9,25 – a factor that could close the global warming debate
Guest post by Frank Lansner (hidethedecline)
The CO2-sensitivity describes the warming effect induced by a doubling of the CO2 concentration in the atmosphere, and is thus the epicentre of the global warming discussion. Estimates of the CO2 sensitivity are very different, and the value range used by IPCC appears unlikely to physically impossible. To show this, I will focus on the factor “Fw” between the total CO2 warming and then the warming from a single doubling of CO2 concentration.
The total CO2 warming effect is obviously many times bigger than the warming from a single CO2 doubling. Example: When changing CO2 concentration from 5 ppm to 320 ppm we have 6 doublings. But on top of these 6 doublings, how much warming effect is introduced when CO2 concentrations are changed from 0 to 5 ppm etc? In the following I use the online model MODTRAN:
Fig. 1. Above is illustrated the warming effect of CO2 for 3 different climatic areas. Zero W/M2 represents the net forcing of the atmosphere fore a given scenario with CO2 concentration set to 0 ppm.
For each area is shown a clear sky scenario as well as a light rain scenario. All other variables in MODTRAN are left as the default values. The results from MODTRAN are total atmosphere outgoing radiation, and thus when changing concentrations of CO2 we get total atmosphere responses incl feedbacks if present.
Fig 1 Shows 6 doublings of CO2 concentration: 5-10-20-40-80-160-320 ppm where every doubling shows warming effect of similar size (–as could be expected due to the logarithmic declining effect of adding more CO2 to the atmosphere).
From the graph above we can see that the total CO2 warming effect today equals around 9 times the warming effect of one doubling of CO2 concentration.
Fig 2. For a better compare between the scenarios on fig1, these are now shown as %-values of the total CO2 warming effect for (Forcing) with today’s concentration of 390 ppm CO2, equals 100%. It appears that clear sky, rainy sky, Arctic area, tropics, subtropics scenarios has a very similar profile indeed and I find that this result shows that we can consider these %-trends to be rather global.
Fig 3. The average global CO2-doubling can now be calculated more accurate to be near 10,8% of the full CO2 warming effect at 390 ppm. (Or, the “CO2-sensitivity” warming effect is around 10,8% of the total CO2 warming effect, globally.)
Thus, the “best estimate” of the factor between total CO2 warming effect and the warming effect from one CO2 doubling – Fw – can be calculated. Best estimate (so far) Fw = 9,25.
CO2-warming-total (K) = 9,25 * CO2-warming-from-one-doubling (K) = 9,25 * CO2 sensitivity (K)
I have used MODTRAN for this result, but it is universal that the doublings must have near same warming effect and thus the individual doubling will have just some fraction of the total value. For now, the factor 9,25 is best estimate.
Hansen – CO2 sensitivity.
Now how does the factor 9,25 between total CO2 warming effect and CO2 warming effect from a single doubling support the viewpoints of James Hansen on CO2 sensitivity?
James Hansen often refers to a CO2-sensitivity of 6 K… 6 K warming effect for each single CO2 doubling:
Fig 4 James Hansens CO2 sensitivity of 6 K gives around 55,5 K of total CO2 effect using the factor Fw = 9,25. As the total warming effect of all greenhouse gasses is assumed to have a warming effect of approx 33 K, the Hansen CO2-sensitivity demands that the total CO2 related warming effect is bigger than all the greenhouse gasses effect combined.
The overall CO2 warming effect is supposed to be around 10-15-2% of the total warming effect of the atmosphere, here we use 15%. Since CO2 is assumed to account for 15% of the total 33K greenhouse effect on Earth, the CO2 total warming effect is around 5 K. So just ONE CO2 doubling of Hansen’s CO2 sensitivity of 6 K has a bigger warming effect than the total warming effect supposed to be possible.
It is therefore highly odd that Hansen’s claim of 6 K CO2 sensitivity has been taken seriously anywhere at any time.
Here the “greenhouse wheel” (see WUWT post Wheel! – – Of! – – Silly!) where supposedly scientists imagine that we by year 2100 can have warming of over 7 K in fact with less than one CO2 doubling to cause this:
Fig 5. To account for their 7 K temperature increase, they must have played with a CO2-sensitivity of perhaps 10 K? So these honourable “scientists” believes that one CO2-doubling might resemble a third of the combined earth greenhouse effect?
IPCC – CO2 sensitivity
Then, how does the factor 9,25 between total CO2 warming effect and CO2 warming effect from a single doubling support the viewpoints of IPCC on CO2 sensitivity?
IPCC AR4 viewpoints for the CO2 sensitivity :
http://en.wikipedia.org/wiki/Climate_sensitivity
IPCC “best estimate” of warming from one CO2 doubling is 3 K.
Using the Fw = 9,25 we learn, that if one doubling warms 3 Km then the total CO2 warming should be around 28 K ( = 9,25 * 3 )
We must then remember again that the total warming effect of the atmosphere is generally accepted to be near 33 K. The warming effect related to CO2 should then be around 85% of the total Earth atmosphere greenhouse gas effect. And without CO2, the atmospheres warming effect should be reduced to 15% of todays atmosphere…. On a globe with mostly water-ocean surface…
The IPCC numbers where each doubling of CO2 represents 3 K it simply does not fit at all with the total warming effect of the atmosphere.
IPCC then claimed:
“Values substantially higher than 4.5°C cannot be excluded..”
Well, 4,5 K for CO2 sensitivity gives a total CO2 effect of 41,6 K. This is 126% of the total earth greenhouse effect, so we could rephrase:
IPCC:
“Values of CO2 related warming substantially higher than 126% of the total greenhouse gas warming cannot be excluded..” …
Idso´s and Lindzens estimates for CO2 sensitivity.
What if we assume that CO2 is responsible for the 15% of the 33K greenhouse warming effect on Earth? This corresponds to 5 K. If true, the CO2 warming from one doubling should be
CO2 sensitivity = CO2warming-total / Fw
CO2 sensitivity = 5K / 9,25 = 0,54 K
So just using the generally accepted knowledge that CO2 sholuld account for around 15% of the total Earth greenhouse effect, and using the also generally accepted knowledge that total Earth greenhouse effect is 33K, then the CO2 sensitivity should be near 0,54K
Idso 1998 suggests 0,4 K, and Lindzen suggests 0,5 K these results appears sound and realistic in strong contrast to values from IPCC and Hansen.
Hansens 350 ppm ”safe level”
Fig 6. When working with CO2 – effect, one cant help wondering what Hansens ”safe level” of 350 ppm CO2 is all about.
Fig 7. NASA´s, James Hansen has claimed 350 ppm to be a safe level of CO2:
– Just 1,5 % less Warming effect from CO2 and we are “safe”.. ?
If CO2 has a total warming effect of 5 K – as previously calculated – the difference between the Hansen “safe level” CO2 warming and todays level is around 0,075 K.
I wonder if the peoble creating the 350 ppm demonstrations knows this?
I wonder how they will react when they find out.
Idso 1998:
http://www.int-res.com/articles/cr/10/c010p069.pdf
MODTRAN:
http://geoflop.uchicago.edu/forecast/docs/Projects/modtran.orig.html
George E. Smith says:
September 10, 2010 at 3:48 pm
“Well old John certainly wrote a funny strain of English. One thing I did notice in his experimental apparatus is that he evidently did his experiments the same way that “the science guy” does his; and emplyed a source of not very long wavelength “heat” that unfortunately is NOT emitted from the earth’s surface or from the atmosphere (of Planet Earth).”
Radiation from a 100 degree C blackbody source (Tyndall’s) is centered around 7 microns.
Radiation from a 16 degree C blackbody source (averge ocean surface temp) is centered around 10 microns.
Your comment reveals this is just all way over your head, George.
George E. Smith says:
September 10, 2010 at 8:50 am
“Several times here (at WUWT) , Phil has offered, that the CO2-Temperature relationship is linear for small amounts of CO2; then logarithmic for medium amounts of CO2; and then square root for large amounts of CO2.”
“Phil”, whoever that is, is correct and this was first demonstrated experimentally 150 years ago.
Jim D:
You write
“If we are to believe the logarithmic doubling sensitivity mantra, then the change in atmospheric CO2 from 4 ppmv to 5 ppmv must have created all manner of chaos on earth.”
CO2 and CH4 follows temperature:
http://hidethedecline.eu/pages/posts/co2-carbon-dioxide-ndash-temperature-73.php
Besides, I showed that we have 9,25 CO2 “doublings” and not just one more doubling.
Another thing: From Glacials to interglacials the ice cover on Earth changed a lot, and this gave the possebility of strong change in albedo that could amplify the temperature change. But when Hansen and co for future warming talk about 3-7 K doublings in temperature due to the supposed little CO2 doubling heat, then there is just not the same amoung of ice on Earth to amplify and thus explain such a huge temperature shift. Today there is only the rather small caps. If CO2 should make Earth temperature rise 1 K for a doubling, this would not really change the ice/snow cover of the Antarctic /with a avg temp of -27), and in all winters we would still have substantial sea ice at the poles.
So the ice/albedo is not likely to explain a future temperature change amplified to 6 K or the like from one CO2 doubling.
Actually Hansen and IPCCs idea of 3-7 K warming just due to a little (0,5 – 1 K ?) heat from CO2, this doe not match with VOstok data from the Antarctic. At not point in all the interglacials did a little temp peak like that result in a strong 3-7K temp rise. So why should it now?
K.R. Frank
Jim D, This is your qoute i meant: “Either CO2 or temperature can change first, but the other will follow with a lag. It doesn’t contradict AGW.
“
Jim D, i think you missed the point of my Jan 2009 article.
Here in fig 4 for example, its rather obvious the temperature after interglacial temp peaks dives down to a new glacial even though CO2 should show max warming effect in the period:
http://wattsupwiththat.files.wordpress.com/2009/01/lansner-image4.png
So therefore, its not just CO2 and temp going up and down together. The large temperature changes over the iceages does occur even when CO2 should have prevented it – if CO2 had much to say.
K.R. Frank
re; John Tyndall
Tyndall was one of the greatest physicists of the 19th century and arguably the best physics lecturer and writer of his generation. An experimenter not a model builder. He succeeded Michael Farrady as professor of physics at the Royal Institute. Farraday was a great admirer of his work which played no small part in the succession. Tyndall wasn’t the first to theorize a greenhouse effect in the atmosphere but he was the first to prove it by experiment. He also proved water vapor overwhelms all the other greenhouse gases and did it the obvious way by directing infrared energy through a column of dry air ,a column of moist air, and a vacuum comparing how much infrared energy comes out the other side in carefully controlled delightfully simple but highly ingenius experimental apparatus. He performed thousands of experiments with different gases at varying partial pressures, varying total mass and distance, using many different gases and different heat sources. In the process he discovered more about the longwave thermodynamics of gases than any single person in history.
For those of you not delighted and charmed reading about experimental physics in original mid-19th century British parlance wikipedia has a decent translation of the highlights in 21st century American dialect.
http://en.wikipedia.org/wiki/John_Tyndall
I suggest everyone get acquainted with it. The proper place to begin is at the beginning. Tyndall is the beginning of longwave thermodynamics of atmospheric gases. He’s essentially also the end of what anyone really needs to know about how greenhouse gases function in the atmosphere. Even 19th century physicists provably knew that atmospheric CO2 is an insignificant greenhouse gas compared to water vapor.
Frank Lansner: I was saying CO2 can follow temperature when there is stronger temperature forcing as in the glacial cycles. At that time CO2 dropped because the cooler ocean absorbed it. The atmosphere-ocean system net CO2 remained constant, so there was no CO2 forcing, and it was passively following temperature.
At the present time, we are adding CO2 to the system by fossil fuels, which is a new forcing, and AGW explains why the feedback should be even higher than the CO2 effect alone. I don’t know what Spencer work keeps getting referred to here, but a positive, not negative, feedback seems to be operating if you look at decadal warming rates in the last 30 years.
Dave Springer says:
“[Tyndal is] essentially also the end of what anyone really needs to know about how greenhouse gases function in the atmosphere.”
——-
The wikipedia article you link says the following:
“He concluded that water vapour is the strongest absorber of radiant heat in the atmosphere and is the principal gas controlling air temperature. Absorption by the bulk of the other gases is negligible.”
Negligible? So is this “the end of what we need to know”?
You say elsewhere that the current assumptions about the CO2-temperature relationship (linear for low concentrations, then logarithmic, and so on) were “demonstrated experimentally 150 years ago.
Were they, really? Did Tyndell attempt to measure the temperature variations, or just the radiation?
Now, if his experiments regarding the CO2-temperature relation were so simple and conclusive, I imagine their accuracy and illuminating power could surely be improved after 150 years, could they not? And they would have enormous convincing force among the ever growing number doubting Thomases. So why are they not being done? Is anybody else attempting to reproduce these kinds of experiments to illustrate the CO2-temperature relation? If not, why is that, since not they could put so many arguments to rest? Why would Tindall be “all we need to know”? Do physicists still rely on the first measurements of the speed of light done in the 17th century? Do we go read Eratosthenes to find out the dimensions of the Earth?
None of this makes any sense to me, sir.
Jim D, you write : “”At that time CO2 dropped because the cooler ocean absorbed it.”
Im not sure what you use the Vostok data for, but in no way can they be used to claim CO2 effect:
http://wattsupwiththat.files.wordpress.com/2009/01/lansner-image4.png
Try wash your blackboard clean clean clean and see what the data actually shows:
1) If CO2 is supposed to be an important forcing in the periods of temperature rise, then CO2 should have a strong effect at 210-230-250 ppm already.
2) at even stronger CO2 concentrations up to 15.000 years after temperature peak, the CO2 is still in max effect higher than most of the time of the temperature increase.
There fore, the only thing you can tell from Vostok CO2 data is, that CO2 is NOT a dominating temperature driver compared to the other natural forcings.
IF CO2 had a huge effect per doubling, well when natural (non-CO2) forcings are just far stronger still.
You cant tell from these data that CO2 has an effect even small, you cant tell that CO2 has NO effect at all.
Summa: CO2 over the ice ages shows nothing about a supposed CO2 effect, except that its not a dominating factor.
K.R. Frank
@frank Lanser
It’s worse than they thought!
As demonstrated by the great experimental physicist John Tyndall who circa 1860 was the first to discover many radiative thermodynamic properties of gases. Through experiment he demonstrated that absorption by GHGs is directly proportional to the number of molecules of gas when the number is below that which will absorb to extinction. Think of it as the gas picking the low-hanging fruit or working like a vacuum pump that can quickly lower the pressure of a high density gas but which has to work harder and harder as the pressure decreases such that it is never able to achieve a perfect vacuum. After the gas has absorbed to practical extinction in its primary absorption frequencies adding more of the gas only serves to increase secondary and tertiary energy absorption modes – for example things like shoulder broadening, scattering, and so forth. These secondary and tertiary modes require exponentially increasing amounts of the gas to be added to get any measurable effect. CO2’s primary absorption band where water vapor doesn’t totally overlap it is at 15 microns and at a partial pressure of 390ppm in a column several miles long there are several times more than enough gas molecules present to absorb 15um radiation to extinction.
I consider it exceedingly generous to concede for the sake of argument that a doubling from present level, absent feedbacks, can raise surface temperature by the IPCC adopted figure of 1.1 degrees Celsius. The only reason I’m willing to concede that is to move the argument forward to the positive feedback argument (which is totally bogus) and then move into arguing that increased CO2 and marginally warmer global average temperature is not only NOT catastrophic but is actually of great benefit to the biosphere and hence to ourselves as we are part of that biosphere.
If someone tries to derail your argument in the future by saying something silly like there must have been a great climate disruption by the doubling from 2ppm to 4ppm just refer them to Tyndall’s work which handily disputes that nonsense. First of all, all life (except perhaps for some extremophiles) would go extinct if CO2 ever fell below about 150ppm and stayed there for long. CO2 is already saturated at 150ppm so discussing what the climate would be like at any lower amount is irrelevant as the earth’s temperature at that point is of no consequence because there’s nothing able to live in it even if the temperature were ideal. Second, the greenhouse effect of CO2 where there isn’t enough of it to completely absorb all the available radiation isn’t exponential but is rather directly proportional to the amount of the gas. I don’t know the exact figure for complete extinction in CO2’s primary absorption region but I’ve seen estimates of anywhere from 20ppm on the low end to 100ppm on the high end as enough for extinction in a column as deep as the troposphere. But even if the greenhouse effect of CO2 was on a logarithmic curve beginning from a partial pressure of zero if we start halving it’s effect after just several halvings we have such a small effect that further halvings are inconsequential as half of a number that’s already close to zero is still close to zero.
Adding insult to injury for “them” is there are many and more powerful variable influences than CO2 concentration at play in the earth’s average temperature from orbital mechanics to solar variability to snow-and-cloud-driven albedo. The whole CAGW charade from end-to-end is hideously flawed. There’s no reason to work on exposing all the small or difficult-to-prove flaws. One should choose one’s battles and only commit to fighting the ones that will decide the war. Two wonderful places to defeat the CAGW scam is in the basic thermodynamic properties of greenhouse gases that were experimentally demonstrated 150 years ago which greatly any additional GHG effect from additional CO2 and in the basic botanical properties of the green plants and cyano-bacteria which benefit greatly from any possible increase in atmospheric CO2 that can be attained from the burning of economically recoverable fossil fuels. These two areas of established fact that have been known since at least the mid 1880’s are enough to derail the CAGW scientific support. Derailing the political support is a different story as it is painfully evident that CAGW proponents don’t let experimentally proven facts get in the way of furthering their agenda.
Francisco says:
September 11, 2010 at 8:11 am
“Were they, really? Did Tyndell attempt to measure the temperature variations, or just the radiation?”
Yes of course he was measuring sensible temperature. That’s what a galvanometer detected to a thermopile is measuring. He was measuring the apparent temperature of a source of heat after the source passed through a column of vacuum, dry air, moist air, air with and without CO2 (called “gaseous carbonic acid” in 1860), and numerous other gases at various concentrations. Tyndall was the first experimental physicist to construct apparatus capable of such measurements. In his lectures he demonstrated the efficacy of his thermopile/galvanometer setup by aiming it at a distant empty wall in the lecture hall and then having a person stand in its view and showing the large deflection in the galvanometer reading when the person entered the field of view. His experimental setup was ingenious considering the limited technology at his disposal from the rock-salt windows on the sample chambers to the polished brass interior to the secondary heat source on the backside of the thermopile that served to keep the primitive voltmeter (galvanometer) in its linear range through a wide temperature regime at the thermopile to using a telescope to read the galvanometer from a distance so that distrubances from a warm body moving about the experimental setup were eliminated.
Francisco says:
September 11, 2010 at 8:11 am
“Is anybody else attempting to reproduce these kinds of experiments to illustrate the CO2-temperature relation?”
Is anyone reproducing Newton’s experiment where he dropped two masses of different weights from the Leaning Tower of Pisa to demonstrate that acceleration of gravity is essentially the same regardless of the weight of the falling object? Reproducing Tyndall’s experiments would make a great science fair project for a 12-year old but there’s really no other reason to prove again what’s already well proven.
That’s why the more informed cadre of climate change alarmists have had to invent positive feedbacks to more than triple any possible independent capability of CO2 to raise surface temperatures and that’s also why they had to reframe the argument from “global warming” to “climate change” because the warming story is so hideously flawed. They had to invent a whole host of delicate balances which when perturbed lead to catastrophic changes in local climates, vastly accelerated ice melt or calving in Greenland and Antarctica, vastly increased incidence of floods and droughts, hurricanes, tornados, and assorted other extreme weather events. It’s a huge house of cards built on speculation with almost no grounding in actual experiment or observation – the output of toy climate models that are woefully incomplete.
Francisco says:
September 11, 2010 at 8:11 am
“Now, if [Tyndall’s] experiments regarding the CO2-temperature relation were so simple and conclusive, I imagine their accuracy and illuminating power could surely be improved after 150 years, could they not?”
Certainly. The primary tool for investigation nowadays is the infrared spectrometer. Tyndall had no way of delineating exactly which frequencies were being absorbed by different molecules and which were not. Now we have very precision measurements of absorption bands for thousands of different molecular species.
See the following to get you started on modern techniques:
http://en.wikipedia.org/wiki/Infrared_spectroscopy
Hi Dave Springer, thanks for all the comments, ill answer later in the evening 🙂
Frank Lansner says:
September 11, 2010 at 11:16 am
“Hi Dave Springer, thanks for all the comments, ill answer later in the evening :-)”
Thanks, Frank. I look forward to it. I take it from your writing that you’re on the other side of the Atlantic from me and english isn’t your first or primary language. I really appreciate you’re indulgence of us Americans few of whom are as fluent as you are in a second language. Tyndall evidently was fluent in several languages as I found him quoting in French and then translating below the quote. He also acquired most of his experimental physics education in Germany as the Germans at that time were far more advanced in the experimental side than Britain. In fact he studied at the University of Marburg under no other than Robert Bunsen whose name is immortalized in just about every chemistry and physics laboratory in the world today by the ubiquitous “Bunsen Burner”.
Frank Lansner: You would be surprised that I agree that at the time of the Ice Ages, orbital mechanics was the dominating mechanism. All that the CO2 was doing at 200-280 ppm was keeping the temperature maybe 6 K warmer than it would have been without any CO2 (probably 15-20 K when you take into account how much less water vapor there would be at those colder temperatures).
So, what I see from your graph is CO2 dropping as the temperature cools due to glaciation. No surprise because the oceans are getting cooler and absorbing it. What would be surprising would be if CO2 was rising when temperature was falling or steady.
Hi Dave,
Interesting to hear about the actual measurement techniques – not many knows about this.
you write:
“.. at a partial pressure of 390ppm in a column several miles long there are several times more than enough gas molecules present to absorb 15um radiation to extinction.”
How do scientists normally test for CO2 effect in laboratories when they cant test the whole atmosphere column? For example, if they want to test “390ppm” – what concentrations do they use in their containers?
You write that in fact the CO2 concentration at 390 ppm is in fact saturated fully? Do you then think that for example MODTRAN is in fact exxagerating the effect of adding CO2 to the atmosphere?
If so, can this be documented or justified further [so that this information can be used in the debate..]?
My impression is that Angstrom (and Tynddal?) showed that there was very little effect from adding CO2 to atmosphere gas. He found that most effect of CO2 is achieved already at 50 ppm.
Is it not true then, that in the 1950´ies, it was suggested, that CO2 at lower pressure – higher altitude – shifted spectra and thus should create heat in higher altitude? ALtitude of less concentration and thus less saturated CO2?
As I understtod, this was the reason IPCC suggested the famous hotspot of warm air in altitude (5-15km) due to CO2. “The CO2 sgnature”. But the CO2 signature never happened, and as it became clear that CO2 had not warmed in higher altitude, it is my experience that the AGW´ers seems to change explanation:
Now, it is no longer in high altitude CO2 warming they expect, its warming “in all altitudes”.
– But how can CO2 warm at surface level when CO2 doenst warm these surface level directly (according to Angstrom and more)?
As upper layers´s warming radiation are totaly dependent on temperaturere – so… where should CO2 heat come from?
K.R, Frank
Hi Frank,
See the first figure at this link.
http://www.sundogpublishing.com/fig8-2.pdf
It’s from the 2006 textbook “A First Course in Atmospheric Radiation” by Grant Petty.
All the figures from the textbook may be viewed at:
http://www.sundogpublishing.com/AtmosRadFigs.html
The first figure is from an infrared spectrometer aimed downward over the arctic (clear dry air). See the big chunk of energy missing from the continuous spectrum at 15 microns? That’s the upwelling energy absorbed by CO2 which is re-emitted in all directions.
It’s this translation of upwelling energy in the GHG absorption bands into energy radiated in all directions which causes the greenhouse effect. In effect they slow down the transport of energy from the surface to outer space. In response to the surface not cooling as quickly it stays a little warmer that it would otherwise. Since the temperature of outer space (3 Kelvins) hasn’t changed but the surface is a bit warmer the larger temperature differential between earth and space speeds up the transport of energy such that a new equilibrium point is reached where energy in equals energy out.
It’s beyond my ability to calculate what the new surface temp equilibrium point is for different CO2 concentrations but there appears to be some genuine and general agreement that it works out to around 1 degree C for a doubling from 350 to 700ppm. I’ve no particular reason to quibble with that as 1C per doubling is no cause for alarm.
@frank (continued):
Still referring to the infrared spectrum looking downward from 20 kilometers note the temperature difference from the shoulder to bottom of the 15 um trough is about 80 Kelvin. Dry adiabatic lapse rate of the atmosphere is 10K per kilometer so at 20 kilometers we’re seeing about half of that. That’s because of re-emission in random directions approximately half of which is downward and the infrared spectrometer can only detect what is coming upwards at it. If the 15 um energy were re-radiated all downwards (like CO2 was a perfect reflector at that wavelength) we’d see that dip a lot deeper – closer to the full dry adiabatic lapse for 20 kilometers or about 200K missing instead of 80K and if CO2 were not abosorbing any energy the dip wouldn’t be there at all.
@frank (con’t)
I gotta take off at any minute so I’m doing this in chunks.
In Tyndal’s setup he couldn’t see any absorption from CO2 at atmospheric partial pressure. The reasons are threefold. First of all he was only looking at a heat source through a four foot column of gas not a 60 thousand foot column of gas. Second his most stable heat source was boiling water at 100C which has a peak radiation frequency of 7 um where CO2 doesn’t have such a strong absorption band. Third he was using an analog device (galvonometer) which at best had a resolution of no better than a tenth or maybe a hundredth of a degree resolution.
But greenhouse gases all work in the same way and he had no problem seeing absorption by water vapor at typical surface partial pressure which absorbs well at 7 microns and is present in hundreds of times greater quantity than CO2.
In his apparatus the absorption mechanism worked the same as in this spectrometer discussion. The polished brass interior of his sample chamber was a very good reflector of infrared so when he saw the needle dip on his galvanometer when a greenhouse gas was in the sample chamber what he was seeing was energy that was being re-emitted straight back at the heat source which, in the view of the thermopile, then looked cooler than it should have just as when the infrared spectrometer was looking down at the arctic surface in the 15um range it looked 80K cooler than it would if the GHG wasn’t blocking the view.
Hope this helps you and others get a better mental picture of what’s happening and how it was observed by Tyndall 150 years ago and later by airborne infrared spectrometers.
Thankyou very much indeed and have a nice flight!!
K.R. Frank