Guest Post by Willis Eschenbach
There’s an online calculator called MODTRAN that calculates the absorption of longwave (“greenhouse”) radiation for various greenhouse gases (“GHGs”), and shows their resulting effect. It does this on a “line-by-line” basis, meaning it examines each interval of the longwave spectrum for each greenhouse gas at each altitude, and calculates the resulting absorption by each species given the concentration and the partial pressure of that species. Figure 1 shows the calculation results for the default values of CO2, ozone, and methane.
Figure 1. MODTRAN results. The jagged red line at the top right shows what is not absorbed by the atmosphere. Colored lines in the background are theoretical “no-absorption” curves for various temperatures. The big “bite” out of the middle section of the jagged red line is mainly water vapor absorption, although it overlaps with the CO2 absorption bands in parts of it. The graph at the lower right shows the pressure, temperature, and the concentration of H20, Ozone, CO2, and CH4 at various elevations. The number “Iout” is the total energy that is not absorbed, so as absorption increases, that number will decrease.
That all seems straightforward, it looks the same as in heaps of textbooks … so where’s the MODTRAN oddity?
The oddity arose as a result of my wanting to know more about the doubling of CO2, and the 3.7 watts per square metre of increased absorption that IPCC claims the aforesaid doubling of CO2 is supposed to cause. To find out what MODTRAN says, I put in 750 ppm of CO2 in the top cell, and I had MODTRAN recalculate the Iout. To my surprise, I found that it was 284.672 … which when subtracted from the starting Iout shown above of 287.844 gives us only 3.2 watts per square metre increased absorption (forcing change) for a doubling of CO2.
I had left the “No Clouds or Rain” choice selected, thinking that the biggest change in CO2 would be in clear-sky conditions. So I figured “well, perhaps clouds or rain increase the absorption when CO2 doubles” … but investigating various cloud results showed that was not the case, they all gave smaller absorption changes. My original intuition was correct, clear-sky conditions give the biggest change in absorption for a doubling of CO2.
So I thought, “well, perhaps I’m looking at the wrong region of the Earth”. The other latitude bands available in MODTRAN are Midlatitude Summer and Winter, and Subarctic Summer and Winter. I took nominal CO2 values to represent the CO2 concentration in 1850 (285 ppmv), default (375 ppmv), doubling of 1850 value (570 ppmv) and doubling of the present value (750 ppmv). I figured that would give me two doublings, and let me see if the increases were linear with the logarithm of the number of doublings. I used MODTRAN to calculate the absorption change in each latitude band. Figure 2 shows those results, with the X axis being the number of doublings, and the Y-axis showing the increase in longwave absorption.
Figure 2. MODTRAN and IPCC values for the increase in forcing due to increasing CO2. The forcing change in each region per doubling of CO2 in watts per square metre is shown after the name in the legend, followed by “T=” and the surface temperature.
First thing I noticed is that the lines are all straight. So MODTRAN does indeed show a linear relationship between logarithm of the CO2 increase and the calculated increase in absorption. So no surprise there.
What was a surprise is that none of the other latitude bands had larger changes in absorption than the tropics. I’d thought that since the IPCC says the global average change from doubling CO2 is 3.7 W/m2, that because the tropics were at 3.2 W/m2, somewhere else the absorption must be above 3.7 W/m2 to make the average correct. But that’s not the case. They’re all smaller.
I also thought that the difference in absorption might be due to the different surface temperatures … but Midlatitude Winter and Subarctic Summer have about the same calculated absorption, yet their surface temperatures are about 15 degrees apart.
Note that what I have shown, the change in absorption, is also called the “instantaneous” forcing, abbreviated Fi. There are various other forcings one can measure. Hansen discusses them here (PDF), and gives a value of 4.52 W/m2 for the instantaneous forcing from a doubling of CO2 according to his climate model (Table 1, p. 7). Presumably his model does a line-by-line calculation similar to MODTRAN to figure out the absorption changes.
The IPCC, on the other hand, says:
The simple formulae for RF [radiative forcing] of the LLGHG [long-lived greenhouse gases] quoted in Ramaswamy et al. (2001) are still valid. These formulae are based on global RF calculations where clouds, stratospheric adjustment and solar absorption are included, and give an RF of +3.7 W m–2 for a doubling in the CO2 mixing ratio.
SOURCE: IPCC AR4 WG1 (PDF) page 140
So it appears the IPCC result is not based on a line by line calculation …
And that’s the MODTRAN oddity. Here’s the question:
1. Why does the MODTRAN calculated line-by-line change in absorption range from a low of 1.7 W/m2 to a high of 3.2 W/m2, while Hansen is saying the answer is really 4.5 W/m2 and the IPCC uses 3.7 W/m2?
Since according to MODTRAN (and logic) clouds reduce the effect of a doubling of CO2, and the IPCC (and presumably Hansen) are using all-sky conditions, that makes the IPCC/Hansen figures even farther from the MODTRAN figures.
Please note that (per Hansen) the instantaneous forcing Fi is greater than the adjusted forcing Fa by about 0.4 W/m2. The IPCC is saying that the 3.7 W/m2 is the adjusted forcing Fa, the forcing after the stratosphere adjusts to the change. So their value for instantaneous forcing would be larger, removing the stratospheric adjustment would put it at about 4.1 W/m2. So the IPCC is closer to Hansen’s value for the instantaneous forcing … but it means they’re further from the MODTRAN calculations.
I don’t know what I’m missing here, and I don’t understand these results, so any assistance gladly accepted.
w.
Hi Willis,
I question whether MODTRAN is simply buggy. Perhaps I don’t understand what it is supposed to be telling me, but I entered 990000ppm CO2 and it told me the ground T was exactly the same as with the actual ppm.
Did you change the “ground T offset” to account for the higher temperature that’s sure to come with the increase in CO2? Perhaps the expected higher temperature makes for more line spreading and hence more absorption.
This probably just confuses the issue even more, but IPCC AR4 shows a range of values for the forcing associated with a doubling of CO2.
The last page of the supplementary info for AR4 WG1 Chap 8 has a table of the apparent forcing for doubling of CO2 for the various models. More specifically, it is “Table S8.1 Parameter values used in a simple climate model (MAGICC) to approximately reproduce results from the AOGCM multi-model dataset at PCMDI.”
http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-chapter8-supp-material.pdf
The estimated values range from 3.09 w m-2 K-1 for MIROC3.2(medres) up to 4.06 for GISS-ER and GISS-EH.
Ramaswamy et al. talks about LLGHG. Did they just assume methane and nitrous oxide would stay on the same trend and not mention it?
Ron House says:
August 18, 2011 at 6:37 pm
As I said, what I am measuring is the instantaneous forcing change. This is the change that occurs before the temperature rise … so indeed ground T will be the same.
w.
Ric Werme says:
August 18, 2011 at 6:43 pm
No, I’m looking at the instantaneous forcing change before any adjustment by the system. If there were no cloud throttle, the eventual effect of the forcing change would be that the surface temperature would rise until the initial radiation condition (amount of radiation Iout) is re-established.
But that’s not what I’m asking about, and there is a cloud throttle.
I’m looking at the instantaneous forcing “Fi”, the immediate change in absorption due to the higher levels of GHGs. I’m comparing it to the Fi from the IPCC, and the Fi from Hansen et al.
w.
Typo: There should be a “be” after “would” in:
“So their value for instantaneous forcing would larger, …”
Interesting.
I will need to reflect on this and perhaps have a little go on MODTRANS
Willis, setting the sensor altitude to 16 km or a top of troposphere value gives higher forcing and removes the slightly opposite stratospheric effect. Top of troposphere forcing is more appropriate to surface temperature as it is connected via the lapse rate. At other latitudes the troposphere is lower than in the tropics down to maybe 12 km.
Charlie A says:
August 18, 2011 at 6:44 pm
The existence of the MAGICC model probably deserves its own post, Charlie. Thanks for reminding me about it.
The MAGICC is a general purpose model that can “mimic” the output of the various models used by the IPCC. It does this by adjusting only four parameters—forcing per doubling (Fa), climate sensitivity, ocean thermal diffusivity, and land/ocean warming ratio. It determines the exact settings for a given model by comparing the input and the output of the model.
This “magic” model doesn’t get a lot of airtime in the IPCC reports … no good advertising that a linear model can replicate the entire model space of all of the IPCC models by just twisting four dials …
However, that’s just what the MAGICC uses to replicate the models, so it’s not quite correct to say the IPCC AR4 shows a range of values for doubling of CO2. The models are showing the range.
The IPCC AR4 (as far as I know, it’s huge) uses a canonical value of 3.7 W/m2. This may be related to the note in the referenced table, which says:
although the quotation in the head post suggests another source for the 3.7 W/m2 figure.
w.
Why bother with MODTRANS?
http://geoflop.uchicago.edu/forecast/docs/Projects/modtran.doc.html
“Note This is an old model (1990’s), illustrative but not necessarily in strict quantitative agreement with current state of the art line-by-line models. ”
Try:
http://geoflop.uchicago.edu/forecast/docs/Projects/full_spectrum.html
The data for the AR5 scenarios is here: http://www.pik-potsdam.de/~mmalte/rcps/
“RCP 8.5” shows CO2 will double – from pre-industrial – in 2045 or so.
Pixel-counting of Potsdam’s “Global CO2 Radiative Forcing” graph shows about 3W/m^2 extra from the doubling. On page 60 of this: http://pik-potsdam.de/~mmalte/rcps/data/RCPs_FINAL_RELEASE_31May2010_OVERVIEW.pdf
Closer, but still more than modtran seems to show.
John W says:
Because I don’t understand how to get the result I want from your site. It automatically readjusts the surface temperature to re-establish the radiation balance … and I can’t find a way to turn that off. Is there one, and I’m missing it?
w.
According to “NCAR”
http://geoflop.uchicago.edu/forecast/docs/Projects/full_spectrum.html
Leaving all other values at default:
CO2 mixing ratio 375 ppm = Equilibrium near-surface air temperature is 16.0 degC (289.1 K)
CO2 mixing ratio 750 ppm = Equilibrium near-surface air temperature is 18.5 degC (291.7 K)
Sensitivity to 2XCO2 = 2.5 C from 375 to 750 @ default conditions.
CO2 mixing ratio 200 ppm = Equilibrium near-surface air temperature is 13.9 degC (287.0 K)
CO2 mixing ratio 400 ppm = Equilibrium near-surface air temperature is 16.2 degC (289.3 K)
Sensitivity to 2XCO2 = 2.3 C from 200 to 400 @ default conditions.
The more I think about it the more I agree with “the heretic”. The notion that the climate response to a forcing could be described by such a simple relationship as the form T=LQ seems counter intuitive. More research is needed, please send grant $.
RE Willis:
” Is there one, and I’m missing it?”
Well, if there is I’m missing it too.
I see what you’re trying to get at now.
Hmmm, I’ll keep looking.
Willis Eschenbach
“We calculate climate change and efficacy using measured
or estimated changes of forcing agents between 1880
and 2000, or, in some cases, the estimated changes between
1850 and 2000.”
What is the total change in forcing from 1880 – 2000 and the estimated change between 1850 and 2000 in w/m2?
MODTRAN is not an LBL (line by line), its a band model. It was when I used it, and still is today
http://en.wikipedia.org/wiki/Atmospheric_radiative_transfer_codes
I think a fairly rigorous treatment of this topic is in this series of blog posts on the scienceofdoom.com blog. Note the following is the twelfth in the series, the links to the others int the series are at the bottom in the conclusions section. Perhaps there is clue in here somewhere.
http://scienceofdoom.com/2011/04/30/understanding-atmospheric-radiation-and-the-%e2%80%9cgreenhouse%e2%80%9d-effect-%e2%80%93-part-twelve-curve-of-growth/
Willis, your first problem is that you are computing the data looking down from 70km.
Forcing should be computed looking up from the surface.
In the image above, the CO2 absorption near 666 cm-1 is actually the CO2 emission from the -53C tropopause. This is a common error in interpreting that particular image. To be clear, at those frequencies CO2 is totally opaque. More than 95% of the energy from the surface is absorbed in the first kilometer. What is measured from space is emitted from much higher in the atmosphere. The spike in the middle of the CO2 band is emitted from the stratopause, at 47 km. (Get it, the cold part is from 11 km and the warm spike is from 47 km.)
Willis, Modtran is band model. Myrhe 1998 uses LBL models.
here is an example lecture using modtran
http://www.google.com/url?sa=t&source=web&cd=1&ved=0CBYQFjAA&url=http%3A%2F%2Fmensch.org%2F5223%2FRadForce_print.pdf&ei=wONNTq_nIo_RiALEuIF8&usg=AFQjCNFykz3SdwWLjD6wnStaJJmiA_dYHw&sig2=y11ZMUvjaj_Sk5E6P4aedg
http://www.barrettbellamyclimate.com/page24.htm
http://scienceofdoom.com/2010/02/05/co2-an-insignificant-trace-gas-part-four/
MODTRAN is a medium resolution spectroscopic simulator that calculates the IR spectrum at a resolution of about 0.5 to 5 cm-1, depending on how this is specified in the program. It is derived from the HITRAN database that contains the high resolution spectral data. I belive that Hansen’s original ‘forcing constants’ were derived from HITRAN. The main issue with MODTRAN is the approximation of the molecular linewidths. Each molecular line has a pressure and temperature dependent Lorentzian linewidth and all of the lines overlap. I did some line by line HITRAN claculations and I used 0.01 cm-1 resolution. I also used 100 m resolution on the altitude.
However, regardless of the differences in the total flux there are two important results that emerge from considerations of the linewidth .
First, the upward and downward LWIR fluxes are not equivalent. The LWIR emission to space does not magically emerge at the top of the atmosphere. It originates from the line narrowing with altitude, mainly from the rotational (lower wave number) water band. The upward LWIR emission from the wings of the lines in the middle troposphere are not reabsorbed at higher altitudes and escapes to space. The downward emission from line center at higher altitudes is reabsorbed and does not reach the surface. This negates the whole radiative forcing flux argument.
In addition, the over 90% of the downward LWIR flux reaching the surface originates in the first 2 km layer of the atmosphere. Similarly, over 90% of the molecular emission to space originates from above the first 2 km layer. The troposphere is really two independent thermal reserviors. The lower 2 km reservoir has a heat capacity of ~2MJ.K-1.m-2 (for a 2 km x 1 square meter air column). The upper reservoir has a heat capacity of ~6 MJ.K-1.m-2 (for a nominal 9 km x 1 square meter column). The both reservoirs are heated during the day by convection from the surface (and transport). The upper reservoir radiates to space all the time. The lower reservior stores the heat at night and cools quite slowly. The net upward LWIR emission at 2 km is ~50 W.m-2. This gives an approximate cooling rate of 0.1 K.hr-1 for the lower reservior. The night time downward LWIR emission at the surface balances the upward blackbody emission from the surface so that the net upward surface emission is between about 50 and 100 W.m-2 depending on humidity. The downward LWIR emission from any low cloud will close this LWIR window completely.
Full summer sun flux at the surface is ~25 MJ.m-2.day-1. Very roughly, about 20% goes to feed the LWIR transmission window and the rest ends up as moist convection. Once the dynamic properties of the surface energy transfer are understood, the whole CO2 induce global warming argument disappears. The observed increase of 100 ppm in atmospheric CO2 concentration has produced an increase of 0.15 MJ.m-2.day-1 in downward LWIR flux at the surface over 200 years. This has to be added to the total flux balance. Solar flux can from zero to 25 MJ.m-2.day-1. Net surface LWIR emission is from zero to ~ 5 MJ.m-2.day-1. These numbers are always changing each day with far larger fluctuations than the 0.17 MJ.m-2.day-1.
There is no such thing as climate equilibrium on any time scale and the equlibrium flux equations used in radiative forcing are a mathematical abstraction that has no basis in physical reality. One of the radiative forcing assumptions clearly stated by Manabe and Wetherald in their 1967 paper is that the surface heat capacity is assumed to be zero. The ‘equlibrium surface temperature’ calculated by the climate radiative forcing models is not even a measurable climate variable. The CO2 doubling argument is a problem that exists only in climate warming theoology. How does a doubling of the atmospheric CO2 concentration change the number of photonic angels that may reside on a climate pin?
More details at
http://hidethedecline.eu/pages/posts/what-surface-temperature-is-your-model-really-predicting-190.php
http://hidethedecline.eu/pages/posts/greenhouse-effect-vs.-gravity—guest-post-by-roy-clark-201.php
Brian W says:
August 18, 2011 at 9:00 pm
Not sure who you’re quoting there, but it’s not me …
w.
steven mosher says:
August 18, 2011 at 9:10 pm
Thank for the correction, Mosh. As a user of the program, do you understand why the absorption numbers it gives (1.7 to 3.2 W/m2 per doubling) are so much smaller than the corresponding Hansen (4.5 W/m2 per doubling) or the IPCC (4.1 W/m2 w/o stratospheric adjustment) numbers?
All the best,
w.
Willis Eschenbach
I’m quoting Hansen’s paper page 2 (9). Try reading your reference.
Ok here’s another question. By how much has the solar constant changed in the last 100 years?
I think the reason is that Modtran is not a climate modelling program – it just gives the absorption of a prescribed gas mixture. When you double CO2, warming evaporates more water. That’s the basis of the positive feedback. Modtran does not make that sort of calculation.
Well, first thing I would check in the version that is posted online. I used it long ago when the code was new and still classified. We used that and lotran. It was validated for its use, that being estimating the atmospheric losses of a thermal signature for both look up and look down threats.
A look up threat would typically be looking from the ground up to 10K,30K and 50K. 50K was the top of our operational envelop. A look down threat, might look from from 50K to 10K. Code was delivered to us and were under contract to use it.
Possible reasons: Some of the error will be due to the fact that its a band model and a good one would get you within 10% of an LBL. Check the relative humidity settings. I cant recall how that is supposed to be set. It may not handle the strat very well.. line broadening.. not sure because the thing on the web doesnt look like what we worked with.. that was more like what you see in the doc below.
http://www.google.com/url?sa=t&source=web&cd=3&ved=0CCYQFjAC&url=http%3A%2F%2Feastfire.gmu.edu%2Fcourse%2Feos556%2Freadings%2FMod4V3R1Manual.doc&ei=PPVNTuWcF-PWiAKs1_icAQ&usg=AFQjCNGRRhBwGPc2nWTZRLBk7JBBK84Wjg&sig2=qyAe56dIVCE9nCgZQsaYEg
Bottom line. I dunno.
My understanding of ModTran is that it is based on an Air Force program to calculate IR visibility and is not related to any IPCC program. I have used it to calculate what I believe to be raw CO2 temperature sensitivity. I normally use it assuming that 292.993 W/m2 is the amount of heat received from the sun that must be expelled in an equilibrium condition–this is also one of those numbers ModTran likes to produce. I usually leave most of the parameters unchanged from their default states.
So, if I start with a CO2 concentration of 396 PPM, I find that I have to set the temperature offset to 1.48 degrees to get an Iout of 292.993 W/m2 and surface temperature of 301.18 deg K.
Then with a CO2 concentration of 792 PPM, I find that I have to set the temperature offset to 2.4 degrees to get an Iout of 292.993 W/m2 with a surface temperature of 302.1 deg K.
Finally with a hypothetical CO2 concentration of 17,920 PPM, I find that I have to set the temperature offset to 8.04 degrees to get an Iout of 292.993 W/m2 with a surface temperature of 307.74 deg K.
It appears something has changed recently as these results are slightly different than those I obtained about fifteen months ago as follows:
Tropical, Clear Air Default Setting Atm Log2 Gnd Tmp Surface Surface Log2 CO2 (CO2/280) Offset Tmp °K Tmp °C Slope 70 -2.0 -0.81 298.89 26.7 0.9 99 -1.5 -0.365 299.34 27.2 0.9 140 -1.0 0.08 299.78 27.6 0.9 198 -0.5 0.52 300.22 28.1 0.9 280 0.0 0.96 300.67 28.5 0.9 396 0.5 1.41 301.11 29.0 0.9 560 1.0 1.86 301.56 29.4 0.9 792 1.5 2.33 302.03 29.9 0.9 1,120 2.0 2.81 302.51 30.4 1.0 1,584 2.5 3.31 303.01 30.9 1.0 2,240 3.0 3.835 303.54 31.4 1.1 3,168 3.5 4.39 304.09 31.9 1.1 4,480 4.0 4.99 304.69 32.5 1.2 6,336 4.5 5.63 305.33 33.2 1.3 8,960 5.0 6.34 306.04 33.9 1.5 12,671 5.5 7.11 306.81 34.7 1.6 17,920 6.0 7.97 307.67 35.5 1.8 25,343 6.5 8.94 308.64 36.5 2.1 35,840 7.0 10.03 309.73 37.6 2.3 50,685 7.5 11.26 310.96 38.8 2.6 71,680 8.0 12.65 312.35 40.2 2.9Dear Willis,
AFAIK there was a major change of the MODTRAN-database concerning CO2 about 8 years ago, because some of the interaction of CO2 with other molecules was missing before.
Brian W says:
August 18, 2011 at 10:27 pm
You expect me to explain what Hansen means by some random quotation from his paper that has nothing to do with this thread? Why would I want to do that?
I give up, Mister Wizard, how much has the solar constant changed in the last 100 years? Please show your work …
What I don’t get, Brian, is what any of this has to do with the subject of the thread. The change in the solar constant is unrelated to the change in absorption from CO2 doubling, why are you brining it up? The subject is the MODTRAN results and their difference from the IPCC and Hansen’s results.
w.
Why are Hansen’s numbers different? It may matter what Version of MODTRAN you use? Versions prior to around 1999 could not adequately deal with multiple scattering events on the azimuth of the line of sight. Scattering may be inappropriately interpreted as absorption.
Nick Stokes says:
August 18, 2011 at 10:47 pm
Thanks, Nick, but that’s all part of the response to the CO2 doubling. I’m looking at the instantaneous forcing, what occurs when the CO2 doubles but before the system responds. As such, warming and water evaporation don’t enter the picture … which is why I’m looking at instantaneous forcing, to avoid all questions of temperature changes and what they might bring.
w.
Spector says:
August 18, 2011 at 10:52 pm
Spector, again, I’m not looking at how much temperature change corresponds to the forcing as you are commenting on. I’m looking at the instantaneous change in forcing due to the change in CO2, and NOT at the change in forcing.
w.
Laws of Nature says:
August 18, 2011 at 10:57 pm
Does anyone have any actual information on this question?
w.
Robert Clemenzi says:
August 18, 2011 at 9:17 pm
Not true for what I’m looking for. Instantaneous forcing at the TOA (top of atmosphere) is the change in the absorption, which is calculated from the top looking down. When CO2 increases, absorption increases, that’s what drives the whole process.
w.
I am just going to give a dumb laymans perspective here. Why is it when there is about 20 watts of natural forcing relating to perihelion versus aphelion and when it is perihelion there it is the southern hemispheres summer so there is more sunlight and it is stronger directed at the water, we don’t all fry? Wouldn’t there be more water vapour to heat us all up. So to me it seems unlikely even if these what appear to be made up numbers do exist they are less significant than the natural numbers. The other point is that if you are north of the Tropic of Cancer or south of the Tropic of Capricorn the amount of sunlight will vary on average by more than 50% but temperatures vary by much less than this of course. So on alarmists theory as soon as it is your time for summer then with all the many feedbacks you will be in big trouble.
Rob Z says:
August 18, 2011 at 11:11 pm
Thanks, Rob. That’s possible … but the MODTRAN numbers are way, way below both Hansen’s 4.5 or the IPCC 4.1 W/m2. I don’t think that’s some problem with scattering events being interpreted as absorption. This is because if you interpret scattering as absorption, your absorption figures will be too high … but in this case they are too low, much lower than Hansen/IPCC.
w.
Well Willis, the first question I would ask somebody to explain is this. At the mean earth surface Temperature of 288 K the calculated (BB) emission would be 390 W/m^2, and that is indeed the value, that Trenberth gives for the surface emission in his (in)famous earth energy budget.
Of that 390 W/m^2, only 40 W/m^2 escapes to space; 10%. Now using your MODTRAN graph (red jaggie) explain how those holes are taking out 90% and only 10% is escaping.
Also note that the vertical scale is W/m^2 per wavenumber increment; and there’s a whole lot more wave numbers at the right hand end of the graph, than there is at the left hand end, so this rendition grossly exaggerates the low wavenumber energy content, and also the amount of energy removed by the “big” CO2 dip.
Plot the same data on a wavelength scale, rather than wave number, and suddenly the peak moves to where that innocuous Ozone dip is around 1000 cm^-1, or 9.6 microns, and the CO2 hole is now down on the tail. But of course, now that right hand end has more wavelength microns, than the left hand end, so again a distortion occurs.
Howcum, nobody ever seems to plot the integrated energy emission as a function of either wavelength or wave number, so we can see where the energy is really escaping..
Also, does that MODTRAN calculator also calculate the thermal spectrum emitted from the atmosphere to separate it from the thermal spectrum emitted at the start from the surface ?
Oh I forgot, when molecules slough off the surface and become part of the “atmosphere” they suddenly and mysteriously stop radiating thermal radiation.
Willis Eschenbach
You sure are a slippery fellow, but since you ask . The current solar constant is stated as 1366w/m2 correct? My Passive Solar Energy book circa 1979 gives the solar constant as 429.2 btu’s/sq. ft./hr. This is equal to 1353.95w/m2, for a difference of 12w/m2 (rounded). This is a nearly four times difference from 3.2w/m2 and using the IPCCs 3.7w is times still more than three times the amount.
My point is Mr. physics authority is that MODTRANS numbers are so far off they are MEANINGLESS!
Oh and CO2 is a feeble absorber of IR compared to water vapor.
A second question I would ask, is: does MODTRAN calculate the whole cascade of absorption and re-emission from the GHG molecules, or does it take the brain dead “Beer-Lambert Law” approach of assuming that captured photon energy stays captured. In the case of the atmosphere, the thermal emission spectrum, is roughly the same as the surface emission spectrum, so it is a bit difficult (experimentally) to measure the original surface surviving flux (at 70,000 ft or wherever it is observed), and separate it from the atmospheric re-emissions. Of course some people believe that atmospheric re-emissions can ONLY be at those very same GHG molecular absorption bands.
Willis I believe the online version is 1995. If you want to know all the changes they are most likely available in the release notes.
And for clarity HITRAN is the database of molecules.
you can also start here . Satillities work because they use RTEs and you’ll vary often find groups doing comparisions of various models
http://rtcodes.ltdri.org/Description_of_the_codes_simple.htm
GCMs will aslo use band models ( Err i think.. need to check)
GIYF
MODTRAN compare LBL validate
Willis: Modtran is not producing an absorption spectrum; it is calculating the outward infrared radiation that would be seen looking down from 70 km at the nearly-blackbody radiation emitted by the earth’s surface AFTER being modified by absorption by GHG’s AND emission from GHG’s as it passed through the atmosphere. At strongly absorbed wavelengths, >50% absorption can occur in tens to hundreds of meters, so few of the photons escaping to space at these wavelengths were emitted by the earth’s surface. At wavelengths strongly absorbed by CO2, the upward radiation has been emitted on the average by CO2 molecules near the tropopause where the temperature is about 220 degK. The photons emitted by the ground that escaped through the atmospheric window (800-1000 cm-1) have an intensity about right for blackbody radiation at 300 degK with an emissivity a little less than one.
When you add clouds, some (30% ?) of the radiation is emitted by cloud tops and some by the ground (70% ?). Low clouds are much warmer than high ones.
The IPCC’s 3.7 W/m2 is the difference in net outward radiation at the tropopause (not 70 km) for doubling CO2 averaged over the whole global (after stratosphere, but not troposphere, temperatures have equilibrated) taking into account average cloudiness, the vertical temperature profile at various locations on the earth, the varying height of the tropopause etc.
Myhre (1998) is available at http://folk.uio.no/gunnarmy/paper/myhre_grl98.pdf. This paper keeps referring back to results and methodology from earlier papers behind pay walls and certainly doesn’t provide a complete explanation.
RE: Willis Eschenbach says: (August 18, 2011 at 11:16 pm)
Spector, again, I’m not looking at how much temperature change corresponds to the forcing as you are commenting on. I’m looking at the instantaneous change in forcing due to the change in CO2, and NOT at the change in forcing.
I believe the ‘forcing’ is the 292.993 W/m2 energy flow that I keep constant. I am assuming a constant solar forcing energy flow for all CO2 concentrations. This result does not come out of a single run. I set the CO2 concentration and change the temperature offset — 2, 2.5, 2.6, 2.65, 2.63 …– until I reach my standard 292.993 W/m2 forcing level. Then I have the temperature required to force the standard amount of energy into outer space. Once I have a table of temperatures and corresponding CO2 levels, I can use the Microsoft Excel Solver utility to make a polynomial approximation of temperature as a function of LOG2(CO2/280) to get the doubling slope from its derivative polynomial.
Moderators: please give the full text of obscure (ie, American) acronyms.
Eg
AFAIK [as far as I know]
WUWT is a global resource, and acronym usage varies widely.
It is my understanding that the Air Force had good reason to make sure these ModTran calculations were accurate. From a climatological point of view, this is a raw CO2 effect–it does not include effects such as increasing cloud cover as a result of increasing temperature. It only cares with how CO2 and the other gases modeled affect atmospheric transparency.
Hello Willis; The effect of CO2 s to block radiation to space (at the co2 absorption wavelengths) from the surface and replace it with radiation fro the top of the CO2 column at these wavelengths. The plot you give in your article makes that abundantly plain as does the down looking radiation spectrum as taken by the IRIS experiment aboard the Nimbus satellite. Knowing this gives an easy way to calculate the average (or for that matter spot) energy retention due to changes in CO2 as follows.
CO2 absorbs from about 13.4 microns to 16 microns. Integrating Planks law (known for nearly 100 years) over this wavelength range for a 288K black body and a 220K black body yields respectively 49.1 watts/ M2 and 16.7 watts/ M2 .
Without CO2 the surface would not be quite radiating 49.1 watts/ M2 over this wavelength range because of the action of clouds. Clouds also absorb thermal infrared emission from the surface and in turn emit to space from the top of the cloud. Much of the cloud is at an altitude of about 2-3 km and at that altitude the top of the cloud is at about 273K. Integrating Planks law for the above mentioned wavelength range at 273K gives 40.4 watts / M2. Taking the generally accepted figure of 60% cloud cover, the emission to space without CO2 would be 40% from the surface and 60% from cloud tops giving;
49.1 * 0.4 + 40.4 * 0.6 = 43.9 watts / M2 without the intervention of CO2
CO2 reduces Earths emission to space by 43.9 – 16.7 = 27.2 watts/ M2 which agrees well with other estimates. Now the energy retention versus concentration is logarithmic, again widely accepted, and in the case of CO2 at 280 ppm it has been logarithmic for about 9-10 doublings (based on the known absorbance of the CO2 column at 280 ppm of around 2000 abs). Thus each doubling contributes somewhere between about 2.7 and 3 watts / M2.
As I said, this is the average for the whole of the planet and as such it agrees very well with the Modtran data you quote. Its easy for example to repeat the calculation using tropical suface and tropopause temperatures. Doing the calculations this way shows up some VERY interesting issues. Firstly the emission temperature is that of the tropopause so it implies the top of the CO2 column is at the tropopause yet established wisdom claims CO2 is well mixed in the statosphere (there is a significant fraction of the atmopshere above the tropopause). If the stratosphere was indeed well mixed the emission temperature would be significantly higher (look at the emission temp ofr the O3 line at 10 microns whcih does come from high in the stratosphere and you will see what I mean) and the impact of CO2 would then be LOWER.
Also you do not show it but I have some Nimbus data for the Antarctic and it shows a PEAK not a dip at the CO2 line. That means that in the Antarctic the imapct of CO2 is to cool not warm. How come? Well the surface is not much warmer than the tropopause but more significantly the equivalent black body temperature for the surface (the apparent temeprature in the atmospheric window) is only 180K which is far colder than the actual temperature. How is this possible? The only way this can happen is if the surface emissivity is low. That means the emissivity of snow and ice in the thermal IR is nowhere near 1 as claimed by the warmists but is infact less than 0.5 which speaks against the claim of massive positive feeedback if the ice melts. I could go on, there is a huge amount of information that can be derived from this analysis.
Willis,
Does this maybe help?
IPCC AR4 refers to Ramaswamy [2001], which is IPCC TAR, and IPCC TAR states the following:
“IPCC (1990) and the SAR used a radiative forcing of 4.37 Wm-2 for a doubling of CO2 calculated with a simplified expression. Since then several studies, including some using GCMs (Mitchell and Johns, 1997; Ramaswamy and Chen, 1997b; Hansen et al., 1998), have calculated a lower radiative forcing due to CO2 (Pinnock et al., 1995; Roehl et al., 1995; Myhre and Stordal, 1997; Myhre et al., 1998b; Jain et al., 2000). The newer estimates of radiative forcing due to a doubling of CO2 are between 3.5 and 4.1 Wm-2 with the relevant species and various overlaps between greenhouse gases included. The lower forcing in the cited newer studies is due to an accounting of the stratospheric temperature adjustment which was not properly taken into account in the simplified expression used in IPCC (1990) and the SAR (Myhre et al., 1998b). In Myhre et al. (1998b) and Jain et al. (2000), the short-wave forcing due to CO2 is also included, an effect not taken into account in the SAR. The short-wave effect results in a negative forcing contribution for the surface-troposphere system owing to the extra absorption due to CO2 in the stratosphere; however, this effect is relatively small compared to the total radiative forcing (< 5%). The new best estimate based on the published results for the radiative forcing due to a doubling of CO2 is 3.7 Wm-2, which is a reduction of 15% compared to the SAR. "
http://www.grida.no/publications/other/ipcc_tar/?src=/climate/ipcc_tar/wg1/219.htm
J.
Roy Clark says:
August 18, 2011 at 9:34 pm
[,,,,]
Very interesting comment Roy. Willis will need to keep this thread focussed (good luck Willis), but your thesis deserves a thread of it’s own IMO.
I would consider it a safe assumption that the program in question is not designed to produce a scientific result but an engineering result within the operational parameters of the equipment it was developed to calibrate. Roughly equate that to “horseshoes and hand grenades.” The equipment being calibrated is purposed not to hit the nail on the head but to at least throw the hammer in the general range of the carpenter (the next technological solution in the chain of response).
Just like much of the “climate science” going on right now where people continue to stroke worthless data trying to curry information out of it, I think this “tool” is useless because it is being recalibrated using curried data.
Keep in mind, always, that when you use programs designed for laboratory conditions to attempt a replication of real world data in non-laboratory conditions you are simply generating a larger margin of error. No matter how much you compare your large error to someone else’s large error, they’re still both errors.
I wouldn’t rely on this program or the results it produces either to model or calibrate data because it doesn’t produce a result, it produces a fuzzy-operator for an active calculation system that relies on statistical floatation simply to find anti-noise. The entire system behind MODTRAN was developed to replicate a “predator reflex” in technological form and I sincerely doubt the program you are using has any comparatively useful level of the comprehensive functionality of the still classified versions.
The above typed, keep in mind that the purpose of the discussions here is to back-track into all the science and “science” that has gone into the current arguments for and against man made global climate change. We are here to nit-pick on individual details of the methodology and tools used by the global climate “community” and it is immaterial which side of the tracks you live on.
… The primary issue *I* have with this “model” software is that the earth is not flat and the sun doesn’t turn on and off above it. The production of any “per uniform dimention” data is useless to the furthering of this scientific endeavor for however long the IPCC studies and other papers continue to insist that the only variables are infra-red radiation and greenhouse effect media (gas, vapor, whatnot). This program isn’t designed to produce scientific results, it is designed to pick out a target from background radiation on a moment-to-moment basis.
Where did you get the 1850 285ppmv CO2 concentration from? Research back in 1850 from around Europe, UK, Italy and Germany, puts this level at 490ppmv using the chemical adsorption method used by some today.
Welcome to the world of toy models. The reason Willis isn’t getting the results he expected is because there are many different toys that all do the same thing. Not only do you have to use the same toys as the other guys you have use the same revision number toy and you have to have all the input parameters identical. It gets worse. In iterative calculations using floating point arithmetic you must also be using an FPU (Floating Point Unit) that rounds in exactly the same way. So you might get a different result between say an FPU in an IBM PowerPC FPU and an Intel FPU.
Count yourself lucky if you got an answer to a complex highly iterative mathmetical calculation that differed by only 20% from the answer someone else got when you took no pains at all to duplicate the environment and parameters. I’m surprised it was that close.
I want to see also surface temperatures generated by such tool. Then we can compare it with some real observations, like winter HadCRUT data in Arctic (70-90N).
http://climexp.knmi.nl/data/tsicrutem3_hadsst2_0-360E_70-90N_n_suseason.png
I am eagerly waiting to see the “greenhouse model” surface T in 1940s, compared with reality. Or the warming in 1910-1940. Or the stationary temperature trend between 1950-2000. Can’t wait.
I liked this bit
by
Charlie A says:
August 18, 2011 at 6:44 pm
a simple climate model (MAGICC)
Wow really? they used MAGICC?
now thats more likely the truth:-)
to approximately reproduce ( is that a sort of, maybe? kind of ? )results from the AOGCM multi-model dataset at PCMDI.”
3.7 W m-2 is a global average. What is Modtran calculating?
Per IPCC TAR global average vs a single vertical profile can cause errors on the order of 5-10%:
“Several previous studies of radiative forcing due to wellmixed
greenhouse gases have been performed using single,
mostly global mean, vertical profiles. Myhre and Stordal (1997)
investigated the effects of spatial and temporal averaging on the
globally and annually averaged radiative forcing due to the wellmixed
greenhouse gases. The use of a single global mean vertical
profile to represent the global domain, instead of the more
rigorous latitudinally varying profiles, can lead to errors of about
5 to 10%; errors arising due to the temporal averaging process are
much less (~1%).” p. 356 or 8/68 of http://www.grida.no/climate/ipcc_tar/wg1/pdf/TAR-06.pdf (1.4MB pdf)
The next page has some history on the value used by IPCC for the equivalent radiative forcing of doubling CO2. For something supposedly based on relatively straightforward physics, I’m surprised to see the value being changed by 15% between SAR and TAR, with a 3.5 to 4.1 W m-2 band for the estimates.
“6.3.1 Carbon Dioxide IPCC (1990) and the SAR used a radiative forcing of 4.37 Wm−2
for a doubling of CO2 calculated with a simplified expression.
Since then several studies,…. The newer estimates
of radiative forcing due to a doubling of CO2 are between 3.5 and
4.1 Wm−2 with the relevant species and various overlaps between
greenhouse gases included. The lower forcing in the cited newer
studies is due to an accounting of the stratospheric temperature
adjustment which was not properly taken into account in the
simplified expression used in IPCC (1990) and the SAR (Myhre
et al., 1998b). In Myhre et al. (1998b) and Jain et al. (2000), the
short-wave forcing due to CO2 is also included, an effect not
taken into account in the SAR. The short-wave effect results in a
negative forcing contribution for the surface-troposphere system
owing to the extra absorption due to CO2 in the stratosphere;
however, this effect is relatively small compared to the total
radiative forcing (< 5%).
The new best estimate based on the published results for the
radiative forcing due to a doubling of CO2 is 3.7 Wm−2, which is
a reduction of 15% compared to the SAR."
Willis,
First off, Modtran is a moderate resolution analysis and not the line by line result you assumed. That doesn’t mean it isn’t quite accurate because as you have noted, one pretty much sees a small linear change when you do something like double or half the amount of co2.
The number 3.7W/m^2 comes from looking down at the troposphere, around 12km rather than way high up in the low ionosphere at 70km. Apparently, the ipcc doesn’t realize that the atmosphere extends past the tropopause. Actually, I’m sure they do but as you noticed, the difference between the co2 value and double that decrease substantially as you go higher. Also, there are embarrassing questions that can arise once you find that the temperature rise to well above Earth’s surface temperature way up there.
You noticed also that the numbers differ with cloud cover versus clear sky. Water and ice are going to absorb and emit more like liquids and solids and not like water vapor. Absorption tends to be virtually independent of temperature while emissions of solids and liquids tend to be more like full blackbody spectrums – but at a lower T than the usual surface amounts. It’s a bit more complex than that as the size of the droplets are in the range of the wavelengths of absorption and emissions and there is also scattering that occurs and different clouds vary in top temperatures, altitudes, optical thickness, droplet sizes. Optically thick clouds are pretty much going to negate much of the effects of the molecular absorption below them so far as the spectrum goes. You will see that in the fact that the big absorption bands don’t go down to 0, but rather go down to a colder black body temperature curve – associated with the cloud top temperature.
Having played with a Hitran model made from line by line calculations, I’ve seen that the curves of h2o or co2 doublings or halvings are not truly linear and that they do vary from that as you go through multiple doublings or halvings. Eventually, your 3.7 W/m^2 tropopause absorption increase/decrease per doubling/halving drops down to half that value after 7 or 8 halvings. After all, the total effect of co2 is under 30 W/m^2 absorption under clear skies with typical h2o concentrations and it’s possible to do an practically an infinite number of halvings. This is do to the atmosphere becoming more transparent and optical absorption path lengths increasing as the concentration decreases.
As far as Hansen goes, he’s published BS in the past, things like assuming Stefan’s law applies to the Earth’s atmosphere and the effective altitude of radiating energy. Sorry, don’t recall the source – some paper in the 90s or late 80s. Concerning his modeling, I recall seeing a paper with Lacis and others where they came up with a pure assumption that water vapor increased with temperature yet cloud formation decreased. BTW, I think they used a detailed 1-D model with Modtran or maybe even Hitran for that one. They also mentioned that another equally valid assumption did not create a decrease in cloud cover with increasing temperature but they Chose the first – and that became gospel.
Since clouds have an immediate effect upon ground temperatures and with less clouds in the sky, the temperature tends to rise due to the increased incoming solar radiation, one can ignore the obvious causality and jump to the foolish conclusion that warmer temperatures and more h2o vapor cause less cloudiness – like the assumption that ENSO causes sunspot cycles.
I think you’ll find that the Modtran calculator is probably quite accurate for the circumstances that the calculations are run. The ipcc is probably using the tropopause looking down or worse, using some empirical formula dating back to the 1960s (Budyko). I think that Hansen has been smoking those funny mushrooms instead of eating them.
CO2 in troposphere is net absorber, in stratosphere CO2 is net emitter.That’s the reason, why
stratosphere is cooling.In stratosphere there is not very much radiation left between 13.4 microns and 16 microns so CO2 molecules cannot absorb very much radiation but there is enough kinetic energy to excite CO2 molecules.There should be stratospheric adjustment, if you are calculating ground temperatures at 70 km height.
George Smith mentions 40 W/m2 going space which Trenberth put in his (incorrect but much reported) heat balance papers. Over at Climate etc you will see a number of mentions of 66 W/m2 and it appears from a slide in a presentation to KNMI by( the late) Dr Noor Van Andel that Trenberth acknowledged that he knows it is 66 W/m2 (Is it scientific fraud to not correct or withdraw his papers?). Then putting in the proper heat transfer by convection and phase change (evaporation at liquid surfaces) which removes heat from the surface there is no need to consider radiant absoption by so called greenhouse gases. It is generally accepted the difference between the adiabatic lapse rate (9.8K/1000m) and the “environmental” lapse rate 6.5K/1000m is due to heat from water vapor. On top of this there is the convective heat transfer to oxygen and nitrogen at all surfaces. These more or less non IR radiating gases exchange heat do to mixing. CO2 will not absorb any radiation from its surrounds if it is the same temperature as the surrounds but at the top of the atmospher it will radiate to space
Modtran is only a model which does not consider other forms of heat transfer.
We are really relying on Hansen and Myhre and Manabe and Ramaswamy running these Modtran/Hitran LBL radiative transfer models properly. [Let alone the fact that we are not sure the models are truly representative of how radiation moves through the atmosphere. Let alone the fact that the first 3.7 Watt/m2 produces a different “temperature” response than the next 3.7 Watts/m2 and so on].
I have never seen it all explained properly anywhere – not even half.
Willis,
I played with MODTRAN about 2 years ago and I discovered a curious thing about it.
For example: if you fix the ground temperature offset at 0 and switch the “hold water vapor” option from “pressure” to “Rel. Hum.” the outgoing radiation for a predetermined setup doesn’t change.
When you set a positive value for the ground temperature offset, switching the “hold water vapor” option from “pressure” to “Rel. Hum.” you get a reduction of the outgoing radiation at the TOA, while setting a negative value for the temperature offset, you get an increase of the the outgoing radiation at the TOA instead.
Since the simulation ground temperature is 299.7K that is 26.5°C, which strange phenomena should happen to WV for that temperature?
I also never been able to establish which is the angle of the field of view of the simulated spectrometer at the TOA. From my point of view, this should be an important parameter because the outgoing emissions from the GHGs should exit the TOA with different angles than the black body radiation coming directly from the ground, and if the simulation has been made for a narrow angle around the nadir view, it could exclude a lot of that outgoing GHGs scattered radiation.
To understand what I mean you could read this pdf from CNR:
http://www.atmos-chem-phys-discuss.net/6/4061/2006/acpd-6-4061-2006-print.pdf
See figure 3 at page 4076, and note in the upper graph the radiation which flows tangential to the atmosphere at about 34km. Note also that its spectrum is the inverse of the radiation at the nadir and that’s obvious for me because this is the part of the radiation spread by the CO2. The more CO2, the more is higher that peak at abt 650cm-1 in that graph. The more CO2, the more energy exits the atmosphere not from the nadir (in that case it exits tangent to the atmosphere)
For this I believe that simulators such as MODTRAN should be used knowing the field of view they are simulating, otherwise while they are very good tools to estimate the effective temperature at ground measuring the outgoing radiation at TOA, they could be meaningless for estimating the effective outgoing radiation a the TOA.
I have read every comment so far. You guys are precious. Reminds me of the men folk sitting around the Dinner table talking tractor language.
“Hey Jeb, how ’bout that new fangled Harvester 735-hp30? Needs the new JD 4589-7blade to really work.”
“Jethrow you crazy. The JD 4589-7blade won’t work. You can only use the International YUT-8blade on the Harvester PTO”.
Please continue.
RE: Main Article
“First thing I noticed is that the lines are all straight. So MODTRAN does indeed show a linear relationship between logarithm of the CO2 increase and the calculated increase in absorption. So no surprise there.”
I have looked at this data over a wide range of CO2 levels, from zero to over 100,000 as a matter of curiosity. The linear log region runs from about 2 PPM CO2 to 792 PPM after that a gradual increase begins, which by 143,360 PPM CO2 yields temperatures about 4 deg K warmer than those predicted by the linear slope theory. As I can think of several reasons why the log relationship might fail at high concentrations of CO2, I cannot say that this is a ModTran quirk.
tallbloke says:
August 19, 2011 at 1:35 am
Roy Clark says:
August 18, 2011 at 9:34 pm
[,,,,]
Very interesting comment Roy. Willis will need to keep this thread focussed (good luck Willis), but your thesis deserves a thread of it’s own IMO.
====================
Exactly what I was thinking when I read Roy’s post.
Continuing Education units given to “climatologists” who read it.
*
Version is important, but scattering IS a photon absorption event, at the quantum level. GK
Cementafriend at 5.42am:
Really interesting point. Has it been discussed in the literature? There is also – as Kiehl & Trenberth (1997) made clear – large uncertainty in the figure they adopt for the wattage of ‘thermals’ (presumably heat transmitted to the air by conduction from the earth’s surface).
I don’t think Trenberth’s failure to update is fraudulent, although it may be poor science.
Typo corner: “These more or less non IR radiating gases exchange heat do to mixing.” I think ‘due’ is needed in place of ‘do’.
wow … model based science seems to be full of contradictions … oh wait … I seem to remember alot of science being done before computer models ever existed … maybe more obseravation and less models would be a more worthy exercise … and no I’m not accusing W. of too much reliance on models …
The online version is definitely one of the older ones. The more up to date versions are described at http://www.kirtland.af.mil/library/factsheets/factsheet.asp?id=7915, and handling the multiple scattering properly is one of the major upgrades.
That older version has known under and over estimates in various respects.
Hi Willis
As I have said before, you cannot “calculate” that which has never been tested. All these “fill in” programs are pure fraud so as to make you think that there are methods, that gave rise to measurements that gave rise to results…. But if you look for them (those methods), you find there are none. All you end up with (always) is the IPCC report.
I believe the original “test results” or values in W/m2 came from the observed global warming (originally 1750 was chosen as the start off date ) versus the increase of GHG’s seen in the atmosphere (since the start off date) where a proportionate allocation for the increase in each GHG was made depending on its increase. To a lesser agree I think they also compared the line by line analysis of each GHG to give a bit more or a bit less weight on the strength of a GHG but only in the areas of the spectrum where earth emits.
Which is of course why everything went wrong.
They did not even understand the “absorption” process correctly. When I made queries I found changes being made in the definition in wikipedia . Quite unbelievable. They also assumed there was no cooling effect by GHG’s.
http://www.letterdash.com/HenryP/the-greenhouse-effect-and-the-principle-of-re-radiation-11-Aug-2011
They had the horse completely behind the carriage. It is the worst mistake any scientist can make. You have assumed what the cause is of a problem before you actually determined it as the cause.
I believe that at some later stage they changed the 1750 date (to 1850?) which could help explain the differences you are getting now…. Obviously nobody is willing to admit to making any error, they had all tested it….
Didn’t they?
I want to thank you Willis for all you have done and said, it helped me a lot. I know I have come at the end of my own investigations. There is nothing more for me to figure out. I know now what is causing the extra warming besides the normal natural warming…. . And it is nothing to do with the CO2.
If you make a print of my tables here,
http://www.letterdash.com/HenryP/henrys-pool-table-on-global-warming
and really take some time to really study them you can easily figure it out for yourself
1) first the so-called ” global warming” is not global at all.
In the SH there is almost no warming. Clearly, you can see a big difference in the results between NH and SH?
But now, how can that be? We know from real science and experiments that the CO2 is distributed everywhere exactly the same. So, if the CO2 were to be blamed, should not the warming be the same everywhere in the world?
So, we conclude it never was the increase in GHG’s that caused any warming.
2) If you look in Argentina (where there was considerable de-forestation) you find severe cooling. If you look at Norway (where there is much increased forestry) you find warming.
3) the fact that SH has little landmass and that the NH has a lot of landmass is an another indicator that should give a clue.
4) we also know that there have been reports here on WUWT but also from the Helsinki university that there has been increased vegetation in the past decades, especially in the NH…..
…..wow. Did you all figure it out?
The warming is caused by us because we wanted more trees and a bigger garden…
Now what are we going to do about the so-called “global warming” problem?
Let us call it something else shall we?
I don’t have time to read all the refs on this. I’m guessing….
1D model? Any attempt to integrate different (re)-emission angles? That is, what is the mean free path length (obviously, a function of concentrations)? And the point made above that re-emission can be at different (longer) wavelengths is probably not considered.
Again guessing, it seems MODTRAN is based on a tool that might have been used to determine whether a high-altitude object could be imaged in IR from the ground. Once a photon is knocked off-course, it is lost. Using that logic, is re-emmission implicitly not allowed in MODTRAN? Is that approach accurate for atmospheric energy balance calculations? Doesn’t sound right to me.
With so many guesses, I must be wrong about a lot of this. Nevertheless, I’d like to echo the sentiment above. Toy models, don’t waste too much time on them.
Just for reference, my primary interest with Modtran was to get an indication of the *raw* CO2 concentration effect on transmission through the atmosphere. I am also assuming that this is under the condition of a fixed heat flow for any given concentration of CO2 as the greenhouse effect is based on a fixed amount of heat from the sun.
I see Willis is measuring the differential heat flow as the CO2 concentration is varied with fixed temperatures. The settings that show reduced sensitivity to CO2 relative to clear tropical air seem to indicate that CO2 is a lesser part the overall absorption of ground radiation in those cases. In other words, I suspect more of the CO2 absorption is being masked by other effects. This is why I have avoided these settings.
I have experimented with the sensor altitude which does seem to get problematic with settings below .05 km. If you reverse the direction of the sensor you get a calculation of the ‘back-radiation.’ All my measurements referenced here (above) were taken at the standard 70 km setting. That is in the mesosphere, nominally 50 km to 80 km. I understand this is that region of the atmosphere where the outward bound, 15-micron CO2 emission photons can finally escape into outer space.
steven mosher says:
August 19, 2011 at 12:03 am
Thanks, Mosh. While Google is indeed my friend, and told me lots of interesting things about the MODTRAN code (developed for the AIr Force, works well compared to other calculations), Google was unable to answer my question—why is the reported increase in absorption (instantaneous forcing) given by MODTRAN for CO2 doubling only about half of the Hansen/IPCC figures for instantaneous forcing?
Google wasn’t friendly enough for that …
w.
RE: Willis Eschenbach: (August 19, 2011 at 10:06 am)
“… my question—why is the reported increase in absorption (instantaneous forcing) given by MODTRAN for CO2 doubling only about half of the Hansen/IPCC figures for instantaneous forcing?”
I am afraid that might be a case of the devil being in the details. You will note that there are two options for dealing with a water vapor. Also ModTran is intended for use with real atmospheres. Hansen may be modeling an aggregate atmosphere. One way to increase the sensitivity to CO2 is make an assumption that reduces width of the open transmission zone. If Hansen provides emission plots similar to those returned by ModTran, it might be possible to make a detailed comparison between the two.
“”””” Brian W says:
August 18, 2011 at 11:53 pm
Willis Eschenbach
You sure are a slippery fellow, but since you ask . The current solar constant is stated as 1366w/m2 correct? My Passive Solar Energy book circa 1979 gives the solar constant as 429.2 btu’s/sq. ft./hr. This is equal to 1353.95w/m2, for a difference of 12w/m2 (rounded). “””””
The 1366 number is the one, I have used until quite recently; based on my eyeballing of almost three complete solar cycles of obsered data, unfortunately from several different satellites.
But I believe if you research the WUWT archives, you will find that quite recently; maybe the last few months even, NASA in fact issued a new preferred number; that is more like 1362 W/m^2, so that is the number I use now. When I learned about this stuff in school, the value in common use was 1353 W/m^2.
Where people get these 192 or 234 or other solar constant numbers form, I can’t imagine. When my wife turns on a stove hotplate so that it glows red, for the 3 1/2 minutes it takes to poach my egg, starting from cold water (plus egg); it is little comfort to me, that the average Temperature of that hot plate , is about 20-25 deg C. I still burn myself, if I touch it while it is poaching my egg.
Not surprisingly, the earth too reponds differently to the actual real incoming solar insolation, compared to what happens with just the annual average insolation. That’s why climate is the integral of the non-linear weather, and not the average of a presumed linear weather.
Roger knights:
The leaving out of forms of “to be” might just be some general semantics / e-prime mischief. I am seeing it happening quite often lately, even in some books.
Frank says:
August 19, 2011 at 12:05 am
Then what is the squiggly red line in the top right? AFAIK, it shows net absorption at every frequency … isn’t that an absorption spectrum? Yes, there is both absorption and emission at every level, but what we are looking for is the net absorption, which MODTRAN gives.
I understand all of that … but I don’t see that it makes a difference, and the cloud calculations are immaterial for what I am looking at, clear-sky conditions.
The IPCC usually talks about the top-of-atmosphere (TOA) forcing. They describe the TOA as:
In other words, say up 70 km or so, looking downwards. But they are often inconsistent in their usages. I do find the following:
which as you say they also use. That seems to me like the dumbest definition on the planet. To start with, the location of the tropopause varies around the planet. Second, they don’t give us a definition of the tropopause. It seems like they picked the hardest, most un-measurable quantity they can pick as their standard, so they can say anything they want about it and no-one can deny it because you can’t measure it … but that might just be my paranoia. However, picking a quantity that cannot be physically measured as your main gauge of change seems … well, I’ll just call it “suspicious” and leave it at that.
In the IPCC glossary, the tropopause is defined as:
That is a useless definition from a useless pack of wankers. The problem is that often there is no clear defined “boundary” between the troposphere and the stratosphere, so real scientists use another definition. They use a definition that involves the location of a specific temperature change. The WMO, for example, uses the following definition:
Nice and clear, can be measured quite accurately … whereas the IPCC “definition” is just mushy new-age junk.
You’d think that there’d be a clear boundary between troposphere and stratosphere, and in the tropics there often is. In the Arctic Summer, on the other hand, the “boundary” is often kilometres deep, a region where there is no vertical change in temperature. The MODTRAN shows no temperature change from 10 to 22 km altitude … so which one is the “tropopause”, 10 km or 22 km or somewhere between? The WMO definition tells us exactly … the IPCC definition tells us nothing.
The answer seems to be, in IPCC science the height of the tropopause is whatever you want it to be. In the previously cited Hansen paper, they show two different zonal estimates of the height of the tropopause, which they used in two different types of calculations (p. 5 lower right) … why not just one standard tropopause height? How can they use two different tropopause heights for two different calculations and still keep a straight face?
Ah, this is climate science, so one hesitates to speculate … however, let me redo my previous figures using what those clowns specify as the tropopause height. From Hansen’s figure, this would be about 100 hPa in the tropics, 200 hPa in the sub arctic, and 150 hPa in the mid-latitudes. Using those figures, I get from MODTRAN:
Tropical, CO2 doubling at 100 hPa = 4.5°C
Summer midlatitude, 150 hPa = 3.8°C
Winter midlatitude, 150 hPa = 2.5°C
Summer subarctic, 200 hPa = 3.0°C
Winter subarctic, 200 hPa = 1.8°C
So shifting to looking downwards from the tropopause gives us different answers … but the different answers don’t help a bit. The average of the MODTRAN numbers still isn’t anywhere near the 4.5 value of Hansen, or the 4.1 value from the IPCC.
I did find an article by Peter Dietz called “Estimation of the Radiative Forcing
for CO2 Doubling” on the late great John Daly’s old web site (ah, you are sorely missed, John). The article is here. He finds a much reduced forcing from the doubling of CO2. I would welcome comments on his analysis, I can follow his explanation but I can’t gauge the quality of his objections and claims.
Thanks for the citation, Frank. Indeed, that’s the recurring problem I have, either paywalled or kinda circular references. In this case, all Myhre does is propose a new constant for the amount of CO2 due to a doubling, 3.71 W/m2 per doubling instead of the old figure of 4.6 W/m2 per doubling. He doesn’t say either where he got the old constant, or whether they calculated the new one and if so how … science as done before the world woke up and asked the climate scientists to show their work.
w.
Just when I thought I was finished there is something to figure out again.
Perhaps the increased vegetation that caused the extra warming was in part also due to the increase in CO2. The circle is complete.
John Marshall says:
August 19, 2011 at 2:04 am
I get it from the ice core data. The man that collected the data you refer to, Beck admits that it is not usable for “background” CO2 levels. See my discussion of the issue here, in particular Figure 5.
w.
Fouse says:
August 19, 2011 at 5:37 am
Not sure what you mean here. At any level, CO2 both absorbs and emits radiation. If it consistently absorbed more than it emits, it would constantly warm, and it’s not doing that … so I’m not clear what you mean by “net absorber”.
w/
Pamela Gray says:
August 19, 2011 at 7:23 am
Oooh, I love it when good-looking women talk farming like that, makes my pulse race and my knees weak … please continue.
w.
steven mosher says:
August 19, 2011 at 12:03 am
GIYF
Possible meanings:
Given It’s Your Fault
Got It Yet Fool? (that’s the nice version)
Gallium Indium Yttrium Fluoride
Grampa Is Your Father (more common in Appalachia)
Goodness! It’s… Yes! Friday!!!!
Happy Friday.
Wills:
“Fouse says:
August 19, 2011 at 5:37 am
CO2 in troposphere is net absorber, in stratosphere CO2 is net emitter.
Not sure what you mean here. At any level, CO2 both absorbs and emits radiation. If it consistently absorbed more than it emits, it would constantly warm, and it’s not doing that … so I’m not clear what you mean by “net absorber”.”
Could he refer to the fact that the CO2 has a non-polarized molecule so that at rest when it is mixed with other GHGs such as WV is most probable it get photons and shares the energy with the surroundings molecules, then vice-versa?
In fact it needs three contemporaneous collisions to bend when it is at rest, while just two collisions are enough to share the “trapped” energy when it is already excited by an LW IR photon.
In fact at troposphere levels MODTRAN shows no emission in the middle of the 650cm-1 pit, the emission peak there rises at altitude levels where CO2 substantially remain the only GHG.
Has everyone (but me) seen this interesting blog? (Don’t walk away before reading the feedback and responses)
http://theendofthemystery.blogspot.com/2010/11/venus-no-greenhouse-effect.html
RE: Massimo PORZIO: (August 19, 2011 at 1:19 pm)
“CO2 in troposphere is net absorber, in stratosphere CO2 is net emitter.”
I believe what is being claimed is the concentration of CO2 in the stratosphere is so thin that it can emit radiation directly to outer space. I used to think that as well, but I have since found out that this only happens in the mesosphere, 50 to 85 km up.
Wikipedia: “Mesopause”
“The mesopause is the temperature minimum at the boundary between the mesosphere and the thermosphere atmospheric regions. Due to the lack of solar heating and very strong radiative cooling from carbon dioxide, the mesopause is the coldest place on Earth with temperatures as low as -100°C …”
“”””” Massimo PORZIO says:
August 19, 2011 at 1:19 pm
Wills:
“Fouse says:
August 19, 2011 at 5:37 am
CO2 in troposphere is net absorber, in stratosphere CO2 is net emitter.
Not sure what you mean here. At any level, CO2 both absorbs and emits radiation. If it consistently absorbed more than it emits, it would constantly warm, and it’s not doing that … so I’m not clear what you mean by “net absorber”.”
Could he refer to the fact that the CO2 has a non-polarized molecule so that at rest when it is mixed with other GHGs such as WV is most probable it get photons and shares the energy with the surroundings molecules, then vice-versa?
In fact it needs three contemporaneous collisions to bend when it is at rest, while just two collisions are enough to share the “trapped” energy when it is already excited by an LW IR photon. “””””
So if the CO2 molecule having a zero electric dipole moment, can be excited into the bending mode oscillation, by absorbing a 15 micron wavelength photon; which is about 85 meV; how much energy must be imparted to the resting CO2 molecule, in a collision with say an N2 molecule, that being the most likely collision candidate, for thermally exciting a resting CO2 molecule into re-emitting a 15 micron photon. At the lower altitudes, where we are assured lies the CO2 that is doing all of the absorbing, the mean time between collisions is much shorter, than the lifetime of the excited state, so that spontaneous re-emission is a rare occurrence, except in the stratosphere, where the mean collision interval gets to be longer than the radiative lifetime.
So what is the mean kinetic energy of a N2 molecule at an atmospheric Temperature of 288 K which is the current claimed value for the mean global Temperature. I’m sure some of you PhD Physicists out there, can work out that simple statistical mechanics problem, and tell us how likely it is for a CO2 molecule to gain enough energy thermally from a collision, to emit a 15 micron photon.
And if a CO2 molecule is thusly excited; what is the probability of it radiating, before it gets hit again by another N2 molecules, and perhaps robbed of iots extra energy ?
Fouse 5.37 am CO2 in troposphere is net absorber, in stratosphere CO2 is net emitter.
At 300 ppm the absorbance of the CO2 column is around 2000 abs, where 1 abs absorbs 90%, 2 abs absorbs 99% and so on. The abosrbance is so strong that it is safe to say, at all levels the 13.6-16 micron radiation is determined entirely by the ambient temperature at that level. While the temperature is decreasing with altitude (troposphere) the net 13.6-16 micron energy will be decreasing with increasing altitude. When the temperature is increasing with altitude the energy will be increasing with altitiude. I suspect that is what Fouse is referring to.
HOWEVER the Nimbus data from space shows a black body emission temperature to space at the CO2 line of 220K. The only place in the atmosphere that is so cold is the tropopause and that means this emission has to be coming from the tropopause. That in turn means there cannot be significant CO2 above the tropopause because if there were it would be absorbing the emission from the tropopause and in turn emiting to space at its black body temperature. Since the stratosphere is warmer than 220K the black body emission temperature would be higher than 220K.
The Nimbus data implies that the top of the CO2 column has to at the tropopause (or the lower stratospjhere which is at about the same temperature). That means the stratosphere is NOT well mixed with respect to CO2. In which case, Fouse’s point is moot.
I think the whole problem with any models is they concentrate on radiation. Surely every part of the atmosphere radiates ? Surely every part of the atmosphere heats up via contact with warm surfaces and convection carries this warm air upwards in a random fashion ? So to my way of thinking the radiation measurements aren’t coming solely from GHGs but the whole of the atmosphere – or am I wrong and do N2 and O2 have special properties that make them exempt from physics.
I simply do not believe the models are anywhere near right and the basic assumptions are too simplified We obviously do not know as much as the modellers seem to think or else their predictions might be even somewhere near observations.
I think absorbtion by a small proportion of the atmosphere serves to slow down the cooling after the sun sets – I doubt it will increase temperatures much if at all.
The sun on the other hand is obviously the main source of energy on earth and there are inconsistencies in what I read about the sun – several credible sources quote different values for the sun’s temperature with a variation of ~10%.
Every GHG document I have read seems to say the incoming insolation is short wave and the atmosphere is transparent to it but ~ 44 % is infrared and ~6% UV – so a significant component of insolation appears to be capable of absorbtion by the atmosphere.
Spector at 3:23.
Interetsing quote you give from Wikipedia however it is one I have considerable problem with. If CO2 is emitting strongly it is also absorbing strongly (emissivity equals absorptivity) and that means that the black body emission temperature as seen from space should be the temperature of the mesopause ie: 175K. But it is not, it is 220K – the temperature of the tropopause hence there is a slight problem.
Note also, any strongly emitting layer of gas will have an emissivity of 1 so the difference cannot be due to low emissivity. This is becuase if a gas layer emits strongly it also absorbs strongly and that in turn means that at the absorption wavelength it will look like a black body (something that absorbs all energy at that wavelength).
Oh, yeah, forgot to mention. The IPCC agrees with the Hansen estimate of about half a degree (Hansen, 0.4°) for the difference between Fi (instantaneous forcing as discussed here) and Fa (forcing after stratospheric adjustment). They say (page 11, bottom right)
This means that Hansen gives global all-sky Fi (at the tropopause) as 4.5W/m2 per doubling of CO2, and the IPCC estimates it at 4.2.
MODTRAN gives from 4.5 (tropics) to 1.8 (subarctic winter) as values for the clear-sky conditions. Assuming ((I can’t find specifics) that “subarctic” means 65°-45° N/S, that “Midlatitudes” means 45°-25°, and that “tropics” is the rest, the area-weighted average of the MODTRAN results is 3.5. This is already well below that of Hansen/IPCC. But it gets worse
Clouds reduce the effect of doubling CO2 in all regions. This is because some percentage of the total DLR is due to the clouds. In that situation, changing CO2 doesn’t matter as much, the DLR stays high due to the clouds whether the CO2 is present or not.
Add to that the fact that the world averages around 70% cloudy. That means the real effect of doubling CO2 will be much less than the clear-sky conditions. Merely adding cumulus drops the MODTRAN result from 3.5 to 2.8. That’s 0.7 W/m2 from just cumulus.
So I’m simply not feeling the love here. We have been assured that the 3.7°C per doubling sits on solid science. But so far, I’m not finding that science. And what science I do have access to, MODTRAN, gives me a much lower number than the Hansen/IPCC numbers. With clouds, and the half a watt adjustment from Fi to Fa, we’re down to an adjusted forcing Fa of 2.3 W/m2, compared to IPCC’s canonical figure for Fa (3.7 W/m2) and Hansen’s number (Fa = 4.1 W/m2).
So no matter how I slice it we’re still a long ways apart.
w.
As I mentioned yesterday, it is OK, but the elevation should be set to the tropopause not 70 km for the more traditional tropospheric forcing. The stratosphere cancels some forcing.
RE: michael hammer: (August 19, 2011 at 4:07 pm)
“…If CO2 is emitting strongly it is also absorbing strongly (emissivity equals absorptivity)…”
That is true, but at that high altitude, the CO2 molecules are so few and far apart that any photons that they emit may have almost a 50 percent chance of getting scot free into outer space without being absorbed another CO2 molecule. At -100°C, the energy of escaping CO2 photons must be balanced by that of the absorbed solar photons in the same time period. These photons come from a very thin slice on the far IR tail of the solar spectrum.
Setting the altitude to 16 km (tropopause) you get 4.5 W/m2 in MODTRAN. Solved.
Willis Eschenbach says:
August 18, 2011 at 11:17 pm
Does anyone have any actual information on this question?
============================================================
lol, Willis, I don’t. And, I’d usually pass on commenting that I don’t know something and then babble meaningless words. But, it seems in vogue to simply comment about a tangential issue or two on this thread. I think mostly because no one else knows, either. But, I didn’t want to miss out just in case this caused some type of euphoria or something. Even though, I’m wasting your time by you reading this tripe, there is a bright spot! I’m not sending you to another web site, pdf, or model that won’t tell you the answer either, as seems to be another “in vogue” thing to do. 🙂
But, knowing you Willis, you’ll keep at it until you find a reasonable explanation. I’d help, but I’ve other adventures of my own. Do share when you do find a reasonable explanation.
James
PS……. To any of those wondering……. no, no buzz, no euphoria….. not even pink clovers and green sky. 🙁
I think you want Figure 4 in the following paper, which compares a number of AR4 AOGCMs to line-by-line calculations for the top of the model, 200 mb (which is an approximation for the tropopause/TOA), and the surface: http://www.cgd.ucar.edu/cms/wcollins/papers/rtmip.pdf
The paper uses clear-sky assumptions, and does not include the stratospheric forcing adjustment, both of which would presumably reduce the total forcing at the TOA-approximation. A related paper which does look at cloud effects is http://cfmip.metoffice.com/iq.pdf – while it is actually most interested in including the tropospheric response to forcing, it does note on page 6 that all-sky forcing would be 4 to 14% smaller than clear-sky alone even for instantaneous measurements.
“It seems like they picked the hardest, most un-measurable quantity they can pick as their standard, so they can say anything they want about it and no-one can deny it because you can’t measure it … but that might just be my paranoia. ”
Yes. It is just your paranoia. They pick TOA because it is _physically relevant_: eg, it is the altitude at which forcing is most likely to be linearly related to surface temperatures. Yes, it makes life more complicated sometimes – the paper I’ve linked to uses 200 mb rather than the real tropopause because not all models produce tropopause-relevant calculations. Yes, the tropopause changes height between the tropics and the poles. Heck, the tropopause changes height due to the addition of GHGs. That doesn’t make the people who work with TOA forcing “wankers” or “clowns” just because they didn’t explain things clearly enough for you.
michael hammer says:
The Nimbus data implies that the top of the CO2 column has to [be] at the tropopause
Not really. Near the tropopause, the continuous CO2 spectra begins to look more like individual lines (due to changes in temperature and pressure). As a result, the wings become more transparent with increasing height. Since the resolution width of the Nimbus spectrometer is fairly broad, the fine structure is obscured (averaged out) and what is seen is mostly the energy released at the bottom of the tropopause. (The bottom is about -55°C, the top is about -70°C.) In addition, the energy emitted in the still opaque spikes are absorbed by the CO2 higher in the stratosphere.
The exception to this is the central peak which remains very strong (and broad) up to the stratopause. In fact, the disintegration of this central peak may be what “defines” the stratopause, since above this point, the atmosphere becomes transparent to CO2 emissions.
Above the stratopause, the atmosphere cools until there is no longer enough emission from the remaining CO2 molecules .. at the mesopause. Above that, the atmosphere warms to over 1,000C.
CO2 Absorption in the Stratosphere
At the tropopause level, I believe the CO2 band at 15 microns is still saturated, but the width of the saturated region is not as wide as at the surface. Even so, I would most of the typical CO2 emission spectrum is likely to be blocked.
I found a website that provides a graph showing the purported absorption of long-wave radiation by the seventh 3-km layer of the Earth’s atmosphere, from altitude 18 km to 21 km, just above the tropopause.
http://homeclimateanalysis.blogspot.com/2010/09/earths-tropopause.html
In the stratosphere, temperatures rise with increasing altitude until they reach a maximum at the stratopause (46-54 km). From that point up, a progressive cooling sets in. This may, loosely speaking, represent the altitude at which outward-bound emission photons from CO2 molecules begin escaping to outer space.
RE: ModTran: I note that the sensor altitude may be set as high as 100 km, 101 does not work.
Forcing
If ‘traditional forcing’ is measured at the tropopause level as Jim D says, then I assume this term was intended to designate the energy flow driving the troposphere as a function of temperature. As the troposphere is becoming thinner at higher latitudes, this may reduce some of the discrepancies between ModTran and Hansen’s results. At an earlier time, this forcing might have been given a name like ‘tropomotivation.’
Willis, spectra tools, like MODTRAN, assume a “pencil of radiation” (basically, a narrow beam) while climate models must integrate that over a horizon-to-horizon semi-sphere. I have not been able to derive the necessary equations, but several sources suggest that this effectively doubles the thickness of the gas column used in a 1D analysis.
Clemenzi at 10:57
Robert, I agree that at the line edges the absorbance is lower but I do not this this invalidates in any whay what I am getting at. Consider, at sea level 300 ppm the total absorbance of CO2 is about 2000 abs (Heinz Hug). If we assume the atmosphere is well mixed (which I question) then the amount of CO2 above any given altitude is simply given by the pressure at that altitude. So the total CO2 absorbance above 0.1 bqar (100 mBar) is simply 200 abs and so on.
Now 1 abs absorbs 90% of the incident light and thus has an absorptivity/emissivity of 0.9. For 2 abs the figure is 99% which is a reasonable approximation of a black body. Thus as a rough approximation we can say that only the last 2 abs of the atmospheric column can radiate to space. From paragraph 1 this means, for a well mixed atmopshere, the pressure at which that radiation will occur (at the line centre of course, the absorbance at the line edges will be significantly lower as you point out correctly) is at about 1 millibar. Now 1 millibar occurs at an altitude of about 50 km which corresponds to the stratopause. If the atmosphere was well mixed with respect to CO2 we should see an equivalent black body temperature at the line centre corresponding to the stratopause. This is about 270K or only about -3C. Clearly this is not observed.
Further, if we go back to the Wikipedia comment that significant CO2 emission is occuring from the mesopause, this is at an altitude of about 80km where the pressure is about 0.01 millibar. The absorbance of the CO2 column above that altitude would be about 0.02 abs at the line centre giving it an emissivity of around 0.02 at the line center reducing as one moves out to the line edges. This is not high enough to significantly affect the observed emission intensity.
I suspect the stratosphere is indeed very stratified and that the CO2 being so much heavier than N2 and O2, pools in the lower stratosphere where the temperature is very close to that of the tropopause.
Also, I think the CO2 line at around 14.5 microns is a single extremely pressure broadened line not a forest of close spaced lines (although admittedly I cannot swear to that).
RE: michael hammer: (August 20, 2011 at 12:29 am)
Also, I think the CO2 line at around 14.5 microns is a single extremely pressure broadened line not a forest of close spaced lines (although admittedly I cannot swear to that).
All you have to do to see this is check out the Savi-Weber HITRAN online utility that provides raw spectrum plots:
http://savi.weber.edu/hi_plot/
Select ‘CO2(Carbon Dioxide)’ [Next] select ‘hitran’ [select frequency] select plot by wavelength and enter minimum (14.5) , maximum (15.5) and hit [plot] for a more detailed view of the center region, enter minimum (14.9) , maximum (15.0) and hit [plot] . These lines represent possible quantum states of the molecule including rotation while it is also vibrating.
For those needing Web Acronym disambiguation:
http://www.gaarde.org/acronyms/
and
http://www.netlingo.com/acronyms.php
Or just read them for fun!
RE: Robert Clemenzi: (August 19, 2011 at 11:06 pm)
“Willis, spectra tools, like MODTRAN, assume a “pencil of radiation” (basically, a narrow beam) while climate models must integrate that over a horizon-to-horizon semi-sphere. I have not been able to derive the necessary equations, but several sources suggest that this effectively doubles the thickness of the gas column used in a 1D analysis.”
It sounds like you are saying that MODTRAN is assuming a narrow beam emitter (or a narrow beam receptor or both) as opposed to hemispherical emitter. ( I have observed that placing the sensor below about 0.05 km results in declining levels.) With the assumption of a uniform atmosphere and distribution of surface radiation, I assume that one could perform an integration of the total energy received over all paths as a function of the total direct path attenuation. If such a correction is not being made, then MODTRAN would not be producing accurate results. I can only imagine this being the case only if the system being tested by the Air Force did not ‘need to know’ the difference.
RE: Jim D: (August 19, 2011 at 8:12 pm)
“Setting the altitude to 16 km (tropopause) you get 4.5 W/m2 in MODTRAN. Solved.”
……
“2.2 Concept of Radiative Forcing…Ramaswamy et al. (2001) define it as ‘the change in net (down minus up) irradiance (solar plus longwave; in W m–2) at the tropopause after allowing for stratospheric temperatures to readjust to radiative equilibrium, but with surface and tropospheric temperatures and state held fixed at the unperturbed values’.
–‘Changes in Atmospheric Constituents and in Radiative Forcing,’ Forster and Ramaswamy, PP 133
Spector says
All you have to do to see this is check out the Savi-Weber HITRAN online utility that provides raw spectrum plots:
http://savi.weber.edu/hi_plot/
Please don’t! There is something very wrong with their plots. Use this instead
http://www.spectralcalc.com
Compare the absorption spectra. They are not even close.
Wouldn’t it make more sense to set the sensor altitude at “0” looking up, so that one can see the effective radiation at the surface?
When I do this I see very little if any effect on W/M2 from varying CO2 levels. There is however, a large effect if you change the Ground T offset. So, it seems likely that there is an assumption in the model that as you warm the air it will hold more water, which will increase the GHG effect.
So, unless CO2 warms the atmosphere, causing more H2O in the air, then CO2 has little effect.
Also, when I set the sensor altitude at 0km, looking up, then change the sky from clear to cloudy an interesting effect happens. The W/m2 INCREASES in a cloudy sky as compared to a clear sky.
This is an interesting result, because it implies a possible error in the understanding of GHG. When the sky is cloudy, solar radiation is blocked, but the water vapor in the clouds does radiate back to earth. However, what is the source of that radiation?
The radiation from the clouds is a direct result of the temperature of the clouds, which is a result of the solar radiation that went into evaporating the water from the oceans to create the clouds. Thus, when we count the back radiation from clouds, we need to subtract the energy used to evaporate the water to create the clouds from the energy budget, or we are double counting the radiation from the clouds, which would lead one to mistakenly conclude that we are in for catastrophic runaway heating if the temperature goes up even a little bit.
michael hammer says:
Consider, at sea level 300 ppm the total absorbance of CO2 is about 2000 abs (Heinz Hug).
Well, he used a fairly low resolution (2 cm-1) which reduced the central peak. Using 0.1 cm-1, the peak absorbance is 130,000. BTW many of the water vapor peaks are between 1 and 12 million.
I suggest that you use MODTRAN looking down, and change the height. The minimum CO2 readings are near 17km. As you move up, the central peak increases to a max near 53km (above the stratopause). Since the central peak is lower above 53km, there must still be a significant CO2 absorption above that point.
According to the references I’ve seen, the atmosphere (including CO2) is well mixed up to the mesopause. (Except for water vapor and ozone, of course.) Above that, it is not.
I think the CO2 line at around 14.5 microns is a single extremely pressure broadened line not a forest of close spaced lines
I have looked at the details of the central peak. There are indeed 20 or so strong individual lines (and many more weak ones) which merge into a single broad line at the surface.
Jim D says:
August 19, 2011 at 8:12 pm
Read the thread first. I discussed this some time before your post.
w.
ferd berple says:
The radiation from the clouds is a direct result of the temperature of the clouds
That is true at the tops of the clouds, but not at the bottoms. When the bottom of a cloud receives energy from the surface, it causes the cloud droplets to evaporate. When the “new vapor” moves up a little, it recondenses into a new droplet and emits the heat of vaporization. This physics allows cloud bottoms to effectively reflect the heat from the surface.
This explains why, on cloudy nights, an IR thermometer says that the surface and the cloud bottoms have the same temperature even though the clouds are actually 10°C cooler than the surface. It also explains how clouds keep the surface warm .. they simply reflect the heat back to the surface.
henry@ferd Berple
that was funny, that last comment.
I am also so amused with all these people thinking you can “calculate” that which has never been measured.
you should read this
http://www.letterdash.com/HenryP/the-greenhouse-effect-and-the-principle-of-re-radiation-11-Aug-2011
and this
http://wattsupwiththat.com/2011/08/16/new-paper-from-lindzen-and-choi-implies-that-the-models-are-exaggerating-climate-sensitivity/#comment-723928
and really laugh about the apparent crazy results from my simple observations…
Spector;
As pointed out above, the AF’s concern is to validate and localize a bogey, a target, using IR. It is not intended for “accurate” geophysics.
RE: Robert Clemenzi says: (August 20, 2011 at 10:57 am)
[Savi-Weber HITRAN Plots]
“Please don’t! There is something very wrong with their plots. Use this instead
http://www.spectralcalc.com
Compare the absorption spectra. They are not even close.”
Yes it does look like someone has messed up their data or introduced a mathematical grating effect into the line-plot program, Now that I have made the comparison; I do not recall it looking that bad in the past. Too bad it was a handy little tool.
Pamela: You got it almost right. You need to add, “… and these men folk sitting around the table jawin’ are not farmers, have never been on a a farm, and have never see a tractor in real life.”
Willis, there appears to be a significant disagreement concerning the MODTRAN plots. You have claimed
Then what is the squiggly red line in the top right? AFAIK, it shows net absorption at every frequency … isn’t that an absorption spectrum?
Several people (including myself) are certain that the spectrum looking down is an emission spectrum. You are convinced that it is an absorption spectrum. One side is wrong, and neither side is able to convince the other. I would like to better understand your analysis of this, perhaps I have misunderstood something.
RE: Robert Clemenzi says: (August 18, 2011 at 9:17 pm)
“In the image above, the CO2 absorption near 666 cm-1 is actually the CO2 emission from the -53C tropopause. This is a common error in interpreting that particular image. To be clear, at those frequencies CO2 is totally opaque. More than 95% of the energy from the surface is absorbed in the first kilometer. What is measured from space is emitted from much higher in the atmosphere. The spike in the middle of the CO2 band is emitted from the stratopause, at 47 km. (Get it, the cold part is from 11 km and the warm spike is from 47 km.)”
I note that the temperature of the region of the mesosphere where the sensor is placed, 70 km up, is about the same as the tropopause so that it might be easy to confuse local thermal radiation with that, which might be coming up all the way through the stratosphere from the tropopause without being absorbed. I note that if I set the sensor, still looking down, to 30 km, the bottom of the CO2 hole seems to get slightly deeper. If CO2 cannot cool the tropopause, we must assume that water vapor is likely to be the primary radiant coolant for that region.
I believe the spectrum looking up is the often thought to be mythical ‘back-radiation’ emission intensity spectrum. It still says ‘Intensity W/(m2 wavenumber)’ on the left. I suspect that solar radiation is not included.
Clemenzi at 11:37.
Robert, with the greatest respect, I have to point out that your explanation generates some interesting paradoxes. Your comments (and the claim of a well mixed atmosphere) would imply that emission at the CO2 line centre would indeed come from the mesopause since the absorbance is so high even the low level at the mesopause would have very significant emissivity. Thus the back body temperature at the line centre would be 175K. A bit further away from the line centre where the absorbance is lower the emission would be coming from the stratopause at 270K. A bit further away from the line centrre again it would be coming from down at the tropopause at 220K and then out in the wings it would be coming from progressively lower in the troposphere with a progressively rising black body temperature. Thus the central region of the absorption line should show a black body emission temperature going from 220k near the edge up to 270K fpor a considerable portion and then down in the middle to 175K. Thats one hell of a gull wing profile. Sure the interferometer on Nimbus may not have enough resolution to detail that but when one convolves a rapidly varying signal with a low pass filter the result is a very noisy spectrum. One can see that clearly in the region between about 16 and 25 microns where there are indeed closely spaced water bands and the Nimbus data shows an intermediate black body temperature with considerable noise. The wings of the CO2 peak in the Nimbus data also show considerable detail yet the central region of the CO2 absorption band is remarkably free of noise – a very clean smooth region with an apparent emission temperature of 220K.
Also according to your data most of that central peak should be from near the stratopause which is far warmer so how come the entire smooth central region shows a 220K black body temeprature? Something does not tie up with your rationale.
michael, you are referring to “Nimbus data” and the bulk of this article is on MODTRAN reconstructions. It would be nice to have a link to what you are seeing.
According to NASA, the Nimbus 3 and 4 FTIR instruments had nominal spectral resolutions of 5 and 1.4 cm-1, respectively. That alone may be enough to account for the differences since the lines are about 0.14 cm-1 apart. In addition, the Nimbus data may have been processed (smoothed) before being presented. There is no guarantee that you are seeing the raw data. (This is actually a common problem in all data, not just climate science. For instance, the Hubble images are highly processed before being made public.)
I agree that some of this does not tie up with [my] rationale. I am still trying to put it all together. Please, point out all the paradoxes, they will help us all to think about this in new ways. At this point, I have not seen anything that suggests that the weird shape you suggest is not the actual shape.
“”””” michael hammer says:
August 19, 2011 at 4:07 pm
Spector at 3:23.
Interesting quote you give from Wikipedia however it is one I have considerable problem with. If CO2 is emitting strongly it is also absorbing strongly (emissivity equals absorptivity) and that means that the black body emission temperature as seen from space should be the temperature of the mesopause ie: 175K. But it is not, it is 220K – the temperature of the tropopause hence there is a slight problem.
Note also, any strongly emitting layer of gas will have an emissivity of 1 so the difference cannot be due to low emissivity. This is because if a gas layer emits strongly it also absorbs strongly and that in turn means that at the absorption wavelength it will look like a black body (something that absorbs all energy at that wavelength). “””””
Actually a “black body absorbs ALL electromagnetic radiation at ALL wavelengths from down to but not including DC, up to and beyond the highest of the high energy gamma radiation, and anything that may be beyond that.
DC is excluded since by definition, NO variation of current aka, acceleration of electric charge can occur, so there can be NO EM radiation at DC.
And for the umteenth time, Kirchoff’s Law citing the absolute equality at any and all wavelengths of emissivity, and absorbance is ONLY true for a material that is in thermal equilibrium with an EM field of radiation; which of necessity has to be a closed system, which the earth’s atmosphere is not, and it most certainly is never in thermal equilibrium, since it is constantly assaulted by a highly varying assortment of EM radiation, from multiple sources, all of which have different Temperatures for their sources, and you cannot have thermal equilibrium and multiple Temperatures together at the same time, it flies in the face of the very definition of thermal equilibrium..
Does it occur to anyone reading here at WUWT, that ALL atomic or molecular line/band spectra of any kind, are prima facie evidence of non equilibrium (in the thermal sense). Resonance absorption or emission processes that are the cause of the very absorption bands that the GHG concept is all about, are all non equilibrium processes; they all involve finite lifetimes of the various excited states, and must terminate eventually.
Get over it; the greenhouse gas warming hypothesis has nothing whatsoever to do with Kirchioff’s Law.
Robert Clemenzi says:
August 20, 2011 at 1:25 pm
Thanks. I’m not sure what you mean by the two, Robert, nor what difference it might make. For me it’s like an argument about whether a ladder goes up or down.
Looking downwards from the tropopause, you see what makes it up from the ground through the atmosphere. If that amount goes down, it means that more is absorbed in the atmosphere. So I’m using it to measure the change in what is absorbed.
I don’t know what kind of spectrum it is. The issue is the change in the absorption, not what name you call the spectrum.
At least that’s how I see it.
w.
The concept is absorption lines when looking down, emission lines when looking up. It just means CO2 and other lines look dark against a bright background when looking down, bright on a dark background when looking up.
The IPCC AR4 says the 3.7 W/m2 number varies by 10% depending which radiative model you use, and some climate models have a 20% variation, so I would not take 3.7 W/m2 as gospel, just a mean of the radiation models.
Willis Eschenbach says:
The issue is the change in the absorption, not what name you call the spectrum.
To me, the issue is where the photons come from and what part greenhouse gases play. Only once the physics is understood can anyone begin to investigate what effect a change in CO2 might have. To be clear, between the surface and space, large parts of the IR spectrum are opaque. The way this opacity changes with altitude defines the thermal structure of the atmosphere.
Jim D says
I would not take 3.7 W/m2 as gospel, just a mean of the radiation models.
Henry@jim
So you agree that this “Modtran” is not based on a method that gave rise to measurements that gave rise to actual results?
I wonder – would also like to know how much the models are saying that the CO2 is cooling the atmosphere?
http://www.letterdash.com/HenryP/the-greenhouse-effect-and-the-principle-of-re-radiation-11-Aug-2011
Emission-Absorption
I believe the difference between the emission spectrum looking down near the surface with a sensor altitude of 0.05 km or greater and the emission spectrum of some higher altitude (subtrahend) would qualify as an absorption spectrum. That result divided by the product of the base value (minuend) times the altitude difference would yield the relative absorption per unit distance.
To actually do something like that, you would have to select the ‘save’ option before running the plot. Then you can ‘view the whole output file’ and copy it to your spreadsheet.
Clementi at 4:07 and Smith at 6:44
Let me say first, the red trace in the spectrum shown in the article is an EMISSION spectrum. It is the energy in watts/sqM which the satellite sees looking towards Earth. If it was an absorption spectrum it would be suggesting the absorption in the atmospheric window was high and the absorption at the CO2 line low. The exact opposite of the true situatioon of course. The smooth coloured curves are computations of Planks law for various temperatures assuming a black body wich means a body for which the emissivity is 1. If the emissivity is less than 1 the object will appear colder than it actually is.
Now in response to George Smith – sure a true black body has an emissivity of 1 at all wavelengths however it is perfectly reasonable to consider whether or not an object appears to be a black body at a cetain wavelength which is what I was referring to. Its only a short hand, if you have problems with that please substitute “a body with an emissivity of 1 at the wavelength of interest”. Your point that emissivity only equals absorptivity in equilibrium is simply not correct. Emissivity/absorptivity is a property of the object not of its temperature or the temperature of objects around it. What is true is that the amount of energy absorbed is only balanced by the amount of energy emitted when the object is in thermal equilibrium. That is a totally different proposition. It comes about because the amount of energy emitted depends on both emissivity and temperature whereas the amount of energy absorbed depends only on absorptivity and of course the amount of energy available for absorption. It is true that emissivity/absorptivity both can change with temperature, for example the emissivity/absorptivity of red hot steel can be quite different to cold steel but the two will still match at all temperatures.
Robert – I agree my use of the Nimbus data is probably a little unfair since I have not cited it. My excuse is that I have been doing some work on this recently along the lines of my comments and it occupies my mind. Unfortunately I don’t know how to post a diagram in this blog otherwsie I would send you the plot. I did get it off the web but unfortunately the site seems to have since been taken down. However lets instead look at the red curve in the subject of this thread which is in fact very close to the Nimbus data (except the spike in the middle of the CO2 absorption band was not there). This shows a largely flat bottomed absorption band for CO2 but with a spike in the middle. According to the scenario you were outlining, the absorption at the line centre is so strong that emission to space should be coming from the mesopause. In that case it should reflect 175K and be a downwards spike. Instead it is an upwards spike to a temperature of about 245K. This would be explicable if the band centre absorption was indeed high and corresponded to an emission altitude within the stratosphere but below the stratopause which is at around 270K . Indeed the Modtran plot clearly has enough resolution (judge by the detail in the water bands between 16 and 25 microns) to show up the gull wing pattern I mentioned earlier yet it is not there. This data suggests most of the CO2 is limited to the tropopause or below with a much lower concentration extending some way up into the stratosphere but not to the stratopause. This is entirely compatible with a poorly mixed stratosphere.
If I put sensor altitude to 20 km in Modtran, there is no extra peak around 667 wavenumber..
At 70 km height there is, so CO2 must be net emitter at the stratosphere.From the troposphere there are not coming many 15 micron photons into the stratosphere.You don’t need photons from the troposphere to excite CO2 molecules.There is enough thermal energy in the stratosphere, that collisions between molecules excite CO2 molecules and after that releases photons.That’s why the upper stratosphere is cooling with increasing CO2.
RE Spector: (August 21, 2011 at 12:34 am)
Correction of previous post:
For “That result divided by the product of the base value (minuend) times the altitude difference would yield the relative absorption per unit distance.”
Replace with “That result divided by the base value (minuend) would yield the relative absorption over that altitude range.”
RE: michael hammer: (August 21, 2011 at 3:13 am)
“… This data suggests most of the CO2 is limited to the tropopause or below with a much lower concentration extending some way up into the stratosphere but not to the stratopause. This is entirely compatible with a poorly mixed stratosphere.”
I am not sure that this applies to the above, but the lower square in the MODTRAN tool output seems to show the assumed variation of temperature, pressure, and concentrations of the ‘greenhouse’ gases with altitude. If anyone knows these to be unrealistic then that could invalidate the results of the tool.
Here is a method to use MODTRANS that appears to work at top of atmosphere.
1. Start with defaults
2. enter current CO2 levels – say 390 ppm
3. Submit
4 – result is 287.687 W @ 299.70 K
5. Double the CO2 to 780 ppm
6. Submit – result is 284.484 W @ 299.70 K
The model is now out of balance as our W have gone down. This is because CO2 is blocking radiation from the surface. But over time W cannot go down as as energy in must equal energy out. So, we must adjust the Ground T offset.
7. Change the Ground T offset to 0.9
8. Submit
9. – result is 287.687 W @ 300.60K
Our model is now in balance. Our energy out balances the original energy in. What this tells me is that a doubling of CO2, clear sky in the tropics, will raise temperatures by 0.9C. The top of atmosphere radiation must remain unchanged, as the energy from the sun is unchanged.
If we repeat this for the US standard atmosphere, and balance th model for energy in = energy out, clear sky we get at TOA:
390 ppm CO2 – 258.673W @ 288.2K – Ground T offset 0
780 ppm CO2 – 258.673W @ 289.07K – Ground T offset 0.87
So, the predicted increase in temperature is 0.87C for the US standard atmosphere for a doubling of CO2, which is not very different than the 0.9C predicted for the tropics.
When we repeat the above using 1976 US Standard atmosphere with 12.5mm/hr rain at 390 ppm CO2 we get the following:
250.98W @ 288.2K – Ground T offset 0
When we balance the model with 780ppm CO2 we get:
250.98W @ 289.03K – Ground offset 0.825
This is slightly less than our clear sky result, which says that we will get a slightly smaller temperature increase from a doubling of CO2 if it is raining.
Repeating this in the subarctic summer, clear sky I get
390ppm CO2 – 261.75W @ 287.20K
780ppm CO2 – 261.75W @ 287.92K – Ground T offset 0.72
Repeating this in the subarctic winter, clear sky I get
390ppm CO2 – 196.564W @ 257.20K
780ppm CO2 – 196.564W @ 257.84K – Ground T offset 0.64
This tells me that the 0.9C temperature increase predicted for the clear sky tropical atmosphere model is likely the worst case situation, as the predicted increase appears less in the other situations tested.
Fouse, your result is a consequence of the air getting warmer with height as you get higher in the stratosphere.
HenryP, radiative models are based on measurements of absorption lines, and theories about how these change with concentration, pressure and temperature. The theories are accurate but can’t be globally perfect everywhere, and to do this you are averaging a wide range of soundings globally.
George E. Smith wrote: And for the umteenth time, Kirchoff’s Law citing the absolute equality at any and all wavelengths of emissivity, and absorbance is ONLY true for a material that is in thermal equilibrium with an EM field of radiation; which of necessity has to be a closed system, which the earth’s atmosphere is not, and it most certainly is never in thermal equilibrium, since it is constantly assaulted by a highly varying assortment of EM radiation, from multiple sources, all of which have different Temperatures for their sources, and you cannot have thermal equilibrium and multiple Temperatures together at the same time, it flies in the face of the very definition of thermal equilibrium..
Does it occur to anyone reading here at WUWT, that ALL atomic or molecular line/band spectra of any kind, are prima facie evidence of non equilibrium (in the thermal sense). Resonance absorption or emission processes that are the cause of the very absorption bands that the GHG concept is all about, are all non equilibrium processes; they all involve finite lifetimes of the various excited states, and must terminate eventually.
I am glad that you emphasized the non-equilibrium thermodynamics.
I have a question for everyone. I have not yet found where I can read about this. The Earth surface radiates energy that is absorbed by GHG molecules. Those molecules re-transmit the energy in two ways: (a) by re-radiating in their characteristic abosrption/emission spectra; (b) by collisions with other molecules. Of all the radiant energy absorbed by the GHG molecules collectively, what fraction is re-radiated, and what fraction is transmitted via collisions? How much does this fraction vary by altitude and pressure?
Henry@Ferd, JimD, Mathew & others
I think you still don’t understand how the CO2 is cooling the atmosphere.
If you understand the principle of absorption and re-radiation
(which is often totally misunderstood)
then you will know and understand why Modtran is just impossible.
(hint: you cannot look at only the part of the spectrum of a molecule where earth emits predominantly – you have to compare the (deflected) incoming SW versus the outgoing back radiated LW and then you have to give me the difference of those two somehow worked out in W/m2)
……it is impossible?
Do take some time to look at the reference paper in the footnote here and you will figure out how re-radiation caused by the CO2 works:
http://www.letterdash.com/HenryP/the-greenhouse-effect-and-the-principle-of-re-radiation-11-Aug-2011
RE:ferd berple: (August 21, 2011 at 7:58 am)
“Here is a method to use MODTRANS that appears to work at top of atmosphere.”
I have used it in the past with the clear tropical air setting to find what temperature it says, with any given CO2 concentration, is required to provide, 70 km up, an energy flow of 292.993 W/m2 . This energy flow number was based on my estimate of the solar constant averaged over the surface of the Earth, the albedo of the moon, and it being one of those discrete values that the program was willing to return. My intent was to get an indication of the *raw* (no feedbacks) effect of CO2 concentration on the temperature of the earth. In the CO2 concentration range we have now, it is predicting a raw tangent slope on the order of 0.9 deg C per doubling.
The program gives answers over a wide range of CO2 concentrations, including zero, but Willis and others have raised good questions about the basic validity of the tool, especially when used outside of the scope of its intended use by the Air Force.
Spector says:
August 21, 2011 at 12:05 pm
0.9C was the worst case no feedback increase I found for a doubling of CO2.
I have some real doubts that it works the way mainstream climate science suggests, otherwise we should be able to focus the DLR to heat an object, not just slow the rate of cooling.
What I’d like to see is a real world experiment with a control to actually show that DLR effects the rate of cooling. I’ve seen one sided models, but without a control they don’t really show anything.
We know that glass for example reflects LR (Greenhouses). So it should be possible to set up an experiment with two identical objects sitting outside at nighttime, and affect the cooling rate of one as compared to the other by reflecting the DLR onto one of the objects. By positioning the glass equal distance from both objects, this should balance out any LR from the glass itself, so the only difference should be reflected DLR.
So far I’ve not seen anyone conduct any such experiment that has shown any reduction in cooling as compared to the control. Has anyone?
Until and unless this can be done then the notion that the colder atmosphere can reduce the cooling rate of the warmer surface has not been demonstrated outside of theory. It may be true, it may not, but it remains unproven and unverified. As such, it is a huge leap of faith to base the future of our economy on an unproven and unverified theory. It could make Stalin and Pol Pot look like saints in comparison.
Willis Eschenbach says:
August 19, 2011 at 4:17 pm
MODTRAN gives from 4.5 (tropics) to 1.8 (subarctic winter) as values for the clear-sky conditions.
I’ve shown a method above where MODTRAN gives 0.9C tropics to 0.64C subarctic winter, for a doubling of CO2, with clouds further reducing this.
Personally I’d like to see an experiment with a control that demonstrates that DLR from the night sky can slow the rate of cooling of a warmer object. The theoretical hand waving reminds me of arguments over how many angels can fit on the head of a pin. No matter how plausible the theory sounds, that doesn’t mean it will hold true in reality. If there is one constant in science, it is that nature continues to surprise us in unexpected way.
michael, This 1974 Nimbus-4 satellite spectra (reference on next page) shows a central CO2 peak. Perhaps the image you were using was filtered (common when comparing high resolution data with older low resolution instruments). It is unfortunate that the MODTRAN algorithms are hidden behind NDAs (non-disclosure agreements). As a result, nothing in those plots can be trusted.
It is my understanding that atmosphere samples have been collected up to the mesopause and returned for analysis. In addition, in situ analysis has been done. As a result, I am willing to accept that CO2 is well mixed up to the mesopause. I understand that the spectra would be easier to understand if this was not true.
As for resolution, the latest version of MODTRAN provides a max of 0.2 cm-1. (The older ones used 20 cm-1 or 2 cm-1.) The plot above has no where near that much (and there is no indication of which version, or resolution, was used). Since the lines in question are about 0.08 cm-1 apart, even the 0.2 cm-1 is not enough. I agree with your analysis, but have been unable to write a program to analyze the mesosphere – the Doppler line broadening formula does not work (is wrong, fails dimensional analysis when using HITRAN data).
The anomaly that bothers me is water vapor near 500 cm-1 (looking down from 70km) – it is too hot and too continuous. I assume that this energy is coming from the troposphere.
BTM, you might be able to find the image you were using at the wayback machine.
HenryP, the amount of CO2 absorption is very small, and leads to atmospheric warming anyway, not cooling. H2O has a much bigger effect of this sort.
ferd berple says:
the notion that the colder atmosphere can reduce the cooling rate of the warmer surface has not been demonstrated
Everyone should know that almost every night the surface is much cooler than the atmosphere above it. Thus, a warm atmosphere is warming a cold surface. At the poles, this temperature inversion lasts for 6 months.
I’d like to see is a real world experiment with a control to actually show that DLR effects the rate of cooling.
Try 2 coolers covered with sheets of glass. Cover one of the sheets with ice to block the DLR. There will be an obvious difference between temperatures inside the coolers. Using liquid nitrogen should make an even bigger difference. There are many similar experiments. For instance, covering a pot of water allows it to boil quicker than not covering it.
Remember, space is about 4K. Therefore, anything warmer than 4K (such as an atmosphere) will make the surface warmer – even if the intervening substance is colder than the surface.
RE: ferd berple says: (August 21, 2011 at 2:09 pm)
“0.9C was the worst case no feedback increase I found for a doubling of CO2.”
I admit that I did not explore the other surface options because I wanted to get a basic or pristine result. I did not consider the other settings to be relevant to my purpose.
I ran what might be called a ‘constant current’ or more exactly a constant energy flow analysis even though the MODTRAN utility was not set up to do that. This meant a laborious hunt and pick method for each CO2 concentration level to find the temperature required to produce 292.993 W/m2 energy flow out at the top of the atmosphere to balance the assumed constant global solar input. Yes, this assumes that the solar input energy absorbed is independent of the CO2 concentration and ground temperature–no cloud feedback effect. I do not claim my results to be any more than a rough indication.
RE: Robert Clemenzi: (August 21, 2011 at 2:24 pm)
“The plot above has no where near that much (and there is no indication of which version, or resolution, was used).”
You can get those details if you select “save text” before the run then “View the whole output file” after the results come back.
Thanks Spector, based on that, the resolution is 2.0 cm-1.
Jim says
http://wattsupwiththat.com/2011/08/18/odtran-moddities/#comment-724825
You lost the plot.
The absorption of CO2 around 2 and 4-5 um is big and is the cause for considerable deflection of sunlight. The 4-5 absorption alon is almost as big as the 14-15 um absorption.
Hence they can (even) measure it (i.e. the re-radiation) as it bounces back from the moon.
So without the CO2 in the air, there would be even more IR coming down on my head here.
Do take some time to look at the reference paper (blue print) in the footnote here and you will figure out how re-radiation caused by the CO2 works:
http://www.letterdash.com/HenryP/the-greenhouse-effect-and-the-principle-of-re-radiation-11-Aug-2011
MODTRAN Output File Application
I note that if I use the “View the whole output file” to copy the results to spreadsheet and then perform a subtraction of the ‘looking up’ from the ‘looking down’ data at the tropical tropopause level (18 km up), the result only shows a complete cancellation around the 15 micron (670 cm-1) CO2 emission band and nowhere else. I take this to mean that the radiation window to outer space is almost wide open at that altitude. This is not true at near ground level (.05 km). Note that the tool-provided wave number plot scale, which is equivalent to frequency, is best for performing energy integrations.
The data used for the plots shows up at the bottom of the file under the heading of “Total” just between “Reflected” and Radiance.” For those unfamiliar with the term, the tropopause is the coldest point in the lower atmosphere and might be thought of as the nominal ‘top of convection altitude;’ it is just under the stratosphere.
Note, for example, that both water vapor and oxygen/ozone also absorb in the 14-15 region. Modtran is just an elaborate fraud to let you think that the “science is settled”
But the real truth is: more carbon dioxide is better.
http://www.letterdash.com/HenryP/more-carbon-dioxide-is-ok-ok
HenryP says: (August 22, 2011 at 12:45 pm)
“Modtran is just an elaborate fraud to let you think that the ‘science is settled'”
Actually, MODTRAN seems to be indicating CO2 is a minor issue; at the tropopause altitude, it is an approximate 90 wave-number wide hole in the middle of a 900 wave-number wide stream .
ODTRAN Moddities++
It has been my understanding that the energy observed with the sensor looking down (energy flowing up) minus the energy observed with the sensor looking up (energy flowing down, i.e. back-radiation) should be the net energy moving out. However when I do this in one case, I get something like the following:
MODTRAN appears to be telling us that most of the radiant energy escaping from the Earth originates not from the surface, but the lower seven kilometers of the atmosphere. Either that or the energy seen looking up is about 2.6 times what it should be. That is the back-flow divisor required to approximate a constant flow out from the surface.
A few more ‘Moddities, Altitude=0 km, conditions above (August 23, 2011 at 11:11 pm)
except:
A. All greenhouse gases except CO2 set to zero:
Looking down: 427.668 W/m2
Looking up: 123.999 W/m2
Flowing out: 303.669 W/m2
99 Km out: 364.554 W/m2
B. All greenhouse gases set to zero:
Looking down: 427.668 W/m2
Looking up: 49.298 W/m2
Flowing out: 378.370 W/m2
99 Km out: 408.200 W/m2
Spector, that makes no sense. Using the “Tropical atmosphere” and T-Offset=2.2
427.668 W/m2 and 301.9K implies 90.7% emissivity.
However, the “real” IR emissivity should be 98% or better.
At 100% emissivity, 301.9K should produce 471.02 W/m2
at 98%, 461.6 W/m2
The following is from the bottom of the data file
BOUNDARY TEMPERATURE = 301.90 K
BOUNDARY EMISSIVITY = 0.980
Every time I look at MODTRAN, there seems to be something else that I don’t understand.
This table of emissivities indicates that perhaps 95% might be better.
RE: Robert Clemenzi says: (August 26, 2011 at 9:45 pm)
“Spector, that makes no sense. Using the “Tropical atmosphere” and T-Offset=2.2
“427.668 W/m2 and 301.9K implies 90.7% emissivity.
However, the “real” IR emissivity should be 98% or better.”
I have also noticed that the maximum output tends to be at 0.05 km and declines at lower altitudes. Given that this was an Air Force test program, I wonder if these might be custom provisions for non mission-critical quirks in the intended application system. It is interesting to note that the plot with all greenhouse gases set to zero (including the Water Vapor Scale) seems to show a ghost of the upper-air CO2 pattern when looking up from 0 km.
I assume that the indication that most of the Earth’s radiation to outer space comes not from the surface, but largely from the atmosphere—and that primarily from water vapor in the troposphere—is more or less correct, as this is just the ticket to allow descending air to overwhelm the 9.8 degree C / km adiabatic heating as it returns to the surface.
RE: Robert Clemenzi says: (August 26, 2011 at 9:45 pm)
MODTRAN Surface Emissivity Anomaly
Robert, after looking over the data returned for a while, it appears to me that the emissivity anomaly that you have noticed is most likely due to the limited range of integration used. Based on the output file, that only runs from wave number (cycles per centimeter) 100 to 1500. (This is equivalent to a wavelength range of 100 down to 6.667 microns.) At these limits, the standard Planck’s Law radiation curve has reduced the emitted power to about 12.5 or 20 percent of the peak value.
Henry@spector&more
Try first to understand how an why re-radiation works before you start doing any calculations….
You have to show me the cooling rate as well as any warming.
http://www.letterdash.com/HenryP/the-greenhouse-effect-and-the-principle-of-re-radiation-11-Aug-2011
Thank Spector, good catch.
RE: HenryP: (August 29, 2011 at 12:00 pm)
“You have to show me the cooling rate as well as any warming.”
Henry, with the MODTRAN tool sensor altitude set to 99 km, looking down and with your preferred abundance of CO2 and temperature offset (and, any other setting you wish to change), the ‘Model Output’ will show you how much power (Io W/m2) is leaving (or cooling) the Earth, at least over the wave number range of 100 to 1500 cycles per centimeter. BTW, the nominal 15-micron CO2 wavelength is at about 667 cycles per centimeter.
For lower altitudes, you normally have to subtract the energy coming back down (sensor looking up) from the energy coming up from below (sensor looking down–which should be larger) to obtain the net cooling energy that is getting out from that altitude. In my August 23 table, that is the last column on the right, showing the net cooling upward irradiance that is not being returned.
Note: I suspect that this program (MODTRAN) presumes an atmosphere with its heat content established by normal convective activity–that, even if clear conditions are specified. Otherwise, I cannot see how it could show more heat being radiated from the atmosphere than that leaving the Earth from the ground.
This tool does not show warming per se; it only shows how terrestrial radiant cooling is hindered or facilitated by the greenhouse gases in the atmosphere. Remember that this is a program created by man–it has limitations.
But Spector,
the SW being deflected and the LW being trapped in the manner as described by me in the quoted link, is a soup coming from the various components. Note that water vapor (0.5%) and oxygen-ozone (21%) also absorbs at 14-15 um. There is no way you can un-entangle the 0.04% of the CO2 out of this mess.
Do you understand the principle of re-radiation?
The re-radiation of earthshine or sunlight (in the areas where the molecules have absorption) happens at all levels.
then you say
it only shows how terrestrial radiant cooling is hindered or facilitated by the greenhouse gases in the atmosphere. Remember that this is a program created by man–it has limitations.
That would exactly exclude the warming that is hindered by the same substances by deflected light from the sun 0-5 um. In fact here, if you have read my footnote in the link that I referred you to , we can identify some of the absorptions from the CO2 as being quite unique. As far as the 4-5 um absorption of the CO2 is concerned, here we have water vapor also with absorption. So again, standing here in African sun, it will be difficult to determine out how much less IR (2 & 4-5um) is on my head because of the increase in CO2 above my head.
the conclusion is that we do not know what the net effect is of the increase in CO2 in the atmosphere as far as the cooling and warming is concerned.
http://www.letterdash.com/HenryP/the-greenhouse-effect-and-the-principle-of-re-radiation-11-Aug-2011
You understand what I am saying? You cannot do any “calculations” without taking into account the whole spectrum 0-20 um. Remember that the cooling by CO2 (at 0-5 um) by deflection of sunlight happens 12 hours a day while the entrapment of earthshine happens 24 hours per day.
Thus, I know that Modtran is a fraud. At best maybe a dinky toy. The problem with this toy is that many people think that the answers it gives are true….
RE: HenryP: (August 29, 2011 at 11:14 pm)
That would exactly exclude the warming that is hindered by the same substances by deflected light from the sun 0-5 um.
Yes, Henry that is all true. This program is at best a raw indication of a part of the issue. It does not show the effects of any solar or short wave terrestrial radiation (wave numbers greater than 1500 cycles per centimeter) or include controversial feedback effects. It only shows those IR radiation levels over the 100 to 1500 wave number band that Air Force (USAF) scientists expected to detect with their equipment while flying at various altitudes, weather, and locations. It does seem to indicate that water vapor is the primary cooling (and heat retention) agent of the lower atmosphere.
Henry@Spector
In that case you are also one of only a few people who actually do really understand the principle of re-radiation i.e.
62.5% back-radiated in the direction where the radiation came from (in a radius of 180 degrees)
37.5% radiated in the other 180 degrees
which explains what I see is happening around me and which is supported by my own observations.
Do you understand why that is so?
RE: HenryP: (August 30, 2011 at 11:28 am)
Henry@Spector
Henry, most of what you see is scattered optical radiation. For radiant heat transfer, the case is different.
Imagine that you are standing between two large non-reflecting walls. You point your IR irradiance meter at one and get a power reading of 300 watts per square meter. Then you point it at the other and also get 300 watts per square meter. We assume these walls are so large that virtually all the energy emitted by one is absorbed by the other. In this case, there is no net energy flow. It is like two people with a pointless agreement to pay each other $300 every month.
On the other hand, suppose you only get a reading of 200 watts per square meter emerging from the second wall. That would mean that it was accepting power at a rate of 100 watts per square meter from the first wall. In the MODTRAN case, with both ‘walls’ at the same altitude, there is no place for the heat energy to go from one but to the other ‘wall.’ That is why I say:
[W/m2 getting out] = [sensor looking down] – [sensor looking up]
You should be able to use this relationship to see just where MODTRAN thinks most of the radiant cooling is happening.
Radiative forcing is typically defined at the tropopause. Here’s an older IPCC definition:
” the change in net (down minus up) irradiance (solar plus long-wave; in Wm-2) at the tropopause AFTER allowing for stratospheric temperatures to readjust to radiative equilibrium, but with surface and tropospheric temperatures and state held fixed at the unperturbed values.[2] 2″
NET Irradiance going UP through the tropopause (~10 km) in the US standard atmosphere you get:
375 ppm = 269.569 – 30.546 = 239.023
750 ppm = 266.335 – 32.436 = 233.899
Change in NET UPGOING radiation is a loss of 5.1 W m-2, significantly higher than the IPCC global average of 3.7 W m-2.
I suspect that 3.7 W m-2 is a better representation, since cloudiness, surface temperatures etc change and I’m pretty sure that ModTran does not allow stratospheric relaxation, whilst the models used by the IPCC did do this.
RE: Matter: (September 12, 2011 at 8:44 am)
“Radiative forcing is typically defined at the tropopause.”
I believe that is correct, but it is interesting that this tends to maximize the impact of CO2 as an absorber because CO2 is radiative emissions to outer space occur primarily above the mid stratosphere.
I believe that MODTRAN is not a climate-modeling program per se, but a program developed by the U.S. Air Force to predict ambient infrared radiation levels that might be observed by aircraft flying in the atmosphere both looking down and also looking up. I believe the radiation seen looking up is only trapped terrestrial radiation at flight level. No solar radiation is included.
It’s results are limited to integrals calculated over the wavenumber range of 100 to 1500 cycles per centimeter (officially 100 to 1500 kayzers) which is equivalent to a wavelength range of 100 microns down to 6.67 microns. As noted above, this limitation does cause about an eight percent integration error, which might have been reduced by extending the integration limit up to 2500 kayzers. (4 microns)
I believe the IPPC values, as you say, are based on additional assumptions about the climate and MODTRAN only yields a raw effect. In tropical clear air, it seems to yield a raw slope of about 0.89 deg C per doubling with Io forced constant. I do not know how qualified this program is for atmospheres with abnormal CO2 concentrations.