Guest Post by Willis Eschenbach
I’ve been messing about with the “Modtran” online calculator for atmospheric absorption. It’s called “Modtran” because it is a MODerate resolution program to calculate atmospheric infrared absorption written in ForTRAN, which calculates the result for each 1 cm-1 wide band of the wavenumber across the spectrum. Not quite a “line-by-line” calculation, but close. Here’s a sample of the input page:
Figure 1. User input page for the Modtran online calculation for infrared absorption. Left side is user input. Upper right graph shows absorption as a function of frequency. The lower right graph shows the GHG concentrations, pressure, and temperature, as a function of altitude. See here for an overview of the model. Click to enlarge
This shows the situation during the subarctic summer, with no clouds or rain.
Along the way, I ran into a curious mystery, one for which I have no answer.
Here’s the peculiarity I found. I decided to see what Modtran had to say about the “instantaneous forcing”. This is the forcing immediately after a change in e.g. CO2 or other greenhouse gas. In Table 1 of “Efficacy of Climate Forcings” , James Hansen et al. say that the instantaneous forcing from a doubling of CO2 is 4.52 W/m2.
So I tested that claim with Modtran using a variety of different locations, with different combinations of clear skies, cloud, and rain. I started by testing every few hundred PPMV increase, to see if the results were linear with the log (to the base 2) of the change in CO2. Finding that they were perfectly linear, I then tested each situation using 375 ppmv, doubled CO2 (750 ppmv) and two doublings of CO2 (1500 ppmv). I noted the absorption at each level, and compared that to the logarithm (base 2) of CO2. That let me calculate the forcing, which is typically given as the change in forcing for a doubling of CO2. Using Modtran, I get the following results:
Figure 2. Instantaneous forcing calculated by Modtran for different scenarios.
Now, this has the expected form, in that the forcing is highest at the equator and is lowest at the poles. The addition of either rain or clouds reduces the forcing, again as we’d expect, except during subarctic winter when some kinds of clouds increase the forcing slightly.
So the mystery is, according to Modtran, the absolute maximum instantaneous forcing from a doubling of CO2 is 3.2 W/m2 in the clear-sky tropics. I can’t find any combination of locations and weather that gives a larger value for the instantaneous forcing than that. And the minimum value I can find is subarctic winter plus cirrus, at 1.57 W/m2. I can’t find any combination giving less than that, although there may be one.
As a result, according to Modtran the planetary average instantaneous forcing from CO2 doubling cannot be any more than 3.2 W/m2, and is likely on the order of 2.4 W/m2 or so … but according to Hansen et al., the real answer is nearly double that, 4.5 W/m2.
So the mystery is, why is the accepted value for instantaneous forcing nearly twice what Modtran says?
Note that the answer to the mystery is not “feedbacks”, because we’re looking at instantaneous forcing, before any response by the system or any possible feedbacks.
All suggestions welcome, except those that are anatomically improbable …
w.
DATA: Excel spreadsheet here. You don’t need it, though. For any situation, simply use Modtran successively for two CO2 values where one CO2 value is double the other, and note the difference in the calculated upwelling radiation. This is the instantaneous climate sensitivity for that situation.
THE USUAL: If you disagree with me or someone else, in your comment please quote the exact words that you disagree with. This lets everyone know your exact subject of disagreement.
NOTE: I see as I finish this that they have an upgraded user interface to Modtran here … the results are the same. I prefer the older version, the graphics are more informative, but that’s just me.
Gee, jai,
Do you think that Gavin threw up a map of real values? Gavin, Gavin Schmidt put up a valid display? Bwahahahahahah!
More thought and less naive acceptance will get you farther in Science. I don’t care who posts it, check it out. Use their equations, then write your own. Test both against measurements. Check their data, look for other similar data, check the equations there.
It’s possible to learn, and then you won’t just be a parrot.
I like modtran. At one time I used it to initially validate the operation of my HITRAN 1-d model. Where there were descrepancies, I combed my code looking for problems and ultimately found them. I wouldn’t say there was perfect agreement but I thought it did a good job. Although I did play around with the model for AGW purposes, its purpose was for something different.
It became obvious that this sort of effort provides very little information because the co2 doubling is around 3.7w/m^2 in clear skies and the Earth typically has less than 40% clear sky. finding that hansen exagerates (or worse) is hardly a new discovery.
This is a nice article and worth learning for those trying to come up to speed on the subject. Modtran is a nice program (or was) and provides (or provided) reasonable information and is useful for gaining an understanding. It’s not really of much use for ascertaining proof or falsification of CAGW hype.
Hi Willis, love your stuff!
“But yes, of the three computer languages I learned during the 1960s (ALGOL, COBOL, and FORTRAN), only one survives”
I’m assuming you meant FORTRAN?
I cut my working programming teeth on COBOL. There is a surprising amount of COBOL still out their in banks, stock exchanges, enterpsise accounting systems and elsewhere. RPG also still forms a huge amout of the legacy code code base on larger organisations as well. There are versions of COBOL for Windows and other plstforms that still get updates and thereis even an object COBOL out there in the wild 🙂 ALGOL on the other hand.
george e. smith says:
April 13, 2014 at 10:47 am
————————————
George,
with regard to the oceans acting as a “blackbody”, nothing could be further from the truth, they are in effect a ”selective coating” covering 71% of the lithosphere.
This is one of the greatest errors in the very foundation, not just of AGW, but the whole radiative GHE hypothesis. A fist-biting error. The greatest error in the history of human scientific endeavour.
Climastrologists have calculated a figure of -18C for the oceans in absence of an atmosphere. From this they conclude that the atmosphere is acting to raise ocean temperatures by 33C. How did they make this horrific mistake? The treated our deep transparent oceans as a blackbody and used only an emissivity value to calculate that a constant 240 w/m2 would give a standard S-B result of 255K. But you cannot use standard S-B calcs on transparent materials…
Empirical experiment shows that in the absence of atmospheric cooling and DWLWIR, the sun can drive our oceans to 80C or beyond. That’s a 98C error for 71% of the planet’s surface at the very foundation of the AGW inanity.
The simple dis-proof to all of AGW is this –
The sun heats our oceans.
The atmosphere cools our oceans.
Radiative gases cool our atmosphere.
97% of climate “scientists” are assclowns.
Want to make an AGW believer thrash and flex? Just ask them the simple question –
“Given an atmospheric pressure of 1 bar, is the net effect of our radiative atmosphere over the oceans warming or cooling?”
It really is that simple. A non-radiative atmosphere cannot effectively cool itself, therefore it cannot cool the oceans.
“”””””…..Konrad says:
April 13, 2014 at 4:16 pm
george e. smith says:
April 13, 2014 at 10:47 am
————————————
George,
with regard to the oceans acting as a “blackbody”, nothing could be further from the truth, they are in effect a ”selective coating” covering 71% of the lithosphere.
This is one of the greatest errors in the very foundation, not just of AGW, but the whole radiative GHE hypothesis. A fist-biting error. The greatest error in the history of human scientific endeavour. …..”””””
Well Konrad; you do seem to be adamant in your assertion.
It is well known, that the total spherical (hemi) reflectance from the deep oceans at solar spectrum wavelengths is about 3%, making the absorption by the ocean about 97%; that’s where all the solar radiant energy is converted into “heat”.
It is also well known that the absorptance of water at LWIR wavelengths (from 3 microns to 100 microns), is in excess of 1,000 cm^-1, so any LWIR radiant energy from the atmosphere, is attenuated to less than 1/e in 10 microns of water, or down to 1% or less in 50 microns of water.
So we then have the deep oceans absorbing 97% or more of both the short wave solar spectrum energy, and also the entire thermal spectral range of LWIR that is the subject of atmospheric warming physics.
So from now on, I can use your authoritative information that those oceans do not emit in any Black body (or 97% gray body) fashion, as definitive proof, that Kirchoff’s Law regarding equality of specral radiant absorptance and spectral radiant emittance, DOES NOT hold for earth’s oceans, so they are in no way near thermal equilibrium.
Thank you for straightening that out for me.
G
ps is lithosphere something to do with rocks ??
Everything that is at a Temperature higher than zero K emits a thermal continuum spectrum dependent on that Temperature.
At 300 k, that spectrum would peak at 10 microns wavelength. So at Temperature of 1 K, the radiation spectrum would peak at about 3,000 microns, or three mm in the microwave region.
So earth’s atmosphere is certainly emitting a thermal continuum spectrum peaked at somewhere in the 10-15 micron range.
But given the low molecular density, and hence collision rates, and the low collision energies at zero or lower Celsius Temperatures, the thermal radiant emittance is very low. For the main atmosphere gases, being diatomic, the radiative polar moments (antennas) are a transient consequence of distorting collisions.
Water molecules on the other hand, have a significant dipole moment due to the 104 degree bend, so it can emit quite well thermally.
So earth’s atmosphere is anything but non-radiative; just low density and emissivity.
Steven
You need HITRAN database to set the parameters in the LBL calculations. A set of parameters and algorithms run in computers is a model. It’s not a band model but a HITRAN LBL model.
Anyone here understand all this?
george e. smith says:
April 13, 2014 at 8:16 pm
————————————
George,
I’m not sure if that was a response to my post. However I am most certainly not claiming our atmosphere is non-radiative. Quite the opposite. The majority of energy leaving our planet is as LWIR from the atmosphere.
What I am pointing out is that in the absence of atmospheric cooling and DWLWIR our oceans would not be at the “blackbody” figure of 255K determined by climastrologists, rather they would be near 353K.
Ocean surface temps are currently around 288K. Therefore our atmosphere is not warming our oceans, it is cooling them. Radiative gases are the only effective cooling mechanism for the atmosphere. AGW is therfore a physical impossibility.
cba says: “It became obvious that this sort of effort provides very little information because the co2 doubling is around 3.7w/m^2 in clear skies and the Earth typically has less than 40% clear sky.”
Nope, the 3.7 W/m2 is for all-sky total Earth, net flux at tropopause with stratosphere adjustment, adjusted for solar absorption by CO2. It is not clear skies. See
http://folk.uio.no/gunnarmy/paper/myhre_grl98.pdf
Nick Stokes says:
April 12, 2014 at 6:30 pm
For some reason, Willis seems to be calculating at TOA (70km). But Hansen is definite about where he is calculating, at the tropopause. He says in his 2005 paper:
“The simplest forcing, and the only pure forcing, is
the instantaneous forcing, Fi. Fi is the radiative flux change
at the tropopause after the forcing agent is introduced with
the climate held fixed. The reason to use the instantaneous
flux at the tropopause, rather than the flux at the top of the
atmosphere, is that, as shown by Hansen et al. [1981], it
provides a good approximation to Fa, the flux change at the
top of the atmosphere (and throughout the stratosphere)
after the stratosphere is allowed to adjust radiatively to the
presence of the forcing agent.”
So I calculated Modtran at 17km, tropics.
375 ppmv CO2 – 289.0 W/m2 upwelling
750 ppmv 284.5 W/m2.
Difference 4.5 W/m2.
What about the Arctic then? I suppose TOA (70 km) is pretty correct there and that means that the effect is even more less there than in the Tropics. There will be a lot more heat going north and south from the Tropics, especially the northern hemisphere will heat up more than the rest of the globe. The imbalance between the influx and out flux in the Arctic will grow. I still want to see the energy balance for different areas, especially the Atctic. I suggest there is no balance anywhere, except for a certain time for every place outside the Tropics. I have no idea how it looks like in the Arctic in the summer time. Could it be balance or not?
Willis this is not just a scientific site you know. Arguments are proffered to counter stupid AGW
statements and politics. And the latest updates on various subjects, not just those that are scientifically based graphs, that I find very boring actually. Cut to the chase what is the conclusions of these observations. I am not at university any more but I can comment without giving references.
A large bathtub holds about 200 litres of liquid at about 15 degrees C. If this were earth’s atmosphere, man’s carbon contribution to the tub equals about 3 tablespoons. Is it reasonable to think this addition of CO2 would reduce cooling and keep the temperature of the tub 3 degrees C warmer/longer than it otherwise would be? (OK, as thought experiments go, its a bit lame, but when you are talking to Warmists, one needs to speak slowly, using small words. Speaking in a loud voice doesn’t make it more comprehensible to them.)
Howsmart, suppose the three tablespoons were full of food coloring or ink, and the tub of water was sitting outside in the sunshine.
You see, that’s what CO2 in the atmosphere is: a dye. It “colors” the atmosphere in non-visible parts of the light spectrum, but it greatly affects the passage and absorption of light at those wavelengths.
The reason that additional CO2 has only a small GHG effect is not that there’s so little of it, it is because there is already so much of it in the atmosphere. MODTRAN calculates that 50% of the warming effect of current (400 ppm) CO2 level would be accomplished by just 20 ppm CO2 (for a tropical atmosphere w/ constant relative humidity). The NCAR radiation code says that 40 ppm CO2 would be needed to get 50% of the current CO2-caused warming, rather than 20 ppm, but, either way, the lesson is clear: we’re well past the point of diminishing returns w/r/t the warming effect of CO2.
Willis,
Everyone (except apparently NASA) knows that the effect of changes in CO2 on the surface temperature will be greater at the poles than in the tropics. The fact that you expect, and found, the opposite is a bit confusing. You do not say, but the figures imply that you are computing values from 70km looking down. I suggest that that is a mistake – you should be standing on the surface looking up. Comparing 200 pm with 400 ppm
Tropical, looking down shows a reduction in IR of 290.76 – 287.56 = 3.2 W/m2
Tropical, looking up shows an increase of 348.23 – 346.97 = 1.26 W/m2
It isn’t clear why these numbers are different, but when doubling CO2 from 200 to 400 ppm, there are about 2 W/m2 that apparently heat the atmosphere and only 1.26 W/m2 that heat the surface. Using the same comparisons at the poles
Subartic Winter, looking down shows a reduction in IR of 198.17 – 196.5 = 1.67 W/m2
Subartic Winter, looking up shows an increase of 163.19 – 160.27 = 2.92 W/m2
Thus showing that the poles get more downwelling radiation than the tropics when CO2 is doubled .. which is what is expected.
At any rate, the point is that the instantaneous change at the surface can not be determined by looking down thru the atmosphere.
daveburton says:
April 14, 2014 at 12:29 am
———————————
The dye analogy doesn’t really work for radiative gases. This is because they act to both warm and cool our atmosphere. That is to say the warming effect decreases with increasing concentration, but the cooling effect increases.
The primary cooling mechanism for our atmosphere is LWIR to space from radiative gases in our atmosphere. In fact the amount of LWIR emitted to space by radiative gases is more than twice the net flux of radiation absorbed by the atmosphere from surface LWIR and direct solar radiation combined.
This is why MODTRAN is worthless for determining atmospheric temperature response to increasing levels of CO2 or any radiative gas for that matter. The only purpose for MODTRAN was determining atmospheric IR opacity for design of air to air missiles.
Radiative subsidence of air masses plays a critical role in governing the speed of tropospheric convective circulation, the primary energy transport away from the surface. Change the concentration of radiative gases and you change the speed of the primary energy transport in the atmosphere.
That is one of the old climastrology tricks. As radiative gases cool at high altitude and warm at low altitude, if you ignore buoyancy changes from increased radiative gases and hold the speed of tropospheric convective circulation constant, then models show low altitude warming.
Radiative gases both warm and cool our atmosphere. The cooling effect is more than double the warming effect. Adding radiative gases to the atmosphere will not reduce the atmosphere’s radiative cooling ability.
jai mitchell says:
April 13, 2014 at 1:30 pm
Great, you’re a genius and I”m not trying to understand, whatever floats your boat. Me, I’m just trying to do the best I can in the face of charming people like yourself, who produce nothing but want to tell others what’s wrong with them.
Critics who produce nothing are always those who are a failure in their field. Lead, follow, or get out of the way, Jai, I’m happy with you doing any of those … but right now, you’re just in the way.
w.
bushbunny says:
April 13, 2014 at 10:45 pm
Certainly you can … and just as certainly, you will not get any traction if you do. Opinions don’t count for much around here, mine or anyone else’s.
w.
What would cool more quickly, a tub full of warm water or a tub full of warm seltzer?
Berényi Péter says:
April 12, 2014 at 4:09 pm
Wikipedia says:
…For instance, the simplified first-order approximation expression for carbon dioxide is:
ΔF = 5.35 × ln C/C₀ W/m²
Plug in 2 and you get 3.7, as opposed to mod tran’s max of 3.2 over by 3.7/3.2 = 15.625
Plug in 100 and you get 24.638 as opposed to mod tran’s 25.497, under by
24.638/25.497 = 3.39%
Obviously, that logarithmic effect of CO2 is not exact, and the formula given by wikipedia is an approximation, intended to give fairly close values over a wide range of
changes in CO2.
Looks to me like for $1200 you can get the source code and support:
http://modtran5.com/purchase/index.html with a discount for educational buyers.
One could always buy it, then ask “support”: “Why? What changed?”…
george e. smith says:
April 13, 2014 at 11:54 am
Also the notion that somehow the increase in CO2 somehow just “nudges out the edges of the absorption “band” and that results in the “logarithmic response to the CO2 increase.
Well surely that too is nonsense, given that the “band” is really a large number of narrow lines, and each CO2 molecules is quite unaware of the presence of any others. Any of those lines is going to behave pretty much the same, all the time.
Except that during the time before a CO2 molecule emits it endures many collisions from neighboring molecules, so it does ‘know’ they’re there.
That gives you collisional broadening. Temperature and pressure dependent.
Also there is broadening caused by how fast the molecule is moving (and which direction) when it emits, that’s Doppler broadening. This is temperature dependent.
See: http://i302.photobucket.com/albums/nn107/Sprintstar400/CO2101copy.jpg
Shows the effect of total pressure on a CO2 spectrum at 0.1 atm, 1atm and 10 atm respectively.
Willis
As a result, according to Modtran the planetary average instantaneous forcing from CO2 doubling cannot be any more than 3.2 W/m2, and is likely on the order of 2.4 W/m2 or so … but according to Hansen et al., the real answer is nearly double that, 4.5 W/m2.
So the mystery is, why is the accepted value for instantaneous forcing nearly twice what Modtran says?
That is the value that Hansen used back in the 80s and was the accepted value then, since then the evaluation is that it’s about 3.7.
A factor in the polar values may be that MODRAN doesn’t take into account the inversion layers that occur there?
Phil. says:
April 15, 2014 at 9:47 am
Did I not cite the source for Hansen’s value? Hang on, lemme check … yes, of course I cited it.
Was it from “the 80s”?
Why no, it’s from 2005 … read the dang citations, Phil. I go to a lot of work to include them, and it will prevent you from looking foolish.
w.
Was it from “the 80s”?
Why no, it’s from 2005 … read the dang citations, Phil. I go to a lot of work to include them, and it will prevent you from looking foolish.
Nevertheless Willis, Hansen was using a value in excess of 4.0 in his 1988 paper which dated from ~1979 hence my comment, as to when it changed that’s another matter (probably 2007 AR4). It was regarded as a high value even then as I recall.