I have been struggling to understand exactly how increasing CO2 levels leads to global warming using basic physics, and the story is complex. The trapping of certain bands of infrared radiation emitted from the Earth by greenhouse gases is well known. The effective cross-section of CO2 of absorption for CO2 in its rotational bands is also well known (HITRAN). Using the current concentration of CO2 in the atmosphere it is also clear that essentially all the radiation emitted by the surface in these bands is already absorbed by CO2 at pre-industrial levels. In fact spectra from space show that the main CO2 bands are saturated in the lower atmosphere with minimal emission from the high atmosphere. The absorption of radiation follows a logarithmic law with distance assuming a uniform concentration of CO2 in air. All that happens if you double the concentration of CO2 in air is that the absorption length is halved. So more radiant energy is absorbed and reflected back to earth at lower levels of the atmosphere than before. However the total energy balance would appear at first sight to be almost unchanged. In fact just such an experiment was performed by Herr. Koch and led Angstrom to dismiss theories of man induced warming already back in the early 20th century (Realclimate: what Angstrom didn’t know).
There are 3 main CO2 bands of IR absorption at wavelengths 1388, 667, 2349 cm-1 (HITRAN) and these are already saturated at current levels of CO2 in the atmosphere. Infra Red measurements from space show that the atmosphere is opaque at these wavelengths. However at high levels in the atmosphere this is not no longer true and this is the only argument for the enhanced greenhouse warming by CO2 warming which makes sense to me (see below).
Spectra of solar radiation and outgoing Infrared radiation. Note CO2 absorption bands ref: Barry & Chorley.
There is a very interesting paper here : http://brneurosci.org/co2.html which describes the basic physics. The absorption length for the existing concentration of CO2 is around 25 meters i.e. the distance to reduce the intensity by 1/e. All agree that direct IR radiation in the main CO2 bands is absorbed well below 1 km above the earth. Increasing levels of CO2 merely cause the absorption length to move closer to the surface. Doubling the amount of CO2 does not double the amount of global warming. Any increase could be at most logarithmic, and this is also generally agreed by all sides.
Lab experiments using tubes filled with CO2 to represent the atmosphere show that the IR transmission is essentially saturated and doubling the amount changes the transmission very slightly . So what is wrong and how are these arguments refuted by the majority of climate scientists? There are two main arguments why global warming is important despite apparent saturation when man adds CO2 to the atmosphere (see Realclimate ). The first of these is rather convincing.
1. IR scatters repeatably upward through layers of the atmosphere until at between 5-9 km the air is so thin that the the atmosphere becomes transparent allowing CO2 emissions here to radiate out into space. At these levels there is little water vapour and CO2 dominates the energy loss. As CO2 concentrations increase so this level shifts to higher levels in the atmosphere since a critical density must be reached for the radiation to escape. These levels are colder (until we reach the troposphere) and IR loss is proportional to T**4 (Stefan Boltzman’s law). This means that slightly LESS energy is radiated to space than before and since the total energy must balance, the Earth warms up to radiate more heat to compensate. Don’t forget that there are windows in the IR spectrum with no absorption other than water vapour allows extra energy loss through evaporation and IR emission from clouds. Clouds also increase albedo. The vertical concentration of H2O and clouds are both temperature dependent. The temperature profile of the atmosphere is called the (adiabatic) lapse rate and is approximately -7 degrees per km falling to -4 degrees per km in the tropics. This is valid up to the Tropopause after which temperature rises again in the stratosphere. So greenhouse warming depends on falling temperature with height, and the anthropic enhanced greenhouse effect due to CO2 emissions is equal to the reduction of IR emissions to space in CO2 bands from the upper troposphere.
2. It is not completely true that the CO2 absorption bands are saturated as the fine structure is quite complex and in the side bands there is still energy left for the atmosphere to absorb. This is a much smaller effect than the first point. The extra absorption caused by an increase of a factor 4 is just a few percent as shown in the figure. In fact already 95% of the radiant energy is absorbed by CO2 at pre-industrial levels leaving a maximum of just 5% for any increase you like. It is often estimated that the CO2 green house warming component of the planet is about 3 degrees C so this extra absorption and emission to the surface would appear to only add just 0.15 degrees of warming.
Saturation now and @ 4*CO2 levels (note LOG scale)
Therefore the main physics arguement supporting enhanced global warming caused by increasing levels of CO2 is the in height and thereby lower temperature of the effective radiating level of the atmosphere to space. The first comment to make is that we never hear this crucial explanation in the popular descriptions of the greenhouse effect. We just hear that more CO2 absorbs more heat radiated from the earth and radiates it back to the surface thereby heating us up just like a thicker blanket does in bed (blankets actually work by cutting down convection losses). However the real explanation above concerns just the outermost layers of the atmosphere. The enhanced greenhouse effect depends on a decreasing temperature gradient with height so that as the effective radiating level for IR by CO2 rises so the energy loss falls and the earth must rise in temperature to compensate. Energy balance demands that there is a perfect match between incoming solar energy and outgoing IR energy. So lets look at this in more detail.
The effective temperature for all IR emissions is around -20 degrees C radiating at a height h of 5km. Now suppose that we double CO2 concentrations and the effective last radiating level rises to say 6 km. The temperature would now be about -27 degrees C as the decrease is almost linear in the troposphere. However the effective surface area is now also greater by an amount 8*PI*R (where R is radius of the Earth = 6350) making 1.6*10**5 sq km larger than at 5 km height. The IR radiation falls off with temperature as T**4 which gives us a reduction of about 18% relative to before.
However if we just look at the main CO2 emission band and use the measurements from space (taken from Houghton’s book Global Warming – A complete Briefing). It would appear that the effective temperature of CO2 band alone is -53 degrees C which is almost at the tropopause ( -60 degrees). So with all else remaining the same (water vapour, methane etc.) the drop in energy loss is just 3% in that single band.
CO2 causes the lower atmosphere to be opaque at the main absorption bands. The mean free path is only about 25 meters, so at these wavelengths the lower atmosphere is already like a thick fog where IR radiation is scattered in all directions. As we rise up in the atmosphere so the density falls exponentially and only at heights of 8-9 kms does the atmosphere then become transparent in the main CO2 bands allowing energy loss direct to space. Doubling concentration rises that level nearer to the tropopause which radiates at a lower temperature. The estimate given for the Earth’s warmng in Houghton’s book is 1.2 degrees for each doubling – so 2.4 degrees would be the heating if CO2 concentrations were to increase by a factor 4. These figures are based on a radiation reduction of 4 watts/meter**2 caused by this effect of the effective radiation level rising to a colder level. In his book Prof. Houghton says this can easily be proved, but I have not understood where this figure comes from nor how it has been calculated.
Feedback Effects
The IPCC predictions of future warming are based on model assumptions of positive feedback effects which are supposed to result from the initial warming caused by CO2 emissions. The main feedback effect is that of increased evaporation of the oceans leading to an increased greenhouse effect of water vapour (already 80 – 90% of greenhouse effect). However it is known that cloud cover in general leads to a net cooling effect on the Earth by blocking incident solar radiation. An increase in cloud cover of 10% would be enough to cancel out global warming effcets of increased CO2 ( Barry & Chorley).
Radiative Forcing Update: I have now found this reference to the equations used to derive the 4 watts/sq m radiative forcing by doubling the amount of CO2 in the atmosphere.
rf = f * ln([CO2]/[CO2]prein)/ln(2) in watts/m ** 2
It would appear that in order to derive the factor f the IPCC assume that all of the 0.6 degrees warming apparently seen since the industrial revoluton is due to CO2 and thereby derive the constant
AF = 5.35 ln(C/Co)
Then we get simply 5.35*ln(2) = 3.7 watts/sq m for the radiative forcing of doubling CO2 !
If it is really true that this formula has been derived only by assuming that all “observed” temperature rise since 1750 is caused only by CO2 increases, then I fear this is a circular argument ! Many skeptics argue that the recent rises in temperature is dominated by a natural recovery from the little Ice Age. In order to be convinced that CO2 is the primary cause of recent warming then I would prefer that this formula could be derived from basic physical arguments rather than introducing a fudge factor preset to prove a theory.
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Pingback: The great boon of CO2 « Liberalism. An alternative blog of Sanjeev Sabhlok
Hi Clive,
you can find a derivation of all necessary formulas from first priciples in every climate science primer.
However, a more accessible explanation is here: http://scienceofdoom.com/2009/11/28/co2-an-insignificant-trace-gas-part-one/
(9 parts now!)
Cheers,
Babelsguy
“the air is so thin that the the atmosphere becomes transparent allowing CO2 emissions here to radiate out into space. At these levels there is little water vapour and CO2 dominates the energy loss. As CO2 concentrations increase so this level shifts to higher levels in the atmosphere since a critical density must be reached for the radiation to escape. These levels are colder ”
If we are talking about a photon of energy emitted by a CO2 molecule from say, 9000 meters, how does putting a CO2 molecule at 9100 meters, which absorbs and re-emits that photon, reduce the energy of that photon?
The entire argument about ‘higher equals colder’ rests on kinetic to emissive energy change, such that a collision between a CO2 molecule and say an O2 molecule at 9100 m results in less CO2 stimulation than one at 9000 m. In this instance yes, the emitted photon will have less energy when emitted to space.
But what would happen in the absence of that CO2 molecule at 9100 m? No energy would be emitted to space. This means the energy is kept in the atmosphere.
So in case 1, a photon passed up a chain of CO2 molecules, the energy is the same when emitted to space. And in case 2, a kinetic->emmisive change and emission would not occur in the absence of the CO2 molecule.
I think you’re missing the point. At higher altitudes, the photon emitted has a lower probability of being intercepted by a CO2 molecule, allowing it a higher probability to be radiated into space.
That confused me for a while too despite my undergraduate physics degree. The trick is realizing it’s not a “chain of CO2 molecules”. When a CO2 molecule absorbs an infrared photon and starts vibrating it usually crashes into other air molecules which diffuses the energy. The average temperature increases. At any given moment some CO2 molecules will be moving faster than others and some will have more vibrational energy. A CO2 molecule with enough vibrational energy may emit a photon and stop vibrating. The average temperature tells how many CO2 molecules will have enough energy to emit a photon. Colder temperatures shift the velocity distribution down and fewer CO2 molecules emit infrared radiation. Air warms up if it emits fewer photons than it absorbs. Escaping heat energy leapfrogs its way up the atmosphere until it radiates into space. More CO2 means that threshold happens higher in the atmosphere. Higher=colder=less energy radiated into space=”greenhouse effect”
As to the CO2 molecule at 9100 m. If it’s not there then the photon continues out into space. If it is there and doesn’t hit any other molecules it emits a photon a few milliseconds later — in a random direction. About equally likely to send a photon back down towards the earth as out into space.
Yes, that mechanism seems correct; However, I think that the Earth’s surface emits only a certain number of photons in the absorption band of CO2; Consequently, when all these photons are absorbed by the CO2 in the atmosphere, whether or not they are re-emitted and regardless of their height, the greenhouse effect will be self-limited and doubling the CO2 in the atmosphere will have no added greenhouse effect.
No because the cartoon seen everywhere is very incorrect. It’s a highly-simplified concept cartoon for the public. A CO2 molecule (and any molecule) collides ~2,600,000 times per second (obviously more when it’s warmer and less when it’s colder) and there’s a chance that CO2 on colliding will acquire molecular vibrational energy and then spontaneously emit electromagnetic radiation at the frequency corresponding to the energy of the molecular vibrational energy so CO2 molecules are constantly producing electromagnetic radiation and constantly absorbing it, and may either gain or lose the molecular vibrational energy on collision, so the energy is transmutable in both directions, so no limit is imposed on electromagnetic radiation quantity in this band in the atmosphere by the quantity transmitted from surface. As you see, it cannot “all get used up” as you think it can.
No that’s incorrect. The CO2 molecules are constantly obtaining molecular vibrational energy on collision and might occasionally spontaneously emit electromagnetic radiation at the frequency corresponding to the energy of the molecular vibrational energy so no limit is imposed on electromagnetic radiation quantity in this band in the atmosphere by the quantity transmitted from surface.
Mr. Grindupbaker. What you imply is nothing more than an example of “perpetum mobile”. The Earth receives energy from the sun with a black body spectrum, simplifying, of 6000º K. The atmosphere obstructs energy from that solar radiation and heats up. The surface of the Earth also receives the rest of that radiation that has not been absorbed by the atmosphere and is heated and consequently emits radiation, simplifying, with the spectrum of a black body at 287º K. There are no other sources of energy than the sun and the earth’s surface that can heat the atmosphere. And if the energy emitted by the Earth’s surface is only capable of being absorbed by the co2 of the atmosphere in a narrow strip with a limited number of photons, that will be the maximum flow of energy that will not be emitted to the open space and will be captured in the atmosphere by the co2, the one that already exists or the one that in the future is added. The atmosphere itself cannot warm itself.
I have been searching all over the place for a proper calculation of actual IR emissions from CO2 at different pressures, temperatures and concentrations. It is quite common in climate science papers to just assert, just as Mr. Grindupbaker, that CO2 emits IR radiation, but as far as I can see this emission is quite complex, as the average time for a CO2 molecule in a vibration state to emit a photon is in the area of 1s, while the average time before it collides with another mollecule at 1atm is about 1ns. (This is what causes absorption, photons are converted into heat and not into new photons)
This of cause changes with pressure, when the chance of collision is greatly reduced. This goes both ways, as the chance of a collision that causes a CO2 molecule to actually end up in one of the vibration modes is reduced at the same time as the chance of this vibration actually ending up as a photon is increased.
I guess the basic starting point would be the probability of a collision causing the CO2 molecule to go into a vibration mode, the probability of a collision of a vibrating molecule causing it to loose the vibration and the probability of a vibrating molecule to emit a photon.
If anyone has any reference to such calculation I would be very interested to hear.
Are you saying that if the alleyway gets too congested with co2 molecules, then they bumpt into each other b/c it is so crowded that emission goes up or absorption goes up.
Thanks – This is by far the best clearest review of the greenhouse effect I have found. It is a great set of articles which describes energy balance and radiative transfer effects in the atmosphere. There is unfortunately no simple formula for the greenhouse effect, since the details of real calculations get complex quickly. Results rely on numerical analysis but confirm a direct warming of around 1.2 degrees for each successive doubling of CO2.
What you’re seeing is that we really have warmed some – every thousand years we have a warm period. The Mycenaean, The Roman and the Medieval are over the last 4000 years. What this additional warming does is to move more heat into the stratosphere. From here it is radiated off into space from H20 and the other gases among them being CO2 which at the moment is only one out of every 2500 molecules – in total saturation in the lower atmosphere but in the stratosphere capable of radiating heat and reabsorbing heat exuding from the troposphere. Nothing complex going on here. What the additional warming appears to be from are the synchronization of the cyclic Milankovitch Cycles.
Why, then, is the stratosphere cooling with increased levels of CO2?
Gorm: Like everything else in the universe, the stratosphere is cooling (or warming) because it is gaining less (or more) energy than it is losing. That is simply the law of conservation at work – the difference comes from or adds to internal energy/temperature. The stratosphere is relatively simple because radiation is the only significant route by which it gains or loses energy. The stratosphere gains energy when ozone absorbs solar UV. Ozone has been reduced for the last few decades of a rise in sources of chlorine free radicals.
Assuming you consider ozone fixed and CO2 increasing, you can understand the origin of predicted cooling from increasing CO2 by applying Schwarzschild’s equation for radiative transfer (for a non-scattering atmosphere):
dI = n*o*B(lambda,T)*ds – n*o*I*ds = n*o*[ B(lambda,T) – I ]*ds
dI = n*o*[ B(lambda,T) – I ]*ds
where I is the spectral intensity of the radiation at a particular altitude and wavelength, dI is the incremental change in that radiation upon passing an incremental distance ds through a layer of atmosphere, n is the density of absorbing/emitting molecules (GHGs), o is the absorption cross-section for a particular GHG at the wavelength of interest, T is the local temperature in the layer, and B(lambda,T) is Planck’s function. In the top equation, the left-hand term is emission by the GHGs in the increment ds and the right-hand term is absorption by the same GHGs.
https://en.wikipedia.org/wiki/Schwarzschild%27s_equation_for_radiative_transfer
When local radiation (I) is less intense than blackbody radiation (B(lambda,T)), dI is positive. If integrating dI over all relevant LWR wavelengths is positive, then that layer of stratosphere is a net loser of energy by LWR radiation. The stratosphere can be a continuous net loser of LWR because it continuously absorbs enough SWR to balance its net loss through LWR. So the term in [brackets] is positive in the stratosphere for LWR. The net loss of LWR (dI) will increase as the amount of CO2 (n) increases. That means that stratosphere will cool in response to an increase in CO2 (or a decrease in ozone).
The troposphere is more complicated. dI is negative almost everywhere in the troposphere, which is why outward radiation decreases from an average of 390 W/m2 near the surface to a little less than 240 W/m2 at the tropopause. The emission from GHGs in any layer of troposphere is equal in the all directions, but the intensity I is greater in the upward direction than the downward direction. This is because it is warmer lower in the atmosphere and at the surface where the upward flux of I originates. So the change in the upward flux, dI or dOLR, is usually negative in troposphere, and it becomes more negative as the density of GHGs (n) increases. This reduces the rate of radiative cooling to space, meaning the planet must warm.
(The local temperature in the troposphere is controlled by several other factors including the increasing absorption of DLR as GHGs increase, absorption of SWR and the convective transport of latent and simple heat. Schwarzschild’s equation alone doesn’t deal with all of these phenomena. For that you need an AOGCM.)
Finally, a sophisticated reader might note that dI is proportional to n, whereas radiative forcing is proportional to log(n). I’ve cheated above by pretending that the [ B(lambda,T) – I ] term is a constant independent of changes in n. At strongly absorbed wavelengths in the lower troposphere, absorption and emission are in equilibrium and B(lambda,T) – I is zero. By definition, temperature-independent absorption and temperature-dependent emission are in equilibrium at the local temperature when radiation has blackbody intensity – because this is an assumption Planck made when deriving Planck’s Law. However, temperature and density change with altitude in our atmosphere, preventing absorption and emission from reaching equilibrium at many locations. Those who say that strong absorption bands are “saturated” typically forget about emission. What they should be saying is that absorption and emission are in equilibrium, that B(lambda,T) – I is zero, and that radiation is unchanged as it passes upward through the atmosphere. This is true for strong absorptions in the lower atmosphere, but not at all wavelengths and altitudes. Radiation and GHGs interact with the local temperature gradient and density gradient in a very complicated way to produce the GHE and enhanced GHE. There certainly would be NO GHE if the atmosphere were isothermal. Given an atmospheric composition and fixed temperature and density gradients, integrating Schwarzschild’s equation from the surface to space and from space to the surface allows us to calculate the instantaneous change in OLR and DLR following a change in CO2 or other GHG. However, I can’t rigorously justify the outcome of such numerical integration and have been forced to resort to a fair amount of hand-waving. The best calculations show that doubling CO2 OLR will reduce radiative cooling to space by about 3.7 W/m2 in today’s atmosphere and produce cooling in the stratosphere – consistent with my handwaving.
Clive, the explanation you have given isn’t correct. The formula of dF = 5.35 ln(C/Co) isn’t worked out from existing climate change.
When the “radiative transfer equations” are solved to give the value of “radiative forcing” for many different concentrations of CO2 and plotted out, this formula is simply a reasonable empirical fit.
It has nothing to do with the actual temperature change and therefore isn’t a circular argument.
You can see this part explained in http://scienceofdoom.com/2010/02/19/co2-an-insignificant-trace-gas-part-seven-the-boring-numbers/
Feel free to ask any questions there, or any other part of the “CO2 – An Insignificant Trace Gas” series – http://scienceofdoom.com/2009/11/28/co2-an-insignificant-trace-gas-part-one/
This paper by Dietze
http://www.john-daly.com/forcing/forcing.htm
seems to be a very good paper on the effect of
doubling co2.
In addition…..
The clickable ” open review….” at the top of the
Dietze paper has several other good links.
In particular the paper by Courtney on Venus
is quite interesting and informative.
My continuing study of the influence of CO2
seems increasingly to show something
like
0.25 deg.K < sens. < 0.5 deg.
emerging as a new range for the doubling
sensitivity replacing the much higher
values cited not too long ago.
Clive,
I have reread the
http://scienceofdoom.com/2010/02/19/co2-an-insignificant-trace-gas-part-seven-the-boring-numbers/
If I have failed to understand that reference,
I apologize for the failure, but, I keep coming up with the same problem:
The treatment of CO2 forcing found in “scienceofdoom”
seems, indeed, to be circular. That is, it seems to
be an example of the “Petition Principii Fallacy”
in which the conclusion of an argument is basically
present at the argument’s start as an unquestioned
premise. The unquestioned premise, to be specific,
is that the recent temperature rise has been driven
by the recent CO2 rise.
Where is it established that the temperature data
is “caused”, in a meaningful physical sense, by
the CO2 data?
I see the “Scienceofdoom” argument
for the ” 5.35 ln (C/Co) ” formula as presuming
that the observed temperature rise is caused by
the observed CO2 rise.
That is to say, the very question which is at
issue seems to me to have been answered at the very start of the putative argument; if we assume that CO2 has driven the recent temperature rise, then, of course we get
the
“5.35 Ln(C/Co)” formula; it simply summarizes the data.
On the other hand,
if, as some authors argue, and, if, as some data
strongly suggests, about 80% of the CO2 data time series
is caused by such things as ocean temperature
changes, then, the calculation of the CO2 forcing
value is too high.
Here is one of many articles which questions
how the commonly accepted 4 w/m2 forcing
value was derived:
http://www.drroyspencer.com/2009/05/global-warming-causing-carbon-dioxide-increases-a-simple-model/
I think that Science of Doom (SoD) is partly using a circular argument! The IPSC figures of 1.7 W/m2 for current and 3.7 W/m2 for doubling concentrations of CO2 would appear to be based on the assumption that all “observed” warming is due to human induced CO2 emissions. However he also states that :
– Myhre at al (1998) “Just for Interest !” calculated the radiative forcing to be – CO2 current (1995) compared to pre-industrial, clear sky – 1.76W/m2, cloudy sky 1.37W/m2. The questions is was this really calculated from first principals or was it also “calibrated” from observed warming.
We know that the Earth’s climate has survived many catastrophes in the past – yet maintained an environment suitable for life over eons. The idea that CO2 levels alone determine the temperature has become a sort of religion. Other more important mechanisms must be at work and it is obvious that the Oceans have to be the main stabilizing influence. Otherwise why did not the climate not run away after the last ice age as CO2 outgased from the warming oceans causing more global warming causing more outgasing?
As Roy Spencer argues CO2 levels have for at least the last million years been an effect of climate change and not the cause ! Can the tail wag the Dog ? Well the IPCC supporters are obviously convinced the answer is yes ! The physics certainly supports a small warming effect of about 1 degree from a doubling of CO2 in the atmosphere, but this can be easily offset by small changes in humidity and cloud cover. These may also be driven by outside factors like cosmic ray intensity, solar wind and the sun’s magnetic field strength .
I think you are correct.
The reason the temperature increases isn’t because of CO2 concentration, since it is already saturated. IMO, the collapse of ecosystems is the reason. Sun light, once it reaches the earth does 2 things and 2 things only. Heats up and life creation (essentially the carbon cycle which requires sun light) If the latter disappears, the radiation that was used to create life, is transformed into heat, which radiates back into the atmosphere. A 10kmx10km plot of desert radiates ~ 700 MW (with a ground albedo of ~ 30%), if you do the math, in dry air, that’s about +0.0025C / hour (yes, hour) of a 10km3 cube of air, if the radiation from the sun is 1kW/m2 (all of it is mostly remitted in the IR band).
The earth warms up because the portion of sun light that was used to create life doesn’t create life anymore (no more ecosystems to do the job). Instead it generates heat, and will do so until we all suffocate.
Finally, the assertion made by the green industrial complex “high CO2 => incompatible with life” if it were true, would be equivalent to “compatible with life => low CO2”, which we know is false. The Cambrian period had 10x more CO2, but was full of life.
Climate change is real, there is no question about it. But it is not caused by CO2.
My best guess is it caused by the collapse of ecosystems, everywhere on the planet, which prevent the transformation of sun light into living things. Instead, it is radiated back in the form of heat, then captured by the atmosphere, which temperature increases because it receives more heat than before.
I am more partial to this explanation. This renders CO2 as symptom and not cause. There is a bigger picture here.
I read your sentence and for the life of me, I cannot understand what you mean. To recap:
CO2 isn’t a symptom of anything, and I didn’t claim it was. CO2 does not increase infrared capture, because the atmosphere is already 100% opaque in the CO2 bands. What it might do is lessen the emission back into space, but it a much smaller effect. I’m not convinced about it. Also, CO2 is active in the far infrared, which is a very very small portion of the light emitted by the sun. Water is far far more efficient. Proof: nights in a desert are very cold, up to a 30celcius drop from daytime.
If the CO2 contribution were correct, all life on earth would have been killed off in the Cambrian. So, CO2’s role is minimal at best, a fraud at worst.
Can you please let me know what you mean?
If it is true that CO2 is not the best candidate
for causing the recent warming, than how valid
are both the derivation and the uses of the
“5.35 Ln C/Co ” formula?
I propose that we try to reduce the confusing
back and forth that typifies so much of the discussions
about global warming by giving what we are discussing
here, recently, both a clear phrasing as a “yes/no” question and an
abbreviated name.
To wit, letting “5.35” stand for the “5.35 ln C/Co”
formula,
The “5.35” question I propose is this:
“Yes”, or “No” do the various sites such
as “scienceofdoom” commit the “Petitio
Principii Fallacy” in that their derivations and
interpretations of “5.35” take it as a starting
unquestioned premise that the temp. time series
data and the CO2 time series data
depict a cause and an effect?
More concisely,
“Yes”, or, “No” is an unwarranted assumption of
cause and effect made in interpreting the recent
temperature and CO2 data?
My answer is “Yes”.
I say “Yes”. I say “yes” because there is a great
deal of data which correlates, in a cause/effect
manner, to the recent temperature rise better than does
CO2. Here, for example, we have
sunspots
http://motls.blogspot.com/2004/09/sunspots-correlations-with-temperature.html
The “PDO”
http://www.appinsys.com/GlobalWarming/PDO.htm
The “SOI”
http://members.iinet.net.au/~glrmc/McLean_deFreitas_Carter_JGR_2009.pdf
etc. etc.
1. Your figure:
“…Saturation now and @ 4*CO2 levels (note LOG scale)..”
Seems quite important to me in getting a hard number
on the “2X sensitivity” number. Could you give me the
citation for this chart?
2. Could you explicate how you get to your
statement
“…so this extra absorption and emission to the surface would appear to only add just 0.15 degrees of warming….”
from the figure I just referred to?
I come up with similar numbers using my own
estimates for 2X warming. Miskolczi likewise
gets 2X values way lower than those of the IPCC.
3. I assume that you recommend having Houghton as a basic
reference. Are there others? I am just beginning to build
up a personal climate science library.
1 This figure is taken from http://www.realclimate.org/index.php/archives/2007/06/a-saturated-gassy-argument-part-ii/ – sorry – I should have referenced it directly. So the data is from what some skeptics call the “Hockey Team”.
2. This statement is based on the following: The main greenhouse gas n the atmosphere is water vapour and 75% of the Earth’s surface is covered in Ocean. Therefore water stabilises the climate and drives all weather. Assuming a total greenhouse effect (water + CO2) of about 20 degrees then the extra greenhouse warming component provided by CO2 (beyond water vapour) would be around 3 degree (10 – 20%). Adding CO2 to the atmosphere gives only a logarithmic increase to warming. Therefore, feedbacks excluded a doubling of CO2 will add only < 1 degree warming and a quadrupling of CO2 < 2 degrees warming. The whole IPCC argument which has mesmerised the world's politicians is based on the hypothesis, unsupported by measurements, that there is a positive feedback whereby small CO2 enhanced warming causes water to evaporate from the Oceans accelerating warming. However, if that was true then we would not be here today to discuss such esoteric issues, because life would have been snuffed out endless times in the past due to volcanic CO2 emissions or outgassing of CO2 after Ice Ages.
@clive “whereby small CO2 enhanced warming causes water to evaporate from the Oceans accelerating warming. However, if that was true then we would not be here today to discuss such esoteric issues, because life would have been snuffed out endless times in the past due to volcanic CO2 emissions or outgassing of CO2 after Ice Ages.”
I guess I followed your argument til the point above. Isn’t the problem also beyond evaporation, that ocean warming causes oceans to release CO2 gas, so you get a feedback loop of CO2 warming and release.
Also, I don’t understand your “snuffed out” comment. Would life be Snuffed out (suffocated?) by a huge CO2 release? Certain plants adapted in the past; and humans can handle what 3%
I’m not trying to be snide- more that I followed your point but then at the end of your May 23rd, 2011 point #2, I crashed on the rocks of the two issues above.
I am sure you know much more than I, could you tell me if I am on track
3. Houghton’s book from around 1995 “Global Warming: the complete briefing” is a very good objective summary of the early IPCC case, it became hijacked by politics. His book even accepts that the medieval warm period was much warmer than temperature found today when wine was grown in Yorkshire and the Danes settled and farmed in Greenland.
Using that chart which you gave, and taking a look
at the “realclimate” citation for it, I come up with
2XAGWsens. < 0.01 deg. K
(anthropogenic component of the temp. rise
resulting from a doubling of CO2 is ls th 0.01 deg. K. )
To get that 0.01 value I used an admittedly simplistic analysis. I do not assert that this 0.01 deg. number is correct, but, I do assert
that it represents a lower end for the range
of values whose high end is given by the alarmist
values bruited about for public consumption by
the IPCC and by “realclimate.com”.
Think of that 0.01 deg. K as selvage for the heated
debate about agw.
It would be best to jump to what follows the
“{ }” brackets, and then go back to what is
between them.
{
When I first started studying agw, I felt that
“realclimate” was a great resource. Slowly, however,
as my understanding grew, I came to see the site
as being more about “AGW” advocacy than about
agw. Often, nowadays, when
I see a “realclimate” citation, if I have an alternative
citation, I don’t bother with it.
In this case we are discussing here of determining
what the “2XAGWsensitivity” is, I am
willing to give “realscience” another chance.
I will try to get thru the reference you gave for that
chart.
To start, regardless of what the “realscience”
site says about interpreting it, it seems to me that that
chart can be used to get a rough idea as
to “2XAGWsensitivity”. Firstly, lets clear up what we
are talking about. For what is following below, as
far as I am concerned, we are talking about how much man will influence the climate if CO2 doubles from its current level.
To make this clear, I replace
“2Xsens.” with ” 2XAGWsens.”,
and get
2XAGWsens. < (0.05)X (33 deg. K)X (0.08)X (0.3/3.0)
< 0.01 deg K
Where
2X AGWsens. is change in global T due to the anthropogenic
component of the CO2 in a CO2 doubling
(0.05) is the percent of atmospheric CO2 that is man caused.
(If we do not pull a “Petitio Principii” and declare that
all CO2 from the start of the Industrial Age is man caused.)
33 deg. K is the total greenhouse effect
0.08 represents roughly 8% of GW being due to CO2
(0.3/3.0) comes from saying that, to a first approx.,
we can ignore the right side widening of the CO2
absorption band, because the H2O band largely
overlays it, and that, again to a first approx.,
we can see the influence of the left side widening
as being proportional to the widening.
}
OK, again, I realize that that 0.01 deg. K is startlingly low.
I am not willing to assert that it is right, but
I am asserting that is right enough to be illustrative
of how far climate science has to go before it finds
a middle ground between that 0.01 and the increasingly wrong
and alarmist seeming IPCC values.
e.g.,
lets make the extreme assumption that the GW effect
of doubling CO2 is the same as the GW effect of
current levels of CO2. That is equivalent to setting that
(0.3/3.0) factor to 1 and we get
2XAGW sens. < .1 deg K
Personally, I suspect that 0.25 deg. K is in the
right ball park for the temp. change resulting from
the anthropogenic component of a doubling of
CO2, without introducing arbitrary amplifying
factors such as the IPCC feeds into their
GCM programs, or assuming, going in,
that all temperature change is man caused.
“33 deg. K is the total greenhouse effect” Oh????
So, James, this would be a hot day?
I was under the impression the moons average surface temperature was 0C.
The difference in temp between earth’s surface and the top of earth’s atmosphere is 33 degrees. That’s the greenhouse effect’s contribution to earth’s warming.
That is the average effect. At high latitudes in winter it is much less.
That is the effect of gravity on the atmosphere. Gravity does work by compressing the atmosphere and because of the law of conservation of energy the potential energy is converted into thermal energy. Greenhouses have nothing to do with it.
Without naturally occurring greenhouse gases, Earth’s average surface temperature would be near 0 degF instead of the much warmer 59 degF. Paradoxically, the top of the atmosphere would also be near 0 degF instead of the much cooler -59 degF. That is the effect of gravity on the atmosphere. Gravity does work by compressing the atmosphere, converting potential energy into thermal energy. This also gives the atmosphere a lapse rate of temperature, which distributes the thermal energy across the depth of the of air, from the warm surface layer to the coolest layer at the top. Thus, the atmosphere acts like an insulator and greenhouse gases have everything to with that.
Heat is concentrated during the act of compressing a gas. The total energy within the gas does not increase due to compression. Once compressed, the overall temperature will decrease (or increase) to the ambient temperature unless acted upon externally.
In short, simply “being” compressed does not make the atmosphere warm… just like compressing air into a tank will raise the temperature, but the heat dissipates over time until ambient temperature is reached.
Greenhouse gasses effectively trap (temporarily) the heat from the sun, and from the surface (and below) and prevent immediate escape into the “ambient” temperature of space. Without greenhouse gasses, day/night temperature differential would be huge.
Gravity does not “cause” a warm atmosphere.
A Thorpe, Jeremy is right.
If you pump up your automobile tire, compressing the air does cause the tire to warm. But by the next day the tire will have cooled back off. Compression of the atmosphere by gravity does not cause it to be warmer than it otherwise would be.
You are right that “greenhouses have nothing to do with it,” but only because greenhouses have nothing to do with the (misnamed) “greenhouse effect” of radiatively active gases in the atmosphere.
I am sure you are correct that the forcing caused by the tiny increase in IR radiation from the extra side bands in the CO2 spectra is very small. So your estimate of <0.1 degree rise for a doubling of CO2 looks reasonable to me. So this argument is a red herring.
The argument as to why doubling CO2 causes warming relies on the upper atmosphere. The density falls off exponentially with height and temperature falls about 6.5 C per 1000 m up to the tropopause. At a certain density (height) most IR photons emitted by CO2 molecules at this height will leave the earth because there are so few CO2 molecules above them. This adds adds a small energy loss to the Earth;s energy balance. If the density of CO2 then doubles then we have to go a bit higher - (something like Ln(2)/slope) to reach the critical density again. But the temperature falls by a few degrees at this height so slightly less Energy is radiated (T**4). If less energy gets out into space then the eventually the surface warms up a little bit so that energy is balanced again.
As far as I understand it this is AGW. I am sure it must be possible to get a reasonable estimate of this effect without writing a GCM model and solving radiative transfer equations etc - and I will try to do it. That said - the effect is generally agreed to be around 1 degree maximum. The alarmists however have tuned the models to include scary feedbacks to pump this up to 3-6 degrees. I think the evidence is now coming in that this is a gross exaggeration. Clearly there are vested interests in keeping the scare story going.
Your statement above seems to imply that the 400ppm of CO2 emitting and absorbing photons in the top atmospheric layer represents some sort of gatekeeping effect. The upper atmosphere emits black body IR across a broad spectrum of wavelengths. There is no significant amount of water vapor at that altitude (http://laspace.lsu.edu/pacer/Experiment/2010/Flight_results/KC_Science_Presentation.pdf), so CO2 is the only thing left to capture any outgoing IR.
CO2’s bands of absorption are not broad enough to make any significant difference in the loss of heat once water vapor is removed from the picture. Any heat CO2 captures at or above that height would warm the surrounding air and increase the black body radiation of all of the components at that altitude, so the only net effect is a huge decrease of net emission in the CO2 absorption bands, with a corresponding increase across the remainder of the black body spectrum. in fact, that’s why satellites show the atmosphere as opaque for CO2 absorption bands, because the photon emission is insignificant compared to the black body radiation.
If there were any significant observed temperature changes at any level of the atmosphere due to CO2, it would be front page news and there would be no need for climate hysterics to massage surface station temperature data.
That is not really true. At a given height the flux of IR upwards is equal to the sum of emissions from all levels below the given height including that directly from the surface, plus the emission from the given level upwards.
The atmosphere itself can only radiate IR from greenhouse gasses – H2O, CO2 and Ozone. The rate of emission depends on the local temperature, and this rate for a given wavelength is determined by the Planck distribution for that temperature. This is usually called local thermodynamic equilibrium.
How is the lapse rate maintained? What really happens is that radiative heating (absorption) from below for any given layer tends to increase the lapse rate away from the adiabatic lapse rate. This then increases convection to restore the lapse rate to the stable adiabatoc rate. Eventually there are so few absorbing molecules left that the lapse rate peters out. This is essentially the tropopause.
It would indeed be very interesting to compare temperature soundings from the 1950s to those of today to see whether the tropopause has really increased in height as a result of higher CO2 concentrations !
Nitrogen and Oxygen are not magically exempt from emitting thermal radiation. ALL matter loses heat through thermal radiation.
But even taking your position that only the greenhouse gases are significant sources of radiation, then my statement is still correct. The emission profile from any layer of atmosphere would be exactly the same as the aggregate absorption profile of the greenhouse gases in that layer. The vast majorIty of the emission profile visible from space would thus be longwave emission from water molecules between 8 and 30um, minus a zone around 15um for Co2 absorption, passing unimpeded through to space from the top of the air layers that still contain water vapor (~24,000 feet.) The profile looking downward from 30,000 ft. at that point would look like that shown on slide 37 at http://www.atmos.washington.edu/~dargan/587/587_2.pdf
From space, the profile looks like:
http://wattsupwiththat.com/2011/03/10/visualizing-the-greenhouse-effect-emission-spectra/
On first glance, that big opaque spot around 15 um looking down from space looks worrisome. But all it is showing is that the average temperature of the CO2 visible from space is much cooler than the average temperature of most all the other gases.
So yes, there is heat being emitted by CO2 in the colder layers above those containing water vapor. I just don’t subscribe to the theory that this extra upper layer CO2 is driving a change in net outgoing energy. There is too much transfer of heat to other gases and therefore other outgoing wavelengths.
Let’s not forget that the effects of water vapor are 100 times that of CO2. CO2 has been in or near total saturation from about 200 ppm. Whereas any time you add heat you increase the water vapor in the atmosphere on a water planet.
Note: IR emission in the H2O bands does exist in the upper atmosphere, that’s how cloud imaging for weather forecast is done.
See here https://io9.gizmodo.com/planet-earth-in-infrared-at-4k-resolution-1682974407
From your last post:
”
The argument as to why doubling CO2 causes warming relies on the upper atmosphere. The density falls off exponentially with height and temperature falls about 6.5 C per 1000 m up to the tropopause. At a certain density (height) most IR photons emitted by CO2 molecules at this height will leave the earth because there are so few CO2 molecules above them. This adds adds a small energy loss to the Earth;s energy balance. If the density of CO2 then doubles then we have to go a bit higher – (something like Ln(2)/slope) to reach the critical density again. But the temperature falls by a few degrees at this height so slightly less Energy is radiated (T**4). If less energy gets out into space then the eventually the surface warms up a little bit so that energy is balanced again.
….this argument is a red herring…
”
I reply…..
Thanks for the timely and thoughtful reply, but,
I have to disagree:
Yes, I have seen this argument for increased CO2 impact before.
I have dismissed itsas specious, but, have not worked it out in detail. It seems to
display a failure to understand the basic thermodynamics
of atmospheric CO2 radiations, especially with regard to
the certain fact that each molecule of CO2 radiates
isotropically. What gets absorbed by CO2, regardless of
altitude, cannot be more gone than gone. I will try to work that all out and get back to you.
But that is moot anyway because we can go back
to my approx. 0.1 deg. nuber which results if we
bend over backwards and say that the effect of doubling
CO2 is as great as the original effect.
2XAGWsens. < (33 deg. K) X (0.05)X (0.08)
< approx. 0.15 deg.
Which is to say,
whereas, the the most widely agreed to
value for the total influence of CO2 on the present GW
situation is 8 %, and,
whereas, the effect of doubling the current atmospheric
can hardly be greater than that 8 % value for the current amount,
and,
whereas, the yearly inventories of CO2 fluxes in and out
of the atmosphere consistently show the anthropogenic
CO2 flux is about 5 % of the natural CO2 flux,
and,
whereas, Segalstad’s direct measurements of the proportion
of anthropogenic CO2 are also around 5 %,
we can multiply 0.05 by 0.08 by 33 to get an upper
limit for how much doubling the current CO2
can affect the global temp.:
< 0.15 deg. K
Here are some refs. for the numbers I have used:
8% of GW due to CO2:
http://www.middlebury.net/op-ed/global-warming-01.html
5% of atmospheric CO2 man made:
http://oceanworld.tamu.edu/resources/oceanography-
Segalstadt direct measurement anthropogenic CO2 percent:
http://www.co2web.info/hawaii.pdf
I am left still wondering how arguments such as
you have referenced can still be made when they
amount to claiming that the differential impact
of CO2 increases as the amount of CO2 increases;
that 1XCO2 causes less warming than does
going from 1X to 2X. What is your ref. for that
argument? I have seen several versions of it and
would like to analyze the particular one you refer
to.
somehow that 5% ref. does not come up.
Let me see if it works with a second try:
5% of atmos. man made:
http://oceanworld.tamu.edu/resources/oceanography-book/carboncycle.htm
Since the human contribution to the ongoing CO2
flux is less than 5%, how come I continue
to read that the recent 30% increase in the
accumulated atmospheric CO2 is man caused?
How can the accumulation
have 30% when the flux has only 5%?
What am I missing here?…..
With what follows below between the
squiggle brackets “{ }”, I will elaborate the above a bit:
{
Using Google I find that
there still seems to be a nearly unanimous
conviction that CO2 increase since 1750 is
anthropogenic, i.e. due to burning fossil fuels.
Even your own site, wherein I find
“…
Mankind burning of fossil fuels has caused a 30% increase in CO2 concentration in the atmosphere since 1750.
…”
seems to concur.
How can this be possible if, even today, the inventory
of CO2 fluxes in and out of the atmosphere consistently
show the man caused flux is less than 5% of the total
flux?
http://oceanworld.tamu.edu/resources/oceanography-book/carboncycle.htm
How can the composition of an accumulation, barring
major differences in retention, be different from’
the composition of the incoming flux?
Am I overlooking something really obvious that
supports this idea that the recent 30% rise in CO2
is man caused? I am not saying that such
does not exist. I am merely saying that I cannot
find it, and, should it exist, I would greatly appreciate having it
pointed out.
}
Although the human contribution to outgoing CO2 flux is small < 5% of natural outgoing, it would appear to be cumulative. 50% of this very small increase in outgoing flux caused by man is already absorbed by the Oceans and by increased vegetation growth, however the other appears to be retained by the atmosphere. This is how most people interpret the Mauna Loa measurements. see also: why-the-co2-increase-is-man-made-part-1
CO2 concentrations have been increasing slowly for 50 years as confirmed by measured in Maona Loa. Although there still may also be a natural increase in CO2 in the atmosphere caused by the ocean warming, most people are convinced that the main component is man. It is a cumulative effect which will eventually reverse when in 1-200 years fossil fuels run out. Thereafter CO2 levels will likely fall
However all this does not mean that AGW is proved. An observed relatively minor increases in global temperatures of about 0.6 degrees are not proven to be caused by this increase in CO2 levels . This is still just a theory which needs experimental evidence. There are other drivers of climate apart from CO2 and climate feedbacks are unproven and could even be negative.
I dispute your comment
“Although the human contribution to outgoing CO2 flux is small < 5% of natural outgoing, it would appear to be cumulative. "
There is absolutely no such appearance.
The statement is a bald lie.
There is no physical evidence of this at all.
Simple logic based on the conservation of matter
says that it is mathematically impossible.
This absurd claim that somehow the atmosphere
selects out fossil fuel CO2 from natural CO2
is key to the whole AGW argument and is
made repeatedly. The most rudimentary
knowledge of physical chemistry and of
statistical thermodynamics shows it to be
patently absurd.
Think about it…
You have a tank filling from two streams
of water, stream A and stream B. In the tank
the streams become completely mixed., and
the tank reaches some final volume of water
as a steady stream of the mixture leaves the tank.
Do you say, in contradiction to the 2nd Law, that
somehow, in the tank's mixture of A and B,
B separates from A and the tank magically accumulates
water that came from B in preference to water that
came from A?
Completely right.
The Earth doesn’t care from where a CO2 molecule originates. All that matters is how long it takes to reach equilibrium again if the amount exchanged between the biosphere and the atmosphere each year increases by a small amount. Left to itself the Earth would return to an equilibrium concentration say after a massive volcanic eruption. All that would happen is that vegetation and plancton would bloom in the medium term to absorb any small excess. The same is true of man made CO2 (provided we don’t tarmac over the planet).
I’m still having trouble understanding this thing. I have read everything on the subject including Dr. Weart’s article.
If we merely double CO2 concentrations, then the added CO2 will mix within the existing atmosphere. It does not seem like this added amount can make much of a difference in the point in the upper atmosphere where newly radiated infrared energy can escape? If this band did grow in height, then the argument stated would make sense? Does the air pressure at sea level change?
What does make sense is that the added CO2 leads to additional thermal energy at the lower altitudes and this eventually mixes throughout the atmosphere. This energy is absorbed within lower altitude band. The fact that the entire atmosphere is opaque in these bands is not relevant to the process. The lower denser air gets warmer first.
I agree that what really matters is whether the effective height in the atmosphere where IR radiation escapes into space is the crucial factor. It is always assumed that extra CO2 diffuses rapidly isotropically throughout the atmosphere. I also find this difficult to believe have not seen any data showing the actual increase of CO2 levels at different heights. Note also that this applies to H2O as well which is 70-90% of the Earth’s greenhouse effect. How water reacts to forcing from CO2 is crucial to the whole debate. Does extra evaporation lead to more clouds thereby increasing albedo ? Do more clouds produce more rain leading to lower H2O levels in the upper atmosphere ? If so then H2O feedback is negative and there will be just 0.2 to maximum 1 degree rise in temperature from a doubling of seasonal and CO2.
One other interesting observation about CO2 is the almost instant response of seasonal and “anthropogenic” changes to CO2 globally. How can emissions from China be immediately observed at the South Pole. I think that the real reason for seasonal changes is the assymetry of water coverage between SH and NH. SH has 80% ocean and NH has <60%. SH summers also have 6% more solar radiation. This is more likely the cause of seasonal changes and long term CO2 levels are driven by Ocean dynamics.
Clive,
Thank you for reviewing these points. I am a firm believer that anthrogenic factors have given rise to much of the recent global increase in temperature. I am disappointed how virulent comments become when one asks to connect the dots on the global warming subject. I have been trying to understand the (large) attribution of the effect of CO2 on the forcing function for warming. I had to come to a similar conclusion that the widening of the absorption band for the higher concentration fell far short of the 1.5 W/m2 from the GISS NASA model as well as the 1.7-3.5 W/m2 as others have proposed.
You struck a chord descibing the attribution as a circular argument. My inclination is that the CO2 concentration is a clear data set that shows the effect of industrialization, etc. The global temperature rise follows that rise with a reasonable correlation and the infrared absorption can plausibly describe an increase. My opinion (I know the expressions) is that a reasonable correlation can be drawn using the global population, the global power consumption (which contributes CO2), the world cattle population, etc in place of the CO2 concentration and come up with the same conclusions.
My main concern is the treatment of CO2/greenhouse effect as THE explanation of the cause for global warming as dogma taught to all elementary school children by teachers who understand only the analogy with glass in a greenhouse. I fear the environmentmental engineering projects spending a great deal of effort and energy at carbon sequestration, etc having unintended consequences but having no effect on the temperature rise.
Thanks again for your insight.
I agree that the indoctrination of children that climate change is dangerous and caused by our evil lifestyle is unproductive.
After this post I eventually got down to calculating the CO2 greenhouse effect from first principals based on the HITRAN absorption lines. see https://clivebest.com/blog/?p=4597
I was then able to derive the logarithmic dependency in the next post.
Clive,
I truly appreciate the effort you put into deriving this. I now see why I haven’t been able to get a satisfactory explanation–few individuals have the background and patience to explain this type of detail to lesser mortals. This type of educating goes much further than the “accept it because the consensus of climate scientists have already settled this” approach. I have a very hard time accepting science which not grounded in classical (or in this case, quantum) physics.
I look forward to following your additional insights into other physical explanations of climate complexities.
I have agraph which plots temperature increments against increments of CO2 in ppm starting at 20ppm and goes to 480 ppm with the temperature increments declining exponentially. Which means only the first 20ppm of CO2 has a significant affect. But have no idea where the graph originally came from I have an idea it’s a graph from an old NASA report in the 70s & 80s and has been reproduced elsewhere but not attributed. Anyone recognise it?
I calculated the temperature response to CO2 levels using radiative transfer. I got following result:
More info here : https://clivebest.com/blog/?p=4697
Anthony Watts has a version of this bar chart on his page, Jo Nova on hers. Clive provides the data in the more conventional format.
From simply the concentration of CO2, it is an easy point to make that the atmosphere is optically opaque to infrared at concentrations well below any historical levels.Therefore all the heat radiating from the surface of the earth is absorbed by the small amount of CO2 whether it is 200 or 300 or 600 ppm. The point is then made that additional CO2 does not contribute anything to warming the atmosphere.
Unfortunately, as Clive has described, the effect of CO2 on warming is a consequence of the temperature gradient in the atmosphere. At the thin, outer layers of the atmosphere, the number of atoms in a given volume result in it being effectively transparent. As you go deeper into the atmosphere, the density rises to the point where it is effectively opaque at the CO2 infrared wavelengths. The CO2 in the atmosphere at this level would radiate out to space and below this level it would be absorbed or reflected within the atmosphere.
The temperature of the atmosphere where this CO2 radiates its infrared outward is much cooler than the surface so Q_Rad? ??T^4 is less than it is at the higher temperatures at lower elevation. As the CO2 level increases the elevation of the “opaque” surface increases and the radiating energy drops.
In the blog post referenced above, Clive describes the exact physics of the phenomenon which, in turn, can be converted into the plot of surface temperature versus concentration, below.
Thank you Clive, and thank all of you who have commented. Everyone has noticed CO2 to temperature correlation throughout earth’s history. The question is cause, effect, or co-indicator and of course subtler feedbacks. I found a Watts per Sq M number ( the range I found was 1.5 – 2.5 ) retained heat from CO2 in the atmosphere.
Given:
Surface area of the earth: 510 million square kilometers,, 510 billion square meters
Use the number of your choice,, 510 billion square meters X 2.0 Watts per Sq M gives only 1.2 Trillion Watts of heat. 510 billion square meters X 4 Watts per Sq. M ( Clive’s number ) = 2.4 Trillion Watts.
Heck, for that mater let us use 10 Watts per Sq. M. to make the math easy. 5.1 Trillion Watts of heat.
I started wondering how does that compare to the heat energy released from hydrocarbons burning. First I just looked at total electricity production. The numbers were easy to find. The production of electricity in 2009 was 20,053TWh. http://en.wikipedia.org/wiki/Electricity_generation
20,053TWh per year / 365 days = 54.94TWh per day
54.94TWh per day / 24 hours per day = 2.29TW
2.29TW heat from electricity alone is the same scale as 2.4TW from CO2 (based on 4 W/Sq.M.)
Electricity is not the only hydrocarbon source of heat, and atmospheric CO2 is only an averaged indication of hydrocarbon use. I found some graphs.
and
Offset and scale to your heart’s content, it is not the CO2 that warms the earth, it is the heat from burning the hydrocarbons.
/home/bill/Pictures/CO2-verses-temperature.png
Oops
The heat produced by burning hydrocarbons would be offset by the fact that more sunlight will be absorbed by plants as the CO2 goes up, and the sugar production by plants is a cooling process. I’m not talking about transpiration by plants, I’m talking about how plants turn sunlight into sugar instead of heat, and as the biomass increases due to added CO2, the amount of sunlight / heat blocked by photosynthesis will increase.
In a stable planet this would be the case, however there has simultaneously been a process of deforestation and desertification going on. Unless we know where the has been an increase or decrease in planetry biomass it is not safe to assume that this relationship holds.
Marc,
An oops. 1 km2 = 1 million m2. The 4 W/m2 is 2400 TW.
Bob
I made this video that proves that catastrophic global warming will never happen, and that climate sensitivity is much lower than some claim:
I have not read all these comments, so possibly another has written what I now write here.
Not to put too fine a point on it, but the statement that the effective radiating layer achieved by adding CO2 occurs at a higher and thus lower temperature is inconsistent with fundamental physics.
The radiating layer is that layer that brings about equilibrium of the Earth’s output energy with the input solar energy. The input is defined by the Sun and its distance from the Earth, the Earth simply responds.
The Earth’s effective radiating temperature is what it has to be to return the incoming solar energy to space, period.
Computing the vertical structure of the Earth’s atmosphere from that statement is not a simple task that can be easily explained to a layman. Terms like ‘saturation’, optical depth, line formation, pressure broadening, and many more need to be understood and then appropriate physics models and then integrations over lines, one by one, etc. must be made and the radiative transfer followed through the atmosphere.
Supposedly, such detailed calculations are made routinely with every climate model, but how accurately they are made is opaque, perhaps even to the modeler, who may himself not understand the details. After all, he is likely an expert on climate, not on spectroscopy.
Reading this and dozens of others climate posts I think all can agree with W. H. Smith’s point above that “climate scientists” well served to have training in virtually every avenue of scientific pursuit to not get blindsided by unseen effects.
Clive, as a science person I have some general points that I think other science people might be asking. Do most general circulation models funded today rely on CO2 sensitivity derived on the assumption that the atmospheric CO2 delta concentration from 1850 to present is solely and 100% (not 50%, or 150%) responsible for the 0.78 C rise in global mean surface temperature?
If the answer to that is near yes, considering that all agree that additive CO2 has fast diminishing sensitivity (if not already negligible,) how can models be prediction more rise in the next 100 years than we saw in the last 150?
If scientists are really expecting water vapor positive feedback to amplify warming on what hypotheses did or climate stabilize in past inter-glacial periods at current temperature or warmer by several degrees than present, rather than run away to a Venus. Some of these periods significantly gained CO2 after their warm stabilization and nevertheless cascaded back into glaciation with high CO2 that only slowly diminished thousands of years later. Isn’t it probable that paleo CO2 graph plots reflect diminished use of CO2 by life’s smaller habitable zone and cooler oceans higher saturation point shifting the CO2 equilibrium toward sinking into the sea until the reverse in warming?
Does your reading suggest that modelers are taking into account that the Sun’s emission is more than twice the intensity of Earth’s since it only has half the time (daytime only) and one direction in which to emit. The Second Law forces the Earth’s emission to be more diffuse over the globe in direction and in time. Therefore, even though the Sun’s spectrum is less weighted in the IR than the Earth’s the intensity is likely close, which means the CO2 in the vapor free outer edge of the atmosphere CO2 could be blocking a lot of heat that otherwise would be penetrating further because CO2’s now higher opacity and thus thermal density means higher emissions at higher altitude knocked back into space. Do you agree with any of this physics?
Also, if higher temp puts more vapor in the air there will not only be more clouds but they will be more transpiration of heat, and the vapor can absorb the CO2 heat and relay it out in lower IR frequencies that are CO2 transparent. Perhaps these feedbacks and others are what has saved life from frying in the last 2 billion years.
Thanks for what you have done Clive.
This is a short reply because I am in India right now.
Models assume natural forcing is mostly insignificant except volcanoes, and that all net forcing since 1850 is anthropogenic. CO2 forcing is enhanced by ‘positive’ feedbacks mainly H2O and offset by aerosols. Amazingly these efts in the models cancel out to result in an essentially simple CO2 log forcing!
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Hi Clive –
Your analysis is very helpful. But – I want to question some specific text – and you can perhaps rewrite the sentence with other wording to help me better understand.
In Argument 1, you write: “Don’t forget that there are windows in the IR spectrum with no absorption other water vapour allows easy extra energy loss through evaporation and IR emission.”
I am completely lost. I assume that some part of the sentence or paragraph is missing. You are taking the effort to tell the reader not to forget some important point – but the point is lost, due to the sentence making no sense.
Thanks,.
Steve
What I really mean is that h2o concentration is determined by evaporation so it’s greenhouse effect is temp dependent as its vertical profile. In addition Cloud cover must depend on evaporation reducing albedo so the end result is complex and not included in models. Wording poor I agree.
I woke up one morning a few months ago and realised that assumptions about CO2 and global warming could not be right. I reasoned that CO2 makes up a tiny fraction of the atmosphere and that the atmosphere is dwarfed by the oceans, so it is not possible for CO2 to have such an enormous effect. Imagine a gas mixture 80%N2, 20% O2 and 0.02%CO2. This would represent preindustrial levels of CO2. An increase in CO2 levels to 0.04%, still represents a very low concentration, particularly in comparison to water vapour which is estimated to be present at a concentration of about 2%. Finding objective information about climate and atmospheric heat has proved difficult, so I am grateful to everyone in this forum for contributions. The principles of physics hold, so now I can the science my students.
There is a very simple problem with your math: it predicts warming in the stratosphere which is not happening. Our satellite measurements of the stratosphere are quite good over the past 25 years or so anyway.
You do understand this is an empirical, and not a theoretical problem, don’t you?
Barry, nobody is monitoring what the temp in the stratosphere is otherwise people would have known that: in the stratosphere the temp is always -92C. That’s cold enough to freeze you to death in less than 10 minutes! All the heat produced on the earth is canceled / neutralized in the first 10km from the ground! Pagan beliefs are for confusing people, not to inform. ”Global warming” is a concocted lie, don’t waste your life on it. Here is the truth: https://globalwarmingdenier.wordpress.com/2014/07/12/cooling-earth/
Nice discussion – without the acrimony and diatribes of many others!
More research on the lines of Harries (Imperial College) could provide a more definitive answer. (Just Google Harries spectrum)
John
I have just read an Harris article, but do not know if it is the salient one. I agree that this is the sort of physics that is important and that understanding what happens to energy in the atmosphere is the crux, but would suggest that drawing conclusions from the outgoing spectrum is flawed. If I look at my bank balance, it tells me nothing about income or expenditure. Similarly analysing outgoing radiation tells me nothing about incoming radiation (which we know fluctuates), or how that radiation was changed before readmittance. I would love to see a complete energy audit of what happens to all energy coming to the earth and emanating from geophysical processes on the earth. Energy is mutable in systems, so energy of one wavelength once absorbed is often re-emitted in another wavelength e.g. microwave in infra red out. If anyone knows of analysis of this nature, I would love to read it.
Clive,
The effective radiating *level* does up in the CO2 doubling scenario, but the temperature there does not go down – it stays the same. What happens instead in that basic physical model is that:
1) The temperature at the surface of the earth increases.
2) Therefore, it takes a higher altitude to drop down to the same temperature as before CO2 was increased (assuming the same temperature gradient vs. altitude).
3) Since the temperature at the effective radiating level *has to stay the same* in equilibrium, the radiating level itself goes up.
Effective radiating temperature in the upper atmosphere has to remain unchanged in the basic model, because in equilibrium, (radiation from sun) = (radiation from earth) = (radiation from effective radiating level) = all of these remain unchanged.
I think the confusion arose because the original paper presenting this argument first mentioned the altitude increase of the radiating level *assuming an unchanged surface temperature* – of course in that case the radiating level temperature drops. But then the article goes on to explain that the temperature drop at the higher radiating altitude does not actually happen, since surface temperature increases.
To summarize results of the basic model: CO2 concentration doubles through the atmosphere; surface temperature goes up, and the earth radiates more as a result; this extra radiation gets absorbed by the lower half of the troposphere; so in the upper section of the troposphere, nothing has changed temperature-wise – the effective radiating temperature is still the same in equilibrium since it has to compensate the constant amount coming in from the sun.
Clive
Going back to your original post, I still find the first argument, why global warming is important despite apparent saturation when man adds CO2 to the atmosphere, extremely difficult to follow (although your statement of it is the clearest I’ve seen).
You say “IR scatters repeatably upward through layers of the atmosphere”, but this is not “scattering” as the term is commonly understood in physics, i.e. Rayleigh or Mie scattering (which give us blue sky). Rather, it appears to be the following process.
The fundamental element is absorption and re-emission of infrared radiation by a carbon dioxide molecules as described and illustrated here:-
http://scied.ucar.edu/carbon-dioxide-absorbs-and-re-emits-infrared-radiation
The re-emitted radiation then encounters another carbon dioxide molecule and the process is repeated multiple times. Is this right?
In a secondary process, a carbon dioxide molecule, after it has absorbed an infrared photon and started vibrating, but before it has the chance to give up that energy by re-emission, may collide with another gas molecule, transferring the energy to it, in kinetic form, and raising the temperature of the gas. The body of gas, like all hot bodies, emits radiation, which increases with temperature. However, this is not the same phenomenon as direct re-emission by the carbon dioxide molecule.
The extent of this secondary process is not clear, i.e. what proportion of infrared radiation is converted to kinetic energy of atmospheric gas molecules and what proportion is repeatedly converted into vibrational energy of carbon dioxide molecules.
It is also not clear to what extent atmospheric temperature is attributable to direct absorption of infrared radiation coupled with collision, rather than by conduction and convection from the earth’s surface.
In the following highly simplified model which disregards both repeated absorption and re-emission and collision, near infrared radiation from the sun cuts straight through the atmosphere (including carbon dioxide), hits the earth’s surface, and heats it up. The earth’s surface re-emits far infrared radiation – upwards only – which is absorbed by carbon dioxide, then re-emitted upwards and downwards. The upward component heads out into space; the downward component hits the earth’s surface again, heating it up further. It then re-emits far infrared radiation again – upwards only.
The process is repeated multiple times (in theory, an infinite number). Each time, half the amount of radiation comes back down to earth, so there is a convergent geometric series. This earth’s surface is heated to an equilibrium temperature at which all the far infrared radiation, emitted by it, heads into space. The atmosphere is headed by conduction and convection from the earth’s surface.
This seems a more plausible model than radiation suddenly reaching a critical height at which it can escape into space.
Richard,
“The re-emitted radiation then encounters another carbon dioxide molecule and the process is repeated multiple times. Is this right?”
Yes that’s right. Although radiative energy is transferred upwards through collisions, this is not the reason for the lapse rate. The lapse rate is caused by convection. In a sense the atmosphere is a heat engine powered by the sun. Heat from the surface flows through the atmosphere to the tropopause where it radiates to space. The amount of CO2 and water vapour determines the height at which the mean free path for absorption is larger than the atmosphere above it. That (average) height is at 255K to balance energy in and out. If the height increases then so must the surface temperature. All things equal it increases by about 1C for each doubling of CO2. So if CO2 quadrupled to over 1000 ppm the tee rapture would rise by 2C
That will be true when the earth temperature reaches equilibrium. My understanding is that the earth is not in energy equilibrium. It is warming up. Doesn’t that mean more energy is coming from sunlight than is going out as infrared radiation?
Richard and Clive thanks for posts. Can anyone direct me to original papers about energy transfers in gas, particularly the atmosphere. At a basic level what happens to an energised gas molecule? How long does an individual molecule retain energy and how much of that energy is dissipated via collisions and how much radiated? If a CO2 molecule collides with an N2 molecule how much energy transfers to the N2 molecule and how is that transferred energy then dissipated? There must be half lives for energy retention. Does energy transferred to N2 then eventually radiate to space at a different frequency to CO2 frequency? My understanding is that in a gas energy principally transfers through collisions and only small proportions through radiation, so given the ratio of CO2 to N2 and O2 it would seem likely that most radiative energy absorbed by CO2 would quickly transfer to other molecules and ultimately be re-emitted in another wavelength?
Another thought I have had since it has been such a cold May and June in Scotland is that since convection is the principal mechanism for energy transfers in the atmosphere, any heating in the lower atmosphere will be counter balanced by cold currents descending from the upper atmosphere. Rather than warming being a consequence of heating, more wind would be the effect? Is the earth getting windier?
Sorry for being so uneducated, but sometime even a child can have a good idea.
Regarding “Therefore the main physics argument supporting enhanced global warming caused by increasing levels of CO2 is the in height and thereby lower temperature of the effective radiating level of the atmosphere to space. The first comment to make is that we never hear this crucial explanation in the popular descriptions of the greenhouse effect. We just hear that more CO2 absorbs more heat radiated from the earth and radiates it back to the surface thereby heating us up just like a thicker blanket does in bed (blankets actually work by cutting down convection losses)”, yes, quite. That is, however, because those communicating with the public have concluded, probably correctly, that their knowledge of science and their capacity for focus is SO meager that the correction explanation would be lose of them. I know: That’s pathetic and wrong.
But there are other, related fallacies which even some physicists and climate scientists get wrong, such as the “surface budget fallacy”. BTW, the best textbook I know which explains all this is Ray Pierrehumbert’s Principles of Planetary Climate, great for his mathematical and detailed explanations, his perspective of how this works on other solid bodies besides Earth, and his excellent set of Python code which can be used both to do his problem sets and do climate experiments yourself. I’ll quote from him (pages 413-414) on this, but I’d recommend getting the context, too. I have also inserted some words in square brackets to provide a bit more explanation.
That last part is pertinent to the recent model-observations reconciliation based upon HadCRUT4. Ray also goes on to point out that Arrhenius got this all right, as did Callendar (1938) and Plass (1959), and then Manabe (1961). Ray does not point it out, but I will: Others did not, e.g., Knut Ångström.
CORRECTION: Plass did not get it right.
An outstanding article. It would appear to me to be very helpful to describe the radiative effect of additional 200 ppm CO2 or so based on the 5 W per m2, as a percentage of the roughly 350 W per m2 of incident solar radiation e.g. I believe this would be about 1%? or am I missing something? Many people have a feeling for percentages if not all the science behind global climate change and this may help a debate.
If CO2 rises from 400ppm to 600ppm the increase in average radiative forcing would be about 2 W/m2. That is about the same as the energy density removed from the atmosphere by a wind farm. So as a percentage it is smaller than 1% and could be offset by a tiny increase in cloud cover. In that respect it is noticeable how the the largest cloud cover is over the warmest tropical oceans in summer months.
The physics explanation is that tropospheric carbon dioxide heat blankets exponentially double in halving time increments.
Blankets of +15 ppm, +30 ppm, and +60 ppm were added successively in +150, +70, and +40 years. The last 8-year 15ppm increment to >400ppm is at a level greater than in the last 2 million-years (Pieter Tans NOAA). The greenhouse effect is cumulative.
Heat is trapped between the ocean surface and the tropospheric heat blankets.
The 93% of manmade global warming in the surface ocean circulates in phase with 11-year solar cycles e.g. as in decadal oscillations such as El Nino Southern Oscillation.
CO2 loads the gun; the solar cycle pulls the trigger.
Since the millennium, the CO2 heat blanket effect dominates over the solar cycle heat input.
Oceans are stratified with warm freshwater over cold salty water; heated from above, there is no convection. Wind-driven and geostrophic near-surface currents, in eleven counter-rotating ocean gyres, transport heat and nutrients polewards. At high latitudes, tropical-origin seawater basal melts floating ice. Freeze-brine carries cold salty water to abyssal depths. This is different from the ocean conveyor model.
Heat sequestration in the tropics is driven by evaporation dependent on the Clausius-Clapeyron exponential function of skin temperature (increase about 7% per deg C). Land evaporation, dependent on windspeed and relative humidity, is mis-used in current climate models. On this basis, a recent peer-reviewed publication computed equatorial evaporation equal at midnight and midday!
This is based on century-long daily sea surface temperature records. It was found on a student cruise between Tahiti and Hawaii where surface and 3m temperatures and salinities were measured hourly. A sign change in the seawater density equation reverses the impact of increasing salinity on density. By a quirk in the seawater density equation water warmer than 36 parts per thousand and 28C does not sink. It forms a westward thickening subsurface layer along the equator. It contributes to the 30C western and eastern Pacific warm pools.
An Imperial College physicist with 50 years publication record has recently shown that Pacific warming was +3C in 2014 and likely +4C by 2016. Climate sensitivity is a nonsense. The doubling CO2 heat trap is also seen in the exponential doubling decrease in Arctic floating ice volumes.
The carbon dioxide heat trap is far more serious than current thinking assumes. Hopefully this is wrong. It is hard to argue for many long daily sea surface temperature and salinity measurements and ice volumes
The latest full text articles are online at:
1) doi: 10.13140/RG.2.1.2201.6169, or http://cirworld.org/journals/index.php/jap/article/view/4596/pdf_178 .
2) doi: 10.13140/RG.2.1.1415.1843, or http://cirworld.org/journals/index.php/jap/article/view/139jap/pdf_95.
Let me point out that the amount of electromagnetic energy, whether incoming or outgoing, converted into atmospheric heating (next to the major portion which is via surface contact) is many orders of magnitude greater for H2O in the form of vapour or liquid than by CO2. The absorption bandwidth for a water droplet is, dependent on size, virtually continuous. As increasing earth temperature increases both forms of H2O, it is clear the greenhouse gas theory does not need CO2 to cause global warming! The fact is, earth’s temperature is stabilised by H2O the reason being that water droplets radiate energy according to the atmospheric temperature. Also, more water vapour means more cloud cover – and incidentally more reflection and re-radiation as well. Sorry folks, the climate is changing because urbanisation/industrialisation is draining the earth’s surface and reducing the production of vapour. It would be a start for the author here to recant the T^4 relation for CO2 emissions, or any dry atmospheric gas, – gases simply cannot radiate significant amounts spontaneously at atmospheric temperature. It would also add to the discussion to note that a blanket does not keep you warm in any way which is related to the atmosphere, it prevents the energy generated internally in the body from escaping by a thermal barrier, that is what raises bodily temperature. And to fit thermodynamics theory, energy is being temporarily displaced downwind from earth’s industrial belts so that when the polar region has got up to speed, the radiation balance will be restored – albeit with a man made pattern for the climate and some direct contribution from internal conversions – eg carbon and nuclear generators.
“As CO2 concentrations increase so this level shifts to higher levels in the atmosphere since a critical density must be reached for the radiation to escape”
But only for energy radiated by CO2. Energy radiated by all other gasses is from exactly the same level as before because we aren’t increasing the quantity of O2 and N2 in the atmosphere.
Thus 0.004% of IR is radiated from a few hundred meters higher, 99.996% is radiated from exactly the same place. Hardly a significant change.
Nitrogen and Oxygen are diatomic molecules whereas CO2, Ozone and H2O are triatomic. This changes the wavelength of the vibrational modes. CO2, H2O and O3 lie all within the thermal (planck) spectrum for earth temperatures whereas O2 and N2 are are much shorter wavelengths – typical of those on the surface of the sun. This means that CO2, H2O and O3 all get excited by thermal energy in the atmosphere compared to a tiny number of O2 and N2 molecules. They emit and absorb IR photons in thermal equilibrium with the surrounding air molecules.
The temperature at a given height up to about 10,000 m is determined by thermodynamics – the adiabatic (moist) lapse rate and not by radiation. This scale is set by the surface temperature. The air thins out with height until IR photons emitted by H2O, CO2 or O3 can escape to space. This cools off the top of the troposphere and sets the scale. The earth remains approximately in energy balance so that the energy lost to space equals the absorbed incoming solar radiation. This effectively determines the temperature of the ‘top of the troposphere/atmosphere’ and equals 255K. The surface temperature approximately is then determined by the lapse rate.
For the atmosphere to radiate from a higher altitude in general, due to an increase in the number of molecules in the atmosphere, its pressure would have gone up. Since this hasn’t happened I don’t see any validity in the suggestion.
If the suggestion is that ‘because CO2 molecules are more numerous higher up’ that adding more is pushing only CO2 molecules to higher altitudes then my previous objection is valid. All mater above 0K emits heat energy, not just CO2, so 99.994% of the atmosphere is unaffected.
Yeah, but “matter” does not emit energy at the same frequencies, and some of these would not conventionally be considered “heat”.
But none the less the atmosphere emits upwards as a black body at all the frequencies you would expect of a black body at that temperature. Only some of those frequencies are impacted by CO2 so I believe what I say is valid; that either atmospheric pressure has gone up in line with the entire atmosphere emitting from a higher, and colder level, or it is only CO2 molecules that are now emitting from higher and colder levels, in which case any increase in heat retention must be relative to the increase in only CO2.
(Because of conversation depth, replying to myself)
@ConcernedCitizen: That’s precisely the point, as Clive explained. The broad absorption/emission band for CO2 at 667 per cm aligns almost perfectly with the main emissions for a blackbody in the range of Earth’s surface temperature. Not only does Earth not produce much in the absorption/emission regions for N2 and O2, but the incoming radiation from Sun is much higher in frequency and, so, CO2/H2O/CH4/O3 are transparent to it. Not so for the outgoing. And, also as Clive described, the only part of the atmosphere that radiates and dumps energy is the top.
I don’t understand your reasoning regarding atmospheric pressure. Can you explain? The partial pressure of CO2 has gone up because we have emitted more, but it is such a small percentage of atmosphere that its effect upon atmospheric pressure is negligible compared to fluctuations in lapse rate and weather.
My understanding of this theory is that by adding CO2 we have thickened the atmosphere, causing it to radiate from a higher, colder altitude. ie, increased the lapse rate, and causing a higher surface temperature. This would of course entail an increase in surface pressure. This hasn’t happened thus I see no validity in the theory.
For instance, if the top of a square meter column of air rises, but the density of the air within it goes down, there is a way that can be done so that the total mass of the air in the column does not change, and so there would be no pressure change. So, y’need to add more specific details.
I understand that Clive, I just don’t see how ‘CO2 radiating from a higher, colder, layer’ causes warming. If a photon emitted 9.9 kms is intercepted by a CO2 molecule 100 m higher up, and radiated again out to space, that photon hasn’t lost energy.
The atmosphere hasn’t got thicker, so its not lapse rate argument either.
I just don’t get it. Sorry if I am being dense, but I don’t see how this theory can be implemented physically other than by the entire atmosphere getting thicker. And it hasn’t.
Sorry Clive, that doesn’t help. Maybe I am being a bit dense, but I just don’t see how having more CO2 molecules higher up means that less energy is emitted.
The emission of a photon by a CO2 molecule can be done by two ways, correct me if I am wrong:
1) The CO2 molecule got hit by a photon emitted by another CO2 molecule.
2) It got hit physically by another molecule (kinetic to photon conversion).
The energy in the second process is height dependent, the higher it occurs the less ke there is, but if the CO2 molecule wasn’t there that ke would stay in the system. CO2 is removing energy in this case, taking ke, converting it to a photon, and emitting it out to space.
In the first case the energy in the photon has to be the same when its emitted, so it is immaterial whether the photon is absorbed ad emitted by a hundred CO2 molecules arranged vertically, passing the photon up and out to space.
I just don’t see any logical process for the proposed theory that ‘more CO2 = emission from higher colder layers = retained heat’
@ConcernedCitizen … Please record your physical justification “This would of course entail an increase in surface pressure”. I don’t see it. Moreover, it’s one thing to state such an expectation or derive it, and another to show that the change is physically detectable. As I wrote, there will be some pressure change due to increases in CO2, albeit small.
OK, so then can you explain why CO2 is radiating from a higher altitude?
Sure, because the per unit volume amount of CO2 over all the atmosphere is higher. In order for OLR to succeed in getting to space, there needs to be little CO2 above it. In other words, the increase in CO2 concentration makes the atmosphere more opaque to OLR. Accordingly, the emissive layer that succeeds is closer to the edge where there is no CO2.
I still don’t get it. How does a photon, emitted by a CO2 molecule at say 9.9 km’s and being absorbed by a CO2 molecule at 10 kms (that wasn’t there previously) mean that photon has less energy?
It depends on the wavelength (energy) of the photon. Most simply escape directly to space. Only a few in the central 15 micron line are absorbed by CO2 molecules higher up. None of this changes the temperature of the emitting layer which is dominated by the thermal energy of the surrounding air molecules. Eventually radiation loss to space becomes large enough to stop convection. That is the tropopause.
ConcernedCitizen: It doesn’t. If you look at a single molecule absorbing and then emitting a photon. That’s not what happens in the lower atmosphere. There a CO2 molecule absorbs a photon, starts vibrating and crashes into other air molecules spreading out the energy. The temperature goes up. At higher temperatures more CO2 molecules emit infrared. At lower temperatures fewer do. If on average a given air volume absorbs more photons than it emits it must warm up. That’s my understanding of the greenhouse effect. Gasses emit infrared photons at energy levels set by the electron energy transitions for that chemical and vibrational state.The photon energy does not change. The number of photons emitted and thus the energy flux does.
As to the CO2 molecule at 10 km up. Nothing says the emitted photon won’t get shot back towards the earth.
Hope this helps
I am not sure the about the source of confusion CC is experiencing. The top of atmosphere concept is elucidating for me. For IR wavelengths within the absorption (and transmission) bands, the atmosphere will attenuate the IR photons from the surface to space as a function of the concentration. CO2 is concentrated enough that the atmosphere would appear opaque.
Looking from space the surface features of the earth would be obscured–the earth would look like a gaseous sphere. The intensity of the photons emitted from this TOA would correspond to the thermal energy determined using Planck’s Law. This is the only energy that can escape from earth to space of that wavelength. As the concentration of the emitting gas increases, the TOA is extended higher in the atmosphere. Thermal equilibrium at that altitude is at a lower temperature so less IR is transmitted. This is the idealized basis of the “greenhouse gas” effect.
I think this is the only correct way to think about the GHE. Using this simple model I was able to calculated the radiative forcing of CO2, and understand the IR spectrum as measured from space. You migfht be interested in these posts.
CO2 Greenhouse effect demystified
and
Radiative Forcing of CO2
Convection and Latent heat drive the thermodynamics of heat loss from the surface and generate the lapse rate. Greenhouse gases just set the scale height of radiative cooling to space. Back radiation is a complete red herring which explains nothing.
I think the co2 saturation story should be or could be the main scientific base to start a global campaing againts agw, if not too late. I am not strong enough scientificly to detect technical flaw to this thread. But if one could structure, debate, and win this hypothesus that doubling or even quadrupling co2 concentration in the atmosphere won’t change significantly its temperature that could be a game changer. Here in Québec our Prime Minister returned from Paris with totally new green policy, stopping any emerging oil exploration and full of new green taxing policy. I thing we can stop, or at least modify, the trend. But we must start with soud scientific arguments like I founb here.
“Saturation” as a limited to the effects of CO2 radiative forcing was proposed by Knut Angstrom around the turn of the 19th-20th centuries. (Knut Angstrom was a relative of the great Angstrom, but not the same.) It doesn’t work, basically because absorption lines “broaden” with increasing CO2. (It’s a little bit more complicated than that, Contact me if you would like to know more.) There are two great links at:
http://www.realclimate.org/index.php/archives/2007/06/a-saturated-gassy-argument/
and
http://www.realclimate.org/index.php/archives/2007/06/a-saturated-gassy-argument-part-ii/
Almost all scientific paper I read take for granted ipcc co2 radiative forcing, witch is suspected to be originating from a circular processus. The way i proceed is examine arguments thoses whose views differ from ipcc one and try to judge at merit. Not an easy task, but quite interesting. Thank you for links reference.
You don’t need IPCC, nor is that even the best. A good thing is to check out online courses, and textbooks. Two good ones are David Archer’s course on global warming, understanding the forecast, and, a more detailed, technical one (but you want technical details, right?), Ray Pierrehumbert’s planetary climate book.
The reason why CO2 forcing only grows logarithmically with concentration is because the central absorption lines are already saturated. These are spectra I calculated using this model.
Yes, and, uh, so? It increases. Did not say central lines contributed any more. But, facts are, especially around 667 per cm, there are lots and lots of lines. That was a detail I deferred in my comment. The fine structure of the central peak is very complicated, but that’s been known for a long time: http://journals.aps.org/pr/abstract/10.1103/PhysRev.41.291
And, if you will recall, only half of the warming is CO2. The other half is from knock-on effects from water vapor, due to greater carrying capacity of atmosphere.
Reference to text cited earlier: http://geosci.uchicago.edu/~rtp1/PrinciplesPlanetaryClimate/index.html
I agree with you. This book is a masterpiece. I have it at home – but it is perhaps a bit heavy for your average punter.
But people want to wade into this water, I don’t see how else.
There is Archer’s book and course.
Calculating CO2 forcing is not simple nor straightforward. But yes it has been done and the answer is known. Even then you have to make some assumptions such as a standard lapse rate. Feedbacks are a second order effect whose effects are not known. If they were then we could calculate equilibrium climate sensitivity (ECS), but we can’t. Instead we have to measure it and the margin of error on estimates hasn’t changed in 15 years. So no we don’t know that half the warming is CO2 and half is due to knock-on effects from water vapor.
Increased H2O GHE is positive… but …
Cloud feedback could be negative
Lapse rate feedback is negative
Clive Best states:
“Increased H2O GHE is positive… but …
Cloud feedback could be negative
Lapse rate feedback is negative”
What about the umbrella effect? Increased CO2 and H2O as your own graph indicates also absorbs solar incident near IR from reaching the Earth’s surface. What is the cooling effect? Careful monitoring of CO2 around the familiar ~15 micron band already supposedly measures a .2 w/m^2 emission power increase per decade near the surface. Please note CO2 recently increases ~25-30ppm per decade, assuming the greatest forcing sensitivity a doubling of the current 400ppm should only lead to a 3.2 w/m^2 if the current ratio maintains. However, as you indicate there should be reduced sensitivity with increasing CO2, so the likely forcing should be less! Moreover, have you considered the reduction in incoming solar near IR. What is the reduction in measured 2-3 micron and or ~5 micron incident solar IR near the surface due to increases in CO2 throughout the upper atmosphere? What is the mutation in solar incident near IR at the Earth’s surface due to changes in atmospheric water vapor throughout the troposphere and to a small extent the stratosphere?
Note: I’m not referring to reflection of incoming solar radiation due to the albedo of clouds, ice etc., but the increased high troposphere absorption and emission to space of incoming solar radiation due the supposed greenhouse gasses, better labeled umbrella gasses. Imo, water vapor cools and it’s not merely due to clouds at all. Thanks for your consideration and …
Have a great day!
Actually, with respect, work on cloud feedback has progressed a lot.
The constant relative humidity assumption of prior work has been verified.
And to the degree the basic model (back of the envelope one, not GCMs) fits the data, which it does pretty well, I call that a win.
“There are 3 main CO2 bands of IR absorption at wavelengths 1388, 667, 2349 cm-1”
These values are wave NUMBERS, not wavelengths.
The wave number of 667 corresponds to a wavelength of 15 microns.
Stupid mistake. I should correct that.
Thermdynamics states emissivity = absorption at every wavelength.
Where there is no absorption there is NO emmission.
Yes you’re right. Another imprecise statement! thanks.
The heat of Venus and the climate on Venus may be understood if you consider the strength of the emr including gamma rays to be many times greater than earth because of its closeness to the sun. Then look at the slowness of the orbit. On earth near the equator a 48 hour day might cause temperatures above the boiling of water. On venus with a much stronger emr, the day is 243 times as long as ours. Some rocks actually boil. Because Venus is large enough to hold an atmosphere and half of the planet is not exposed to the sun, the enormous winds between hot and cold areas are created. Gamma rays and Xrays are absorbed by solids. The gases are a side effect. What gases absorb is irrelevant.
Feel free to share the calculations that accompany your theory.
Clive,
What have you learned about the fudge factor? Is it derived from the cirular argument expressed above?
No it is not a circular argument -I got that wrong. I finally ended up writing my own radiative transfer code to derive the greenhouse effect. I was then able to get about the same logarithmic result. see Radiative Forcing of CO2.
So the formula is good.
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“As CO2 concentrations increase so this level shifts to higher levels in the atmosphere since a critical density must be reached for the radiation to escape.”
It does not necessarily follow. You must specify the mechanism by which the level shifts higher in the atmosphere.
Shifting it higher in the atmosphere requires energy. If you say that energy comes from the increasing temperature, you are arguing something akin to pulling oneself into the air by one’s bootstraps. Moreover, it would be a positive feedback – increasing temperature, lofting the CO2 higher, increasing the temperature, and so on. Eventually, the CO2 would achieve escape velocity, and launch itself beyond Earthly influence.
All that really says is that the density of air falls with height. So if CO2 as a percentage of air rises from 0.03% to 0.06% then the level at which it falls to the critical density to let IR photons escape to space also goes up. Density falls off exponentially so the height rises by something like log(2) or 60%.
This is still an argument lacking a mechanism. Density alone does not provide height. If you took the Sun away, the entire atmosphere would collapse into a solid mass at the surface – very dense, in relative terms, but with hardly any height at all.
You must have an energy source to sustain the particles at higher altitude. E.g., there is always a diurnal bulge in the atmosphere on the Sun side, centered close to the direction of the Sun (with some offset due to thermal inertia). The diurnal bulge is quite sensitive to solar activity, with the center of mass extending further outward by hundreds of km when solar activity is high (see figure 2.3 at link). The extra energy from the Sun is what sustains the atmosphere at those higher altitudes.
When I said “with the center of mass extending…”, I meant it in a generic sense to indicate the peak of the distribution depicted in the figure cited. I probably should have said “center of area” to avoid potential confusion with actual mass concentration.
Clive – thank you for spelling out the crux of the AGM argument (as I understand your explanation – a decrease in radiative energy loss with decreasing T as one goes higher in the atmosphere). What about the decrease in absorption that occurs as the temperature drops because of a reduction in doppler broadening (sharpening of the IR absorption band)? I am not qualified to comment but I found William Happer’s lecture where he cites spectroscopy experiments conducted using weather balloons very compelling.
Clive, that “Radiative Forcing Update… reference” link has gone dead.
However, I found an archived copy of it here:
http://www.webcitation.org/query?url=http://geoplasma.spaces.live.com/blog/cns!C00F2616F39D0B2B!592.entry
Oops, I botched a tag; sorry. Trying again… (you can delete the botched one)
Clive, that “Radiative Forcing Update… reference” link has gone dead.
However, I found an archived copy of it here:
http://www.webcitation.org/query?url=http://geoplasma.spaces.live.com/blog/cns!C00F2616F39D0B2B!592.entry
great thread. great links. great comments. here is a link that may aid in the understanding of dependence of the greenhouse effect on altitude… https://www.skepticalscience.com/saturated-co2-effect.htm
It seems that one has to do the calculation to get a good appreciation of how sensitive the IR absorption is to [CO2]. I got frustrated and so I made up my own simple model (see appendix below). It is immediately clear from the solutions to the rate equations that the value of the reaction cross-section for IR absorption per molecule of CO2 is critical (as one might expect). By my estimates, for a cross-section of 10^^-23 m^^2, the IR photon loss to outer space is more-or-less saturated at very low levels of CO2 (~10 appm CO2 has an absorption efficiency of ~99% at 10-20 km). For a cross-section of 10^^-25 m^^2 the IR photon loss to outer space is more-or-less saturated at levels of CO2 that are similar in magnitude to the atmospheric levels.(~100 appm CO2 has an absorption efficiency of ~99%). It is clear that the absorption is not saturated in the wings of the absorption bands for increasingly smaller absorption cross-sections. There will be a range of cross-section values that are important from the perspective of additional photon absorption for the levels of [CO2] that are relevant to the atmosphere (I should determine that sometime). It could be that, in the freqency range where values of the CO2 absorption cross-sections are low enough that the absorption is unsaturated, the absorption cross-sections for water vapour are larger than those for CO2 – wouldn’t that be interesting? My problem is getting good, tabulated, cross-section data for the IR wavelengths of interest. Naturally, the IR absorption cross-section spectra will also vary with height in the atmosphere (temperature and pressure dependence) bur even values at STP will be useful for bounding the assessment problem. Can anyone point me to a good source of easily accessible tabulated cross-section data?
Appendix –
The differential equations describing the steady-state passage and dissipation of photons in the atmosphere per cubic metre are:
(dP_0)/dx = -S * P2*P0 + xg*P1
(dP_1)/dx = S * P2*P0 – xg*P1 + xgp* P1
where P2 is the number of CO2 molecules per m3, S is the cross-section for absorption, xg is the probability of re-emission and xgp is the probability of the photon energy being transferred to another gas molecule in the atmosphere (H2O, N2 or O2 mainly) and x is the distance in m. P0 and P1 are the numbers of photons that are free and bound respectively. Solution of these equations gives the number of free photons as a function of height. It is assumed that any photon that is free at 10-20 km is lost to outer space.
I am not convinced about the black-body radiation argument: (a) can a gas be considered as a black body? (b) even if the argument was true, and photon emission was reduced at lower temperatures (higher in the atmosphere), absorption should also be lower for other reasons (e.g. less Doppler broadening). Being a failed physicist I would want to see some experimental data showing the effect of temperature on photon emission – does that exist?
This is the correct approach that you describe. The cross-sections for CO2 absorption of IR have been measured and tabulated in the HITRAN database. The important ones on earth are the vibrational excitation quantum lines in the 15 micron band. I think the local thermodynamic equilibrium of the atmosphere is important because CO2 molecules can also be excited by collisions. So although air does not act as a black body, the IR emission of CO2 is temperature dependent and goes as T^4. Here is my simple picture.
Incoming solar radiation heats the earth’s surface. The surface radiates as a black body at temperature Ts. The atmosphere consists mostly of diatomic molecules (N2, O2 Argon etc) and triatomic molecules (H20, CO2, O3). Only triatomic molecules have vibrational quantum excitation modes in the Infrared. H2O has a rather broad wavelength spectra whereas CO2 has just 3 main bands, but on earth only the 15 micron band is significant.
Gravity generates an exponential falloff of density with height. H2O, CO2 and O3 absorb and reemit IR photons in local thermal equilibrium at the relevant height (Kirchoff’s law). By inhibiting the direct radiative heat loss from the surface to space, the atmosphere generates itself a lapse rate. This is because convection begins to move heat up through the lower atmosphere more efficiently than radiation. Only with a convective atmosphere under gravity can the greenhouse effect work.
For each wavelength in the CO2 band there is an effective emission height where the mean-free path for IR photons is greater than all overlying layers. IR photons from this level radiate directly to space. Likewise for O3, although Clouds complicate H2O.
I once calculated the effective emission heights for CO2 using HITRAN, assuming a standard atmospheric lapse rate and profile. ( https://clivebest.com/blog/?p=4597 ) This is the resultant spectra I calculated for different concentrations for CO2.
These actually get smeared out by pressure broadening. The central line cross-section is so high that it currently emits from the stratosphere where temperature increases with height. This means that this wavelength actually cools the planet with increasing CO2 levels. You can actually see this in Nimbus spectra.
A simple excel spreadsheet model that approximates the GHE can be downloaded from this post. https://clivebest.com/blog/?p=4345
Clive
Clive
I’m a non scientist trying to understand exactly what CO2 actually does. You have helped a great deal, but I still have questions. As you stated, the absorption length for the current concentration of CO2 is around 25 meters. I’ve also read that almost all of the IR absorbed by CO2 is thermalized via collisions with nearby molecules, and is rarely re emitted (1 in a billion at sea level per Will Happer). So how does this relate to the “effective emission height ” scenario? It seems there would be very few photons left for CO2 to emit at such height if it’s all being thermalized very near the surface.
What happens to the thermalized energy? I would guess convection and water vapor transport it upwards. If so, I don’t see this contributing to any warming.
I understand that radiation is the only way for all this energy to exit to space. Surely CO2 at a very cold “effective emission height” is not able to do it all. Water vapor must be a major radiator. Why wouldn’t water vapor easily compensate for any diminished radiation caused by a higher CO2 emission height?
Any help tying this all together would be appreciated.
Jim,
I think the trick is the following. So long as the earth (surface+atmosphere) loses heat through radiation to space the atmosphere will set up a lapse rate. This is because by far the easiest way to move heat upwards is through evaporation from the oceans and convection to where it can radiate freely. That is why we have thunderstorms and weather due to Coriolis forces. Net radiative losses occur at high latitudes to offset net absorption in the equator. As CO2 increases the tropopause should get higher. However, as you rightly say water vapour is the ace card. No-one really knows how clouds and H2O will play out. Clouds reduce albedo cooling the earth, whereas H2O (water vapour) enhances the greenhouse effect. My hunch is that water is the ultimate negative feedback because otherwise the oceans would have boiled away billions of years ago.
Jim: “I’ve also read that almost all of the IR absorbed by CO2 is thermalized via collisions with nearby molecules, and is rarely re emitted (1 in a billion at sea level per Will Happer).”
I don’t think that is right. Kirchoff’s Law basically says that when a gas is being exposed to radiation following a temperature profile equal to the local temperature a local thermal equilibrium exists whereby the emissions at EVERY band are equal to the absorption rates at every band.
The greenhouse effect works because the lapse rate usually makes the atmosphere cooler at any location than the radiation profile it is being exposed to. This gradient continues to the tropospause where Clive rightly points out that the stratosphere temperature then increases with height, but only during the daytime. At night the lapse rate would continue cooler at higher elevation to space.
I agree, however, that water transpiration, clouds and convection dominate the regulation of atmospheric temperature. The areas where there is little water vapor, like at the poles, deserts and the tropopause, then CO2 can have an amplified role.
“I don’t think that is right. Kirchoff’s Law basically says that when a gas is being exposed to radiation following a temperature profile equal to the local temperature a local thermal equilibrium exists whereby the emissions at EVERY band are equal to the absorption rates at every band.”
I think the idea here is that emission from the same excited state is rare (though I thought maybe 5%, not 1 in billion). There is still matching emission, but just from GHG in equilibrium with ambient, not matched to the particular absorption event. I don’t think that version of K is quite right. It says emissivity equals absorptivity. What is actually absorbed and emitted depends on incident intensity for absorption and temperature for emission.
“It says emissivity equals absorptivity. What is actually absorbed and emitted depends on incident intensity for absorption and temperature for emission.”
That sounds like what I tried to articulate. The emission profile is identical to the absorption profile when there is a local thermal equilibrium. Temperature, of course, is a measure of mean molecular kinetic energy. This is a property of the gas as a whole, not of a molecule. Whether one individual molecule is emits what it absorbs before interacting with other molecules I don’t see as relevant to the GHE, Kirchoff’s Law or anything else. The higher the gas pressure the more convection (collisions) will dominate over radiation to determine an instantaneous molecular state.
Imagine a gas at 288K sealed within a perfectly insulated and infinitely thin balloon. Now transport the ballon into outer space. If the gas is argon then it will remain at 288K for ever. However, if the gas contains .03% CO2 then it will radiate ~15 micron photons according to Stefan-Boltzmann’s law until the gas ever more slowly cools to 3K.
Well, not forever, Argon also has infrared lines
The Infrared Spectrum of Argon
R. M. Woods and B. J. Spence
Phys. Rev. 45, 669 – Published 15 May 1934
Hans,
You are of course correct : “Forty-six lines between 0.69? and 1.80? are listed.” Luckily these are almost off-scale on a 288K black body spectrum!
A building as the atmosphere…
The walls of the building represent the Earth’s atmosphere. The outer surface is the top of the atmosphere and the inner surface is the atmosphere close to the Earth’s surface.
A building with no windows and no CO2…
Consider a building with modest insulation that is heated at a constant rate from inside. Assume that the building is insulated equally well everywhere resulting in a uniform temperature of the outer surface. In steady state there is a higher temperature inside the building compared to the fixed exterior temperature. The temperature at the outer wall surface is higher than the exterior temperature. The temperature at the inner wall surface is lower than the interior room temperature. These temperature differences maintain an export of heat at the same rate at which the interior is heated.
A building with no windows but with CO2…
If now the heat resistance (CO2) of the walls is instantaneously increased, at first the outer surface temperature drops and the inner surface temperature rises, while the interior temperature is still unchanged. In this situation less heat escapes from the building than is released by the indoor heating system. The imbalance leads to a slow ascent of the interior temperature that continues until the outer surface temperature returns to its original value.
The initial cooling of the outer surface temperature is analogous to the quasi-instantaneous cooling that occurs in the upper half of the atmosphere. The cooling is only transient and has no permanent component.
A building with windows and no CO2…
Assuming instead that there are parts of the building envelope that are more weakly insulated than the remainder, as is typically the case with thin glass windows. The outer surface temperature in equilibrium is higher at the windows than it is at the walls. A larger fraction of the total energy escapes via the windows compared to how much they contribute to the total area of the building envelope.
A building with windows and CO2…
Now, let the heat resistance (CO2) of the wall envelope increase. The outer surface temperature of the wall is again diminished instantly. But once in the new equilibrium, even more energy escapes through the windows and less through the walls.
The permanent cooling of the outer surface temperature of the walls is analogous to the cooling in the higher atmosphere.
An insulated building undergoing heating illustrates the blocking effect of CO2-induced mid to upper atmospheric cooling. The separation between walls and windows physically is analogous to the separation into opaque and transparent radiation bands spectrally, and energy transfer as heat conduction in the walls of a building is analogous to radiation in the atmosphere.
adapted from Appendix A: An analogy for the blocking effect from … http://www.earth-syst-dynam.net/7/697/2016/esd-7-697-2016.pdf
Clive, perhaps you have found another reference to the one you linked to in your Feb 4, 2010 explanation of radiative forcing::
“Radiative Forcing Update: I have now found this reference to the equations used to derive the 4 watts/sq m radiative forcing by doubling the amount of CO2 in the atmosphere.”
since the reference linked no longer exists (“authors have deleted the site”). If you cannot find another source with the same equation, and since the one you cited no longer exists, then what basis for the equation you cited can you use to substantiate its validity and foundation?
BTW, I’ve found over the years that in climate science referenced links many sites seem to have been taken down. I have thus since then stored (on my computer) the actual authors, their university or research institutes, dates of information provided and the basis of references the authors use. Though more time consuming and tedious on my part I at least have my original source to refer to if data (or basis) is questioned or if I find future reason to question or compare it with other sources I find later. There’s more than enough junk science and junk cleverly disguised as science on the web, even from established universities. .. one in particular but there are others I’ve found…. crackpot scientists promoting their own theories with foundations that are either actually just circular arguments or well known physics equations used out of context…. which most readers, even scientists won’t catch necessarily unless scrutinizing the series of multiple equations spread over several pages of “reports” carefully (fine tooth comb).
You have a dead link on this page: http://brneurosci.org/co2.html
The Earth’s surface receives solar radiation from the Sun. All of that energy
has to escape back out to space. The only place for it to escape is back out
through the atmosphere. Heat flow between the surface of the earth and the top
of the atmosphere is related to the temperature difference between those
points, and also dependent on the raidative resistance of the air layer
between them. The atmosphere has high radiative resistance due to greenhouse
gasses. So the temperature inside the lower atmosphere has to rise to keep the
heat flowing out through the top at the same rate it is coming in – creating a
large temperature drop across the 10 miles of atmosphere. That results in a
lapse rate of temperature, i.e., the air cools with height, about 6 deg per
thousand feet. Without the atmosphere, the heat would simply escape by
raidating directly to space, and the temperature of the surface would be
lower. The energy flow from the earth to space is the same with or without the
atmosphere, but the earth’s surface temperature is higher and the top of the
atmosphere is lower with the atmosphere in place. The outside of a panel of
glass of a greenhouse is hot to touch and even hotter on the inside. The top
of the atmosphere is extremely cold while the earth’s surface is quite warm.
The atmosphere is not thin and solid like glass. It is thick, compressible and
convective like gas.
Good points, except I think the lapse rate is 3.57 degrees per 1,000 feet gain in altitude.
indeed, other factors bring it down to 3.57. i was referring to the immediate adiabatic response which is closer to 5.6.
“All of that energy has to escape back out to space”
Not really, if it doesn’t, the temperature will warm, that’s all. I’m being pedantic, but a lot of climate science has rested on assuming equilibrium, and there is none unless you average, and then you lose your signal.
I think it arose from the helpful assumptions of steady state which are useful for fast processes, but I really think for climate it is the beginning of the ‘averaging’ disease that leads people to see simple solutions to preposterously complex problems as being plausible. Climate is a long term average of many short term cyclical processes and that makes it hard to assign cause to effect.
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Without naturally occurring greenhouse gases, Earth’s average surface temperature would be near 0 degF instead of the much warmer 59 degF. Paradoxically, the top of the atmosphere would also be near 0 degF instead of the much cooler -59 degF. That is the effect of gravity on the atmosphere. Gravity does work by compressing the atmosphere, converting potential energy into thermal energy. This also gives the atmosphere a lapse rate of temperature, which distributes the thermal energy across the depth of the of air, from the warm surface layer to the coolest layer at the top. Thus, the atmosphere acts like an insulator and greenhouse gases have everything to with that.
Clive Best: “The mean free path is only about 25 meters”
WR: Clive, is that number of ’25 meters’ correct for CO2? Is there a source for the length of the free path for (other) re-radiating gases, for example H2O?
And what should the free path be (for CO2 and H2O) at a height of – let’s say – 5 kilometer?
Wim,
The number 25m is for CO2 near the surface, and is just an average value over the 15 micron emission. The CO2 molecule gets thermally excited into 100s of quantum vibrational modes. These then decay emitting a photon. Those moving upwards are absorbed by other CO2 molecules and the process is repeated until the air becomes so thin that for a given wavelength the photon escapes into space carrying energy. This is the effective emission height for that wavelength. I calculated this here in this post : The CO2 GHE demystified
H2O is more complicated and there is a wide band of emission frequencies. It is a much more effective greenhouse gas, but most water vapour is in the lower atmosphere. There is also the complexity of evaporation (latent heat), cloud formation etc. Water vapour also changes the lapse rate reducing CO2 greenhouse effect. The full effects of H2O on the climate are still not fully understood !
Hello Clive, thanks for your answer. The following paper finds a free path for a photon before absorption by CO2 at the surface of 32.75 m: http://www.biocab.org/Mean_Free_Path_Length_Photons.html
Because of the high density of water vapor at surface level, the free path for water vapor must be much shorter. I would be interested to know the free path for a photon in relation to water vapor molecules for the humid tropics, the Arctic and the Arctic and also for the world’s average.
Nullschool shows values for water vapor (total precipitable water, TPW) in the humid tropics of around 50kg/m2, of 3kg for the Arctic and a half kg or less for the coldest parts of Antarctica. The world average is supposed to be 25 kg m2. Total precipitable water is for the whole atmospheric column. https://earth.nullschool.net/#current/wind/surface/level/overlay=total_precipitable_water/orthographic=71.35,-0.96,300/loc=81.367,20.330
Because water vapor diminishes rapidly with altitude, there is a large difference in density of water vapor between the surface and higher in the atmosphere. I found some data here: https://atmos.washington.edu/~dennis/321/Chapter_01_Text.pdf
“The partial pressure of water vapor in the atmosphere decreases very rapidly with altitude (Fig. 1-7). The partial pressure of water vapor decreases to half of its surface value by 2 km above the surface and to less than 10% of its surface value at 5 km.”
Could you estimate what the free path for a photon at the surface would be before it is absorbed by water vapor for the above mentioned four cases: humid tropics, Arctic, Antarctica and ‘world average’?
I am very interested in the answer.
The mean free path of CO2 molecules at STP is measured to be about 5.6×10?8m. Where are you getting 25 meters from?
The mean free path of CO2 molecules at STP is measured to be about 5.6×10-8m, which 56 nm. Where are you getting 25 meters from?
I really mean the mean free path of photons emitted by CO2 molecules – not their collision mean free path ! The mean free path of such photons varies by orders of magnitude with each emission line. The only correct way is to treat each line separately. Looking at Beer-Lamberts law it looks like the average is 1.5m rather than 25m. I can’t honestly remember where I picked up the figure of 25m from !
Clive, you may find this link very interesting… http://geosci.uchicago.edu/~rtp1/papers/PhysTodayRT2011.pdf
Yes Brilliant !
Raymond Pierrehumbert is the real expert. I even bought his book ‘Principals of Planetary Climate’.
Clive …. great presentation, like it, though IMO, no one will ever be able to solve climate using radiative physics. Based on just “what is”, it is obvious that the GHG theory has very little to do with surface temperature, and more to do with energy stored in the system, having no Warming effect at all, but serving as a reservoir of energy in the absence solar insulation. Hence, the hottest temperatures are found in the areas of the least amount of overall GHG concentration, and in areas of high humidity, day time highs are actually lower.
In essence, GHG actually take energy out of the system and store it during day time heating and return it to the system during night time cooling, decreasing the range of temperatures. This spreads temperature changes out over time and space. GHG works just like the ocean, but on shorter time scales, …. the ocean absorbs heat and stores it for long periods of time, whereas, GHGs having a much smaller heat holding capacity act in shorter time frames. Both the ocean and GHGs move stored energy around, primarily toward the North Pole, and apparently less so towards the South Pole, given the lack of warming in Antarctica.
The overall impact of CO2 is limited by the total amount of energy available. The amount of IR in the CO2 spectrum is limited. Even if some of it is reradiated back to the surface, that radiation will be transformed to the overall spectrum of the surface, thus capping the actual amount of energy available for CO2 to absorb. As you say, there is already more CO2 than is necessary to hold this energy, …. adding more CO2 just dilutes the effect …. kinda like adding ice cubes to a pot of hot water …. the heat is distributed, and the temp actually goes down.
Physics would like to belief that the radiative in/out must be balanced at all times, but this is simply false, because there are just too many heat sinks on earth, and the cloud feedback serves to ensure that the amount of energy absorbed never stays the same.
Just my opinion … 🙂
heat is distributed, and the temp actually goes down? locally, yes. global average, no.
Ted, IMO, globally is a meaningless term with regards to climate. All temperature graphs, surface based, satellite based, balloon based, doesn’t matter, … show that the so called “global warming” is in reality just arctic warming. Arctic Warming is due to a lot of things, influx of warm water, influx of warm air, cyclonic activity breaking up ice, blowing it out of the arctic to warmer latitudes, decreased ice allows more heat to escape from the water warming the air and less ice lowers albedo. What it is NOT driving Arctic Warming is CO2.
A parallel effect of CO2 is global, global greening. When we look at global greening, we find that the entire globe is indeed greening. Thus, the CO2 fertilizing effect of CO2 is confirmed in the greening data. In contrast, we are told that CO2 operates on temperature via radiation, and as such it would be expected that it would operate the same globally. However, as mentioned, we do not see “global” warming, but rather we see that a specific region drives the global average. Thus the warming is not global.
This is a major issue, IMO opinion. The presentation of the mechanism of GHG Warming would according to physics, operate the same everywhere, implying the entire globe is warming. This is accompanied by all kinds of carastrophy stories, dying penguins, drowning polar bears, species going extinct everywhere. But the fact is, the entire globe is not warming, just the average temperature is being driven up by arctic warming.
From a physics perspective, the equation will have to account for a large number of heat sinks that act as capacitors. The Sun shines, but the majority of that energy is not available for immediate outward radiation. The different heat storage mechanisms, oceans, GHG, biomass, kinetic energy, ice etc, breath on their own time frames, and in order to accurately model the energy flux, one has to be able to accurately determine if a sink is taking in energy or releasing it. Some of those sinks are chaotic, and thus it is impossible to predict. I don’t think any of the models are remotely close to modeling the various heat fluxes within the system ….. and they fail.
CO2 is but a small participant in this system compare the overall heat capacity of all atmospheric CO2 to the other sinks, and ya have to wonder how anyone comes to the conclusion that CO2 is a major player.
Well said. Agree.
The heat-trapping nature of carbon dioxide and other gases was demonstrated in the mid-19th century. Their ability to affect the transfer of infrared energy through the atmosphere is the scientific basis of many instruments flown by NASA. There is no question that increased levels of greenhouse gases must cause the Earth to warm in response.
TED MACKECHNIE: “There is no question that increased levels of greenhouse gases must cause the Earth to warm in response.”
WR: Always one important word is forgotten: “initial”. Yes, there is an INITIAL warming in case of extra absorbing/re-radiating gases. But:
(1) First it has to be measured (!) that the total (!) quantity of those kind of gases increases
(2) Any warming (at the surface) always leads to activation of cooling processes. Cooling processes tend to diminish any initial warming effect.
(3) In case of a measured warming all (!) other potential sources of warming must be excluded before conclusions can be drawn about a temperature effect of absorbing / re-radiating gases.
Ted, yes, greenhouse gases absorb and emit energy. No disagreement. However, the impact on global surface temperature is a different story. CO2 radiation onto a water surface (70% of earth surface) results in either evaporation or storage of heat into the system, the surface temperature need not change at all. Further, as that energy is absorbed, it is transformed to the black body spectrum, thus converting the energy specific to CO2 into energy that is no longer within the CO2 range, no different from SW when it strikes the surface. OLW measurements clearly show a cause effect relationship between SST and OLW. SST is impacted by the interplay of clouds, sun, and the oceans own behavior such as PDO, AMO, El Niño, etc., has nothing to do with CO2.
I agree with you on all those points. Obviously IR from the sky does not have a sustained effect on surface temperature on a short time scale like one minute or one hour, or maybe not even one day. The blaring question is at what time scale does GHG IR start showing up in the rise in average temperature? one month, one year? Somehow that heat put into the huge buffer of the atmosphere translates into global warming, possibly a small amount…over a very long time scale. But perhaps that small amount is capable of setting off all those other triggers that could result in rapid global warming and climate change. To me, it is kind of like asking the question…how many times do you have stir the cream in the coffee until it finally mixes in?
But SST would not be as warm on average without CO2 in the atmosphere. And overall global warming may indeed affect PDO, etc. Warmed by sunlight, Earth’s land and ocean surfaces continuously radiate thermal infrared energy (heat). Unlike oxygen or nitrogen, greenhouse gases absorb that heat and release it gradually over time, like bricks in a fireplace after the fire goes out. Without this natural greenhouse effect, Earth’s average annual temperature would be below freezing instead of close to 60°F.
“greenhouse gases absorb that heat and release it gradually over time”
I don’t think this is correct. My understanding is that if a CO2 molecule absorbs a photon of energy, 99.999???% of the time, that energy is converted to kinetic energy via collision with oxygen and nitrogen molecules. This is because the average collision time ( in the dense atmosphere near the earth’s surface ) is orders of magnitude shorter than the relaxation time of an exited CO2 molecular. At the tropopause, radiative energy release becomes dominant because of the much thinner atmosphere means fewer collisions and much longer average time before a collision occurs.
How do excited Ñ2 and O2 molecules release energy? Do they emit photos of lower energy? If so do we measure the full energy efflux from the planet, or just concentrate on IR? Only a small amount of the energy from the sun is IR, the rest is more energetic radiation that gets absorbed by molecules and eventually by energy transfers is released as heat. Does the planet radiate more microwave energy than in the past?
What happened to the idea that most of the IR absorbed by C02 is re-emitted? I disagree that vibrating CO2 greatly warms the other gases. N2 and O2 have extremely low thermal conductivity. The atmosphere is truly warmed by conduction and convection at the surface of the earth. The surface is the only hot plate in town. The mixing then warms the atmosphere, which then self cools through the established lapse rate, resulting in the the coldest temperatures on earth literally occurring just 5 to 10 miles above our heads. CO2 warms the surface with re-emitted IR through the physics of optical depth, all explained by Elsasser’s radiation chart. As anthropogenic CO2 increases, it increases the optical depth of the IR re-emission column, resulting in a gradual increase in global average temperature. for your entertainment… https://www.youtube.com/watch?v=PTfnuX-HVk8
Much of what you say is true. However, the million dollar question is – How does the lapse rate get maintained? The answer is that it can only be maintained because heat is lost to space from the ‘top of the atmosphere’ by IR radiation. In effect the atmosphere is a huge heat engine moving heat from the surface via convection and evaporation up to colder layers where it then radiates into space. Convection slows at night and during the polar winter it stops.
IR emission and absorption by CO2 molecules far below the emission height is unimportant compared to convection and thermal equilibrium through collisions. Each level in the atmosphere is in local thermodynamic equilibrium at the local temperature. The rate of CO2 emission follows Stefan Boltzmann’s law at the local temperature.
also, you may find this interesting… https://www.youtube.com/watch?v=we8VXwa83FQ
“The peak for atmospheric OLR occurs for ~ 300ppm which just happens to be that found on Earth naturally. Can this really be just a coincidence ? It is almost as if convection and evaporation act to generate a lapse rate which maximizes radiation cooling by CO2 to space. If this conjecture is true in general, then any surface warming due to a doubling of CO2 levels would be offset somewhat by a change in the average environmental lapse rate to restore the radiation losses in the main CO2 band. In this case the surface temperature would hardly change.” – Clyde Best
I agree the “global” average environmental lapse rate would increase and tend towards adiabatic as convection and evaporation affect more and more volume of the atmosphere world-wide. But beneath each volume (column) of additionally mixed air there is a surface area of the earth that has warmed up to drive the mixing. The more surface area warmed, the greater the global average temperature. Thus doubling of CO2 increases the area of surface heating and mixing globally and thus the increase the global average surface temperature, as we have measured over the past 100 years, and especially the last two decades. The rise in the emission height is actually an indicator of the convection. Greater area and depth (volume) of the atmosphere is getting mixed.
I appreciate all your articles, programs and graphs. Very informative. You do good work.
Opps, i meant -Clive Best.
“What happened to the idea that most of the IR absorbed by C02 is re-emitted?
Answer: Physics
I’ve read several physicists who show that absorbed IR energy is almost always converted to kinetic energy via collision with oxygen and nitrogen molecules. They vary somewhat is their calculations of average collision time and average relaxation time, but the bottom line is always the same: at sea level, the probability of an exited CO2 molecule emitting a photon is minuscule.
Here are a couple links to some in depth discussions of this issue:
rabett.blogspot.co.uk/2013/04/this-is-where-eli-came-in.html
A couple notable quotes:
“The fate of the energy in a vibrationally excited CO2 molecule can be thought of as a race between emission of a photon taking essentially all of the vibrational energy away and a collision that does the same. Here Eli is going to tell you who wins the race……”
“Comparing the radiative rate kR (the inverse of the lifetime) to the collisional deactivation rate kM[M], provides a quick estimate that only one out of 100,000 CO2 molecules excited into the (0,10,0) by collision or absorbing a photon, will emit.”
Also
http://sealevel.info/Happer_UNC_2014-09-08/Another_question.html
A couple notable quotes:
Q: So, after a CO2 (or H2O) molecule absorbs a 15 micron IR photon, about 99.9999999% of the time it will give up its energy by collision with another gas molecule, not by re-emission of another photon. Is that true (assuming that I counted the right number of nines)?
Happer: [YES, ABSOLUTELY.]
Q: In other words, the very widely repeated description of GHG molecules absorbing infrared photons and then re-emitting them in random directions is only correct for about one absorbed photon in a billion. True?
Happer: [YES, IT IS THIS EXTREME SLOWNESS OF RADIATIVE DECAY RATES THAT ALLOWS THE CO2 MOLECULES IN THE ATMOSPHERE TO HAVE VERY NEARLY THE SAME VIBRATION-ROTATION TEMPERATURE OF THE LOCAL AIR MOLECULES.]
So who is right, Will Happer and other physicists, or the “back radiation” explanation of the GHE seen in most pro AGW websites (and the above mentioned You Tube videos)?
They’re both right. They aren’t contradictory. The CO2 molecules are constantly obtaining molecular vibrational energy on collision and might occasionally spontaneously emit electromagnetic radiation at the frequency corresponding to the energy of the molecular vibrational energy so CO2 molecules within micrometres of Earth’s surface can be bombarding the surface with electromagnetic radiations. It’s caused by molecular collision. The surface is only a feed into the atmospheric “shimmer” of it. In that frequency band it’s pouring down (and up, and sideways) from CO2 molecules throughout the atmosphere that obtain it by collision, as I explained, and not (or hardly ever) by absorbing electromagnetic radiation from the surface (except in the lowest few hundred metres). Mostly what a CO2 molecule absorbs was emitted by another CO2 molecule (or perhaps H2O in the overlapping band) but in the LWR produced by molecular collisions is going to be overwhelming larger.
At a given level…
CO2 absorbs IR and warms.
CO2 warms N2 and O2 through collisions.
CO2, N2 and O2 emit some IR in all directions.
At the adjacent higher level…
CO2 absorbs IR and warms.
CO2 warms N2 and O2 through collisions.
CO2, N2 and O2 emit some IR in all directions.
And so on to the grand emission height.
So you are correct in saying that it is not just CO2 that radiates IR in all directions (and in very small amounts). All the gases do! But it is CO2 at each level that repeats the process of absorption, vibration and re-radiation. The net effect is the same…the column in the sky emits IR back to the earth and warms it.
The AGW are not incorrect in identifying GHG as the cause of back radiation. The slowness of radiative decay does not change the net result.
As always I am left wondering why CO2. Warming that has been observed on this planet has progressed with industrialisation, but CO2 is not the only thing that has changed and not the only potential driver of warming. At a theoretical level CO2 could be causing an effect, but like all bad experiments, we have more than one uncontrolled variable and we may be looking at the least important because we are unable to sort wheat from chaff.
Back radiation from high atmosphere:
Less than half of this radiation heads earthwards since it is above the horizon.
Most of it will be absorbed or reflected on its way down by greenhouse gases, particularly water. 69% of the planet is on average covered in cloud ( so I have read) and where there is no cloud, there are water molecules and other greenhouse gases. What is the probability of a low energy photon reaching the earth’s surface having traversed this crowd of obstructions?
Surface effects consequential on industrialisation and population growth:
Heat from Human industry. This heat is primarily produced in urban environments. It is generally emitted along with other emissions – smoke stacks, car exists, factory outlets… A fair degree of this heat become trapped in the smog and is back radiating well past sunset. Clouds trap some of this energy and radiate it at night. This energy, carried in clouds, drifts from above the city taking heat to other places. There is therefore a dampened release of heat and this particularly elevates nocturnal temperature when normal temperature lows occur.
Buildings and roads both absorb substantial amounts of heat during the day and cool down at a slower rate than other parts of the environment. This then elevates night time temperatures, particularly in the period after sunset. In 1850 the majority of people on the planet lived in rural environments and metalled roads were few. The population, if I remember, was about 1bn, it is now 7.5bn with more than half living in cities. Roads are black, absorb considerable amount of heat and slowly release it at night. City buildings do the same. This leads to a dampening of nocturnal cooling and the heat emitted is absorbed by and refleced back by clouds. Again this will work to raise temperature lows and hence average temperature.
I don’t know if the calculations have been done, but I suspect that if someone has the time, they will find that the heatsink capacity of urbanisation and roads now outstrips that of CO2 in the atmosphere.
That is why I thought Clive analysis of Australian temperature was fascinating, since it shows that minimum temperature is higher. This is what you would expect it a heatsink was affecting night time temperatures.
So a CO2 molecule will raise the temperature (vibrations) of surrounding molecules and consequently cause a little connection. Of course in the upper atmosphere, collisions are rarer and emission may predominate there. But, poor little photon has a long way to go if it choose to head down. It has to go through armies of greenhouse gases, particularly water if it has any chance of reaching the surface.
In Scotland where I live I have noticed that the climate is milder then when I was a child. I have not noticed warmer summers, but winters are milder and night temperature are less cold. Is this caused by CO2 or other factors associated with industrialisation, population growth and urbanisation? Or nothing to do with humans at all?
The picture that “back IR radiation” from CO2 molecules in the atmosphere is warming the surface is in my opinion simply wrong. Heat always flows from the surface upwards through the atmosphere to space. A simple picture is that doubling CO2 increases the height of the tropopause. The surface apparently warms a bit because the height of the lapse rate increases. The temperature at the ‘top of the atmosphere’ remains the same.
Clive,
Studies have demonstrated clear evidence of an increase in tropopause height with a decrease in tropopause temperature and pressure since 1980. That does support the notion that the tropospheric mixing is extending the lapse rate higher, which infers a higher global avearge surface temperature.
I don’t understand your “back radiation from CO2”. There is obviously measurable IR coming from the sky. It is not just from CO2 as I explained earlier. It is IR emission from all gases in the optical depth of the whole atmospheric column. As the column fills with more GHG, this IR increases.
At the risk of using an analogy…which while helping to grasp a concept but at the same time ignores essential details, I suggest this. The IR from the sky above a certain location is like a very long vertically standing flashlight loaded with batteries. We can detect the heat from the lamp at the surface. The lower batteries are very strong (charged) due to absorption by GHG and reheating of the non-ghg gases though vibration/collision. The upper batteries get progressively weaker but still contribute to the brightness of the flashlight lamp. Their contribution increases as the atmosphere warms and thickens and the tropopause rises and cools. The upper batteries increase in charge as GHG is added (or perhaps more weak batteries are added to the upper end of the flashlight tube).
Clive Best: “ As figure 2 shows above outgoing CO2 radiation peaks at around 4000m altitude. “
WR: To be able to leave the atmosphere (= the Earth) photons must have a free path to space which means that a photon will not be intercepted by an absorbing molecule during it’s way to space. Hence my question: the 4000m CO2 emission peak as mentioned above, is that a theoretical peak (for example in a modelled atmosphere without H2O) or are the calculations for the reality of the Earth’s atmosphere (with intercepting molecules like H2O)?
For example Fig. 5b from https://clivebest.com/blog/?p=4597 suggests a much higher emissivity height than 4000 meter.
Besides, as I understand, the free path for a photon at the surface is some tenths of meters or even much less. As the density of the air at 4000m has not diminished dramatically and the main absorbing gas H2O also is not absent, I wander how there could be such a long free path (even to space) for by CO2 radiated photons, already at 4000m.
There is that which happens between photon and molecule and that which happens between molecule and molecule. Radiation coming from all directions and radiation being emitted in all directions. All this happens in microseconds and at best frequency. I think it is a bit like has laws where you can’t know anything specific, but where you have to rely on a statistic for velocity e.g. Root mean square. On average is energy taking longer to leave the planet as a consequence of greenhouse gases? Are these gases having a small insulating effect? There seems to be evidence that this happens, but if this is the case the shift to a new equilibrium for any concentration should be established immediately and if the effect is like insulation, there should be a diminishing return, so that a doubling of concentration does not double the insulation. This is just my way of visualising at the moment and I’m sure that a physicist who knows much better than me will shoot me down in flames almost immediately.
Atmospheric insulation is not like material insulation (blanket, fiberglass, foam, etc). Whereas material insulation is of fixed thickness and air is trapped, the atmosphere has varying thickness (in response to any kind of heating) and is free to mix. Also, whereas material insulation is of fixed composition, atmospheric composition can be changed (ie the addition of GHG). And apparently, the atmospheric insulator’s R value goes up linearly with increase in temperature (see link in previous response). So it is not just adding GHG insulation that is increasing the greenhouse effect, warming and thickening of the atmosphere itself may be increasing the greenhouse effect…a positive feedback.
While you can measure IR radiation in any direction the flux downwards is IMHO irrelevant because the atmosphere cat any height if in thermodynamic equilibrium mainly the through M-B kinetics. So the temperature is more dependent on thermal equilibrium than any heating effect from layers above.
I can’t believe that anyone has tracked an individual photon, so presumably we are talking about a statistical photon, the average path which allows for collisions and emissions?
Clive and Mr Broccoli,
You may find this interesting on the R value for the atmosphere… https://www.aps.org/units/fps/newsletters/201210/hafemeister.cfm
Satellite measurements confirm less long wave radiation is escaping to space at carbon dioxide absorptive wavelengths. Surface measurements find more long wave radiation returning back to Earth at these same wavelengths. The result of this energy imbalance is the accumulation of heat over the last 40 years. Apparently the downward flux is cumulative over long time and space scales. I don’t think trying to track the real time path of IR photons will help explain the GHE. It’s like scale analysis…one can only write a relevant equation if the variables operate on the same scale of magnitude.
When a UV photon interacts with ozone, work is done and IR is emitted. How do we know that the heat coming down towards the earth is emitted by CO2 and not the result of some other process? Over the period since 1850 the earth’s magnetic field has been weakening. A consequence of this is that there is increased penetration of high energy photos smashing into molecules and creating heat. I read a couple of papers on this some time ago and they had calculated that all the excess heat that we experience could be a consequence of this. I’ll try to find the references.
I think it is the overall process of UV photons splitting oxygen to form ozone which maintains the ozone layer. Thereafter Ozone acts both as a greenhouse gas to block upwelling IR photons and as a sun block to UV photons. So it is a balance between GHE and albedo. The result seems to be that IR wins out – see a nimbus spectrum .
Well, that is something to think about. A strengthening magnetic field is associated with a cooling of the Earth, while weakening is linked to warming… https://www.theguardian.com/notesandqueries/query/0,,-1404,00.html
In order for the Earth’s temperature to remain constant, the outgoing energy radiated by the planet and its atmosphere must equal the incoming energy from the sun that is absorbed by the planet. To balance the present incoming energy, the planet must radiate to space an amount of energy equivalent to the emission from a black body at 255 K. Since the surface of the planet is, on the average, at about 288 K, it emits too much energy to maintain the energy balance. The observed emission spectrum shows that the IR-absorbing gases in the atmosphere reduce the temperatures at which emissions to space occur. This lowers the effective emission temperature of the planet and maintains its energy balance. The planet can only do this by having an atmosphere that is compressible and in hydrostatic balance, resulting in the observed lapse rate of temperature.
“To balance the present incoming energy, the planet must radiate to space an amount of energy equivalent to the emission from a black body at 255 K.”
The “255K” is not relevant to Earth’s actual emission to space. The surface emits based on temperature.
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Greenhouse gases absorb heat. They then radiate this heat. Some of the heat will head away from the Earth, some of it will be absorbed by another greenhouse gas molecule, and some of it will wind up back at the planet’s surface again. But what is heat in this context? And where does this heat actually cause temperature increase? I believe the heat is simply longwave IR radiation. Sure greenhouse gases vibrate when they absorb IR, but since they immediately re-emit IR, they do not heat up in the sense of temperature. Nor do their vibrations cause an increase in temperature in other gases by collision, as the IR is re-emitted much faster the rate of collision. So, air does not directly warm up because of greenhouse gas (GHG) absorption at a given altitude. So then, how does earth and its atmosphere warm up from all that re-emitted heat? It is simply the net downward flux of IR heat being absorbed by the surface. The surface then warms up by vibration and conduction. The air takes in this heat through conduction, buoyancy, convection, turbulent mixing and wind which ultimately warms the rest atmosphere, establishing the average lapse rate. The natural net downward flux is about 5% of the incoming solar energy, resulting in an average surface temperature that is 60 deg F warmer than it would be if the air had no greenhouse gasses. But as we add more GHG, higher concentrations are mixed through the depth of the atmosphere (as well as across the globe). This increases the optical depth of GHG resulting in an increase in downward net flux reaching the surface, giving rise to average global temperature through the mixing process described.
Ted Mackechnie: “but since they immediately re-emit IR, they do not heat up in the sense of temperature. Nor do their vibrations cause an increase in temperature in other gases by collision, as the IR is re-emitted much faster the rate of collision. So, air does not directly warm up because of greenhouse gas (GHG) absorption at a given altitude.”
WR: A temperature effect for the atmosphere is measured (in the laboratorium) which implies absorption of radiative energy and transference of the kinetic energy to other (N2 and O2) molecules. See the discussion with Prof. Happer here: https://sealevel.info/Happer_UNC_2014-09-08/Another_question.html
oddly though, the absorption of IR by ghg does not directly warm the atmosphere. the IR that is returned to the earth’s surface through optical depth warms the surface which then warms the air through conduction, convection and advection, i.e. weather. case in point, when you turn on an IR lamp, your skin is what warms up, not the air. this needs to be better explained to convince everyone what the heck is going on!
Thought you might find this interesting considering the subject of doubling co2
https://iopscience.iop.org/article/10.1088/1361-6463/aabac6/meta
I do not have the patience to read all the comments on this blog but just mention some things which often seem to get overlooked. At low heights, when a green house molecule such as co2 absorbs an infrared photon as a quantised vibrational state, it typically releases that stored energy by collision because the mean time to re-emission is greater than the time to collide with another atmospheric molecule. The greenhouse gas molecule is then in in thermal equilibrium with the atmosphere. At high altitudes, the low temperature is a measure of the low velocity of the molecule which combines with the greater distance that the molecule has to travel in the sparse atmosphere to have a collision. This increased mean-time between collisions means that the excited atom loses its energy preferably by emission rather than collision. This emission is random in direction so some infrared photons head back to earth. Ultimately the energy balance of the earth against solar radiation is determined at the top of the atmosphere rather than the bottom. I hope this is helpful and apologise to those who may have already made this point.
Ken Lynn
This is absolutely correct!
Hello, I’m a collage student. Can I ask some question about carbon dioxide in atmosphere?
First, In my measurement using FTIR, the integral area under spectra line is different of pure CO2 (0.3torr) and CO2 (about 0.3torr) in atmosphere. Next, I also mix Nitrogen (760torr) and pure CO2 (0.3torr). The absorption strength (area under spectra line) is (atmosphere > mixing nitrogen > pure CO2). But according to Beer’s law, they should be the same. It’s the effect of collision bordering or others you may know? Second, for Hitran, When they determine line intensity ( area under spectra line), do they use pure sample or sample gas in atmosphere? Because according to my measurement using FTIR, I find that the area seem to be different between pure CO2 and CO2 in atmosphere. Thank you !!
These are excellent questions and I am not sure I know all the answers!
Certainly in the real atmosphere CO2 lines are pressure broadened due to collisions with air molecules mainly Nitrogen but also oxygen and water vapour. So if you simulated the real atmosphere then you should get the same result. However it is complicated because temperature and pressure fall with height so you would get different spectra at different heights. So a measurement of ‘Back IR’ looking upwards from the surface would depend on the mean free path of IR photons for a given frequency.
So far as I know HITRAN gives the line strengths of pure CO2. They explain quote:
So they are more similar to the energy levels of Hydrogen or more complex atoms. So they are not equivalent to those measured in the atmosphere.
Thank you very much !!
Can I ask one more question?
When I calculate line intensity of Hitran, I use integral area “A” (area under spectra line) and Beer’s law “A”=sigma*density(n/cm^3)*optical path (cm). This sigma values is the line intensity. Is that right? However, I calculate pure 0.3 torr CO2. The area of 2313.3 cm-1 is about 0.02. Thus, line intensity is 1.72E-20. But Hitran give us 6.21E-19. Are there some steps I ignore during calculation? Thank you !!
janwilly5562, a friend of mine, who is a leading atmospheric physicist and an expert on this topic, has a paper “in the works” which might interest you. It isn’t published yet, but he has given me permission to share it with you, on the condition that you keep it in confidence. If you’d like it, then send me an email; you can find my email address on my sealevel.info web page.
I am an engineer with a vast amount of experience designing and building factory automation. My gift is the gift of insight. I have used most of the phenomena in my college physics book. This blog and the comments on this blog are a gift.
My question is that if a 15 micron photon were to be absorbed by a water vapor molecule and the water vapor molecule later radiated a photon itself, is there any reason to expect that since the water vapor can absorb and radiate over a fairly wide spectrum that the new radiated photon would be at a 15 micron wavelength?
Comments on this blog seem to say that there is there is a much higher probability that the water vapor molecule will collide a non GHG molecule and share its mechanical energy with it than re radiate the new energy.
Well, I don’t think water vapor absorbs very well at 15 µm, so I think you mean CO2, right?
I’m no expert, but my understanding is that a variety of other energy quanta, as well as the movement of the molecules, can add or subtract from the energy level (and thus wavelength) of the emitted photon. So even in the (rare!) case of a molecule absorbing a photon, and then losing that energy by emitting anothe photon (rather than collisionally transferring the energy to another air molecule), the emitted photon could still be at a slightly different wavelength than the absorbed photon.
E.g., suppose that a molecule absorbs an exactly 15.08417 µm photon (which is the center of one of CO2’s absorption lines). Then suppose that same molecule happens to be moving north when it emits another photon, in a random direction. If the photon happens to be emitted in the same direction that the molecule was moving (north), the photon is blue-shifted slightly (slowing the molecule). But if the photon happens to be emitted in the opposite direction (south), then the photon is red-shifted slightly (speeding up the molecule).
This can be used for a strange and interesting “refrigeration” technique, using lasers. You tune the laser(s) to just slightly below a strong absorption line of a pure substance that you’re trying to cool (i.e., to a slightly longer wavelength), in a vacuum chamber. Hit the target substance with the laser(s), and wait for the “same” wavelength to be re-emitted by the target substance.
The re-emitted light will be centered on the substance’s absorption line, which is slightly above the wavelength of your laser. But the laser light will be preferentially absorbed by molecules which are moving in the direction opposite the direction of travel of the laser’s photons (which, from the perspective of the molecules, are blue-shifted). The net effect of absorbing photons which average slightly lower energy than the emitted photons is a slowing of the molecular motion, i.e., a cooling of the substance.
I’ve been looking at this on and off for a couple of years and finding great difficulty tracking down information on it. I am perplexed why this is not well understood, given that it is fairly basic physics. My understanding to date is that a molecule absorbs a photon which may cause the molecule to change, cause an electron to jump to a higher orbit, cause the molecule to vibrate, or cause the molecule to rotate. Photons with a wavelength of 15 microns are absorbed by CO2 and cause vibration. From my readings it would appear that at ground level about 99.999% of this kinetic energy is transferred to surrounding molecules, causing a degree of convection. This leaves a small proportion that is re-emitted. Again my understanding is that re-radiation occurs at frequencies that correspond to frequencies of absorption, but not necessarily the frequency of the photon that was absorbed. In the case of CO2 this gives three possible frequencies for emission and in the case of water several more.
Moving up the air column, the air become thinner so this possibly increases the frequency of emission, since there are fewer molecular collisions. The atmosphere at this height is much colder and this reduces emission rate. I am not aware of research that has accurately measured collision rates or emission rates and certainly have read that Beer Lambert law does not apply in an open atmosphere. My understanding is that at ground level, an IR photon travels about 10m before being absorbed and in the upper troposphere this is about 50m.
I do not yet know how oxygen and nitrogen emit energy in the high atmosphere, possibly some form of black body emission? I also don’t know how much of an energy audit we have. Our satellite measurements have only been available for a couple of decades and I don’t know if we have any historic data on microwave emissions and changes over that time. Energy comes into our planet as high energy and leaves as low energy. I don’t think there is accurate historic knowledge of inputs, throughputs and outputs.
Does CO2 have a role to play in warming the atmosphere? Given that it emits a tiny fraction of what absorbs about a millisecond after it absorbs a photon, it is hard to see that this scattering is significant. I have begun to wonder if it’s role is to act as an energy pump, rapidly transferring photonic energy to kinetic energy that is principally held by oxygen and nitrogen. It seems probable that it fairly rapidly transfers about 10,000 times more energy by this route rather the by radiation. If anyone is good at calculations, I would be interested to see how this computes. At ground level a CO2 molecule could be transferring 1000 photons worth of energy to the air every second. If we know the number of CO2 molecules in the atmosphere, the absorption rate through the column, the kinetic transfer rate with height and the emission rate it would provide a simple equation that could accurately describe exactly how much heating any greenhouse gas contributes to energy in the atmosphere.
Knock me down in flames of I’m being niave.
If the earth had no atmosphere its temperature would be similar that of the moon. The sun heats the surface to a black body temperature which always balances radiative losses to space. Once you have an active atmosphere with water vapour, CO2, Ozone, Nitrogen, O2 etc. the dynamics change. The surface heats the atmosphere through convection, conduction and evaporation. The atmosphere becomes a heat engine generating a lapse rate and the all earth’s weather. H2O is by far the most important active gas because nearly 70% of the surface are oceans.
Each level in the atmosphere reaches a thermodynamic temperature. CO2 molecules have the same thermodynamic temperature and can get excited into vibrational energy levels emitting IR photons. H2O does the same. The only difference is that CO2 selects photons in a narrow 15 micron band, and these can get absorbed by ‘cooler’ CO2 molecules above them which absorb some of the energy before re-emitting energy above. Eventually the air thins enough that such that these can photons escape to space. The net energy loss is reduced slightly because this level is colder. As a consequence the surface warms a little to return to equilibrium.
If the temperature warms then more H2O evaporates and cloud cover increases. This counteracts the effects of CO2 for two reasons. 1) Clouds reflect sunlight, reducing solar energy absorbed by the surface. 2) The lapse rate diminishes reducing the lapse rate. The net affect though is probably a small warming but as yet hardly noticeable.
Clive, although the Earth and Moon receive the same level of solar insolation, even if the Earth had no atmosphere its average temperature would still be warmer than the average temperature of the moon, if they had the same albedo.
That’s because the Moon rotates only 1/27-th as fast as the Earth. That means each side of the Moon is heated by the Sun for 27 times as long as each side of the Earth is heated; and then cools for 27 times as long, as well.
That means that, even if the Earth had no atmosphere, the temperature extremes on the Moon would be much greater than on the Earth. The highs would be higher, and the lows lower.
But since radiative emissions are proportional to the 4th power of surface temperature, there would be more rapid energy loss during the Moon’s higher highs, so the difference between high temperatures on the Moon and Earth would be less than the difference between low temperatures on the Moon and Earth. In other words, the Moon’s average temperature would be lower than the Earth’s average temperature.
I agree with the rest of what you wrote, except there’s a typo in the last paragraph (“the lapse rate diminishes reducing the lapse rate”).
Minor correction: the lunar day is about 29.5 Earth-days in length, not 27.
Are you saying that CO2 does not cause much warming? Is it a green herring?
The Antharctic region has recently had a cold record. I wonder if there was a net cooling effect from CO2 there, due to the lower level of the tropopause. At around 8-9kms
In any case there ought to have been a lower warming effect.
Clive’s intuitively pleasing idea of a characteristic height for ir photons to escape (with say 50% probability) to space is of course an effective value actually resulting from an integral over a range of heights with a range of corresponding probabilities. For each part of the spectrum.
If the effective value of the characteristic height lies closer to the tropopause then the calculation probably becomes more sensitive to the precise values input and at some CO2 concentration there might be a net cooling even if this wouldnt be the case now.
Then the Antharctica might be used as a means to store the excess water from rising sea levels as more ice there.
I havent tried to make the calculation. But at this point I get the impression that everything seems to be laden with feedback mechanisms reminding of the Gaia theory. And as if it was all deliberately arranged by some intelligence to open opportunities for the protection of life.
How likely could it be that such an intelligence would be a malthusian?
On the other hand perhaps it would be a eugenicist…?
Can’t see any mention of SF6. Sorry if I missed it. Is it really 20,000 times more potent ‘greenhouse gas’ than CO2? How is ‘greenhouseness’ measured? Is there a unit?
Thank you very much for your research!
1) Are you sure that thermal emission law (Stefan–Boltzmann) applies to fluorescence?
2) Doesn’t the energy migrate down the spectrum, out from the opacity band, on the way to space, because transparent bands get less occupied on altitudes (thermodynamic equilibrium)?
3) Are current models built rather for Martian atmosphere? focusing only on very thin CO2 because altering composition gas mixture with density, pressure, temperature and absorption/emission spectrum is just impossible to model effectively?
4) We know that negative feedback loop capacity is way broader than few degrees. History has seen tens degrees of variation. Still we have all three phases of water, we are stabilized as if in a triple point cell. Latency in these feedback chains causes oscillation. If you look at the multitude of different cycle lengths, you can guess how many there is! (excluding Suns and orbital oscillations of course). Positive feedbacks generate higher harmonics in the system.
Clive, I like your site. You and some of your contributors have taken their skepticism and looked at it a bit more empirically. I’ve done the same and am looking for an open discussion, constructive criticism and anything I’ve overlooked.
Start with an example:- hot, sunny, windless day on the equator. First location : On an asphalt road (tarmac), second location : The nearby ocean.
The asphalt is at 70-90C and the water is a nice 15-18C. You could not walk bare foot across the asphalt, but the water would be very pleasant.
The same watts/m fall on both, and the emissivity/absorptions coefficients of asphalt and water are fairly similar. (0.96 water, 0.9-0.92 asphalt)
At 15-18C the water re-radiates much less LW-IR into the atmosphere than the asphalt at 70-90C. (Stefan-Boltzmann equation (E = ??T4) )
The difference is water is a much better conductor/convector so most of the heat from sunlight is quickly convected and conducted below the surface. The heat is thermalized in the water, and ocean temperature rises by an very small amount.
So earth’s oceans store most of the heat long term on this planet which does screw with our mental image of how the greenhouse effect ‘traps’ heat.
We do know this intuitively, which is why water temps can be warmer than air at night, and why the sea is at it’s warmest in late september.
Despite this rather important process never being discussed in popular explanations of global warming, a climate scientist would not be phased because what average global temp. (AGT) studies look at it is an increase over time, and all other things being equal, this correlates directly with CO2 increase giving them their climate sensitivity factor.
But, getting back to the hot asphalt; At 70-90C it re-radiates LW back to atmosphere which is selectively absorbed by water vapor and CO2 at 4.2 and 14-16 microns respectively. Using Beer-Lambert shows that most of that heat is absorbed within the first 10-20m from the ground (logarithmic).
The absorbed heat is then thermalized. The 410ppm CO2 molecules are evenly distributed through the atmosphere of 21%O2 and 78% N2 and other trace gases, collisional broadening of neighbouring N2 and O2 molecules wash out the absorption peaks, broadening them and reducing amplitude until the heat is averaged out in the volume of atmosphere.
LW re-radiation does occur but now broadly across the LW band and not just 14-16micron or 4.2 micron bands, plus at the new averaged temperature. Given the temp. differential within the CO2 extinction pathlength (10-20m) is quite small, nett radiative transfer either up or down is close to zero. Convective (and conductive) heat transfer takes over as the main mechanism for conveying heat transfer through the atmosphere.
Heat is then conveyed to the upper atmosphere by mostly convection and some conduction.
Convective and conductive are more effective heat transfer mechanisms, and radiative works best when the temp. of the source is much higher than where it is radiating to. With temps +20m and -20m in the air being similar, there is very little net radiative heat transfer.
At some point as the air thins, and extinction pathlengths get longer, radiative does re-assert itself a little, but the point is every re-absorption at now 4.2microns(as there is little water up there) and 4-16 microns, heat gets smeared out still and further thermalization & re-emission occurs broadband helping the heat to escape to space faster.
Does anybody have a good estimate of CO2 extinction coefficient at 14-16 microns? I have tried calculating from HITRANS data, but not conclusive.
If the extinction pathlength in the lower atmos. really is 10-20m, then increasing CO2 might shorten it slightly, but would not really make the lower atmosphere any hotter.
So what other things could increase AGT? Here’s one idea:-
We know now the oceans & seas stores almost all earth’s heat. Every m2 of water stores much more than a m2 of land.
The earth has an slightly eccentric orbit around the sun. The perihelion (closest point) is approx. 147million km from the sun and the aphelion(furthest point) is approx. 152million km from the sun.
At the moment (2019) the southern hemisphere will be experiencing it’s summer during it’s perihelion (closest) and the Northern hemisphere the opposite at it’s furthest point.
That means more sunlight is hitting the southern hemisphere in summer than the Northern hemisphere gets in it’s summer.
Given that the ratio of land/ocean in the Northern hemisphere is approx. 60/40 and the southern hemisphere 80/20 you get more heat being stored in the oceans which in theory should contribute to an increase in the AGT.
Thanks Bill,
Your comments regarding the Ocean and land surface (asphalt) are very true. At night the land cools faster and convection can stop, whereas the oceans maintain the same surface temperature, and heat loss through evaporation and convection. Nowadays I have a very simple model of the atmosphere. On average every level in the atmosphere is in local thermodynamic equilibrium. The local temperature is determined by the (moist) lapse rate. This varies with latitude and with season. In the lower atmosphere IR photons from CO2 are almost irrelevant as a heat flux source. A CO2 molecule is more likely to be excited into a 15 micron vibrational energy level through collisions with nearby N2 and O2 than it is through absorption of any IR photon from below. So the atmosphere is essentially a heat engine moving energy from the surface upwards to the local ‘tropopause’. Convection essentially runs out of ‘steam’ at the tropopause which is also changing in height with latitude and season. What keeps the heat engine running?
It is IR radiation to space that keeps the heat engine running. That total energy loss must equal the incident energy from the sun. The density of the atmosphere falls with height, so there are effective emission heights for different wavelengths of CO2, O3, H2O. Cloud tops can also radiate directly to space and reflect sunlight. The IR spectra you see from satellites like Nimbus show exactly this. So if you suddenly increase CO2 the effective emission height gets a bit higher which is initially at a colder temperature so slightly less radiant heat escapes to space. The surface warms a little to restore energy balance.
see : https://clivebest.com/blog/?p=4597
Clive
P.S. Lots of other things might change as well of course like clouds, water vapour etc. but that is another story.
Hey Clive, So if we can agree that the oceans act like giant capacitors, it also follows that the heat balance of incoming solar radiation to outgoing does not have to balanced immediately. In fact it would be seasonal with more incoming solar than outgoing in the summer and the other way around in the winter. The reason I mention is the convective zone in the troposphere determined by the lapse rate is quite slow compared to radiative heat transfer, and separates the initial radiative from the surface with that happening above the tropopause. Can we really say that the heat radiated from the stratosphere is any slower with additional CO2 since absorption/re-emission is so fast? Given as the oceans negate the need to immediately balance ingoing/outgoing heat and the convective slow zone separates the two; can we really say that lower atmospheric temperature will really increase with increased CO2?
That is a nice analogy Bill. Yes the oceans act like large capacitors storing energy in summer and releasing it in winter. As a result energy is never really in balance, because if it was there would be no weather. So heat is continuously moving through the oceans and atmosphere diurnally and seasonally. I see radiative transfer as a bit of a red herring. Heat radiates to space as fast as possible just like your home looses heat as fast as possible when it is cold outside. Convection only works because heat is radiating out to space. That is why in the Arctic/Antarctic winter convection stops and the stratosphere almost reaches the ground. Temperatures can reach -50C in Antarctica. CO2 is just a small factor which determines the rate of radiative energy loss to space cooling dependent on latitude and season. Seasonal weather dominates still temperatures wherever you live.
Thanks Clive. I like what you said about Antartica. I think the lowest recorded temperature there was something like -89C. Like you then, I see the stratospheric radiative heat transfer as a bit of a red herring. It is somewhat re-assuring that most of what we have been talking about seems to be in alignment and perhaps all of this points to one conclusion where the rational behind climate sensitivity being a direct correlation between Global temp. and CO2 is oversimplified. This brings into question whether even the lower bound of 1C is even realistic, and hopefully this will help quell the ‘climate catostrophe’ alarmist talk which I don’t think is in any way accurate or helpful. Perhaps a little ambitious but maybe leading to a more reasonable approach where an increase in CO2 is no longer promoted as being the biggest issue facing humanity.
Hi Clive,
Good clarity explaining the greenhouse effect. But I have a couple comments on part 1:
“IR scatters repeatably upward through layers of the atmosphere until at between 5-9 km the air is so thin that the the atmosphere becomes transparent allowing CO2 emissions here to radiate out into space. At these levels there is little water vapour and CO2 dominates the energy loss. As CO2 concentrations increase so this level shifts to higher levels in the atmosphere since a critical density must be reached for the radiation to escape. These levels are colder (until we reach the troposphere) and IR loss is proportional to T**4 (Stefan Boltzman’s law). This means that slightly LESS energy is radiated to space than before and since the total energy must balance, the Earth warms up to radiate more heat to compensate.”
Minor point: high cloud tops reach 14 km, so maybe water is significant in these altitudes?
Major point:
At 400ppm and 5 km in the US Standard Atmosphere, the density of CO2 would be .2961 g/m3. At 9 km the density would be .1877 g/m3. Doubling the CO2 to 800ppm means that those densities would be reached at 11 km and 13.9 km.
Comparing the increased spherical surface area from 5 to 11 km altitude, if you are trying to get rid of 300 W/m2 at 5 km, you can get rid of the same amount of watts for only 299.44 W/m2. If you are trying to get rid of 300 W/m2 at 9 km, 299.54 W/m2 at 14 km will do it.
If you go from 300 W/m2 to 299.44 W/m2, you can get rid of the same amount of radiation at a temp that is 56 degrees cooler. From 300 to 299.54, it can be done 53 degrees cooler.
Going from 5 km to 11 km, you only drop 39 degrees. From 9 to 14 km, you only drop 13 degrees.
My point is that the increased altitude leads to increased surface area from which to radiate, and that increase is faster than the temperature drop. So it looks to me like point 1, which seems to be the stronger point, is completely wrong. What do you think?
Sorry for late reply.
1. The change in surface area between the surface and say the tropopause is actually very small. 4.pi(R+r)^2 where r = 20km and R = 6371km. This is approximately 2r/R or 0.6% so the effect is rather small.
2. Certainly clouds change the radiative balance of the earth and large convective clouds can short circuit the greenhouse effect
I have a better post which explains how increasing CO2 density increases the effective radiation height for CO2. I think this also answers your point about changing CO2 densities with height.
Here it is
The CO2 GHE Demystified
High thin cirrus clouds tend to enhance the heating effect, and low thick stratocumulus clouds have the opposite effect, while deep convective clouds are neutral. The overall effect of all clouds together is that the Earth’s surface is cooler than it would be if the atmosphere had no clouds.
Hi Clive, I went back over what I did and I stand corrected, I subtracted the watts required at the new altitudes from the watts required at the current altitudes and then changed the differences into blackbody degrees to come up with 56 and 53 degrees. I should have taken required watts and converted them to temperatures first, the differences are less than one degree. So yes, the temperatures drop faster (13-39 degrees) as the altitude goes up while the radiation requirements remain within one degree.
Got a problem with this idea, especially the second sentence: “IR scatters repeatably upward through layers of the atmosphere until at between 5-9 km the air is so thin that the the atmosphere becomes transparent allowing CO2 emissions here to radiate out into space. At these levels there is little water vapour and CO2 dominates the energy loss.” This presumes that only CO2 and water vapor can radiate to space. All matter above absolute zero emits IR radiation. Only greenhouse gases can absorb some of it, but ALL MATTER EMITS IT in a blackbody pattern that reflects its temperature. When CO2 blocks energy at a certain wavelength, it shares the added heat with the molecules around it through contact, and the energy is emitted at all wavelengths in a blackbody pattern reflected by the temperature. The area under the spectral emission graph is the total energy emitted by the entire air column and reflects the average temperature of the column. The CO2 absorption, sharing of heat, and subsequent emission of radiation in a blackbody pattern does not change the total heat output of the atmosphere, it merely changes the wavelengths of emission. This creates a deficit in the wavelengths where greenhouse gases absorb, but also a corresponding SURPLUS in the wavelengths not absorbed by greenhouse gases.
Add up the area under a top of the atmosphere spectral emissions graph. Find the corresponding blackbody temperature with the same area under its graph. Put that line on the graph. It will reveal wavelengths subtracted by absorption and other wavelengths increased by heat sharing with neighboring molecules.
The entire atmosphere acts as a blanket by contact with the ground and convection, and all molecules emit thermal IR radiation in a blackbody pattern reflecting their temperature. Because of this, I don’t think greenhouse gases are the driver in global warming.The Ice Age left us with ice caps, glaciers, and chilled deep-ocean water. If the surface is 288 K and the crust of the Earth gets warmer with depth, why do we have near freezing waters in the depths of the ocean between the surface and the warmer rocks? It is because of cooling left over from the ice age and perpetuated by the ice caps. The Ice Age was driven by volcanic hyperactivity, and now that the volcanic activity has settled down, the glaciers are melting, the ice caps will melt, and the deep ocean will warm until Earth finds its equilibrium. CO2 is rising with human activity, but I don’t think it’s causing the warming. In the past it rose and fell with warming and cooling because a warm ocean has to release it and a cold ocean absorbs it. I think that volcanic frequency is the driver and CO2 is along for the ride. Check out when the Antarctic Ice Sheet started building up, they say it was when the CO2 went from 760ppm to 600ppm. If 600 ppm triggered ice buildup on Antarctica, how can 400 ppm today be causing it to melt?
Water in the depths of the oceans is at 4°C temperature because that’s the temperature at which its density is maximum. So the enormous pressure that’s there basically forces the water to stay at that temperature. It is energetically more convenient for the excess heat to flow up to the surface than to spread uniformly. The Ice Age has nothing to do with that.
Wrong. The weight of the water column does not cause the water to be 4 C. Otherwise you could cool water by piling more water on top of it. The cold deep ocean water is generated by the following: Ocean water in the tropics is made salty by evaporation. Then it circulates towards the poles along the east coasts of the continents. In the north pacific it is cooled at the surface by the cold weather, near Greenland and Antarctica it is cooled by contact with ice. The chilled salty water reaches 4 C and sinks, storing cold water at the bottom of the ocean. Since the cold water is caused by the temperature of the poles, and the polar temps are suppressed by the presence of ice sheets, and the ice sheets are remnants of the Ice Age (and in the case of Antarctica the Eocene to Pleistocene temperature decline), the cold deep ocean waters are most certainly a byproduct of the Ice Age.
If you got rid of the ice caps the deep ocean water would eventually warm, exchanging heat with the surface through upwellings and getting heated from below at the thermal vents. The column would be arranged by density with salinity playing a large part, but the bottom would not be permanently set at 4C if there were no surface areas that cooled to that temperature. (see thermohaline circulation)
I keep seeing this argument… “A CO2 molecule would most likely bump into several other gas molecules before re-emitting the infrared photon. The CO2 molecule might transfer the energy it gained from the absorbed photon to another molecule, adding speed to that molecule’s motion. Since the temperature of a gas is a measure of the speed of the molecules in the gas, the faster motion of a molecule that eventually results from the IR photon that was absorbed by a CO2 molecule raises the temperature of the gases in the atmosphere.” But how can a CO2 reradiate IR if it shares the vibrational energy with other molecules? A photon is a photon… quantum energy. I doubt it shares any energy by collision. It simplly reradiates. Much of that “glow” returns to the earths’ surface, and the surface then warms. Then the atmosphere is warmed by mixing. Another fault in the “photon conduction theory” is that it forgets that after emission of the photon, the CO2 molecule stops vibrating. Thus, no change in temperature.
Starting with the last statement and working backwards: CO2 won’t stop vibrating unless it reaches absolute zero. Although greenhouse gases absorb IR, all molecules emit thermal IR when they vibrate see NASA: https://radiojove.gsfc.nasa.gov/education/educationalcd/RadioAstronomyTutorial/Workbook%20PDF%20Files/Chapter3.pdf
If photons had to be emitted at the exact wavelength at which they are absorbed, then the ground would have to emit the same wavelengths of light it receives from the sun. CO2 absorbs certain wavelengths, about 8% of the watts emitted by the ground, and at 330 picometers diameter that’s going to raise the molecule’s temperature slightly, about 1.43 degrees K. CO2 will then emit thermal IR in a blackbody pattern consistent with its temperature, as all matter does. As the heat is shared with other molecules by impact, those molecules will also emit radiation in a blackbody pattern consistent with their temperatures. This spreads the heat out very thinly.
The big mistake IMO is that we think the radiation measured at the top looking down and at the bottom looking up only comes from the surface and the greenhouse gases. It is actually coming from the surface and every gas in the measured air column because all matter emits thermal IR in a blackbody pattern that reflects the average temperature of the air column. There are dents in the spectrum where greenhouse gases absorb wavelengths and there are corresponding surpluses at other wavelengths from the heat being shared and translated (into a blackbody pattern). These can be seen if you add up the area under the spectrum curve (the total energy detected), find the blackbody curve with the same area (which will show the average temp of the air column), and superimpose that curve on the spectrum graph. Some areas will fall below the curve where greenhouse gases are absorbing, and some will be above the curve where a corresponding surplus is emitted.
I was refering to the extra vibration the CO2 molecule picked up when it absorbed an IR photon. The CO2 molecule looses that extra vibration when it emits an IR photon a short time later. Of course a parcel of air emits as a grey body due to its temperature, which is governed mainly by the environmental lapse rate, which is established mainly by convection and other atmospheric processes. I have a hard time understanding how CO2 warms the free atmosphere directly by photon induced vibration. Air is a very poor conductor of heat. The earth’s surface emitts energy upwards toward space as longer wavelength or thermal radiation. Some of this thermal radiation is absorbed and re-radiated by the atmosphere’s CO2 molecules back toward earth’s surface, providing an additional source of heat energy. That is how earth radiation buget charts describe the heating of earth and air.
A CO2 molecule that absorbs a IR photon will start to vibrate. It is because the CO2 actually has a vibration state that it can absorb IR photons. O2 and N2 do not have vibration states and therefore do not absorb IR photons. If this vibrating CO2 molecule collides with another molecule there is a rather large chance that the vibration energy will be transferred into movement energy in the two molecules. Thereby heating the gas itself.
But the chance that it actually radiates a photon is much lower, as the average time between collisions is much lower than the average time unit spontaneous release of a photon.
The average time between absorption and emission for a CO2 molecule at atmospheric temps is about 1 second (https://sealevel.info/Happer_UNC_2014-09-08/Statz67-lifetimes.pdf). In that length of time, the CO2 molecule will be hit by nitrogen molecules about 7.6 x 10^28 times, sharing vibrational (heat) energy with them. Air does conduct poorly, but the heat transfer is much faster than radiation in a vacuum, which is why thermos bottles have a vacuum in their walls rather than air. The heat is transferred by conduction, but the amount of heating is negligible. A molecule that is heated 1.43 degrees can share that with other molecules, but at 400 parts per million there isn’t much to go around. So the “warming” by contact is minimal, and the same amount of warming would happen at 200 ppm because the same amount of radiation from the Earth would be absorbed by the same number of molecules.
When thinking about back radiation to the Earth: a study was done by H Douglas Lightfoot and Orval A Mamer in 2017. Measurements were taken at 12 locations worldwide. Back radiation (from all gases including CO2) ranged from 420 W/m2 near the equator to 97 W/m2 near the South Pole. Ground radiation at the location near the equator is about 484 W/m2, and the ground emission at the location near the South Pole was about 117 W/m2.
In order for radiation to actually heat the surface, incoming radiation has to exceed outgoing radiation. The net flow of radiation at both locations was away from Earth, so Earth could not be warmed by the back radiation. It does slow down cooling, but that is a function of the entire atmosphere (which was emitting all the back radiation). My point is that back radiation can’t warm the Earth unless warm air moves over cold land. The general condition is that the average air temp above a location is lower than the ground temp, so it doesn’t warm the ground at all but it does slow the cooling.
If CO2 returns 15W/m2, and the Earth is emitting 391 W/m2, CO2 can’t warm the surface at all. Not trying to nitpick, just sharing info. The CO2 back radiation would have to exceed 391.
There is another problem though. The radius of each CO2 particle is so tiny that even a “hot” CO2 particle’s radiation will diminish by the time it reaches Earth. (by r^2/(r+d)^2) That’s why back radiation has to be considered from the entire atmosphere collectively, it is simply a reflection of the air column’s average temperature.
Living in the North of Scotland I get my own peculiar version of greenhouse warming. It’s called clouds, we get lots of them and at this time of year they predominate. Being so far north means that in November we have about eight hours of light per day, a light that comes from a sun barely rising above the horizon. This is not a warming sun. If the sky is clear and coudless, we can expect a daytime temperature of about 3C and a night time temperature of -3C. If however there is cloud, the temperature is much warmer. At the moment we are in a cloud and the day temperature is 9 degrees and the night temperature is the same.
When I search for why temperature is warmer when it is cloudy, I only find explanations that clouds are heated by the sun, then radiate infra red and this heats the environment. While this may be true in some circumstances, it is certainly not true in the Scottish winter.
A cloud is mainly air containing droplets of water. It is not just the water that contains heat, but the whole column of air, since thermal disequilibrium cannot, in a free system, exist for long. The heat that is measured is not a measure of radiation from the cloud, but instead a measure of the internal kinetic energy in the cloud molecules. The energy probably originated from water evaporation in the Carabean and has carried across the Atlantic. This is a massive amount of energy transfer.
Why am I talking about good old H2O?
Water is by far the most important warning gas in the atmosphere. In tropical latitudes solar energy causes massive amounts of evaporation and the heat capacity of water allows that energy to be retained from Equatorial regions and transferred all the way to the poles. I have read that water is thirty times more potent as a greenhouse gas than C02. By this I assume that some of this is because it absorbs across a wide spectrum of wavelengths compared to CO2’s finger print absorption bands. It may also be because it’s heat capacity is considerably greater than most molecules, having the capacity to store great amounts of internal energy.
In the lower atmosphere water composes between 0 to 4% of the molecules and on average makes up about 1 to 2% of the lower atmosphere – the exact amount is unknown. If water is 30 times more potent than CO2 which is present at 0.04% then water will be responsible for absorbing 750 times more energy than CO2. At 2% of air composition this would double to 1500 times more energy than CO2. So why then so much focus on CO2 when we do not know enough about water?
Water has the added complexity that when it transfers energy to the atmosphere it condenses and sticks to other water molecules making clouds. Some block out sun and reflect back to space while others prevent energy escaping from the lower atmosphere. On balance clouds are thought to cool more the heat the atmosphere.
Any small change in annual insolation will affect the evaporation rate on earth. Although water cycles fast in the atmosphere the mean level in the atmosphere is the important measure since so much heat is tied in with this molecule. We do not know how much mean water content has changed, or the typess of cloud which predominate, but possibly CO2 is a side show beside water,
CO2 retains absorbed heat for a very short time. I have read that the energy absorbed from a photon will typically be transferred to other molecules in micro seconds and that only about 0.01% of absorbed energy is re-released as a photon. If CO2 has a role in heating the atmosphere it can’t be by radiating energy since what it does is conduct energy into oxygen and nitrogen molecules. I don’t know if anyone has looked at CO2 as an energy pump. It certainly seems to have the ability to rapidly pass energy on to the system. Does this mean that CO2 can have a warming effect but that the process of radiative forcing is not how it happens. If CO2 was able to transfer a million photons of energy to the atmosphere in one second then it would indeed have the possibility to cause a degree of warming in the lower atmosphere. However as well as passing on heat from radiation it should also have the capacity to emit energy from molecular collision as radiation. In the upper atmosphere CO2 could have a role to play as an emitter of radiative energy.
Of course almost everything I have written is speculation and surmise. Without a proper understanding of molecular interactions with photons and other molecules the science remains incomplete. At the moment atmospheric science is more like sociology than good hard physical science. We need to understand behaviour at the molecular level and build from that. Do we have the means to measure the basic components? At STP how long does a CO2 molecule hold heat. What happens to that energy? How do oxygen and nitrogen molecules hold and release energy? What happens at ground level? What happens at 10,000m? I am sure that much of the information is there, but it needs to be brought together.
Clive perhaps you with your excellent blog could become the collector of missing information. Perhaps you could have a board with all the parameters that need to be known and people who know the answers, or indeed have other questions that need answered could add them to the matrix. This after all is physics and the one wonderful thing about physics is that it condenses complexity into a few letters of a formula. Physics, the purest form of poetry.
Graeme, You make some interesting points.
Clouds are an enigma and their role in regulating climate is not fully understood. Your observation that low cloud in winter has a warming effect is true. Land surfaces cool at night by radiation and if the skies are clear then they can radiate directly to space through the IR window and by radiative transfer by CO2 and H2O (vapour). Clouds block that process by absorbing IR and re-emitting it. Clear skies means rapid cooling in winter. That is also why temperatures can fall below zero in deserts which have little H2O and zero clouds.
The situation is different in summer for the UK, and the tropics most of the year. As the sun heats the land so convection clouds form during sunny summer days. These low clouds cool the surface by reflecting sunlight back to space. They seem to act almost like a thermostat ensuring temperatures don’t rise too much. Of course you need nearby oceans for this to work. As the surface water temperature increases more evaporation takes place moving latent heat upwards to the dew point level where clouds form. In the tropics you often get a thunderstorm in late afternoon. The clouds disappear overnight allowing further cooling and the whole process repeats itself the next day.
Even now climate scientists cannot tell you whether global warming will be enhanced by clouds or curtailed by clouds. I think logically clouds must act to diminish warming. So long as we have oceans on the earth temperatures will be moderated by evaporation, cloud formation and storms.
The Clausius Claperyon equation determines the evaporation rate from the ocean surface with temperature.
Has anyone made practical measurements, say by lifting the test equipment with a balloon and measuring the absorption / temperature change at different heights, different CO2 / CH4 / H2O – concentrations and gas pressures in test cylinders?
Trillions of Dollars will be consumed to control the atmospheric CO2. It would be reasonable to use a few million Dollars to get a confirmation to the vast number of theoretical estimates made thus far. Am I right that Svante Arrhenius is still, after some 130 years, the most frequent reference in scientific articles?
Another question about the estimates published by the IPCC and declarations by CRU;
Has anyone any understanding why the global average temperatures are based on manipulated weather station recordings? If I know right, dropping off of “pieces” of recent (after year 1960) temperature recordings, an additional increase to the calculated average global temperature has been obtained. When looking at the “pieces” of records which have been dropped off, the logics seem unclear to me. If I know right, IPCC has not published their algorithms when calculating averages.
You’ seem to be overlooking the most profound effect of carbon dioxide. Its effects on vegetation. A higher concentration will cause increased growth in plants. While significantly reducing water consumption . The effect will vary greatly depending on conditions But a change from grassland to forests for example would have a noticeable effect on local weather. I expect an increase in CO2 to cause a worldwide patchwork of changes. I think the term localized weather change may be a better description.
By reflecting away 30% of the ISR the terrestrial albedo, sustained by the atmosphere, makes the earth cooler than it would be without that albedo/atmosphere.
Because of the non-radiative heat transfer properties of the terrestrial surface BB LWIR radiative energy upwelling from the surface is not possible.
The surface is warmer than ToA per Q = U A dT same as the insulated envelope of a house.
If the above statements are correct the greenhouse effect does not exist.
Zero GHE, Zero GHG warming, Zero CAGW.
It’s that simple.
It’s all science.
It’s all over.
Nick Schroeder, BSME CU ‘78
Colorado Springs, CO
Nick Schroeder
“Because of the non-radiative heat transfer properties of the terrestrial surface BB LWIR radiative energy upwelling from the surface is not possible.”
Without a real scientific proof of your strange claim, all you write here is no more than pretentious blah blah, Mr Schroeder.
It’s not as simple as you want to have it.
That’s science’s reason to exist since we began to think.
Rgds
J.-P. D.
First – apologies. I am a doctor and Neuroscientist and ignorant but keen to understand.
I think I see the argument about carbon dioxide temperature forcing being the result of higher levels of the atmosphere (5-9 km) radiating energy into space less effectively because of the lower temperature there, though I struggle with understanding the magnitude of this effect.
But is not the carbon dioxide at these higher levels of the atmosphere already saturated by incident infrared radiation from the sun, and therefore effectively transparent to infrared?
First, you need to understand that ALL air molecules radiate infrared thermal energy into space. see: https://radiojove.gsfc.nasa.gov/education/educationalcd/RadioAstronomyTutorial/Workbook%20PDF%20Files/Chapter3.pdf
(Only greenhouse gases absorb it, but ALL molecules radiate it based on their temperature.) The atmosphere does not radiate energy less effectively because of increased CO2. CO2 absorbs the radiation at the 15 micrometer wavelengths, shares the heat with other air molecules by contact, then ALL the air molecules radiate infrared radiation in a blackbody pattern that reflects their temperature. This simply results in a decrease of radiation near 15 micrometers and a corresponding surplus of radiation at other wavelengths. The total amount radiated is the same.
The idea that greenhouse gases raise the temperature and non-greenhouse gases don’t is a fallacy. The entire atmosphere acts as a blanket to warm the Earth. Greenhouse gases merely cause a deficit in certain wavelengths while indirectly causing a corresponding surplus in others.
Thanks, Ray.
Now that I can understand!
There must be some people who believe in carbon dioxide causing global warming who have a different view?
Richard
Yes. My view, based on what I’ve found, is that surface temperature is set by sunlight and pressure with a constant cooling done by the water cycle. I can show you the math if interested. I believe any global warming is part of an ongoing recovery from Ice Age conditions. The Ice Age was brought on and sustained by volcanic hyperactivity, and the temps fluctuated from 3 degrees hotter to 6 degrees colder during that time. The Ice Caps, glaciers, and cold deep waters are all left over from the Ice Age. As long as there is a lack of sustained volcanic hyperactivity, I’d expect warming to continue until we reach an equilibrium possibly 3 degrees warmer than today. The tragedy is that many would blame it on an increase in CO2 and dismantle the economy, and fail completely to stop it. Evaporation constantly cools the Earth’s surface 192 K to produce a worldwide average rainfall of 990 mm. If we want to fight global warming, evaporation is the most powerful mechanism. One third of the Earth’s land is desert. If it were irrigated and the dry lake beds filled with water, we might have a fighting chance.
Ray said:
“If we want to fight global warming, evaporation is the most powerful mechanism.”
Where do they find these people?
Paul, take the amount of rainfall worldwide = 990 mm. It evaporates at the surface absorbing heat energy, and releases that heat energy away from the surface to make clouds and rain. Take 990 mm and multiply it by Earth’s surface area to find the total amount evaporated annually. Then take the latent heat of vaporization for water to find the total joules absorbed. Then go from joules per year to joules per second and find the total watts per square meter. Then convert that to degrees and see if you don’t find that evaporation is constantly cooling the Earth’s surface 192 degrees Kelvin.
Now if the Earth’s surface is being constantly cooled 192 degrees from evaporation, why would I not think that evaporation is a powerful cooling mechanism?
And let me ask you this: are you sure that the Earth’s blackbody temperature is about 254 K, and greenhouse gases warm the Earth about 34 degrees?
We first average the radiation, and then derive the average blackbody temp of 254 K, right?
Except that radiation is a fourth power of temperature. So if you average fourth powers, you can get the average of their roots?
3 to the 4th power is 81. 5 to the 4th power is 625. Their average is 353, and the 4th root of 353 is 4.33. You tell me Paul, how 4.33 is the average of 3 and 5, and I will tell you where I came from.
It gets even better when you factor in the dark side of the blackbody, which is included by averaging the radiation over the whole surface. The dark side of the blackbody sphere would have a surface temperature of zero.
Zero to the 4th power is 0. 6 to the 4th power is 1296. The average is 648, and the 4th root of that is 5.05. Is 5.05 the average of zero and 6?
I say all that to say this: if you calculate the blackbody temperature of each point on the blackbody sphere based on the angle and radiation at that point, then average all the points together, the real average blackbody surface temp of Earth is about 142 K, not 254 K. So 34 degrees of warming is fiction based on a faulty calculation that averages fourth powers (radiation) to calculate the average of the roots (surface temperature).
Do your homework and I’ll tell you “where they find these people”.
You said it yourself: “It evaporates at the surface absorbing heat energy, and releases that heat energy away from the surface to make clouds and rain.”
The net balance is zero.
Wrong. Surface is cooled 192 K, heat is released at cloud level. Heat then flows upward by conduction and convection until it is radiated into space. The heat doesn’t flow back down. The water cycle moves heat away from the surface, constantly cooling it.
Hi Clive,
Thanks for talking the time to demystify this issue. I studied thermodynamic and heat transfer when the earth’s population was 3 billion and the 7 of Rome had published ‘Limits to Growth’…. I’m a little rusty now, so a couple of questions please:
You explain, CO2 radiates to space from a height with temperature -53°C. As its concentration increases, the radiating height rises, but is at a colder temperature, so lower energy emmission.
Is the tropopause (or near it) the limit to this effect? If yes, at what CO2 level will the radiating height reach such a limit where the radiating sphere of CO2 is saturated?
Another question, is the amount of energy radiated dependent the CO2 concentration? So would increase CO2 radiate more energy at the same temperature?
I have not seen a good answer to the question of how the 2XCO2 3.71W/m2 was derived.
To me it looks like it comes from the assumption that 20% of the Earth’s energy imbalance
of 150 W/m2 is from CO2.
20% of 150 is 30W/m2, it took 8 doubling s of CO2 to increase the level from 1 ppm to 256 ppm.
That would make each doubling have a value of 30/8= 3.75W/m2, with a slight lowering for the
difference between 256 ppm and the postindustrial level of between 270 and 280 ppm.
I have not found any support for the idea, but I also don’t believe in coincidences.
There is no simple derivation. The physics is really quite complicated as it involves integrating over all the quantum emission lines of CO2.
Here is my attempt to justify the formula !
https://clivebest.com/blog/?p=4697
Clive, thanks for the response!
I sometimes think it is not that complicated, the residual energy under the curve
after the primary 15 um band is saturated, is small, like the secondary lobe on the Fourier plane.
I look at James Hansen’s early work, like 1981,
https://pubs.giss.nasa.gov/docs/1981/1981_Hansen_ha04600x.pdf
and he appears to be starting with temperature, not W/m2 imbalance.
He get to the 2XCO2= 4W/m2, because the model produces 1.2 C of warming.
I followed your link, and if you intended to use the log rather than the ln (natural log),
for your 6.6 X LOG(C/C0), then I agree that, the 2XCO2 forcing would be in the ~2W/m2 range.
But you also stated that your results were 20% higher, which is confusing, since
6.6 X log(2) =1.99W/m2, which is lower than the normally accepted 3.71 W/m2.
I am more of a lab person, and like things that can be tied to empirical data,
and from what I can see, the warming from added CO2, is basically just that,
the feedbacks are both positive and negative.
If the forcing warming were lower, there would be some room for positive feedbacks,
but the net results would still be that 2XCO2 would have an ECS between 1 to 1.5C.
The only empirical data I have found is feldman et al 2015.
http://asl.umbc.edu/pub/chepplew/journals/nature14240_v519_Feldman_CO2.pdf
He found a .22 W/m2 increase as CO2 increased from 369 to 392 ppm, in downwelling longwave radiation. His spectral range stopped at 550 cm-1, and so could miss some of the
lower energy decay levels from the initial 667 cm-1 dipole moment.
Assuming the first law of thermodynamics is intact, what does not come down, must be going up!
.22 W/m2/ln(392/369)=3.64, so 3.64 X ln(2)=2.52 W/m2.
This is in close agreement with Hansen et al 1997 2XCO2 top of the atmosphere number.
https://pubs.giss.nasa.gov/docs/1997/1997_Hansen_ha01900k.pdf
Table 2, 2xCO2 TOA 2.62 W/m2.
I’m a novice in this field, but interested to understand.
A basic question please…
Assume no forcings or feedbacks, with CO2 at 400ppm so IR in the 15 micrometre band is fully absorbed.
Why is there any increase in temperature when CO2 increases let alone doubles?
Thanks.
It’s not fully absorbed in the 15 micron band. The atmosphere thins out with height thanks to gravity, so there is always an emission height where IR photons emitted by CO2 molecules escape to space no matter how much CO2 levels increase.
If that emission height is below the tropopause then the new emission height is cooler and so emits less energy thanks to Stefan-Boltzmann . The central line in the CO2 IR spectrum already emits in the stratosphere, so as it gets higher it emits more because up there temperature increases with height ! You can see that upward spike in all satellite IR spectra.
The net effect though is to decrease IR heat loss to space – so the atmosphere warms up a little bit. I prefer this model to the idea that back radiation heats the surface. The sun heats the surface !
Back radiation does not heat the surface…it slows the rate at which the surface cools. Teresstial radiation does not heat the atmosphere very much…weather does that. Weather makes the tropopause twice as high over the tropics than over the arctic. Solar radiation and back radiation keep the surface warm, which produces weather and mixing that deepens the troposphere.
Thank you.
However, a lapse rate is established whether or not there is weather, due to “radiative-convective equlibrium” (https://www.gfdl.noaa.gov/blog_held/19-radiative-convective-equilibrium/), and this rate is nearly dry or moist aduabatic… ironically the same rate produced by weather (mixing). Clive, I think you touched on this before. So which is causing the higher trop in the tropics? What is causing the trop to rise over the decades, yet the soundings are not warming?
The atmosphere is not just one layer. There are many layers from the earth’s surface to the tropopause. When CO2 increases, concentrations increase in all layers, throughout the depth of the atmosphere. This causes the total IR directed toward the surface to increase, which increases the surface global average temperature over time. I call it the stack affect…like the more batteries you add to the vertical flashlight the brighter it glows (sky glow). A layer does not have to be saturated to contribute to the atmosperic stack. A single satrurated layer near the surface does not prevent IR from irradiating the rest of the atmosphere.
Thank you
Clive,
This article supports the notion that energy radiated by Earth, no matter how it is absorbed and radiated from the atmosphere, cannot warm Earth… https://ozonedepletiontheory.info/gg-theoretical-problems.html
If the ground gets three units of energy…two from the sun and one from the atmosphere…doesn’t it seem reasonable that ground that absorbs 3 units of energy will be warmer than ground that is only absorbing 2?
ABSOLUTELY WRONG !!! You are assuming so called back radiation (LWIR) has comparable energy as incoming SW solar radiation. Why does the inside of you car get hotter than h*ll on a sunny day and doesn’t warm squat at night, even though it is still getting your magical back radiation?
Jim, perhaps you’ve been misled by the Dean of Canada’s Environmentalists, Prof. David T. Suzuki, PhD, CC, OBC, FRSC:
Contrary to Suzuki he claimed, the heating of the interior of your car on a sunny day is not by the (misnamed) so-called “greenhouse effect.”
Back-radiation is not “magical.” It is real, and measurable. But it is not what heats up the interior of your car on a sunny day.
If you’d like to learn about it, I recommend the “Amicus brief” and “Physics & geophysics” sections, here:
https://sealevel.info/learnmore.html
I in no way compared back radiation to SW radiation. That is your take in the short time range of minutes or hours, in which case you are ABSOLUTELY CORRECT!!! But, in the long term of months or years, the net effect of back radiation is to keep the ground warmer than it would be without it. Even your car would end up with a warmer long term average because of continuous back radiation. Yes, a small increase in the average, but cover the earth with cars, and the earth’s average would be slightly higher also. That is the greenhouse effect. Check out if this link (from which I fetched the absorption idea for my initial comment) and let me know what you think. Regards.
The average temperature of the ground is 288 K. So the average radiation given off by the ground is 391 W/m2. The average temperature of the entire standard atmosphere is 250 K, so the atmosphere returns an average of 221.5 W/m2 to the ground. The average net flow of radiation is therefore 169.5 W/m2 from the ground into space worldwide.
You folks are holding on to the idea that CO2 absorbing radiation leads to higher ground temperatures by depleting the amount of energy emitted around 15. You have to remember that all molecules, including all air molecules, emit radiation in a random blackbody pattern with a peak based on temperature. When CO2 absorbs radiation near 15, the heat is immediately shared with molecules around it and they all emit radiation in such a backbody pattern. The net effect is a decrease near 15, and a corresponding increase at other wavelengths. The sum total of the energy emitted is the same, only the amount at each wavelength is changed.
All air molecules are emitting radiation towards the ground and also towards space.
When you look at an emission spectra chart taken by satellite, you need to tally up the entire area covered by the spectral lines. You then need to compare that to a blackbody curve that has the same area under it. This will reveal the average temperature of the air column below the satellite. If you superimpose that blackbody curve over the spectral chart you will see a deficit of wavelengths around 15 but you will also see the corresponding surplus at other wavelengths. CO2 is not causing a warming of surface temperature, it is simply converting the radiation emitted from one wavelength to another.
Regardless of where back radiation comes from (all the gases of just the GH gasses), that radiation adds enegy to the black body, which changes the shape of the Planck curve over time. Eventually, the peak of the curve shifts to a warmer temperature. Black bodies matter :). Here is a neat intercative animation… http://physics.bu.edu/~duffy/HTML5/blackbody_radiation.html
Ted, what you’re saying is that the atmosphere causes the surface temperature to be higher than the blackbody temperature. That is correct, but It makes all the difference in the world if the warming is coming from every gas molecule in the atmosphere or just the GH ones. If every molecule above absolute zero emits radiation, then back radiation is coming from every air molecule and GH gases function only to suppress energy given off at certain wavelengths while simultaneously amplifying the energy given off at other wavelengths. No net heating effect with increased CO2.
You should also re-examine the calculation of the blackbody surface temperature for Earth. If you average the radiation first as most people do, you commit a mathematical error. That error is made because the average of 4th powers (radiation) fourth rooted, is not the same as the average of the roots themselves (temperatures). You come up with a wrong blackbody temperature for Earth of about 255 K. If you instead do a point by point analysis of the blackbody temperature at each angle including the dark side of the sphere and then average those temperatures, you get a correct blackbody temperature of about 143 K. I would plead with you to do the math because the standard idea that Earth’s temp is 34K warmer than blackbody is a huge math error. Yes, blackbody temps really do matter.
I‘ve been pondering for some time past what effect CO2 concentration has to the daily warming on earth through the sun.
Every explanation about the cause of climate change tells me things about effects of GHGs in one direction only. It goes always about trapping heat in between earth and atmosphere caused by CO2 – if we constrain it to frequency windows of CO2.
But what is going on in the opposite direction? Doesn’t the CO2 also absorb energy from the sun on the way down to the earth? I assume that has to be an effect at least. No, CO2 absorbs fairly all irradiation energy within CO2 absorption bands, right? And if so, why do I always only can find the same graphics concerning irradiation towards earth with the same amount of energy that hit the ground? No a single digit behind the comma calculating this effect that I could found.
There has to be an explanation of diminishing of irradiation energy within the absorption band of CO2 for the pre-industrial time and for today – if the CO2 concentration is crucial.
The sun emissions contain much more irradiation energy within the CO2 absorption bands at the point of entering the atmosphere, than earth radiates up to the atmosphere. This tells us Plancks laws. How can the GHGs effect of CO2 only affect direction up to space, and shall not affect direction down to earth?
To simplify it imagine a greenhouse. Now put another- slightly bigger – greenhouse around it. And another one, and another one… I can imagine the smallest greenhouse in the center keeps warmer during nights. But do you expect the smallest greenhouse gets the same amount of radiation and warmth next sunny day, than being solitarily?
A thought…
Well, if rather all irradiation energy will be absorbed already by a low concentration of CO2 toward earth, the raising of CO2 could be neglected within this view. But, in this case, why can’t we neglect it up to space?
Maybe someone can explain me this lack of views in science. And hopefully we will understand better all these various theories of irradiation, absorbing, heating, CO2 etc.
Thanks
Visible light gets from the sun (very hot so higher frequency em radiation) ) to ground level easily and does some heating at ground level. The heated mass being not extremely hot radiates infrared which can then be affected & stopped by various atmospheric gasses at varying pressures & densities before it gets to escape back out to space or gets redirected towards the ground.
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Hi Clive
Reading the beginning of the article I was surprised to hear that the absorption length of IR in atmospheric air was 25m. I have watched a number of “Police Camera Action” type programes in which cameras sensitive to IR emitted at ambient temperatures were used from helicopters to detect people on the ground and the image, although low resolution is quite clear. If the absorption of IR at the ~ 10 micron peak was anything like the figure you quote it would be like looking into thick fog.
http://www.icc.dur.ac.uk/~tt/Lectures/Galaxies/Images/Infrared/Windows/irwindows.html
A quick search uncovered the chart on the above, which shows the atmosphere is opaque to most wavelengths but has a window of transparency for the visible wavelengths, as you would expect, and another of almost equal transparency centred at 10 microns. It seems clear therefore that the radiated IR could reach space, but that reducing the transparency of this window by adding CO2 would result in energy being trapped in the atmosphere, altering the energy balance and powering extreme weather systems.
Some of the web page sources quoted are now unavailable so I wonder, where did the 25m figure originate?
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Does any body know the absorption length of thermal infrared radiation in 100% CO2. Thanks
Consider a thin layer of gas with a vertical thickness, a constant density, and a constant temperature. Assume the gas in the layer is transparent to the incoming visible energy from the Sun, but partially absorbs outgoing infrared flux. The layer of gas thus absorbs some of the infrared radiation coming up from below and then radiates in both the upward and downward directions. Thermal equilibrium is reached when the upward and downward fluxes of the layer are equal. This equilibrium is reached when the layer of gas raises the temperature of the layer below it by a factor of 1.19 (*). Now, the amount flux absorbed in a stack or column of layers depends on the optical depth of the absorbing gas. The optical depth is an exponential function that has the property of converting multiplications into additions of exponents, such that the total optical depth of a series of absorbing layers is just the sum of the optical depths of the individual layers. For a continuously varying absorber the optical depth at a particular wavelength is expressed in terms of the path integral of the density and the absorption coefficient. The combined effect of many infrared absorbing layers with the 1.19 equilibrium factor can lead to dramatic increases in surface temperature, as in the case of Venus.
(*) http://web.mit.edu/12.004/TheLastHandout/PastHandouts/Chap07.Atmospheres.pdf, pages 5-6.
That is a pure radiative transfer model.
On Earth convection and ocean evaporation drives the lapse rate towards a moist lapse rate. At night in dry deserts radiative cooling dominates, elsewhere convection and latent heat loss dominates assuming CO2 levels remain below say 2000 ppm !
You can’t “saturate” absorption of infrared, it is rescattered, it gets reemitted again. That makes all the discussion on this page bunk.
I think you’re missing something. Higher altitudes have lower temps, but those temps are not set in stone. If we add a layer of CO2 that absorbs energy from below, won’t that layer be warmed by the same amount of energy it absorbs, so that the emission from the top is the same as it was before?
If we add more CO2 to the atmosphere then the tropopause increases in height slightly. That is because thermal photons emitted by CO2 molecules can only escape to space when the mean free path is larger than the top of the atmosphere. The temperature at the tropopause remains constant to balance energy. This forces the surface temperature to rise slightly because the lapse rate essentially remains the same.
CO2 warms AND cools
https://www.nasa.gov/feature/goddard/2021/nasa-satellites-see-upper-atmosphere-cooling-contracting-climate-change/
Isn’t it a little wild to use the Stefan Boltzmann law for emission from a gas with distinct emission lines and thus a spectrally highly non uniform emission coefficient? That’s quite far from a black body (uniform emission coefficient of 1).