One commenter asked about CO2 absorption in the solar spectrum.
If CO2 absorbs incoming solar radiation then surely an increase in CO2 will reduce incoming radiation and balance any increase in longwave radiation.
The important factor is the usual question of quantifying the different effects.
Let’s take a look.
CO2 absorption in the 0.17-5um band, with solar spectrum overlaid
The CO2 absorption spectrum is from the line list browser of the recommended spectralcalc.com. The line list only goes down to 0.17μm (170nm), hence the reason for the graph not starting at 0.0μm.
The solar radiation is overlaid. Well, more accurately, the Planck function for 5780K is overlaid (simply drawn using Excel). Note that the CO2 absorption spectrum is on a log graph, while the radiation is on a linear graph. For those not so familiar with logarithmic graphs, the peak absorption around 4.3μm is 10-18, while the two peak absorptions just below 1μm are at 10-26 – which is 100,000,000 less.
The value of seeing the solar radiation spectrum overlaid is it enables you to see the relative importance of each absorption area of CO2. For example, the solar radiation between 2 – 4μm is only 5% of the solar radiation, so any absorption by CO2 will be quite limited.
Here’s the comparison with the important 15μm band of CO2. A 6μm width is shown, overlaid (blue line) with the 12-18um longwave radiation of a 288K (15°C) blackbody:
CO2 absorption in the 12-18um band, with terrestrial spectrum overlaid
Just a little explanation of this graph and how to compare it to the solar version.
The average surface temperature of the earth is 15ºC, and it emits radiation very close to blackbody radiation (watch out for a dull post on Emissivity soon).
The proportion of radiation of a 288K blackbody between 12-18μm is 28%. What we want to do is enable a comparison between the CO2 absorption of solar radiation and terrestrial radiation.
Averaged across the globe and the year the incoming solar radiation at the top of atmosphere (TOA) is 239 W/m2 and the radiation from the earth’s surface is 396 W/m2. This works out to 65% higher, but so as not to upset people who don’t quite believe the earth’s surface radiation is higher than incoming solar radiation I simply assumed they were equal and scaled this section of the earth’s terrestrial radiation to about 28% of the solar radiation on the earlier graph. We are only eyeballing the two graphs anyway.
So with this information digested, the way to compare the two graphs is to think about the absorption spectra of CO2 simply being scaled by the amount of radiation shown overlaid in both cases.
As you can see the amount of absorption by CO2 of solar radiation is a lot less than the absorption of longwave radiation. Remember that we are looking at the log plot of absorption.
Is That the Complete Story?
Really, it’s more complicated, as always with atmospheric physics. There’s nothing wrong with taking a look at the approximate difference between the two absorption spectra, but luckily someone’s already done some heavy lifting with the complete solution to the radiative transfer equations using line by line calculations. For more on these equations, see the CO2 – An Insignificant Trace Gas series, especially Part Three, Four and Five.
The paper with the heavy lifting is Radiative forcing by well-mixed greenhouse gases: Estimates from climate models in the IPCC AR4 by W.D. Collins (2006). There’s a lot in this paper and aspects of it will show up in the long awaited Part Eight of the CO2 series and also in Models, On – and Off, the Catwalk.
Solving these equations is important because we can look at the absorption spectrum of CO2 in the 15μm band, but then we have to think about the absorption already taking place and what change in absorption we can expect from more CO2. Likewise for the solar spectrum.
Here are the two graphs, which include other important trace gases, as well as the impact of a change in water vapor. Note the difference in vertical axis values – the forcing effect of these gases on solar radiation has to be multiplied by a factor of 1000 to show up on the graph. The blue lines are CO2.
Net absorption of solar radiation by various "greenhouse" gases
Longwave radiative forcing from increases in various "greenhouse" gases
You can also see that the CO2 absorption in shortwave is across quite narrow bands (as well as being scaled a lot lower than terrestrial radiation) – therefore the total energy is less again. The vertical scale is energy per μm..
From these calculations we can see that with a doubling of CO2 there will be a very small impact on the radiation received at the surface, but a comparatively huge increase in longwave radiation retained – “radiative forcing” at the tropopause (the top of the troposphere at 200mbar).
So Is That the Complete Story?
Not quite. If trace gases in the atmosphere absorb solar radiation, is that so different from the surface absorbing solar radiation?
Or to put it another way, if the radiation doesn’t strike the ground, where does it go? It’s still absorbed into the climate system, but in a different location (somewhere in the atmosphere).
But as one commenter said:
The other point [this one] you make is simply not true and/or also not proven. There is only so much energy that can be taken up by a molecule.
This is a theme that has arrived in various comments from various posts. So the concept of How much work can one molecule do? is worth exploring in a separate post.
Hopefully, it’s clear from what is presented here that increases in CO2 absorption of the solar radiation are very small compared with absorption of longwave radiation.
Science of doom, you say:
“For example, the solar radiation between 2 – 4μm is only 5% of the solar radiation, so any absorption by CO2 will be quite limited”.
According to various sources that I consulted the amount of energy coming onto earth is 46-47% from the infra red region of the sun. So this presentation is flawed from the beginning.
For example, when I stand here in the African sun, in the summer, I can only allow my skin a few minutes exposure, then I have to look for cover. The radiation on my skin gets too hot. But, if during the same day, the humidity rises, that same direct heat from the skin becomes less. You can feel this. This is the reason why the temperature on the coast (where humidity is higher) is always a few degrees less than more inland. So carbon dioxide, like water vapor does exactly the same thing….. it cools the atmosphere. My question was and is: by how much?
There is also no mention in your graphs of all the absorptions of CO2 including those in the UV region which have only been discovered lately.
You also say : “We are only eyeballing the two graphs anyway”.
When there is so much at stake here.?
You cannot do that.You have to come with an experiment and with actual test results. in W/m3 (0.04%-0.06% CO2)/m2/24 hours cooling and warming. We know that Svante Arhenius formula was wrong, so where is the right formula? Don’t come with stories that really is only a believe system. We have to have formulas like Newton made, real science that everyone can test and rely on.
No eyeballing.
Because the results that I want, proposing the correct formula, simply donot exist, there is really little point in continueing this debate.
scienceofodoom wrote
Without looking up the whole derivation this looks a bit low. The peak radiation figure at ground level on a perpendicular surface is to the sun – to my vague recollection – of the order of 1400-1500 watts/sqm. This is after some filtering by the atmosphere but discounting clouds which can both decrease incident ground radiation and also increase it above the base figure.
The earth disk is pi r^2 and the earth surface area is 4 pi r^2 so the average insolation should be (say) 1450 / 4 = 362 W/sqm at ground level and higher at TOA.
- actually I have just seen another figure of 1396 W/sqm (seems low to my recollection) so giving a TOA of 349 W/sqm.
Update to my post – I had a typo in the 1396 W/sqm – should be 1369 W/sqm – resulting in 342 W/sqm – this is using the solar constant and earth orbit geometry and applies at TOA.
My slightly higher figure – from recollection – may include back radiation from atmosphere (?) The figure was what I used as a base for my terrestrial measurements and was approx 1440 W/sqm.
Yes, please explain the 239 as many sources give a radiation power density of 1,370 W/m2 or so.
I’m really enjoying the journey and the guide and I’m excited about some of the foreshadowed adventures.
henry Pool
On the comment that “..2 – 4μm is only 5% of the solar radiation..”
Perhaps we could say, there is a discrepancy between your presentation and this presentation. So the question becomes Which one is flawed?.
In fact what is “infra red”?
Infra-red is >700nm and approximately half of the radiation from the sun is in the infra-red. But from 2-4um there is only 5% of the energy.
You can see this in any graph of solar energy. And it quite closely matches the Planck function of 5780K which is shown in the graph. You can do the calculation yourself, just take the Planck blackbody formula and plot it on a graph and measure the area under different parts of the curve.
The Hitrans database is the most comprehensive database of absorption, this is what spectralcalc draws on.
In the UV, almost no solar radiation makes it to the surface anyway, so CO2 – or any other trace gas – absorption in the UV area is irrelevant, it’s all absorbed by O3 and O2 in the stratosphere. Increasing CO2 means an change from around 0% to ?
Really not sure what you are saying here. You like Newton’s formulae?
You don’t like the Beer-Lambert law of absorption?
You don’t like the 1st law of thermodynamics?
You don’t like Kirchoff’s law of emissivity = absorptivity?
Why trust Newton?
For Jerry and Dave McK:
See The Earth’s Energy Budget – Part One for explanation of the energy budget basics.
TSI, total solar irradiance at top of atmosphere = 1367 W/m^2
Averaged over the surface area of the earth = TSI/4 = 342 W/m^2
Taking into account the earth’s albedo (reflected radiation) = 239 W/m^2
In fact, many of these numbers cannot yet be known accurately enough. Perhaps in The Earth’s Energy Budget – Part Four this might be explained further.. but even though we put in numbers like 1367W/m^2 there is some +/- here.
Likewise with the albedo. Anyway, the important thing is to understand the relationship between the numbers above, check out the original post..
Scienceofdoom.
Just to be picky, your statement was actually
Which is somewhat misleading without reading all your posts and filling in the missing bits.
Also, does the earth radiation include the albedo backscatter or is it addition to the backscatter radiation?
I’ve also read a variety of discussions about this topic, some of which state that the long-wave IR incoming is a significant fraction of long-wave IR going out – perhaps even equal?
henry Pool:
Well, the reason I said “eyeball the two graphs” is that the solar absorption of CO2 is so obviously less than the absorption of terrestrial radiation in the 15um band. If they looked slightly close we might have to try some maths.
But from your other comments, physicists post-Newton don’t get a look in, so evaluating the absorption via the Planck function (radiation from a black body that you question) using the Beer-Lambert law of absorption (see CO2 – An Insignificant Trace Gas? Part Three ) would be a wasted effort?
What experiment can we do to satisfy you? We can measure the radiation from the sun and the zero UV that we already measure at the earth’s surface due to absorption by ozone and oxygen on the way in shows that any trace gas absorption in the UV has no extra effect. Because it’s already almost zero:
Jerry:
It’s good to be picky. Picky means getting to the bottom of things.
Well, atmospheric physics is a big topic, not easily explained in a few words.. Not aimed at being misleading, sometimes I have to state the facts and refer people to other posts to avoid very long (20 page) explanations..
The earth’s radiation is completely and totally the energy radiated from the surface of the earth due to its temperature. So a 15′C surface radiates 390W/m^2. And the energy vs wavelength follows the well-known Planck function.
Any solar radiation reflected is in addition. Luckily, the solar radiation can be easily discriminated from terrestrial radiation due to the aforementioned Planck formula.
I have found many people stating: “50% of the solar radiation is infrared therefore we can’t tell which is terrestrial and which is solar..”
“Infrared” = >700nm. And so the comment is irrelevant.
“Longwave” as the shorthand climate scientists use is greater than 4um and terrestrial. “Shortwave” as the shorthand climate scientists use is less than 4um and solar.
The overlap is less than 1%. The “infra-red” is a red herring
Can you explain the last question? I don’t understand it.
Oh. I had to think what that really means.
It’s averaged over day and night side and the poles that get but a fraction so it’s the ‘whole ball of wax’ average, correct?
So at noon on the equator you’re really getting close to your 1300W/m2 hitting the ground, right?
I have to pay close attention.
Dave McK:
It’s the whole ‘ball of wax’ average.
If you stand at the equator at noon under a clear sky you get something close to the 1367W/m^2 so long as no aerosols and no surface reflecting any radiation.
If you are out on the water and it’s calm and there are minimal aerosols then you will get something like 1300 W/m^2.
Check out the average albedos in Positive Feedback, Albedo and The End of All Things
We all have to pay close attention. Atmospheric physics is a journey, not a destination..
I will read it now. Your course is advanced for me. I’m off the dean’s list due to this one but it’s very, very interesting.
Thank you for answering my questions.
Done with my assignment. I only comment to show if I got the main point.
There are other positive feedback systems, too. A grass or forest fire is an example. A storm is a couple at once. Fission is the classic.
All of these things have a terminal condition that’s arrived at through larger equilibria – burning up all the fuel, for example.
There never is a problem with local reversal of entropy.
Life is that.
Trivia- if you look at a satellite view of Africa (at night) during dry season- at any time there are fires all across the savannah. That’s a 5 million sq mi swath right across the continent where the equatorial red stain of heat always is shown.
I suppose it practically must have been geothermal or cometary heat to reverse an ice age once it was established, eh? A nice swarm of ice comets at 50kps would boil some atmosphere. Dirty ones would be even better if they sooted up the poles.
p.s.
When you do the topic of ‘what can one molecule do’, please include cellulose.
The CO2 absorption of incoming, has, for me, never been an issue for doubting the claims that CO2 is going to trigger a climate catastrophe.
To henry Pool:
You wanted an experiment, right?….. Refer to the Figure Science of Doom posted in these comments. Look at the spectrum of sunlight that arrives at sea level (through the zenith) for a “standard” atmosphere. We have the means to model this observed spectrum of sunlight.
1) We use our best spectral models for atmospheric opacity of the Earth’s atmosphere. At minimum these models include the molecules present as a function of height. It can also include such and such aerosols, water droplet column density, what have you, although for these specific purposes clouds are omitted. These computations produce cross section for absorption or scattering (units: m^2) vs. wavelength of light (or wave number), for a specific set of conditions (temperature, molecular density). These models are quite sophisticated feats of quantum mechanical mastery (from experimental measurements and theoretical quantum predictions), and include, for example, the effects of temperature and molecular density that affect the widths and peaks of the molecular cross sections.
2) At every wavelength interval we integrate the cross section by the run of absorber number density with height. To give you a more intuitive feel for whats’ being done, this quantity is approximately the product of the cross section (m^2) times the column density of the atmosphere overhead (integrated number of absorbers and scatterers per m^2 vertical column). The resulting dimensionless quantity is known as the optical depth, labeled as the Greek letter “tau”, as a function of wavelength.
3) Take the Sun’s light spectrum incident at the top of atmosphere and multiply it by e^(-tau), wavelength by wavelength. The result is a predicted detailed spectrum of (zenith) sunlight that reaches sea level.
Compare prediction to observation. Match up? Yes, almost in entirety, with some isolated mismatches (molecular physicists go back to their laboratories and to their molecular model computations). Done.
Note that the above ratio, I/I_o = e^(-tau), does not include scattered light or molecular emission of the atmosphere. That’s another, more elaborate, calculation, of radiative transfer.
So my question was: what is the new formula for warming caused by CO2? We know that Svante’s Arrhenius formula was incorrect, IF IT WERE CORRECT EARTH SHOULD HAVE BEEN A LOT WARMER. So, I am looking for the test results from the experiments that evaluate the warming and cooling properties.
I could have said that the warming of CO2 must be insignificant because water vapor also absorbs in the 214-15 um region. But I chose not to confuse issues.
If you did not understand the arguments I will give it again:
Here is the famous paper that confirms to me that CO2 is cooling the atmosphere by re-radiating sunshine (12 hours per day).
http://www.iop.org/EJ/article/0004-637X/644/1/551/64090.web.pdf?request-id=76e1a830-4451-4c80-aa58-4728c1d646ec
Note that they measured this radiation as it bounced back to earth from the moon. Follow the green line in fig. 6, bottom . Note that it already starts at 1.2 um, then one peak at 1.4 um, then various peaks at 1.6 um and 3 big peaks at 2 um.
This paper here shows that there is absorption of CO2 at between 0.21 and 0.19 um (close to 202 nm) (UV):
http://www.nat.vu.nl/en/sec/atom/Publications/pdf/DUV-CO2.pdf
There are other papers that I can look for again that will show that there are also absorptions of CO2 at between 0.18 and 0.135 um and between 0.125 and 0.12 um.
We already know from normal IR that CO2 has big absorption between 4 and 5 um.
So, to sum it up, we know that CO2 has absorption in the 14-15 um range causing some warming (by re-radiating earthshine, 24 hours per day) but as shown and proved above it also has a number of absorptions in the 0-5 um range causing cooling (by re-radiating sunshine). This cooling happens at all levels where the sunshine hits on the carbon dioxide same as the earthshine. The way from the bottom to the top is the same as from top to the bottom. So, my question is: how much cooling and how much warming is caused by the CO2? How was the experiment done to determine this and where are the test results? If it has not been done, why don’t we just sue the oil companies to do this research? (I am afraid that simple heat retention testing will not work here, we have to use real sunshine and real earthshine to determine the effect in W/m3 [0.04%]CO2/m2/24hours)
I am going to state it here quite categorically that if no one has got these results then how do we know for sure that CO2 is a greenhouse gas?, i.e that the net effect of CO2 is warming rather than cooling?
blah, blah,blah, no test results, no formula’s
The reflection of the solar radiation reflected from the earth and back from the moon is a very interesting idea.
But we can actually just measure it at the earth’s surface before it bounces off. It makes the measurements more accurate and yet more interesting.
It’s not new information that the solar spectrum is absorbed by many trace gases – they are in the Hitrans database shown above. And you can see them in the solar radiation received at the earth’s surface I showed in the graphic in an earlier comment
Here is the CO2 capture cross-section (from the same location) between 1.0 and 1.5um, shown on a linear axis to make it clearer the relative importance:
and from 1.0 to 2.0, again on a linear axis:
Repeating this:
Shows that you haven’t absorbed any of the information above. The proportion of solar radiation greater than 4um is less than 1%. If CO2 absorbs everything between 4-5um it has a maximum 1% effect on solar radiation received.
Take a look at the CO2 – An Insignificant Trace Gas series. You’ll be pleased to find not a single mention of Arrhenius, but you will see the formulae that govern the absorption and re-radiation by any gases.
And as Spaceman Spiff explained we have an experiment already – we can measure exactly how much radiation is absorbed (not lost) by the atmosphere by every single gas – we just measure the solar radiation at the surface.
Unfortunately, I don’t think you want “test results” and “formula’s” because when Spaceman Spiff explained them you dismissed them as “no test results, no formula’s”.
The Beer-Lambert law of absorption you can find in Part Three of the CO2 series.
Spaceman Spiff
I asked a while ago on a different thread about the why of the varying visual/optical depth of the atmosphere dependent on atmospheric pressure… and i think you have in a round about way answered it… thanks
Im still unsure whether its caused by absorption or scattering of visible light… (its just the ole weather prediction method o using distant geographical objects appearance for the incoming weather…during a high pressure they appear more distant, with noticeably less visible detail… )
scienceofdoom
Another random Q that this thread got me thinking about from reading spacemans post…
Are the short wave/sun light reaching surface calculated from the zenith always? I ask just because this would seem counter intuitive if there is scattering of short wave through atmospheric conditions… because it would be relativly constant at the zenith irrespective of variable scattering, but would be more noticeable at greater angles to the surface? Early or later in the day. It just seems like spaceman was saying that its calculated always from zenith…
Im just a farmer end o the day, but sunlight is variable even under clear skies(according to my skin anyways
)… or are averages used from varying times o day to measure short wave reaching the surface.
It seems too me that satellite measurements of global brightness/dimming would be better in general for covering yer bases as far as sunlight measurements go.
Mike Ewing:
For a 1-d analysis of radiation and absorption the conditions are usually stated. So, for example, one paper I was just reading had the sun at 60% from the zenith for its analysis.
Also parameters like latitude and time of year will be stated.
The GCMs, of course, take into account the angle of solar radiation hitting each part of the earth, with the consequent scattering and absorption effect of aerosols and clouds – and the albedo effect on the ground.
Some of these factors are well understood – like the dependence of the albedo of the ocean on the angle of solar radiation.
Others are poorly understood, like aerosols and clouds. The great Ramanathan describes clouds as the “gordian knot” of climate prediction.
Henry@all there
try looking at a few good graphs that show the incoming solar radiation and the outgoing earth radiation simultaneously on the same scale..
You would note the difference between what is measured on top of the atmosphere and at sealevel.
Almost 30% of incoming radiation is re-radiated to out of space because of the combined efforts of oxygen/ozone, water vapor and carbon dioxide – (on a sunny day, – we exclude clouds and cloudformation -)
Now if you look carefully at the outgoing radiation (from earth) you would have noticed that only a tiny little corner of earth’s radiation at between 14-15 is cut off due to the presence of CO2. This is because water vapor also absorbs strongly in that region.
So if I “eyeball” these graphs, then it looks to me that the carbon dioxde cuts down less than 1% of earth radiation and if I look at how much it cools it looks a lot more than 1% of sun’s radiation. So I say that the net effect of CO2 is probably cooling rather than warming. At worst, I would say that it is probably evens or close to evens between the warming and cooling.
It is you who does not understand or do not want to understand…. You have to find empirical proof that would show us that the one is greater than the other. In units like W/m2/M3 (CO2 -0.03-0.06)/24 hours. So, if you have those results, why not just give it to me? How much cooling and how much warming is caused by the CO2 (in exact values and at what concentrations) ?
& how was the testing done?
What is wrong with this statement?
“Man-made CO2 doesn’t appear physically capable of absorbing much more than
two-thousandths of the radiated heat (IR) passing upward through the atmosphere.”
Made by this man:
http://www.middlebury.net/op-ed/global-warming-01.html#bio
In this paper:
http://www.middlebury.net/op-ed/global-warming-01.html
Mike Ewing (re. absorption line profile dependence on T and P):
At the risk of boring you and the other readers to death, here is a brief tutorial:
To a very good approximation the shape of the cross sectional profile of a transition (in units of m^2) as a function of the difference in wavelength measured from the central transition wavelength lambda(0) (call this difference “dl”), can be described as a “Voigt” function ( see, e.g., http://en.wikipedia.org/wiki/Voigt_profile ). This function is the result of convolving the collision/pressure-broadened natural line profile with a Gaussian function representing the Doppler shift distribution of the gas molecules in a thermal bath: cross-section = G*(f/D) *exp{- (dl/D)^2}). G is a constant, f is a measure of the quantum mechanical probability of the transition in question, D is a characteristic width of the function called the Doppler width D = (lambda(0)/c) * sqrt{2kT/m} and is a measure of the most probable Doppler shift in wavelength units, with lambda(0) = central wavelength of the transition, m = mass of molecule and k is Boltzmann’s constant (J/K). Smaller masses and larger temperatures result in larger characteristic Doppler shifts D.
The natural (i.e., always present) line profile of the cross section of the line transition ultimately derives from the Heisenberg Uncertainty Principle regarding uncertainties in the energies of the particular quantum states involved in the transition and the (expectation value) lifetimes of said states. Interactions between the molecules (e.g, CO2 — CO2, or CO2 — other) further increase the uncertainty in the energy of a transition between quantum states and/or makes accessible other nearby quantum transitions. The shape of this natural line cross-section vs. separation from the transition’s central wavelength (dl) is approximately Lorentzian: cross section = L*(f/w) * w^2/(w^2 + dl^2), where L is a constant, f is a measure of the quantum mechanical transition probability, w is the characteristic width of the function, here set by the inverse quantum mechanical lifetimes of the states for the transition and the rate/type of interactions with other molecules. Greater pressures/gas densities result in larger values of w.
Left to themselves and random collisions, gas molecules set up a distribution function in kinetic energies (Maxwellian in the classical limit). The quantity sqrt{2kT/m} is the peak speed in this distribution function, and the mean (translational) kinetic energy per particle is (3/2)kT.
Temperature affects the distribution of quantum levels occupied by the molecules — and therefore determining what transitions are energetically probable. It also affects the degree of Doppler broadening (molecules of a given mass move more rapidly at higher T) and therefore the cross section function. Temperature varies with height in the atmosphere.
The atmospheric pressure and the number density of each constituent of molecules as a function of height affect the absorption line’s cross section values for dl > 3D (recall D is the characteristic Doppler width), and at essentially all wavelengths if the temperature is sufficiently low and/or the pressure is sufficiently high (thus Doppler broadening rendered unimportant).
Figures 9-1 through 10-5 at this book’s website http://www.sundogpublishing.com/AtmosRad/resources/Figs/index.html will be helpful, although you’d benefit further by purchasing the book (I am not the author, but it is a wonderful text accessible to advanced undergraduate students of the physical sciences).
I hope this was of some help.
scienceofdoom,
How does the most ephemeral of variables- clouds- become so important to climate prediction?
The time scales involved seem completely exclusive.
Henry@Spaceman Spiff
“I hope this was of some help”.
Answer: No.
Henry@ Hunter.
It took me 3 months to figure this out, mostly because people got stuck into a type of conditioned thinking. You have to become a non lateral thinker. this is my final report on global warming
FOR MY CHILDREN, & FAMILY AND FRIENDS LIVING IN THE NORTHERN HEMISPHERE
You may not know this. For a hobby I did an investigation to determine whether or not your carbon footprint, i.e. carbon dioxide (CO2), is really to blame for global warming, as claimed by the UN, IPCC and many media networks. I guess I felt a bit guilty after watching “An inconvenient truth” by Al Gore, so I had to make sure for myself about the science of it all. If you scroll down to my earlier e-mails you will note that I determined that, as a chemist, I could not find any convincing evidence from tests proving to me that CO2 is indeed a major cause for global warming. As my investigations continued, I have now come to a point where I doubt that global warming is at all possible…. Namely, common sense tells me that as the sun heats the water of the oceans and the temperatures rise, there must be some sort of a mechanism that switches the water-cooling system of earth on, if it gets too hot. Follow my thinking on these easy steps:
1) the higher the temp. of the oceans, the more water vapor rises to the atmosphere,
2) the more water vapor rises from the oceans, the more difference in air pressure, the more wind starts blowing
3) the more wind & warmth, the more evaporation of water (evaporation increasing by many times due to the wind factor),
4) the more evaporation of water the more humidity in the air (atmosphere)
5) the higher the humidity in the air the more clouds can be formed
6) Svensmark’s theory: the more galactic cosmic rays (GCR), the more clouds are formed (if the humidity is available)
7) the more clouds appear, the more rain and snow and cooler weather,
8) the more clouds and overcast conditions, the more radiation from the sun is deflected from the earth,
9) The more radiation is deflected from earth, the cooler it gets.
10) This cooling puts a brake on the amount water vapor being produced. So now it is back to 1) and waiting for heat to start same cycle again…
Now when I first considered this, I stood in amazement again. I remember thinking of the words in Isaiah 40:12-26.
I have been in many factories that have big (water) cooling plants, but I realised that earth itself is a water cooling plant on a scale that you just cannot imagine. I also thought that my idea of seeing earth as a giant (water) cooling plant with a built-in thermostat must be pretty original….
But it was only soon after that I stumbled on a paper from someone on WUWT who had already been there, done that …. well, God bless him for that!
i.e. if you want to prove a point, you always do need at least two witnesses!
Look here (if you have the time):
http://wattsupwiththat.com/2009/06/14/the-thermostat-hypothesis/
But note my step 6. The Svensmark theory holds that galactic cosmic rays (GCR) initiate cloud formation. I have not seen this, but apparently this has been proven in laboratory conditions. So the only real variability in global temperature is most likely to be caused by the amount of GCR reaching earth. In turn, this depends on the activity of the sun, i.e. the extent of the solar magnetic field exerted by the sun on the planetary system. We are now coming out of a period where this field was bigger and more GCR was bent away from earth (this is what we, skeptics, say really caused “global warming”, mostly).
But apparently now the solar geomagnetic field is heading for an all time low.
Look here:
http://wattsupwiththat.com/2010/01/07/suns-magnetic-index-reaches-unprecedent-low-only-zero-could-be-lower-in-a-month-when-sunspots-became-more-active/
Note that in the first graph, if you look at the smoothed monthly values, there was a tipping point in 2003 (light blue line). I cannot ignore the significance of this. I noted similar tipping points elsewhere round about that same time, (e.g. in earth’s albedo, going up). From 2003 the solar magnetic field has been going down. To me it seems for sure that we are now heading for a period of more cloudiness and hence a period of global cooling. If you look at the 3rd graph, it is likely that there wil be no sun spots visible by 2015. This is confirmed by the paper on global cooling by Easterbrook:
http://wattsupwiththat.com/2008/12/29/don-easterbrooks-agu-paper-on-potential-global-cooling/
In the 2nd graph of his presentation, Easterbrook projects global cooling into the future. These are the three lines that follow from the last warm period. If the cooling follows the top line we don’t have much to worry about and the weather will be similar to what we had in the previous (warm) period. However, indications are already that we have started following the trend of the 2nd line, i.e. cooling based on the 1880-1915 cooling. In that case it will be the coldest from 2015 to 2020 and the climate will be comparable to what it was in the fifties and sixties. I survived that time, so I guess we all will be fine, if this is the right trendline.
Note that with the third line, the projection stops somewhere after 2020. So if things go that way, we don’t know where it will end. Unfortunately, earth does not have a heater with a thermostat that switches on if it gets too cold. Too much ice and snow causes more sunlight to be reflected from earth. Hence, the trap is set. This is known as the ice age trap. This is why the natural state of earth is that of being covered with snow and ice. This paper was a real eye opener for me:
http://wattsupwiththat.com/2009/12/09/hockey-stick-observed-in-noaa-ice-core-data
However, man is resourceful and may find ways around this problem if we do start falling into a little ice age again. As long as we are not ignorant and listen to the [-----moderator's snip----]
Obviously: As Easterbrook notes, global cooling is much more disastrous for humans than global warming.
Note that in Easterbrook’s projection graph, the line showing the increase and decrease in global temperatures of the northern latitude is dashed. It looks like the northern hemisphere is always getting the brunt of the extreme weather.
So if you get tired of all that ice and snow, you may know that you are always most welcome to come and stay with us here, in the southern hemisphere!
Blessings from your child, brother, dad, friend,
date: 24 Jan. 2010
hunter:
Rather than say “doesn’t appear physically capable”?
He should say “without any experiments and theory I was able to deduce (guess?) that CO2 has very little effect”
There’s no mention of any atmospheric physics in his “treatise”:
- absorption equation integrated across all wavelengths
- re-emission of energy by these trace gases throughout the atmosphere
- the integration of these equations vertically through the atmosphere
I.e, the radiative transfer equations, well-proven by the way. He didn’t disprove them, just ignored them.
Skeptical people might say he isn’t even aware of them..
Or evidence:
- how can the top of atmosphere OLR only be around 240 W/m^2 when the radiated energy from the ground is around 396 W/m^2?
- how can the downward longwave radiation in the CO2 band be so high (see CO2- Part Six, Visualization )
Then later:
Won’t? Can’t?
Perhaps the writer is unaware that N2 has almost zero absorption. And the O2 only “absorbs” incoming UV solar radiation by breaking apart into atomic oxygen – then forming ozone, etc. But absorbs almost no longwave radiation.
People can write any old stuff, it’s fascinating.
But hunter, surely you didn’t think it was good? Did I do such a bad job on the CO2 series ?
Hunter,
This webpage provides a (bit dated) overview of the effects of clouds on climate:
http://www-das.uwyo.edu/~geerts/cwx/notes/chap09/rossow.html
NASA has articles here:
http://earthobservatory.nasa.gov/Features/Clouds/
If you need more meat with that:
http://isccp.giss.nasa.gov/climanal.html and
http://isccp.giss.nasa.gov/role.html and
http://ams.allenpress.com/perlserv/?request=get-abstract&issn=1520-0477&volume=80&page=2261
In a nutshell:
low, thick clouds cool in net
high, thin clouds warm in net
Also: indirect effects of aerosol injection, by providing more potential condensation nuclei for cloud droplets to form. Net effect: in the lower troposphere the SW cloud albedo increases.
hunter:
Because it doesn’t matter how long one cloud stays in the atmosphere. What matters is how much cloud.
Generally clouds provide a cooling effect of about -18W/m^2. Compare with CO2 radiative forcing under a doubling of CO2 of around 4W/m^2.
What effect does warming have on clouds? What are the feedbacks?
I think Roy Spencer sees clouds as the major influencer on the last 100 years of temperature (don’t quote me on that last point).
Thanks spaceman and science o doom..
Henry, i myself am skeptical o many many things, i have to be able to test em or observe em myself before i buy into much o anything(especially if the person telling me stands to gain outta my belief)
But in regards yah hypothesis up there… i know the hydrological cycles are as science o doom puts it the gordian knot o climate prediction(and unlike Alexander, yah cant just hack it with a sword) So more co2= heat=water vapor= heat = wind +water vapor=cloud(what kind? rain? high low cloud? etc) So sure, uncertainty, but where are you getting certainty in the result?
But ok, ive spent a bit o time kicking around the jungles in the tropics in my younger days, and those massive thunder heads undoubtedly cause cooling… but the mercury can still hit 50C before they do… Or as cool as mid 30s. And sure it can happen here at the mid latitudes, although less frequently… But surly it crossed your mind that adding a persistent climate forcing “could” expand the climate bands? Essentially growing the tropics, and sub tropics etc. And still be inline with that reasoning….
I personally find paleoclimatolgy fascinating, and what we know from that is the globe can certainly be warmer than it is today, i dont think co2 is the only factor determining climate(continental drift certainly shows a correlation with hot house/ ice house phases) But climate can/has and does change.. pretty much constantly.
henry Pool:
You have the mistaken impression that WattsUpWithThat is a repository of scientific knowledge. If you’re truly interested in understanding the behavior of the natural world (just about everything outside of the “social world”), then you will (a) stop repeating the above mistake, (b) make a serious effort to understand for yourself what science currently understands by reading, well, the science.
Radiation transfer is a multidisciplinary science, understood and applied successfully over the past century by:
-terrestrial climate, atmospheric physicists
-Astrophysicists (stellar atmospheres, stellar interiors, stellar winds, interstellar medium absorption, intergalactic absorption, Solar System Planetary atmospheres, exo-planet atmospheres, accretion disks,…. the list is nearly endless)
-laser physicists
-X-ray imaging scientists
-the list is very, very long…
Does it really seem all that likely to you that you (or perhaps Mr. Watts?) actually understands something so foundationally fundamental to matter-light interactions that 10s of thousands of scientists in multiple sciences, in multiple subfields within a scientific field, through ~100s of thousands of publications over the past century somehow did not and do not?
One would think that out of zillions of spectral observations of nature over the past century, nature would have told us a few times (at least) how very, very mistaken we are.
That said, one should not mistake science’s not knowing everything for knowing next to nothing.
scienceofdoom,
Actually you did pretty well.
I am poking around this with sharp sticks, so to speak, and like to see where extraordinary claims get us.
The main take away I have in this is that CO2 is very limited in its over all impact on the energy budget.
Your answer irt clouds is what I thought it would be.
Thanks,
Henry Pool -
Peek at the last page if you have to know the ending – but don’t spoil it for anyone who is enjoying the process of getting there…lol
I don’t want to disrupt a smooth narrative and I appreciate the fine scholarship and here comes the disjuncture:
two statements seem rough:
” how can the top of atmosphere OLR only be around 240 W/m^2 when the radiated energy from the ground is around 396 W/m^2?” (duration not specified)
“Because it doesn’t matter how long one cloud stays in the atmosphere. What matters is how much cloud.” (Hard to characterise a knot by one thread)
I trust you to resolve everything as the plot unfolds. That confidence means I stay on my hinges better and don’t jump from my seat and burst out…lol – the carpet doesn’t get so much of my coffee; I get more. The matrimonial models have a negative sign on the consequences of the HostileSpouseCleaning oscillation to account for a GloriousMeanTemper. One forgets at one’s peril. Calm is good.
Dave McK:
Because not all of it makes it to the top.
Water vapor, H2O, CH4, N2O and various other little trace gases absorb radiation and warm up, and so warm up the atmosphere around them and then – any gases that are able, radiate energy in all directions.
Some of this “all directions” is down.
See:
CO2 – An Insignificant Trace Gas? Part Six – Visualization
CO2 Can’t have that Effect Because..
The Earth’s Energy Budget – Part Two
On clouds I think I was answering another question. “How could they be so important if so ephemeral?”
scienceofdoom said:
“Generally clouds provide a cooling effect of about -18W/m^2. Compare with CO2 radiative forcing under a doubling of CO2 of around 4W/m^2.”
For clarity, this statement could use a bit of context. The *total* contribution of CO2 to earth’s energy budget is significant — all by itself amounting to over 30 W/m^2 (without the resultant feedbacks with water vapor or other greenhouse gas sources, etc). The value of ~4 W/m^2 is for a doubling of CO2 from 280 ppm to 560 ppm. The value quoted for the cooling by clouds is their total contribution.
Geophysicist David Archer has a fine web page demonstrating a radiative atmosphere, with all of the more important greenhouse gases whose concentration can be varied by the user, keeping track of temperature and gas concentration gradients vertically through the atmosphere. One can view the spectrum from any altitude, either upward or downward. It can even model simple water vapor feedback. Try it out here. These are not the results of the best radiative transfer calculations (aka, “Line by Line”), and so should serve for illustrative/educational purposes only.
Better than computing the TOA fluxes with this tool is the learning one can do by comparing the relatively detailed spectra as one varies the concentrations of greenhouse gases. See here for a nice tutorial (geared to an undergraduate student), Chapter 4 of his excellent textbook (errata).
Well, I actually stickled over that wattmeters is a measure of intensity – equivalent to a temperature- where a quantity is really the valid measure, e.g. watthourmeters – equivalent to heat. Sorry to make it a distraction because I know it all gets sorted.
Spaceman Spiff
Sorry your posts keep getting caught by the filter, no idea why.
Henry@ Spaceman Spiff
You don’t need all of those experts. really. Come here to Africa and then you measure the light on a sunny day at a specific time and also the temperature. Then wait for a cloudy day and measure the light again and the temperature at around the same time.. Then you know the “anomaly” caused by clouds. And when you look at that difference, you too will begin to understand the importance of clouds and cloud formation and how I came to my (own) 10 steps.. I mean what is 0,6 or 0,7 degrees warming over 100 years? I doubt even if the thermometers were that accurate 100 years ago. BTW it was not me who started the question here about clouds. I did not hear about Svensmark from WUWT. I stumbled on WUWT when I was just looking for some keywords on earth’s albedo. The quotes and theories that I have from WUWT were all figured out by myself, even before, but it does come in handy to have everything together.
Actually, I wished you were right. I think global warming is infinitely better than global cooling. But I know global cooling is coming so I have to start warning you people to clean up your act. Last year winter was a lot cooler here in the SH than the year before and this year the winter in the NH was a lot cooler than last year. All indicators are that global cooling is coming. Now people have changed global warming into “climate change”. That way you can even “explain” the cooler weather. But is that going to help when we all start freezing up? (I don’t think the cut by the moderator was justified)
Spaceman Spiff@henry Pool:
1) I was addressing your criticisms of the radiative transfer and molecular opacities, not the role of clouds.
2) All climate scientists will tell you that clouds remain a significant source of uncertainty. I was posing no argument with this. But a heck of a lot has been done in the past 20 years in the relationship between clouds and climate. And it’s not as if Svensmark hasn’t been heavily criticized in the peer-reviewed literature. The following web site compiles this literature, with topical organization — this one on “debunked” papers:
http://agwobserver.wordpress.com/anti-agw-papers-debunked/
Search for Svensmark.
It is also true that Svensmark’s cosmic ray/cloud-albedo idea is just that — a speculative hypothesis without (yet) a coherent physical mechanism.
henry@spaceman spiff
1) I did not really see the proof from you that CO2 is a greenhouse gas and you also did not prove to me that the 70 odd ppms (0.0075%) that were added to the atmosphere since 1960 are indeed significant – I need to see actual test results that show a progression when you use atmospheres containing different amounts of CO2 ( at the relevant concentrations) taking into account that CO2 also causes cooling….(see my initial posts).
Question:
Also, I think we need to investigate the role of water – which apparently is a much stronger greenhouse gas – or so I hear.
The average water vapor content in the atmosphere is 1% which is a lot more than the 0.04% of CO2. All burning, cooling and energy processes by humans add more water vapor, even nuclear power…. (for cooling). Then we also have many dams, ponds and pools made by humans which surely must add more water vapor (shallow water easily warms up). So my question is: why does no one talk about that?
Singling out CO2 is short sighted. I believe more CO2 is better, it is like fertilizer. Everything you eat today depends on CO2. What people must complain about is the CO (from incomplete combustion) and gases like SO2 (from impurities in the fuel). CO2 is good.
2) The proof of the pudding is in the eating. My 10 steps make a lot more sense than all your complicated stories.
You want to believe your stories, that it is fine with me. I already predicted flooding of the rivers in the US and Europe because of all that extra snow and ice in the NH winter. It is already coming true. I predict further that more global cooling is on hand.
Maybe the picture on top of your site is an omen. It looks cold. Better make sure you prepare for the big freeze.
henry Pool
They do. Maybe you are looking in the wrong places. Water vapor is a major focus of research. There are many 100′s of papers on it (I’m sure 1000′s).
Without understanding the basics, any story will sound attractive. If you want to understand the basics, including the relative role of water vapor vs CO2 –
check out the CO2-An Insignificant Trace Gas? series and by Part Five you will see how the role of water vapor is calculated.
I’m sure your story will resonate with a lot of people. We’ll stay with the complicated stuff here.
henry@scienceofdoom
Come off it. I cannot believe you. If you want to prove a point or a rule or a law you must be able to produce a formula. Where is it?
There is no formula. I studied the IPCC reports. What they did is look at the global warming values. Someone decided that CO2 or greenhouse gases must be to blame (let us have a planet, add some CO2 , see if the temp. goes up, it did, so that must be it. What else can it be?) and then they looked at the concentrations of the gases at 1750 compared to 2005. Then they assigned radiative forcings attributed to the individual gases that would explain the warming. It is really just a weighting. That is the only formula I could find. But what is this? That is looking at a solution for a problem if you know what the cause is of your problem. You can only do that if you are 100% sure of the cause of your problem. It is an error that many doctors and scientists have made, myself including.
If you want to be a good scientist you must first prove your theory with a formula – then we can begin to look for the solution of the problem – in this case – global warming – if it it still happening. I see many people are beginning to doubt whether global warming is still happening.
henry Pool:
In Part Three – as previously explained.
In Part Five you will see Ramanathan and Coakley’s 1978 paper discussed with a link to their paper. Why not take a look? 25 pages of equations, here’s a small extract:
The IPCC report has references. In the references are papers like this one. For example, chapter 2 of the 2007 report: “Changes in Atmospheric Constituents and in Radiative Forcing” has 17 pages of references.
So where does it show the warming and cooling of CO2 in W/m2/m3 {CO2 0.03-0.05%}/24 hours?
henry Pool:
You have been convinced that no one has any equations, “the whole thing is all made up”.
Why not take some time to read at the least the series on CO2 on this blog? And think about it. And look up some of the references in the IPCC report. And then come back and ask some questions.
Your convictions are strong but you have demonstrated to anyone reading here that some of those convictions are based on lack of information, and some are based on false information. The fact that there is a large body of work – with equations – to support various ideas about the possible effect of CO2 on climate should make you pause and rethink. You’ve just confidently asserted that that isn’t the case. Take some time to review the information provided.
You think you have some answers, but you don’t. This problem is really very simple. Took me only 3 months to figure it out and I was a staunch Al Gore supporter! you should remove your censorship in my post as people will be wondering what you took out….
henry Pool
Next time you are at WUWT at a sun based thread, read and follow Leif’s comments and links… he knows his stuff. And look at it objectively. Im not saying it has no credibility, but look hard at the evidence for and against.
You are showing a conformation bias, we can all be guilty o that..(i have designed a positive displacement turbine thats gonna make me a billionaire!!!! muhahaha
)
Like i said in my previous post to you, i am a skeptical individual by nature. And certainly find some of the more apocalyptic AGW claims questionable… And i realize it can be a question o trust as far as sourcing information… But the basic physics regarding the absorption properties of co2 is/and has been well understood for quite some time. And this blog here has to my knowledge the best threads breaking this down, and showing it that i have come across so far.
How they interact with other factors in a chaotic system may have areas of less certainty. But the basic greenhouse system is what makes this planet habitable. And is really beyond question, i can observe this by noticing that the average global temperature isnt -18oC or so.
Id urge you read dooms co2 series, it is well written. Yah can still be skeptical o AGW and understand the physics of the greenhouse effect.
henry Pool said:
—-
“…Singling out CO2 is short sighted. I believe more CO2 is better, it is like fertilizer. Everything you eat today depends on CO2. What people must complain about is the CO (from incomplete combustion) and gases like SO2 (from impurities in the fuel). CO2 is good.”
and
“2) The proof of the pudding is in the eating. My 10 steps make a lot more sense than all your complicated stories.
You want to believe your stories, that it is fine with me. I already predicted flooding of the rivers in the US and Europe because of all that extra snow and ice in the NH winter. It is already coming true. I predict further that more global cooling is on hand.”
and
“Come off it. I cannot believe you. If you want to prove a point or a rule or a law you must be able to produce a formula. Where is it?
There is no formula. I studied the IPCC reports. What they did is look at the global warming values. ”
and
“…If you want to be a good scientist you must first prove your theory with a formula – then we can begin to look for the solution of the problem…”
and
“You think you have some answers, but you don’t. This problem is really very simple. Took me only 3 months to figure it out and I was a staunch Al Gore supporter!”
—-
You’re putting us on, right? April Fools’ Day and all that? You really had me going there until you insinuated Al Gore. (Am I right? Or…?Or….?) Either way (IMO) your recent statements above have effectively quashed any further attempts of carrying on a fruitful, science-grounded discussion.
Poe’s Law
an anti-AGW parody blog
henry@spaceman spiff
My point of departure was Al Gore’s movie. At the time, I believed that the correlation given there was correct i.e that CO2 causes global warming. But I determined that it was the other way around. Global warming causes more CO2 in the atmosphere. As any good chemist knows: CO2 dissolves in water and if you want it out of the water you just have to make the water warmer.
I am glad you think you are more clever than me. But at least someone greater than Al Gore was here. Read my posts carefully again and you too will soon understand that clouds and rain and colder weather is already upon is. It all starts there where we know it must start: at the sun. Study the processes of the sun and you will soon realize that global cooling is coming. Make sure you are not left outside in the cold.
http://wattsupwiththat.com/2010/04/02/artic-sea-ice-extent-update-still-growing/#more-18100
If you see the ice creeping up on you at your front doors, you know:
global warming is over. we now have to seriously look at global cooling and the consequences of that for every day life. No time for playing games and funny science.
especially for henry Pool-
from Etiquette : “..I am trying to keep posts and comments on topic. If the topic [the article] is the future of the world, go right ahead, otherwise try and stay roughly on the topic.”
I will be moderating or removing comments which move too far from the topic. Too far is totally subjective. The two comments above are “too far”. They can stay as illustrations.
Henry@the moderator and @Mike Ewing
I will show the moderator that my above comments are still on the topic but I can understand that you lost my train of thought.
I think after the last two winters, the vast majority of people in the Northern Hemisphere (with perhaps the exception of Eastern Canada and West Greenland) are fully aware that we have entered a period of global cooling.
So I am saying: perhaps it is the other way around: i.e. there being a relationship between increased CO2 and global cooling —
If by now you have understood what I have written here, you will follow that in my mind this might not be such a far fetched idea…
::::
My theory might be true after all, the cooling properties of CO2 might be greater than the warming properties. The net effect of more CO2 may cause cooling, not warming….Without proper testing proving the opposite, this is what I have been suspecting all along…..:
We know that CO2 has absorption in the 14-15 um range causing some warming (by re-radiating earthshine, 24 hours per day) but as shown and proved it also has a number of absorptions in the 0-5 um range causing cooling (by re-radiating sunshine). This cooling happens at all levels where the sunshine hits on the carbon dioxide same as the earthshine. The way from the bottom to the top is the same as from top to the bottom. So, my question was: how much cooling and how much warming is caused by the CO2? How was the experiment done to determine this and where are the test results? If it has not been done, why don’t we just sue the oil companies to do this research? (I am afraid that simple heat retention testing will not work here, we have to use real sunshine and real earthshine to determine the effect in W/m3 [0.04%-0.06%]CO2 /m2/24hours).
When they analysed the spectra, did they look at all the absorptions, namely also at those of CO2 in the UV – that have only been discovered recently? I also doubt that spectra analysis would work here – you have to come up with a more real time experiment.
Namely, for example, I think especially the cooling of CO2 caused at 4.3 um might be considerable because this is where the sun’s radiation is at its hottest (on your skin). Note that the temp. on the coast on a sunny day (no wind) is always a few degrees cooler than more inland. This is due to same cooling caused by water vapor in the sun’s solar spectra – as you know, I am saying CO2 does exactly the same thing. Without CO2 in the atmosphere more (hot) IR radiation would be slammed on top of our heads.
So what is the net effect of CO2? How do we all know for sure that CO2 is a greenhouse gas when clearly Svante Arrhenius formula has long been proven wrong and nobody has come to me with the right formula?
henry Pool
I will add to the etiquette that continual repetition of points, again at the discretion of the moderator, will also be removed.
You are very keen to the make the same points then ignore any answers.
The solar radiation >4um is <1% of the total solar energy. As has already been noted.
And "no one has come to you with the right formula".
We'll let current and future readers decide for themselves if your questions have merit. And if the various answers provided have merit.
I would have more interest in trying to answer specifics if you had shown any interest in absorbing any answers so far.
First henry Pool post deleted for repetition.
henry Pool – if you want to be part of a discussion here, show that you have attempted to grasp the content of answers to your comments.
If you ask a question that shows that you have actually read and thought about earlier responses, your comment will stay up.
I hate to put this comment here, but your RSS feeds appear to be broken.
Thanks, I appreciate you letting me know. It’s now fixed according to the great people at wordpress.
CO2 does not cause less sunlight to hit the earth only by absorption, it can also do so by Rayleigh scattering. Has anyone considered this effect? Is it included in the IPCC calculations? References would be greatly appreciated.