition of the greenhouse effect would need enough information to distinguish it from other processes.
EM - any reason not to accept my original attempt in this thread? With slight editing:
... the effect whereby the mean surface temperature of the Earth is higher than it would be if the atmosphere contained no greenhouse gasses*.
* replace by "gasses that can absorb and emit radiation" if you wish.
BE: "@geronimo. The term 'delay' in a dynamic scenario, would be easily replaced by the word 'trapped'. Would it not?"
Possible, but as I pointed out, if the Sun suddenly went dead the "trapped" heat would eventually make it's way out of the atmosphere. So it isn't trapped at all, it's delayed and would leave if the heat wasn't being continuously renewed from its original source.
You asked for a simple explanation. That's my simple explanation, if it's wrong it wouldn't be the first time for me to be wrong. Nor the last.
My disagreement is because I see radiation from the surface temperature, that intercepted by GG, to first have travelled only a short distance. From successively greater heights, that distance increases as density decreases until it escapes. That is the dynamic process in the steady state: escape is rapid enough to be insignificant for temperature - no trapping. The steady state is one of significant energy within the atmosphere. That energy, thermalised, dictates atmospheric volume.
On your question of an atmosphere without GG. It would have a volume because of contact with a surface having average temperature above its condensation temperature. It would have a pressure gradient due to gravity and there would be mixing due to convection. I have no idea of its volume or temperature other than being different to a greenhouse atmosphere.
As to your definition. GE to my mind should not reference surface temperatures as it is the bottom of atmosphere temperature which concerns us. The surface radiating temperature is that which becomes necessary to drive the cooling process and it achieves that from solar energy: your t → ∞ description.
You are dancing on the head of a pin, trying to define the greenhouse effect while dodging the physics.
Martin A: perhaps that could be refined even further: “gases that can absorb energy.” As the atmosphere is over 99% NOT greenhouses gases, then it is fair to presume that these gases are also being warmed, else we would be walking around in a permanent frost, being burned by the occasional “greenhouse” molecule.
Let us compare the Earth with the Moon: the Moon has a negligible atmosphere, so thin that it could be declared non-existent. Were the Earth to be similar, then, as observed on the Moon, there would be baking of its surface by day, and freezing of it by night, as the heat gained is lost to space. An atmosphere of ANY composition would prevent this loss, as the gases would absorb some of the heat during the day, and prevent its loss during the night. It is how this heat is gained that is in question, for the “greenhouse effect”; this effectively states that it is the presence of GHGs that are the principle cause of the warming. That has to be errant nonsense, as the greenhouse gases comprise such a small proportion of the atmosphere. I moot that it is the conduction of heat from surfaces heated by the Sun to gas molecules in contact with that surface, and the subsequent movement of those molecules away from the surface, thus distributing the energy throughout the atmosphere, that prevents us from freezing.
This can be best be seen by observing the process in reverse: on a clear, still night in winter, frost may appear on the ground; exposed water surfaces may freeze, yet the air temperature just a short distance above ground may be above freezing. This is a phenomenon I have witnessed, not only in this country, but in the Persian Gulf, where the air temperature was warm enough for warm-weather clothing to be worn without cold discomfort. This indicates that the cooling of the air is primarily by contact with surfaces that are radiating heat to space; this is why plants can be merely covered to protect from frost, and do not have to be contained.
To declare that “greenhouse effect” depends upon “greenhouse gases” ignores what is observed on Venus.
Mar 7, 2017 at 10:34 AM | Radical Rodent
It also tends to ignore the lack of warming actually noticed on Earth.
Give enough semi intelligent climate scientists a typewriter each, and after a hundred years, some of them may come up with a more credible theory than the Orang Utans equipped with soft fruit. The Climate Scientists will complain that not providing Orang Utans with harder fruits such as apples for them to confuse with oranges, gave them an unfair advantage.
"...perhaps that could be refined even further: “gases that can absorb energy.”
Well *all* gasses (scuse my merkanized spelling) can absorb energy (eg by being heated or being compressed or being accelerated or being transported in a bottle to 30,000 ft in a plane.)
Martin AYou are dancing on the head of a pin, trying to define the greenhouse effect while dodging the physics.Mar 7, 2017 at 9:35 AM | Unregistered CommenterEntropic man
As you wish EM. I was trying to respond to BE's request for a definition that did not include a physical explanation.
Do you believe that other physical 'effects' (for example, the Doppler effect*) can only be defined if a physical explanation is included in the definition?
* Definition from Dictionary.com:noun, Physics.the shift in frequency (Doppler shift) of acoustic or electromagnetic radiation emitted by a source moving relative to an observer as perceived by the observer: the shift is to higher frequencies when the source approaches and to lower frequencies when it recedes.
gc, RR - The only real avenue to arguing that the greenhouse effect does not exist is to argue that the laws of physics as currently understood are erroneous.
That has to be errant nonsense, as the greenhouse gases comprise such a small proportion of the atmosphere.
We've been through this before. CO2 is only a small proportion of the atmosphere (H2O not such a small proportion) by volume, but they are 100% of the gasses that interact with radiation. The other gasses (N2, O2) might just as well not be there. The key question is How far on average does an IR photon travel in the lower atmosphere before being absorbed by a CO2 or H2O molecule..
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