Update: see further discussion here
NOAA has a webpage on radiative forcing here, which includes a list of equations relating GHG concentrations to radiative forcing, substantially identical to the expressions in TAR.
Below is a figure showing, on the left, the graphic at NOAA illustrating their calculation and, on the right, my emulation of this graphic from original GHG concentration data using the radiative forcing equations summarized at NOAA – so I’ve obviously got this calculation down pretty well. My text for generating this graphic is online here http://data.climateaudit.org/scripts/forcing/forcing.noaa_graphic.txt.
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The calculation uses my collation of GISS GHG concentration data which I’ve posted up at http://data.climateaudit.org/data/hansen/giss_ghg.2007.dat . I’ve done my own collation because the GISS information is maintained (messily) in several different files:
1850-2000 from http://data.giss.nasa.gov/modelforce/ghgases/GHGs.1850-2000.txt
2001-2004 from http://data.giss.nasa.gov/modelforce/ghgases/GHGs.Obsv.2001-2004.txt
2005-2006 from individual files for each gas, estimating 2005-2006 for two trace gases where data not shown
The function to calculate forcing provides for implementing different sets of equations, not all of which are tested yet.
Whlie NOAA implementation was straightforward, this is not the case for Hansen et al 1988 and other articles. Sometimes the problems are units: Hansen et al 1988 Appendix B expressed forcing in terms of global temperature change and not in terms of wm-2. Unlike the original article, Gavin Schmidt’s Hansen et al 1988 scenario data is expressed in wm-2 (a unit not yielded by the equations of the original article.) IPCC 1990 discusses the conversion to wm-2 as follows (p 52):
“Values derived from Hansen et al have been multiplied by 3.35 (Lacis, pers comm) to convert forcing as a temperature change to forcing as a change in net flux at the tropopaus after allowing for stratospheric temperature change. These expressions should be considered as global mean forcings; they implicitly include the radiative effects of global mean cloud cover.
Using this conversion, the equations for CFC11 and CFC12 immediately translate. However, the translation for other equations is not as easy.
IPCC 1990 Table 2.2 says that, fr CO2, CH4 and N2O, they say that the “functional form [was derived] from Wigley 1987; coefficient derived from Hansen et al 1988”. I can confirm the functional form from Wigley 1987, but Hansen et al 1988 set out coefficients for different functional forms. I’ve been unable to locate any of the IPCC 1990 coefficients in original articles – I wonder where they came from.
The same problem occurs for the overlap equation for CH$ and N2O in IPCC 1990. Although the overlap term is attributed to Hansen et al 1988, the expression in IPCC Table 2.2 does not occur in either Hansen et al 1988 or Wigley 1987 – where did it come from?
I can get the IPCC 1990 overlap expression to yield sensible values, but I can’t get the Hansen et al 1988 expression to yield sensible values so far – if anybody else can, I’d appreciate the info. IPCC 1990 also mentions (also on p 52) a typographical error in Hansen et al 1988 (“0.014 should be 0.14”).
In summer 2007, Gavin Schmidt reported the GHG concentrations for the three Hansen 1988 scenarios at and the total radiative forcing (wm-2) for the three Hansen scenarios here .
I’m hoping that I will be able to replicate the Hansen radiative forcing total (at RC here http://www.realclimate.org/data/H88_scenarios_eff.dat) from the GHG concentration data (http://www.realclimate.org/data/H88_scenarios.dat) using contemporary equations and then compare this to the observed radiative forcing. In passing, I note that the structural links between Hansen et al 1988 and IPCC 1990 are quite close and provide some mutual clarification.
Climate Audit 
44 Comments
My question is this, and I appreciate in advance any response.
The intial before feedback response to any increase in CO2 is greatly affected by the amount of H2O in the atmosphere. CO2 is thought to be well mixed globaly. However both water vapor and outgoing long wave radiation are not well mixed.
If therefore the area of greatest outgoing longwave radiation (the tropics) also has the most water vapor, which steals from the warming work CO2 is trying to do in the tropics, and the area of least infrared radiation, the poles, has the least water vapor, then would not globaly averaging these three factors, increased C02, H2O, and outgoing infrared radiation, produce an over sensetive response estimate to increased CO2?
What is the wm-2 before feedback response to increased CO2 in the tropics vs say antartic? These numbers can not be the same can they be?
If possible, please state how water vapour compares.
Steve:
Typo
CH$ ==> CH4?
Also I think some of the links are missing.
David – This is why the models predict more warming at the poles than at the equator.
Steve,
The first dat file is not opening correctly. The second and third are fine, so are the txt files. For some reason my computer (operating system = Vista) thinks the first dat file is a video. Anyone else have that problem?
It’s incorrect to call that all “forcing”, since most of the CO2 and CH4 was there in pre-industrial times. That actual “forcing” part would be the change, not the total radiative effect.
Also, while it may be accurate to a first approximation to add the effects of all of these gases, their absorption bands do overlap, and the net effect is always less than the sum of the individual effects.
#7, they use 1750 estimates as a benchmark for calculating a delta
The problem is not in reproducing the results of the equations .
The problem is when they say :
With that everybody’s back to square one .
What models ?
If several , were the results (which results ?) averaged ?
What does the 10 % mean ?
As the radiative transfer depends on aerosols , humidity , temperature , cloudiness , lapse rate , day or night etc , what were those assumed ?
There is obviously also an amount of averaging having been done – both spatially over the whole atmosphere and temporaly over an unknown period of time .
How was that averaging done and how model results compare to the reality ?
The above quote asks much more questions than it gives answers .
Steve: I’m showing this replication merely as a first step in analysis, not for any other reason. I want to use the algorithm for analysis.
Re David, Bob, poles vs equator
— and which is, in fact, exactly what is happening, and what happened (sfaict) in paleowarming episodes.
Cheers — Pete Tillman
Re: http://www.esrl.noaa.gov/gmd/aggi/ , AGGI % incr/annum, Fig.2
It would be nice to see a plot of this annual increase, and compare same to the plot (posted here AWB) of the annual incr of %CO2 in atmos. Should be pretty closely correlated, but YNK…
TIA, PT, whose R (or any plotting routine) skills are non-existent
Tom Vonk, they also say “empirical” and “models” in the same breath. Apparently true empiricism is dead, and reality is less important than virtual reality. PHE, the difficulty with your question lies in answering the question of how much more, or less water vapor is it the air now than there was years ago. Does anyone know that to any degree of certainty? I don’t know.
Steve – Regarding comments #7 and #8, this is actually quite an important issue. The NOAA plots are, at the least, misleading, by not using the actual estimated radiative forcings of CO2 and other forcings for each of the years plotted. I discuss this issue iin my weblog Why We Need Estimates Of The Current Global Average Radiative Forcing. The relative role of CO2, as a radiative forcing, is overstated.
Why ignore nitrogen and oxygen?
This is a question that has just occurred to me today. Why do nitrogen and oxygen (together forming 99 per cent of the atmosphere), not figure in the greenhouse effect equations? IPCC AR4 says simply: “These gases have only limited interaction with the incoming solar radiation and they do not interact with the infrared radiation emitted by the Earth.” This is the only mention I can find on this issue in AR4 (with no reference given). This seems too simplistic, so I must be missing something. They absorb energy, can retain heat and have a temperature (and can presumably radiate heat). They must help to buffer temperature between day and night, warm days and cool days, and even between seasons. If they were the only gases in the atmosphere, surely the atmosphere would be able to retain some of the Sun’s heat energy and maintain a temperature above what it would be without an atmosphere(though presumably less than it does in reality). This seems an important point to me, and not one to be dismissed in a single sentence. If they have no role, then for such major proportions of the atmosphere, there should be a clear explanation why.
14: Right on, sir! While the N2 and O2 don’t directly interact much with IR, they take the energy away from the GHGs through collisions. Local Thermal Equilibrium is very important. I’m wondering just how this all affects radiation of IR.
I’m confused by a couple of these comments about heating at the equator versus the poles. I thought the greatest heating was supposed to occur in the tropical troposphere at about 300 mb pressure altitude.
PHE
N2 and O2 do not have a vibrational dipole moment and therefore do not have strong absorption in the IR.
Their primary IR role is to help transfer thermal energy to the active molecules and pressure-broaden the narrow absorption lines from CO2 and water-vapor. They have a big role in heat transfer by convection.
The air near the ground warms up rapidly once the land warms up, which confirms that the heat capacity of the air is too small to have much buffering effect.
Hi Steve,
The problem I have with these estimates is that they are based on GISS data. I have pointed out before that GISS has a positive bias. I personally don’t know why this is but Roger Pielke Jr. suspects it is because of an extrapolation of the polar data. I also see that ozone is not included in the calculations, Why? Do think this is why Roger Pielke Sr. says there is an over estimation of not only CO2 forcing but total radiative forcing?
17;
Can you explain this further? Most of the whole air column heats up through convection every day, and that easily requires all the energy that is received from solar radiation during a day.
This explains it all:
#20
Hey – this link is a good rigorous description of AGW too!
19 jae
All? The land doesn’t warm up? There is no radiation back out to the stratosphere?
I’ll quit at this point and let you and PHE have a nice dialog together….
RE: #14
Nitrogen and oxygen do not absorb in the infrared region of the electromagnetic spectrum (ca. 1-1,000 microns). Nitrogen is transparent to all visible and uv light above 200 nm (2,000 A.). Oxygen absorbs weakly below 300 nm in the uv, and this absorption leads to the production of some ozone, which strongly absorbs uv light below 350 nm. Although there is not that much uv light energy in the sunlight, there is enough in the 350-400 nm range to cause problems for living organisms as well as a variety materials such as rubber and painted surfaces.
Nitrogen and oxygen do not absorb infrared radiation because these molecules do not have a permenant electric dipole moment and one cannot be produced by collisions. Water has a permenant electrical dipole moment and absorbs infrared radiation quite strongly. Carbon dioxide does not have a permenant electric dipole moment but a transient one can be induced by collisions. In fact carbon dioxide is a weak absorber of infrared radiation in comparison to molecules that have permenant electric dipole moments.
Why don’t we ever see a climate forcing factor for water at specified set of conditions e.g., 25 deg C, one atmosphere pressure and a nice 70% relative humidity? Because that forcing factor would be quite large and totally overwelm all other climate forcings factors combined.
What contribution do dissolved gasses play in the absorbtion spectra of water droplets? Do O2/N2/H2O molecules become sublimed when frozen water droplets absorb IR?
#19
Excluding for the moment the radiatively active (so-called GHGs) which except for HOH constitute a very small portion of the atmosphere, almost all of the solar heating occurs at the ground surface (be it sea-level or mountainous). The radiatively inert gases…N2, O2 and Ar…are primarily heated by conduction…contact with the mostly solar heated ground. Because of the low thermal mass of these gases, on a square meter per square meter basis, only a small amount of surface heat is expended for the air molecules to reach thermal equilibrium. Thus warm surfaces can transfer heat to a large quantity of air. It is convection which transports this conductively heated air upwards with the rising air coulumns being replaced by cooler air descending in the cycle of convection.
The role of HOH is much more complex in that a massive amount of thermal energy is carried aloft (by convection and diffusion) in the form of latent heat accumulated from wet surfaces by evaporation and released at altitude by condensation or sublimation. The temperature of much of the troposphere is controlled almost completely by these processes with advection coming into play as warmer air created in the Tropics circulates northward to be replaced by cooler air moving southward from the higher latitudes. The major external variables which relate to tropospheric temperates concern the phsyical state of atmosphetic HOH, avport, liquid or solid, and their independent ability to absorb, reflect and re-radiate accumulated raidative energy.
IR (or UV or visible or microwave….) is not all that’s involved here. It depends on the subject which in this case seems to be non-IR and non-UV and non-visible light behaviors of gasses in the atmosphere and how they all interact when taking the IR, UV, visible, into account.
Pat Keating # 17
The first statement is irrelevant to the question and partly wrong .
N2 and O2 have a collision induced dipolar and quadripolar momentum and do absorb/emit in far IR .
Regardless of that , they play a major role in the energy transfer as they collisionnaly desexcite the GHG and of course radiate by their own account as any matter radiates .
The second statement illustrates the above .
As I have already shown , only 5 % of the CO2 molecules are in the vibrationnaly excited mode (1% in the stratosphere) .
So any absorbed IR is transferred on the N2 and O2 molecules by collisonnal deexcitation .
Symetrically the major source of CO2 vibrationnal excitation is not the IR absorption process but the collisionnal excitation .
That’s why collisionnal interactions between the GHG and other molecules are the single most important process in the radiative transfer in the troposphere and the stratosphere .
Tom Vonk, #27
Does this mean that the atmosphere is more IR transparent than one would think by looking at the CO2 absorption lines?
The following is conditional on the question this being the final word on GHG forcing.
(Published in Kopp, G., Lawrence, G., and Rottman, G., The Total Irradiance Monitor (TIM): Science Results, Solar Physics, 230, 1, Aug. 2005, pp. 129-140.)
Venus’ shadow caused a 1.4 wpm-2 drop in TSI.
The low estimate of GHG forcing can be totally mitigated by a sizeable satellite. How big?
Venus diameter 7,521 miles, divided by the distance at transit 25.7 million miles, a shadow a little bigger than 2 miles in diameter. I might be a bit off with that math.
But installing a permanent cloud sized sun occluding satellite in a stable orbit seems easier then enforcing world wide co2 restrictions.
> Steve – Regarding comments #7 and #8, this is actually quite an
> important issue. The NOAA plots are, at the least, misleading, by not
> using the actual estimated radiative forcings of CO2 and other
> forcings for each of the years plotted. I discuss this issue iin my
> weblog Why We Need Estimates Of The Current Global Average Radiative
> Forcing href=”http://climatesci.org/2008/01/04/why-we-need-estimates-of-the-current-global-average-radiative-forcing/”>
> . The relative role of CO2, as a radiative forcing, is overstated.
>
> Roger
>
> Roger A. Pielke, Sr.,
> Senior Research Scientist CIRES and Senior Research Associate ATOC
> University of Colorado at Boulder Professor Emeritus Colorado State
> University pielkesr@cires.colorado.edu
> http://cires.colorado.edu/science/groups/pielke/
>
—
This article provides a very detailed look at radiative forcings, including a discussion of IPPC’s water vapor feedback estimates. It may have been linked somewhere previously?
This seems to be a common mode of thought at this web site. It seems to boil down to this line of thinking.
“I am ignorant of the science of climate, but I will not accept what the experts say, so I will not believe anything they say until they explain to me the detailed science”. IMHO, it’s up to you to go out and do a University course in climate, it’s not up to them to spoon feed every detailed question on science.
Re: #32, #33
Experts have been wrong before. The basics aren’t really that hard, if you can understand partial differential equations. It certainly seems reasonable to me that somebody with a scientific education should be able to get these types of questions answered without having to take a university course.
There seems to be a kind of “band gap” between the simple cartoons of the sort the IPCC provides and the actual mathematical development found in textbooks like Thomas and Stamnes. IMO if the climate change issue is important enough to ask the governments of the world to massively interfere with just about everybody’s lifestyle, it’s important enough that somebody should be responsible for filling this “band gap” for the sake of scientists and engineers who want to audit the science.
One way to do this might be a set of graded FAQ’s, with answers at several different technical levels. People in the field could be responsible for assuring that the answers were technically correct, and people out of the field for assuring that the answers were reasonably understandable.
There’s an awful lot of ill-informed skepticism out there. For example, this paper showed up in the BB today. (Here’s my amateur critique.) This sort of stuff wastes the experts’ time, and confuses people more distant from the subject.
Hear! Hear! We have an internet that could provide the physical infrastructure for something more interactive, especially for people in other technical fields. It should be used, IMO.
Bugs says:
Your response demonstrates a common mode of thinking among alarmists: focus on the on the most uninformed opinion expressed and claim it represents the views of all skeptics. This allows the alarmist to avoid dealing with the more nuanced opinions of the well informed skeptics who raise legimate questions regarding climate science.
I think you also put too much weight on the value of climate science theory at university. When I went to university most textbooks simply presented the facts that students are expected to learn. Students learn them and don’t often care whether the facts are wrong because they still have to produce the facts as presented in the textbooks on an exam paper. The system ensures that bad science takes a long time to refute once it makes it into a textbook.
For example, for years medical textbooks said that ulcers were caused by stress and any aspiring doctor that claimed otherwise would be lose marks. It took years before a maverick scientist proved that bacteria was really caused ulcers.
RE 32. Sorry. when the Government, as in california, wants to install government mandated
thermostat controls in my house to control how warm and toasty I am, and when that government
takes this action because it believes without question the “findings” of climate science,
Then I do think I have a right to be spoon fed.
Lucia, knit me some socks already!
Bugs #32…
This seems to be a common mode of thought at this web site.
This seems to be a common alarmist straw man.
Medical science is highly diverse and complex. Overall, the success in this area is remarkable, with people’s lives and health being significantly improved. That one specific area had an error does not surprise me at all. I do not think the science or projections are anything like 100% perfect. The general response of the climate over the past two decades is pretty convincing, however. AGW is real, increased CO2 is the forcing that is causing it.
Bugs says:
Understanding the human body is no more difficuly than understanding climate. The big difference is medical science can seperate the good from the bad through trial and error. That said, medical science must meet some pretty high standards before humans can be used to the theory. Medical scientists are not allowed to say ‘trust us’ – they have to demonstrate convincingly that the benefits of a therapy outweight the risks. Medical scientists or the organizations they work for are liable if they make scientific errors and then try to cover the errors up.
Why do climate scientists think that they do not need to live up to those standards when it comes to justifying a huge social experiment that will affect the lives of everyone on the planet?
Bugs says:
That is what you believe but steves work on this blog makes it clear that basis for that claim is not a firm as you would like to believe. If you claim is correct then climate scientists should be able to prove an engineering quality exposition to back it up. If they can’t/won’t do that then they can no business asking society to make investments based on their science.
Hi Guys,
I’m reposting this also look at the link it has pretty graphics and charts for the absorption bands of different gases
The problem I have with these estimates is that they are based on GISS data. I have pointed out before that GISS has a positive bias. I personally don’t know why this is but Roger Pielke Jr. suspects it is because of an extrapolation of the polar data. I also see that ozone is not included in the calculations, Why? Do think this is why Roger Pielke Sr. says there is an over estimation of not only CO2 forcing but total radiative forcing?
http://www.junkscience.com/Greenhouse/
Paul Linsay #28
Yes .
Take for instance the asymetric stretching mode of the CO2 molecule that is IR active (001 at 2349 cm^-1) .
This mode stands in very strong resonance with the IR inactive vibration mode of the N2 molecule at 2331 cm^-1 .
In LTE there will be the same number of excited N2 molecules deexciting as the number of deexcited N2 molecules exciting through collisions with CO2 molecules .
Both the number of 001 CO2 molecules and (1) N2 molecules is given by the Boltzmann distribution and is constant .
This example shows among others that one has to be VERY cautious when talking about Kirchhoff’s law
(and other macroscopical laws) in processes dominated by quantum mechanics .
The process in which a CO2 molecule absorbs 2349 cm^-1 radiation and excites an N2 vibrationnal mode as well as its symetry clearly doesn’t obey the Kirchhoff’s “law” despite the fact that energy is conserved .
Now you double the number of CO2 molecules .
Then you double the number of 001 states (increased absorption at 2349 cm^-1) and you double the number of collisions
with N2 molecules .
So you double the number of excited (1) N2 molecules .
End result ?
Part of the 2349 cm^-1 IR radiation was transferred to an IR inactive N2 vibration mode and is not available for reemission by CO2 .
This is an example of intermolecular V-V (vibration-vibration) energy transfer .
Beside that you have many V-T (vibration – translation) energy transfers where an excited IR active mode stands in thermal equilibrium with the translation continuum .
The same applies of course also for H20 which largely dominates the radiative transfer anyway .
Again a word of caution .
This sort of argument shows the sensibility of purely radiative/collisional processes to a doubling of CO2 and it is shown that the result can’t be obtained by considering CO2 alone .
It doesn’t say what is the radiation itself in LTE and more specifically it doesn’t mean that radiation energy somehow “disappears” .
Once the gas is in LTE , it is at constant temperature , the energy states are populated as per Boltzmann law and everything that is excited must be deexcited and vice versa by all available processes .
I have some very basic questions that I would like some answers to and appreciate in advance any response.
The IPCC states a before feedback sensitivity of doubled CO-2 at .8 degrees centigrade. How do they average the very different global responses and different outgoing LW radiation?
What is the before feedback IPCC sensitivity of doubled CO-2 in the tropics?
What is the before feedback IPCC sensitivity of doubled CO-2 in the North Polar regions?
What is the before feedback IPCC sensitivity of doubled CO-2 in the South Polar regions?
What is the outgoing W/sq-m radiation in each of these areas.
What percentages of the earths outgoing LW radiation is in each of these areas.
I have only seen what others have called the “cartoon” global average chart displayed by the IPCC. It appears obvious to me that what should be averaged are the different latitude responses to the different W-sq-m radiation in the different latitudes. Simple example (I do not know the real numbers)… The tropics radiate 9 times the LW W/sq-m radiation as the south-pole. The tropical doubled CO-2 sensitivity to this radiation is .25 degrees due to the high humidity in the tropics. The polar region doubled CO-2 sensitivity is 2 degrees due to the lack of humidity. Geographically these areas may be the same size, yet 90% of the LW radiation and the response are in the tropics. Therefore the response for the two combined areas is .25 / .25 / .25 / .25 / .25 / .25 / .25 / .25 / .25 / and 2. The two areas combined have a sensitivity of .425 degrees relative to the total W/sq-m radiation of these locations. Should not the response be given as a W/sq-m number and not a temperature?
Is this at all logical?
Is this what the IPCC does?
I know far more is involved in this, and getting the true response would be as difficult as getting the world average temperature. I am just trying to understand on a very basic level how they arrived at a global average response of .8 degrees per doubled CO-2
If these gases absorb and emit in sometimes overlapping and sometimes disjoint parts of the infra-red spectrum, with some bands saturated, others transparent, and others variable, then is it not partially misleading to suggest that the individual actions of these gases combine linearly, as the graph and associated logarithmic concentration equations imply?
CO2 emissions from soil may be overestimated, according to a new study from Australia. See http://abcmail.net.au/t/328902/1045236/6187/0/
According to Myhre et. al 1998, present radiative forcing is about 2W/m^2. This seems far too high. If we were to have a 1m^3 column of air stretching from the earth’s surface up through the atmosphere, how long would it take 2 watts of energy to heat this by 1 degree C.
The heat capacity of air is 1 joule / gram / degree C.
The weight of air would be equivalent to 760mmHg by 1 sq meter. So the air would weigh 10 tonnes, or 10000000 grams, therefor it would take 10000000 joules to raise 10000000 grams of air by 1 degree C.
2 watts x 5000000 seconds = 10000000 joules
so it would take 5 million seconds for 2 watts of energy to increase the temperature of this 10 tonnes of air by 1 degree C. 5 million seconds is nearly two months, but if the IPCC average is 1 degree C rise every 33 years, what happens to all the heat over the remaining 32 years and 10 months. (33 years minus 2 months)
According to this, 99% of the heat created through CO2 raditive forcing is NOT used in raising the temperature of the atmosphere. I have heard that a lot of the heat created through CO2 radiative forcing gets absorbed by the oceans, but I didn’t realise 99% of it was. Is this so, or have I placed a decimal point in the wrong place?
Chris