The greenhouse effect is real. If there were no greenhouse gases in the atmosphere, earth would be a cold place. Compare Mars versus Venus – Mars has minimal greenhouse gas molecules in its’ atmosphere due to low atmospheric pressure, and is cold. By contrast, Venus has a lot of greenhouse gas molecules in its’ atmosphere, and is very hot. Temperature increases as greenhouse gas concentration increases. These are undisputed facts.
outgoing radiation = incoming radiation – changes in oceanic heat content
The image below from AER Research explains the radiative balance.
http://www.aer.com/scienceResearch/rc/rc.html
About 30% of the incoming shortwave radiation (SW) is reflected by clouds and from the earth’s surface. 20% is absorbed by clouds and re-emitted back into space as longwave (LW) radiation. The other 50% reaches the earth’s surface and warms us. All of that 50% eventually makes it back out into space as LW radiation, through intermediate processes of convection, conduction or radiation. As greenhouse gas concentration increases, the total number of collisions with GHG molecules increases. This makes it more difficult for LW radiation to escape. In order to maintain equilibrium, the temperature has to increase. Higher temperatures mean higher energies, which in turn increase the frequency of emission events. Thus the incoming/outgoing balance is maintained.
Click for larger image
http://www.aer.com/scienceResearch/rc/m-proj/lbl_clrt_mls.html
The important greenhouse gases are: H2O, CO2, O3, N2O, CO and CH4. The reason why the desert can get very cold at night is because of a lack of water vapor. The same is true for Antarctica. The extreme cold in Antarctica is due to high albedo and a lack of water vapor and clouds in the atmosphere, which results in almost all of the incoming radiation returning immediately to space.
An earth with no CO2 would be very cold. The first few tens of PPM produce a strong warming effect, and increases after that are incremental. It is widely agreed that a doubling of CO2 will increase atmospheric temperatures by about 1.2C, before feedbacks. So the debate is not about the greenhouse effect, it is about the feedbacks.
Suppose that the amount of reflected SW from clouds increases from 20% to 21%? That would cause a significant cooling effect. Thus the ability of GCM models to model future temperatures is largely dependent on the ability to model future clouds. Cloud modeling is acknowledged to be currently one of the weakest links in the GCMs. Given the sensitivity to clouds, it is perhaps surprising that some high profile climate scientists are willing to claim that 6C+ temperature rises are established science.
So the bottom line is that the greenhouse effect is real. Increasing CO2 will increase temperatures. If you want to make a knowledgeable argument, learn about the feedbacks. That is where the disagreement lies.
Ahh, foinavon, here it is:
http://www.drroyspencer.com/research-articles/satellite-and-climate-model-evidence/
What say you?
Smokey: “As stated here repeatedly, the term ‘denier’ has an unsavory connotation with holocaust denier.”
And “alarmist” has unsavoury connotations of scientists lying in the pursuit of money and power.
REPLY: Better check the definitions there Brendan, because in references, there is no place where “alarmist” has “unsavoury connotations of scientists lying in the pursuit of money and power”.
from http://dictionary.reference.com/browse/alarmist
a⋅larm⋅ist
/əˈlɑrmɪst/ Show Spelled Pronunciation [uh-lahr-mist] Show IPA
–noun
1. a person who tends to raise alarms, esp. without sufficient reason, as by exaggerating dangers or prophesying calamities.
–adjective
2. of or like an alarmist.
Origin:
1795–1805; alarm + -ist
see also http://en.wikipedia.org/wiki/Alarmism
Now let’s look at “denier”
http://en.wikipedia.org/wiki/Denier
one of the Wiki items is: Denial (state of), a person who denies something e.g.”He is a holocaust denier.”
See also: http://dictionary.reference.com/browse/denier “A person who denies.”
You lose on these points. Don’t bring up the issue again, because I have a low tolerance for discussion of it. – Anthony
Hi all,
and thanks to Steve for addressing another interesting topic.
However I want to ask about something which seems very interesting in the discussion, but completly ignored/downplayed in the original article.
The question, what exactly happens if the CO2-concentration is doubled (lets just say from 300 to 600ppm):
Apparently not much in the lower atmosphere as there is already a significant amount of CO2 there and the IR-radiation decays over a few 10m or so.
A doubling does affect the side bands but only changes little and the radiation at low heigths is then transferred into kinetic energy, which basically means once it is re-radiated most of it will be in a spectrum where water dominates the CO2.
So, I think the problem might be something like: At what height a doubling of CO2 would increase the absorbed energy (in a certain band) by 10%?
(or similar)
And the related question (from what I read here I guess this height is nowhere near the earth surface):
How much does this change affects the tempeature down here?
(And is this effect significant compared to others . . like clouds and so on?)
All the best
LoN
Maybe it’s the engineer in me but I do get irritated when I see the statement that the greenhouse effect is equivalent to 33C. It is not. When comparing current conditions to no atmosphere, you cannot separate the GHG and other atmos effects such as reflection, absorption etc. Because of these effects solar insolation at the surface averages about 232 w/m2. With no atmosphere the solar insolation rises to 315 w/m2. Without showing all the calcs this reduces the GHG effect from 33 C to 12 C. It is only 33C if the solar insolation is held constant. This is not physical. Whenever the atmosphere composition is changed you cannot hold insolation constant. Rising water content will reduce solar insolation due to not only reflection but also absorption. this is the negative feedback mechanism of water, the only GHG that partly absorbs solar radiation. It doesn’t take much increase in reflection/absorption to negate the CO2 effect.
Wrong two bodies.
The thought experiment envisions two bodies in a radiation field. Think of them as Earth with two different amounts of CO2 in the atmosphere. The argument is that adding CO2 cannot change the temperature of the body.
PLS says:
I don’t know who you were even responding to here with your first sentence but multiple responders including myself have explained to you in quite a bit of detail and from different angles why your argument is absolutely wrong.
Just to clarify what is wrong with this current incarnation: If you by “in the radiation field”, you mean a radiation field other than that produced by these two bodies themselves, then you do not have a closed system and the 2nd Law cannot be applied to it.
And, of course, anyone who has ever tried walking barefoot across an asphalt surface with some white paint on it (or across asphalt and cement surfaces) would immediately be able to tell you that you are wrong.
And, finally, if you mistakenly apply the 2nd Law to systems that are not closed, you can prove all sorts of things such as the notion that a refrigerator is a violation of the 2nd Law!
Gary says:
I understand your point…but I think how this is best stated is that the presence of our atmosphere causes multiple effects, the “greenhouse effect” which causes warming and other effects (reflection or absorption of some of the incoming solar radiation) that cause cooling. So, I don’t think it is incorrect to say that the greenhouse effect itself causes ~33C of warming. But, yes, it is important to also understand that the presence of water vapor…and especially condensed water vapor (clouds)…in the atmosphere cause reflection and absorption of some of the incoming solar radiation.
“multiple responders including myself have explained to you in quite a bit of detail and from different angles why your argument is absolutely wrong.”
Turn about is fair play, Joel. Persisting in your metaphysics and never admiting to material error does not engender responsible argument from your opponent.
gary gulrud says:
Care to cite an example of exactly what it is that you are talking about?
Lottta water going under the bridge here and some of it seems to be getting quite muddy.
I read most of what has transpired since I left my last note; and I have some differences of opinion with some of it, but there’s too many posts to identify individually.
Somewhere I believe it was Joel Shore who talked about ordinary atmosphere gases transferring theremal energy back to GHGs in collisions; and he implied that the atmosphere gases like N2 and O2 can’t radiate; being symmetrical diatomic molecules.
That’s not true. Thermal radiation following a somewhat black body spectrum, is emitted from all real physical bodies simply as a function of their temperature. The mechanism of that radiation is regarded in Classical Physics as deriving from the acceleration of elctric charges, which all physics substances contain.
You may recall that the early nuclear atom, was thought to radiate energy at a frequency corresponding to the orbital rotation rate of the eouter electrons which somehow were in orbit about the nucleus. This idea quickly fell on the scrap heap, as a result of the realization that an orbiting charge is in constant acceleration, and therefore must be constantly radiating EM waves; so it muct be continuously losing energy.
For you non-physics folks out there; quantities like velocity and momentum, are “vector” quantities; whiich means they have both “speed” and “direction”, and change of direction is an acceleration just as vhange of speed is. The continuous energy loss of accelerated charges, is the reason for the existence of the Stanford 2-mile Linear Accelerator. Electrons lose too much energy going around race tracks in circular type accelerators like Bevatrons and the like; hence use a straight line instead to reduce the energy losses.
So along came the Bohr atom with its stable non-radiating electron orbitals; which became probability clouds of where the electron might be found at any time; and radiation only occurrred during certain transitions from one permissable electron level to another. The resulting wavelength and energy emitted was the difference betweeen the energies of the two levels.
But that gives us line spectra with emission only at certain avelengths, and led to the science of atomic spectroscopy.
A diatomic molecule like N2 or O2 has six degrees of freedom; three translations, three rotations and one vibration, and it is usually only the vibrational mode of diatomic molecules which is non absorbtive. Threst do result in charges accelerating, leading to a radiated continuum of thermal radiation which depends only on the temperature (E=kT) where (k) is Boltzmann’s constant. It is interesting that Boltzmann derived the black body radiation law (Stefan -Boltzmann law) R = sT^4, where s (sigma) is the Stefan Boltzmann constant.
This was before Max Plack derived the exact spectrum of black body radiation, and launched the quantum era.
So the ordinary atmospheric gases DO (sorry about the caps foinavon) radiate thermal radiation solely as a function of their temperature, and since they radiate a black body spectrum, and not a line spectrum, only a portion of that radiation is in the absorption band of say CO2 or other GHG such as water.
So the downward radiation from the warm atmosphere (as well as upward) is a black body spectrum (roughly) and not a re-emission of the CO2 15 micron resonance line which is a vibration molecular mode of an assymmetrical kind (bending). Because the temperatures are not uniform throughout, then there are many overlapping BB spectra at slightly different peak wavelengths which is one reason why the whole thermal spectrum of earth is not a simple BB spectrum. But remember that the Stefan-Boltzmann T^4 relationship still holds.
I don’t think I agree with Steve Goddard that we would get quite cold without CO2 in the atmosphere. Maybe later on I will describe a desert island sand and stick experiment to show why I believe that isn’t so. Hell ! buy a Mai-tai, and we’ll use the little umbrella to scratch in the sand.
George
George Smith 15:22:16
“So the ordinary atmospheric gases DO (sorry about the caps foinavon) radiate thermal radiation solely as a function of their temperature, and since they radiate a black body spectrum, and not a line spectrum, only a portion of that radiation is in the absorption band of say CO2 or other GHG such as water.”
George, thank you for the refresher. However, gases don’t radiate a blackbody spectrum. Their spectrum is composed of thousands of discrete lines, each with its own emissivity. Here is a low resolution absorption spectrum for the atmospheric gasses. The upper panel indicates the blackbody spectrum at the indicated temperatures.
Solids and liquids may often be approximated as blackbodies, but obviously anything that has visual color cannot be a perfect blackbody.
http://upload.wikimedia.org/wikipedia/commons/7/7c/Atmospheric_Transmission.png
George E. Smith said:
First, I think you may have mixed me up with someone else as I didn’t talk about the transferring of thermal energy in collisions as far as I can recall.
However, in talking about why small amounts of trace gases such as CO2 play a disproportionately-large role in our climate, I did say the N2 and O2 don’t absorb infrared radiation…and, barring definitive evidence to the contrary, I stand by that. For example in Fundamentals of Fourier Transform Infrared Spectroscopy by Brian C. Smith ( http://books.google.com/books?id=cL_cvNCoEmkC&pg=PA11 ), it says
It is my understanding that the radiate in the microwave not the IR spectrum. If that is true than it is accurate to say that they do re-radiate energy and that they do not radiate IR.
Perhaps that is the important point?
I do not recall where I stumbled across that reference so cannot give a link to a source.
Larry
Folks — Sorry — good effort — but as the huge number of posts in reply show — there can’t really be a useful primmer on the Green House Effect
This is not surprising as once one gets a Ph.D. hood for work in physics the Prof. whispers to you the “Secret of / to the Universe” — Unfortunately I can not divulge this to the uninitiated (under the pain that the Universe will just collapse back into the …… and disappear) and as for the rest of those of us who have been initiated — well we already know it.
What I can do however — is drop a few oblique hints that may be illuminating (pardon the pun?)
1) Let’s start with an everyday experience — Look at your self in a mirror — no physicist can explain to anyone else how you can see yourself — or any coherent image for that matter (except by reverting to classical Electromagnetism)
2) In point of fact while QED (Quantum Electrodynamics) is considered to be the most validated theory that we have ever constructed — no closed form Quantum equation can explain in detail the energy levels of any atom except hydrogen (even H requires some fudging let alone what happens when you shine a photon on a H2 molecule) — even Helium (monatomic gas) is a problem — let alone a triatomic molecule such as CO2 or H2O
3) We do even worse when we have to consider more than one molecule or atom of the same species in a very rarefied gas (with only elastic collisions) let alone when we mix gases
4) Now let the atoms have some inelastic collisions — things rapidly become a hand waving exercise — left to the reader
5) Now if we let the gas molecules have some center of mass motion (temperature) when absorbing and reradiating then the Doppler effect starts to change the effective energies of the transitions and of course the individual molecules are also exchanging CM energy in their collisions
6) Skipping ahead a couple of graduate courses — Some of the absorption and reradiation transitions can be “forbidden” in the case of an isolated atom or molecule due to the “wrong quantum numbers” — however, when you let atoms collide and the other “funny stuff” — the transitions just might become allowed
7) some of the atoms or molecules can carry some of the excitation energy (due to photon absorption) with them when they move a considerable distance (particularly at low densities where because of the low probability of collisions (long mean free path) and the low probability of the transition (long effective lifetime) of the state (so-called metastable) — now they can appear somewhere else a long way from where they absorbed and already ready to radiate
8) there is a lot more and we are just trying to explain how a monochromatic beam of photons can pass through an isolated column of gas
9) Note nothing has been said about oceans, ice caps, clouds, aerosols, cosmic rays, solar magnetic fields, breaking waves, or any of the other things which make this an interesting topic
PS: — everything we treat in physics is considered a “closed systems” — in reality — perhaps the Universe is a “closed System” — But nothing else is
“”” pochas (19:14:23) :
George Smith 15:22:16
“So the ordinary atmospheric gases DO (sorry about the caps foinavon) radiate thermal radiation solely as a function of their temperature, and since they radiate a black body spectrum, and not a line spectrum, only a portion of that radiation is in the absorption band of say CO2 or other GHG such as water.”
George, thank you for the refresher. However, gases don’t radiate a blackbody spectrum. Their spectrum is composed of thousands of discrete lines, each with its own emissivity. Here is a low resolution absorption spectrum for the atmospheric gasses. The upper panel indicates the blackbody spectrum at the indicated temperatures.
Solids and liquids may often be approximated as blackbodies, but obviously anything that has visual color cannot be a perfect blackbody. “””
OK so perhaps I should have said “continuous spectrum” rather than “Black Body”. Yes I know about black grey, red, and blue bodies; and that no real body is a black body but some come close.
I believe I used the term thermal radiation.
The Wiki reference you gave (very nice plot thanks) is all about absorption spectra. It doesn’t say a thing about thermal radiation spectra.
The word “Thermal” generally implies thew concept of “Temperature”; and I believe I said that the thermal radiation was solely a function of temperature.
Now all of the ABSORPTION spectra in your Wiki post are either atomic or molecular (mostly) absorption spectra; they are a unique p[roperty of an individual molecule, or an individual atom.
No individual atom or molecule, has any idea what you are talking about when you mention the word TEMPERATURE; it is not a property of individual molecules or atoms.
Now I agree with Joel, that N2 and O2 don’t absorb in the long wave infrared. sorry for the mixed attribution there Joel.
Those absorption spectra are line spectra, and the intrinsic line specra are broadened by effects such as Doppler shifts, which are a result of the kinetic energy of the molecules themselves in a gas; which is a function of temperature (E=kT). The intermolecular collisions which are a function of total molecular density (pressure) also result in line broadening. The shorter the time interval between molecular collisions, the bigger is the energy shift. (Heisenberg ? maybe dE.dt > h/2pi )
So I don’t disagree that the absorption spectra of those molecular or atomic species in the atmosphere are line spectra which have to be explained in quantum mechanics, as westhighlander implies (or one might infer from his comments.
But I was not talking about those absorption spectra (other than that they exist); I was talking about the thermal emission spectrum of those gases; which depends roughly on the 4th power of temperature (yes I agree no real body is a true black body); but the BB spectrum bounds their possible thermal spectrum at the same temperature.
If we want to resort to quantum chromodynamics to explain global warming; we would need more space, and formatting and font capability than Anthony’s fireside here.
Then we might as well use Einstein’s general relativity, rather than Newton’s gravity or Keppler’s laws of orbital mechanics to explain the seasonal changes in climate.
We don’t need a 500# bomb to swat a fly. But Westhighlander’s comments do remind us that we can get a long way removed from “climate sensitivity”, or “forcings”, or any of the other trappings (like “anomalies”) that pass for science in the field of “Climatology”.
I believe that the Japanese recently described that as “ancient astrology”; and that might be unkind to the ancient astrologers.
But I shall have my own bookburning, and do some warming myself by setting fire to “The Infrared Handbook” of Wolfe and Zissis, and “Elements of Infrared Technology” by Kruse, McGlauchlin and McQuistan, along with all my optics and quantum electronics texts; and learn to rely on Google and Wikipedia for the gospel truths. And I need a new Handbook of Chemistry and Physics that contains all those new sciences like forcings.
George,
I’m afraid you will soon burn Google too. It will find this for you:
http://netfam.fmi.fi/PBL07/Savijarvi_Radiation-PBL.pdf
showing a LW spectrum not looking like a BB spectrum at all.
George E. Smith (08:56:56)
“But I was not talking about those absorption spectra (other than that they exist); I was talking about the thermal emission spectrum of those gases;…”
The two types of spectra are identical, as far as the frequencies of absorption/emission. I don’t want anybody to get the idea that gases absorb at discrete frequencies and emit as blackbodies. They don’t.
Referring to the first illustration:
Does this description represent the balance over just the land mass, or an average over the land mass and the oceans combined? If just the land mass, then it seems it would be very different over the oceans, and if this is just the land mass then can you post something explaining the balance over the ocean?
Your humble gardner.
jae (20:52:21) :
Nope, jae, that doesn’t address the point.
Lindzen made a very specific prediction. At a time when tropsopheric moisture content variations were not easily assessed, he predicted that moist (cumulus) convection, which is expected to increase with atmospheric warming under enhanced CO2 concentrations, would result in a drying of the upper troposphere. This proposed drying would be a negative feedback that would partly offset the positive feedback from enhanced water vapour at lower altitudes.
When it became possible to determine tropospheric moisture content relaibly, and assess the response to greenhouse-induced warming, it became cleat that Lindzen’s hypothesis was incorrect. The upper troposphere desn’t “dry” in in response to tropospheric warming….in fact it “moistens” (much as models predicted, as it happens).
Your blogger doesn’t address this point at all. He speculates (rather discursively) about all sorts of other things. But these don’t relate to the Lindzen hypothesis which was sufficiently specific that it could be assessed categorically by real world measurements.
The big picture is: global temperature and the amount of atmospherically CO2 through the centuries is cyclical. Sometimes somewhat capriciously but still unmistakable. Cyclic patterns in nature are always caused by a source with cyclical characteristics (e.g. global temperature by the sun cycles) and/or third order negative feedbacks.
Without negative feedback some values should grow continuously. So, if there has been a proven positive relationship between rising CO2 levels and rising temperature in the past, rising CO2 levels should have caused the increase of temperature “for ever”.
Nor temperature, nor CO2 levels have ever shown such characteristics.
And because nature cannot distinguish between “natural” CO2 and “manmade” CO2 (this dichotomization is of course rubbish), there will be always some negative feedbacks in place. So even the anthropogenic greenhouse gas levels and the global temperature will always decrease at a certain point as we actually have seen in nature. There for the IPCC 4th Evaluation Report’s conclusion that from now on atmospheric temperatures are likely to continuously increase, should be perceived as a falsified hypothesis.
“”” pochas (09:43:58) :
George E. Smith (08:56:56)
“But I was not talking about those absorption spectra (other than that they exist); I was talking about the thermal emission spectrum of those gases;…”
The two types of spectra are identical, as far as the frequencies of absorption/emission. I don’t want anybody to get the idea that gases absorb at discrete frequencies and emit as blackbodies. They don’t. “””
Well I think I’ve restated enough that nothing emits like a black body.
The paper cited by Igl above contains a whole lot of meteorological stuff that is outside of my knowledge base; so I’m not able to comment intelligently on that. I notice he does mention “continuum radiation” from water; as well as line spectra.
But for the moment I will just accept that gases don’t emit any thermal radiation; despite the fact that every text book I’ve ever seen particularly on infra-red technology have all stated that every single thing in the universe emits thermal radiation due to its temperature; and yes I accept that nothing in the universe emits black body radiation.
I would like to know just what that water “continuum radiation” is though; and what causes it.
By the way; Kirchoffs law only relates to a body that is in thermal equilibrium with its surroundings at a given temperature; well I suppose my textbooks are wrong on that too.
I wonder why the sun seems to emit a “continuum ” radiation, even though it isn’t solid or liquid; well I suppose plasmas do contain accelerating electric charges.
And for the record I’ll repeat; no not all thermal radiation spectra are blackbody spectra; but they are thermodynamically limited to radiate less than a BB (at any wavelength); well at least that’s what my textbooks say.
George,
From Pierrehumbert’s ClimateVol1.pdf:
“A Nitrogen molecule N2 in isolation does not interact to any significant extent with infrared light; one might think that collisions do not change this picture, as N2 has no lines to be broadened by collisions. Nonetheless, during the time a collision is taking place the pair of colliding molecules momentarily behaves somewhat like a more complex four-atom molecule, which has transitions that can indeed absorb and emit infrared radiation. This leads to collision-induced absorption, whose associated absorption coefficient is generally a smooth function of wavenumber. Because of the lack of line structure, such absorption is referred to as a continuum. There are many possible processes through which collisions can induce absorption. The collision can impart a temporary dipole moment to a rotation or vibration that ordinarily had none, allowing it to absorb or emit a photon. The collision can break a symmetry, allowing transitions that are otherwise ”forbidden”
by symmetry principles”
So maybe you are 10% right 🙂
Dick H. Ahles (12:03:57)
“”” lgl (12:50:53) :
George,
From Pierrehumbert’s ClimateVol1.pdf:
“A Nitrogen molecule N2 in isolation does not interact to any significant extent with infrared light; one might think that collisions do not change this picture, as N2 has no lines to be broadened by collisions. “””
Thanks Igl; so Peter Humbug to the rescue !
Well I always wondered what the source of thermal (hot body) radiation was whether BB or “pseudo BB”, because I knew it couldn’t be an infinite sequence of line spectra and somehow have anything like that Planck spectral behavior. Don’t remember which of my books pointed out that any material body has at least electric charges, which undergo accelerations as a result of the “molecular” temperature.
You have to remember that my graduation day was 52 years ago; when there wasn’t any quantum chromodynamics; hell the “8-fold way” was the cats meow. And to add insult to injury; ALL of my High school and college textbooks went into a box that supposedly went on a boat, but a month later, it failed to come off that boat on the Manhattan docks; so I have had to go by memory mostly since then; replacing only those that had any pertinence to my work needs which wasn’t much in the high tech industry.
Maybe 90% of what I learned in school was never ever used in my daily work; so there’s some cobwebs in there I know.
I’m intrigued by that transient supermolecule concept though. The lay public doesn’t know how much stranger than fiction the truth really is; maybe that’s what keeps me going.
George
We are always taught that nothing can go faster than the velocity of light; well actually, I believe the pedantic version is that nothing can go faster than (c); the velocity of light in vacuo.
For example, relativistic charged particles travelling very close to (c) upon crashing into a solid media; say a Cesium Iodide crystal, suddenly find themselves travelling faster than the local velocity of light (c/n), so if for no other reason they have to slam on the brakes, and during that braking deceleration you get Bremsstrahlung radiation which IS a cointinuous spectrum of “braking radiation”, which I think is the literal translation of Bremsstrahlung. Anna v is probably an expert on this stuff; I only remember it from my days messing around with scintillation detectors; although I used Anthracene and Stilbene Crystals instead oc CsI, since I was interested in Neutron detection; and my Po/Be neutrons always came with tons of gammas. We were too poor to be able to get Pu/Be neutron sources; not to mention that unmentionable word.
But somehow, I don’t think atmospheric IR radiation can be regarded as Bremsstrahlung of a sorts.
George