The effectiveness of CO2 as a greenhouse gas becomes ever more marginal with greater concentration

Team Sisyphus uniform design - back

Team Sisyphus uniform design – back (Photo credit: nicomachus)

The political target of limiting the effect of Man-made global warming to only +2⁰C can never be attained.

Guest essay by Ed Hoskins

According to well understood physical parameters, the effectiveness of CO2 as a greenhouse gas diminishes logarithmically with increasing concentration and from the current level of ~390 ppmv, (parts per million by volume). Accordingly only ~5% of the effectiveness of CO2 as a greenhouse gas remains beyond the current level.

This inconvenient fact is well understood in the climate science community. It can be accurately modeled using the Modtran program maintained and supported at the University of Chicago.

The logarithmic diminution of the effect of CO2 is probably the reason why there was no runaway greenhouse warming from CO2 in earlier eons when CO2 levels were known to be at levels of several thousands ppmv.

Remarkably, IPCC Published reports , (TAR3), do actually acknowledge that the effective temperature increase caused by growing concentrations of CO2 in the atmosphere radically diminishes with increasing concentrations. This information is in their report. It is well disguised for any lay reader, (Chapter 6. Radiative Forcing of Climate Change: section 6.3.4 Total Well-Mixed Greenhouse Gas Forcing Estimate).

The diminishing percentage effectiveness of CO2 as a greenhouse gas as acknowledged by the IPCC and its concomitant diminishing temperature effect are as follows:

increment cumulative

0-100 ppmv: according to David Archibald / Modtran data ~2.22°C ~2.22°C

100-200 ppmv: plants die below this level of CO2 +~0.29°C ~2.51°C

200-300 ppmv: noted as the preindustrial CO2 level +~0.14°C ~2.65°C

300-400 ppmv: current level IPCC attributes all as Man-made +~0.06°C ~2.71°C

400-600 ppmv: business as usual till 2100 +~0.08°C ~2.79°C

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600-1000 ppmv: improving levels for plant growth +~0.06°C ~2.90°C

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Accounting for the diminution effect the actual temperature reductions achievable, the calculated achievable values are in the range of few hundredths to a few thousandths of a degree Centigrade. As the margin of error for temperature measurements is about 1.0°C, these miniscule levels the temperature effects for all the efforts of those nations attempting to control their CO2 emissions, (only about 12% of world CO2 emissions), are marginal, immeasurable and thus irrelevant.

These minute temperature changes have to be seen in the context of normal daily temperature variations at any a single location of 10⁰C to 20⁰C. It can be as much as 40⁰C to 50⁰C over the course of a whole year.

Although the IPCC tacitly acknowledges that this crucial diminution effect with increasing concentrations effect exists, it certainly does not go out of its way to emphasise it. Like the Medieval Warm Period, that they attempted to eliminate with the Hockey Stick graph in 2001, the panel knows that wide public knowledge of the diminution effect with increasing CO2 concentration would be utterly detrimental to their primary message.

“Man-made CO2 emissions are the cause of climate change”.

The IPCC certainly does not explain these devastating consequences for the CAGW theory in their Summary for Policy Makers. This is because the IPCC is an essentially political organisation, that is solely tasked with the promotion and presentation of Man-made Climate Change from CO2 emissions, as an accepted and non-contentious fact for world’s politicians.

Thus the IPCC is entirely misleading in its central claim for Policy Makers, as they say:

“Warming of the climate system is unequivocal. Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations.”

Any unquestioning, policy making reader is lead to assume that all increasing CO2 concentrations are progressively more harmful because of their escalating Greenhouse impact. But the opposite is so.

From the present concentration of atmospheric CO2 at approaching 400 ppmv, only ~5% of the effectiveness of CO2 as a Greenhouse Gas remains.

This can only give rise to a maximum of a further of ~+0.21°C. Thereafter beyond 1000+ ppmv the effect of increasing levels of CO2 can only ever be absolutely minimal even if CO2 concentrations were to increase indefinitely.

It is for this irrefutable physical fact that the widely held alarmist policy ambition

“to constrain Man-made temperature increase to only +2.0 °C”

could in fact never be reached, however much more Man-made CO2 was emitted.

It is impossible to ever reach the much vaunted policy upper limit of +2.0 °C that has been promoted by politicians as a target upper limit of temperature effect caused by man-made CO2 emissions.

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Has anyone ever managed to get an alarmist to accept this? I’ve never seen it on the blogs I visit. Too much of An Inconvenient Truth, I suspect.

sailboarder

So it all hinges on guesses about feedbacks. No wonder R Lindzen focusses so much attention on getting empirical data on that detail.

Mike H

It would be greatly appreciated if somebody could provide me with a layman’s way of explaining this to people. Even when I tell people the logarithmic path CO2 returns from additional

Jeff L

Your conclusion of we can’t get 2 deg C warming rests on your “5%” more statement. What exactly do you mean here? 5% of what? Unless you think climate sensitivity to CO2 is zero, there will be a contraption of CO3 that will yield a 2 C rise in temps as there is no upper bound to the sensitivity equation. As you said, it is logarithmic so the concentration may be high but it should be a finite & definable number.

Mike H

Screwed up above. My apologies
It would be greatly appreciated if somebody could provide me with a layman’s way of explaining this to people. Even when I tell people the logarithmic path CO2 follows is not in dispute, just the shape of the curve, they don’t get it. Dr. Ball once explained it as painting a window black. Each coat is going to have less and less of an effect. But that doesn’t provide a good parallel explanation as to why. If anybody could help me out, it would be greatly appreciated.
Thanks in advance

John Stratton

Mike H … the 10th blanket doesn’t keep you a whole lot warmer than the first 9

MODTRAN calculates that 50% of the warming effect of current (almost 400 ppm) CO2 levels would be accomplished by just 20 ppm CO2 (for a tropical atmosphere w/ constant relative humidity):
http://www.burtonsys.com/climate/MODTRAN_etc.html
The NCAR radiation code says that 40 ppm CO2 would be needed to get 50% of the current CO2-caused warming, rather than 20 ppm, but, either way, the lesson is clear: we’re well past the point of diminishing returns w/r/t the warming effect of CO2.
The alarmist projections of wild increases in temperature are based on assumptions of dramatic amplifications of the warming effect through positive feedbacks. But for the tropical atmosphere MODTRAN calculates only +65% amplification from water vapor, and that’s really an upper-bound, because it doesn’t taking into account various negative feedbacks, such as water-cycle (evaporative) cooling.

Phil.

Guest essay by Ed Hoskins
According to well understood physical parameters, the effectiveness of CO2 as a greenhouse gas diminishes logarithmically with increasing concentration and from the current level of ~390 ppmv, (parts per million by volume). Accordingly only ~5% of the effectiveness of CO2 as a greenhouse gas remains beyond the current level.

But at higher concentrations it will transition to a square root dependence which will give a higher sensitivity.

Kev-in-Uk

Isn’t this is EXACTLY the type of message that the 50:1 video needs to get across – i.e. the IPCC’s own ACCEPTED science says that warming will slow and take many years to reach the acclaimed doom and gloom ‘critical’ levels (if at all!)…….the trouble is that for a video presentation it needs to be made short and snappy for lay folk to grasp quickly……

oldseadog

Mike H part two:
Me too.
But I guess that a simple explanation would be one inconvenient truth too many for many “climate scientists”.

oldseadog

Kev-in-UK:
Got it in one.

climatereason

Phil
Have you got a graphic of some kind that demonstrates your point? It is difficult to visualise your comment especially as you provide mo actual figures or links. Thanks
Tonyb

Bloke down the pub

This is one of the reasons warmists bang on about ocean ‘acidification’. They know mother nature won’t play ball with warming so they need something else to scare the children with.

The sentence in chapter 2 AR4
“Note that for CO2, RF [radiative forcing] increases logarithmically with mixing ratio”
is so very well hidden. You would never know it was there if you didn’t read it.
Is Ed Hoskins going to tell us how the magic numbers were calculated?

Brian Macker

” Thereafter beyond 1000+ ppmv the effect of increasing levels of CO2 can only ever be absolutely minimal even if CO2 concentrations were to increase indefinitely.”
One can add CO2 to the point where lead will melt on the surface of Venus. Just keep adding CO2 until you get to 92 bar of pressure at the earth’s surface. Then you have essentially recreated the Venusian atmosphere, and the surface temps would rise to 872 °F. Not sure why you think this statement is true.
“Accordingly only ~5% of the effectiveness of CO2 as a greenhouse gas remains beyond the current level.”
False. If CO2 concentrations were to increase indefinitely we could get to a situation where 90% of the atmosphere (which is now ten times more dense) then on up to Venus style atmosphere. This would entail a much larger than 5% increase in temperature. Isn’t 872 °F more than 5% greater than say 90-100 °F even when I convert to Kelvin. Let’s see 305 K vs 739 K. Yep that’s a >100% rise in K.
So please reword this information so that it is true if you mean something else. As written these are falsehoods. Adding CO2 would eventually effect atmospheric density. Are you talking about replacing part of the atmosphere with CO2 while maintaining the same atmospheric weight of 14lbs per square inch at sea level, so that the maximum would be 100% CO2 at one earth atmosphere of pressure sea level when finished? Obviously that cannot go on indefinately because you have to stop at 100%. So that must NOT be what you mean. So what do you mean?

DC Cowboy

The ‘alarmists’ pin their hopes on ‘positive feedbacks’, which, as an engineer who specialized in feedback systems prior to giving up Phd work as a lost cause, I find to be tenuous at best. If there were ‘positive feedbacks’ as the ‘alarmists’ believe the earth would have spiraled into a Venus like atmosphere hundreds of millions of years ago. The fact that it hasn’t if prima facia evidence that there are no large ‘positive feedback’; mechanisms at work in the earth-atmosphere system.

Dr Burns

It makes even the non alarmist claims of climate sensitivity look ridiculous. http://wattsupwiththat.com/2012/08/13/best-volcanoes-and-climate-sensitivity/
There’s no concrete evidence that CO2 has any effect at all on global temperature … it could all be the soda bottle effect.

“recreated the Venusian atmosphere”
So how do you envisage the change in orbit?

steven

This fact also explains why CO2 is so important in accelerating the warming at the end of an ice age, when atmospheric CO2 is very low.

Peter Miller

Are there any other publications on this?
If this is true, then its implications are truly epic.

Arno Arrak

This annoys me:
“…According to well understood physical parameters, the effectiveness of CO2 as a greenhouse gas …..etc…”
The effectiveness of CO2 as a greenhouse gas is zero. The physical parameters are not well understood by the pseudoscientists pushing for global warming. There are two reasons for thinking that its effectiveness is zero. The first one is derived from the absence of any kind of warming for the last fifteen years. There is more carbon dioxide in the air now than ever before but it’s not doing its warming thing. Without warming, no greenhouse effect and no AGW is possible. Has that alleged warming ever existed? The answer is no. If you check the global temperature curve you will find that there has been no greenhouse warming for the last 100 years. The second reason is Ferenc Miskolczi. The correct way to determine the greenhouse effect is to account for the activity of all greenhouse gases present. In our case this means carbon dioxide and water vapor. Arrhenius did it only for carbon dioxide which leaves his theory incomplete. If you use both carbon dioxide and water vapor you find that an optimum window for absorption of infrared radiation exists that they jointly maintain. If you increase carbon dioxide and thereby increase IR absorption water vapor will diminish to restore the optimum absorption for the atmosphere as a whole. As a result, total absorption of IR by the atmosphere does not change when carbon dioxide is added, and this is what Miskolci observed in 2010. Such cooperation between the two greenhouse gases amounts to negative water vapor feedback, the exact opposite of what IPCC uses to get their very high warming predictions. Since greenhouse warming gets its energy from absorption of IR radiation and since total absorption no longer follows carbon dioxide concentration it follows that greenhouse warming is impossible. We see that of course today when the highest carbon dioxide ever has no warming effect.

Red Baker

A log graph of CO2 effect on temperature would be very appropriate for this article.

Mike H, here’s a stab at an explanation for laymen.
The misnamed “greenhouse” effect of greenhouse gasses like CO2 is based on the fact that they are not truly colorless. They have a “tint,” though we can’t see it, because it’s in a part of the light spectrum that our eyes don’t detect. GHGs are transparent in the visible part of the light spectrum, but they absorb (block) parts of the IR spectrum.
Adding such gasses to the atmosphere has a warming effect on the lower atmosphere, because the light arriving at the earth from the sun is much “bluer” (shorter average wavelength) than the light emitted from the earth. Because the earth is relatively cool, the light emitted from the earth is mostly IR. So anything in the atmosphere that blocks IR but is transparent to visible and UV will have a warming effect, because it lets in most of the arriving solar radiation (that warms the earth), but blocks a much larger percentage of the departing radiation (that cools the earth).
Even though CO2 levels are measured in parts-per-million, there’s nevertheless already so much CO2 in the atmosphere that it blocks nearly all of the IR that it can possibly block. So adding more CO2 doesn’t have much effect on temperature. For CO2’s main absorption bands, we’re way, way past the CO2 levels at which the IR is all absorbed. Only for very narrow ranges of wavelengths at the fringes of those absorption bands, where CO2 is a very weak absorber, can adding more CO2 appreciably increase the amount of IR blocked.
However, adding even a small amount of a different GHG (such as one of the CFCs or HCFCs) can have a much larger warming effect, by blocking a part of the IR spectrum for which the atmosphere would otherwise be transparent. That’s why you may read that CFCs like Freon-12 are thousands of times more potent as GHGs than CO2. It’s not that there’s anything fundamentally special about Freon-12, it’s just that there’s so few Freon-12 molecules in the atmosphere that some of their absorption bands aren’t already blocked.
 
Here’s an analogy. Consider moth-eaten blankets to be like GHGs, and different positions one the blankets correspond to different parts of the IR spectrum. The blankets have big holes in some places, but nice, dense wool fabric in others.
Different patterns of holes in the blankets are like different GHGs. They pass some parts of the IR spectrum, and block others. So “CO2” blankets have one pattern of holes, “CH4” blankets have a different pattern of holes, “CFC-12” blankets have yet another pattern of holes, etc.
Now, envision an obsessively compulsive neat-freak piling on moth-eaten blankets to try to keep warm in a chilly night. He exactly straightens and lines up each blanket on the bed.
If he piles on a dozen identical “CO2” blankets, with the holes all lining up exactly, he won’t be much warmer than if he had only one or two “CO2” blankets. But if he adds a “CH4” blanket, with many of its moth-holes in different places, then he’ll be a lot warmer, because some of the CO2 blanket’s holes will be blocked by the CH4 blanket, and vice-versa. And if he adds a “CFC-12” blanket, with some of its holes in different places than the holes in the CO2 and CH4 blankets, he’ll be warmer yet.
Right now, we’ve got about 10 or 20 CO2 blankets piled on. Adding another 5 or 10 or 20 CO2 blankets will keep us a tiny bit warmer at the frayed edges of the holes, but it won’t make near as much difference as adding some other kind of blanket.

davidmhoffer

Brian Macker;
False. If CO2 concentrations were to increase indefinitely we could get to a situation where 90% of the atmosphere (which is now ten times more dense) then on up to Venus style atmosphere.
>>>>>>>>>>>>>>>>>>>
Seriously? Since only 20% of the atmosphere is oxygen, how are you going to get CO2 over 20%? Or are you assuming some massive source of oxygen as yet unknown that will suddenly spring into existence in order to be converted to CO2? Or by “adding” CO2 do you mean brand new C and O that don’t exist anywhere at all coming into existence? By magic? Transported through a black hole maybe? Or big space ships that scoop it up from Venus and import it to Earth?
The rest of your comment is similarly irrelevant to any reasonable discussion of the science.

0-100 ppmv: according to David Archibald / Modtran data ~2.22°C ~2.22°C
Something wrong here: if you use Modtran for the first step, looking down from 70 km height, 1976 US standard atmosphere, no clouds or rain, the difference between 0-100 ppmv CO2 is near 7°C.
Modtran also says if you go from pre-industrial 280 ppmv to a double 560 ppmv, the temperature increase is ~0.9°C, which is quite different from the 0.14°C extra (from 300 to 600 ppmv) in your calculation. What is going wrong here?
Of course, that all is before any (positive or negative) feedbacks…

Latitude

daveburton says:
May 8, 2013 at 2:19 pm
===========
excellent……thank you!

The Sage

Logarithmic is not asymptotic. Logarithmic means that each doubling in concentration has the same effect as the previous — so if going from 100ppm to 200ppm gives +0.2875C, then from 200ppm to 400pmm is another +0.2875C and going from 400ppm now to 5% (another 7 doublings) gets you the +2C.
Of course you’re probably going to have to bake the CO2 out of a fair chunk of the carbonate rock on the planet to get that much into the atmospehere. Just burning the fossil biosphere wouldn’t do it.

This implies that it’s meaningless to cut CO2 emissions now unless the rest of the world—i.e., Asia—does the same, AND makes massive cuts, to lower the current CO2 level to, say, 350. Lacking a worldwide effort, any cuts in the West will merely slightly slow the rate at which additional CO2 accumulates.
This also implies that the IPCC’s charts showing a substantial difference in warming between scenarios where CO2 continues to rise at current rates (“business as usual”) and where its rising is halted and emissions continue only at present levels are badly wrong—especially if CO2 has a long residence time. There should be nearly no difference between them.

steven said on May 8, 2013 at 2:09 pm, “This fact also explains why CO2 is so important in accelerating the warming at the end of an ice age, when atmospheric CO2 is very low.”
No, atmospheric CO2 levels have never been “very low” on planet Earth, even during ice ages. CO2 levels are thought to have been a few hundred ppm for at least 50 million years. CO2 levels are held in a relatively narrow range largely because of a simple biological feedback mechanism: With less than about 200 ppm, plants stop growing because they can’t scavenge carbon from the atmosphere, so they stop absorbing it. But as CO2 levels go up, plants grow like crazy and absorb it. (The oceans also buffer CO2 levels.) Even at ~200 ppm CO2, which is probably as low as it has ever gotten, MODTRAN calculates that there’d still be about 10x as much CO2 as is needed to produce half of the current CO2-induced warming.
 
Arno Arrak said on May 8, 2013 at 2:11 pm, “The effectiveness of CO2 as a greenhouse gas is zero… If you increase carbon dioxide and thereby increase IR absorption water vapor will diminish… As a result, total absorption of IR by the atmosphere does not change when carbon dioxide is added…”
That’s wrong, Arno. Even if there were such a negative feedback mechanism (for which there’s no obvious physical explanation, since warm air holds more H2o vapor rather than less), it still would not reduce the warming effect of CO2 to zero. Negative feedback can reduce the magnitude of an effect, but never to zero.

davidmhoffer says:
May 8, 2013 at 2:21 pm
Not so difficult to reach much higher CO2 levels beyond the 20% oxygen: lots of CO2 is buried in very thick chalk layers on lost of places. That is where the ancient CO2 levels went. Add some acid to it (like a few thousands of volcanoes all erupting over thousands of years) and you will have any desired quantity of CO2 in the atmosphere.
Not that I expect that to happen in the near future, but in theory that is possible without using any oxygen. And it happened a few times in the planet’s history, see the Deccan Traps…

dcfl51

Brian Macker, you make an interesting point but it doesn’t stand up to scrutiny. How could we increase CO2 indefinitely ? Burning fossil fuels causes carbon atoms in the fuel to combine with oxygen atoms in the air to produce CO2. As only 21% of the (dry) atmosphere is oxygen we surely couldn’t cause the CO2 concentration in the atmosphere to exceed 21% even if we burnt the entire planet. And we would all have died of asphyxiation well before we could accomplish this.
Remember that all of the carbon in fossil fuels was fixed from the atmosphere by plants in the first place so releasing this back into the atmosphere can, at worst, create the CO2 concentration under which life self-evidently originally flourished. Even 550 million years ago, before the first plants invaded the land, the CO2 concentration was only 7000 ppm (0.7%). I don’t know how air pressure at the earth’s surface would be affected – CO2 is a heavier molecule than oxygen – but surely a change in the composition of 0.7% of the atmosphere would make tiddly squat difference.

rgbatduke

Um, the article is not very effectively written. What the author MEANS to say isn’t that the target of <2C warming cannot be achieved, it is that it cannot be missed, no matter what happens to the CO_2.
Neither statement is true, of course. We can no more believe the predictions of MODTRAN than we can any other climate model computation. A more direct computation of the temperature increase expected on a doubling of CO_2 (only) to 600 ppm is a still highly uncertain 1 to 1.5 C, at least 0.3 of which we have already observed. But the uncertainty in TOTAL warming goes beyond this, as it involves unproven climate feedbacks almost entirely from the water cycle, where water already provides over 95% of our total GHE and where water is enormously complex in its integrated effect on the climate. Water vapor is a powerful GHG in much higher concentration than CO_2 in the atmosphere. Water has a huge latent heat of vaporization and fusion and is a major factor in the transportation of heat from one place to another laterally and from the ground to the upper atmosphere vertically. Water is key to plant growth, and plants moderate climate in a number of ways. Then there are the other feedbacks from things like soot and aerosols co-produced with CO_2 in most burning circumstances. Then there are the largely unknown effects of the major decadal oscillations, which modulate the EFFECTIVENESS of water as a feedback mechanism by modulating where oceanic heat and water vapor go.
Truthfully, we do not know what will happen to the climate by 2100. Perhaps it will warm more than 2 C. Probably it will not (and a lot of climate scientists are coming to believe that, as the Earth continues to stubbornly refuse to warm in parallel with a steadily increasing CO_2 concentration). Perhaps be can have an impact on the warming or cooling we eventually do experience. Perhaps not — it is simply not possible to separate out the fraction of the warming and cooling observed over the last 2000 years and say "this much is due to CO_2". Not when we cannot predict or explain the gross variations observed over that timeframe, not when those variations are as large or larger than what has been observed and attributed to CO_2 in the comparatively recent past.
rgb

Mike H says:
May 8, 2013 at 1:16 pm
It would be greatly appreciated if somebody could provide me with a layman’s way of explaining this to people. Even when I tell people the logarithmic path CO2 follows is not in dispute, just the shape of the curve, they don’t get it. Dr. Ball once explained it as painting a window black. Each coat is going to have less and less of an effect. But that doesn’t provide a good parallel explanation as to why. If anybody could help me out, it would be greatly appreciated.
Thanks in advance
John Stratton says:
May 8, 2013 at 1:24 pm
Mike H … the 10th blanket doesn’t keep you a whole lot warmer than the first 9

Neat. But for parallelism with the “5%” theme, a more accurate and striking way of putting it would be to say, “the 20th blanket doesn’t keep you a whole lot warmer than the first 19.”

dcfl51

Dave Burton, warmer air is capable of holding more moisture than cooler air. But observations made over the past 60 years show that global relative humidity has actually been falling in contradiction of the standard model assumption that it should remain constant. Miskolczi’s result shows that, as near as dammit, the fall in humidity matches the increase in CO2 in terms of its impact on the greenhouse effect. This is the basis of Miskolczi’s claim that the sensitivity of the climate to 2xCO2 is zero.
http://www.friendsofscience.org/assets/documents/FOS%20Essay/Climate_Change_Science.html#Water_vapour
Observations trump theory.

davidmhoffer

Ferdinand Engelbeen says:
May 8, 2013 at 2:47 pm
davidmhoffer says:
May 8, 2013 at 2:21 pm
Not so difficult to reach much higher CO2 levels beyond the 20% oxygen: lots of CO2 is buried in very thick chalk layers on lost of places. That is where the ancient CO2 levels went
>>>>>>>>>>>>>>>>>>
Well certainly. By the same token, you can pile up flap jacks high enough on top of coal to make diamonds. Also true and also irrelevant to any practical discussion about what humans may or may not be doing with carbon.

From Yahoo:
http://malaysia.answers.yahoo.com/question/index?qid=20130201141638AAHawXn
there is an estimated 3.5 x 10^23 grams of carbonate rock on the planet. The mass of the atmosphere is 5 x 10^21 grams. So there is about 100 times more carbonate rock than there is gas in the atmosphere. Normalizing for the number of moles of each and assuming all the carbonate is present as CaCO3, factoring in the difference in molecular weights, this works out to about 10 times as many moles of CO2 available as there are moles of atmosphere
Thus with all carbonate acidified, the atmosphere gets 90% CO2, 10% air. Even a little higher if one uses all oxygen to burn up coal, oil and gas (if there is enough of it)…
Sometimes it is better to do the calculations before betting on the answer…

The logarithmic fall-off of the effect of CO2 on the greenhouse warming of the Earth is one of the powerful arguments against man-made global warming and climate change.
Thanks Ed, good article.

davidmhoffer

Ferdinand;
Thus with all carbonate acidified, the atmosphere gets 90% CO2, 10% air.
>>>>>>>>>>>>>>>>>
And how is this acidification accomplished? There’s enough iron in the earth’s core to cover the earth surface with a sheet of steel. True, and irrelevant. ‘Tis one thing to say something is possible, another to say that there is any means of achieving it that is worth discussing from the perspective of human activity. The original commenter made the claim that if “we” keep adding CO2 to the atmosphere it will get to 90% and make earth like Venus. We’re not capable of any such thing, anymore than we are capable of turning coal into diamonds by the weight of flap jacks or covering the earth’s surface with a sheet of steel.

KNR

facts! you don’t need no stinking facts when you have’ faith’ in the cause .

george e. smith

“””””……This inconvenient fact is well understood in the climate science community. It can be accurately modeled using the Modtran program maintained and supported at the University of Chicago……”””””
So what means “accurate modeled” ?
Does it mean that the mathematics in MODTRAN is robust, and if you input the same variables it always gives the same answer, or do you mean that MODTRAN accurately predicts what happens when atmospheric CO2 is changed.
Can you give a reference to a graph of MODTRAN prediction versus measured CO2 that shows this logarithmic relationship ?
I understand the concept of mathematics usually replicating the results if you input the same numbers; that’s why we use mathematics; but I wouldn’t call that “accurate modeling”
Phil says that at higher concentrations (of CO2) the relationship transitions to square root. Presumably then, there is somewhere where it is neither logarithmic, nor square root.
I’m used to both of those functions being valid over the entire possible range of variables; otherwise they are not of much use. Usually in mathematics, names have specific and usually precise meanings.

davidmhoffer says:
May 8, 2013 at 3:04 pm
Also true and also irrelevant to any practical discussion about what humans may or may not be doing with carbon.
Depends of what humans do with what carbon: cement manufacturing sets CO2 free from carbonate rock, be it that part of it is recaptured when the cement/concrete hardens and more over time. But still quite impressive CO2 emissions from that (human) source.
SO2 emissions from high sulphur coal and oil burning also set CO2 free from carbonate rock.
What worries me is the too low calculation by the author of the increase by Modtran for the first step 0-100 ppmv, which affects all following steps.
Further:
Accordingly only ~5% of the effectiveness of CO2 as a greenhouse gas remains beyond the current level.
One can’t say that. As said before by somewone else, it is a logarithmic function, not an assymptote. A logarithm has no limit…

george e. smith says:
May 8, 2013 at 3:19 pm
Can you give a reference to a graph of MODTRAN prediction versus measured CO2 that shows this logarithmic relationship ?
As far as I know, Modtran is a simplified version of Hitran, which is fully based on lab measurements of thousands of detailed absorption lines of different atmospheric components at different compositions and pressures. So far pure physics, translatable to the real world, but only for a clear atmosphere.
The “modelling” is in the description of the real atmosphere where clouds play a huge role… That is the more problematic part…

John Finn

daveburton says:
May 8, 2013 at 2:19 pm
Even though CO2 levels are measured in parts-per-million, there’s nevertheless already so much CO2 in the atmosphere that it blocks nearly all of the IR that it can possibly block. So adding more CO2 doesn’t have much effect on temperature. For CO2′s main absorption bands, we’re way, way past the CO2 levels at which the IR is all absorbed. Only for very narrow ranges of wavelengths at the fringes of those absorption bands, where CO2 is a very weak absorber, can adding more CO2 appreciably increase the amount of IR blocked.

I think there might be a bit more to it than you suggest. As more CO2 accumulates it increases concentration in the higher, colder, drier regions of the atmosphere. The average height at which radiation is emitted to space, therefore, increases. Because more emission is taking place at colder altitudes the rate of IR emission falls (S-B Law). This creates an imbalance whereby:
Incoming Solar Energy is greater than Outgoing IR energy
which means that the surface and atmosphere will warm – and continue to warm until equilibrium (incoming=outgoing) is re-established. Saturation in the lower in the lower troposphere, therefore, is not really relevant.

I have never seen in an IPCC Report the logarithmical graph of diminishing return as CO2 concernatrations increase. The important work on this was done in the late 19th Century. This had a major impact on the CO2 causes Ice Age theory but it also took the wind out of the earlier speculation by Svante Arrhenius about the AGW
Here is a version of the table produced by Callendar in 1938:
http://enthusiasmscepticismscience.wordpress.com/2010/06/25/the-anatomy-of-virtuous-corruption-disagreements-permissible-unmentionable-and-inconceivable/infraredabsorbsion_callendar-2/

Mike H

DAve Burton: Thank you very much.

Kev-in-Uk

berniel says:
May 8, 2013 at 3:43 pm
isn’t that just based on ‘limited’ wavelength absorption though?
but anyway – someone mentioned incoming vs outgoing earlier upthread – and in my opinion, this is the crux of the matter; i.e. that at some point (assuming incoming remains constant) the #stored’ incoming energy (as a reuslt of co2 !) has to reach a state whereby it ‘outgoes’ at the required faster rate – and equilibrium is achieved – ot is the logartihmic characteristic of the CO2 which means that EXCESSIVE temperatures can never be achieved. as per another comment – to achieve mega amounst of CO2 (thousands of ppm) is simply not possible without releasing a bucketload of ‘other’ co2 from carbonates, etc……..fossil fuels simply cannot do this alone AFAIK.

Kev-in-Uk

apologies for all the typos – typing too fast, and a sticky keyboard (kids!) doesn’t help! (thats my excuse anyways!)

Rob JM

Simple explanation based on first principles, aka the Beer Lambert law.
Firstly this article is correct in that each doubling of CO2 has half the effect of the previous doubling, The IPCC stuffed up with their claim of each doubling having the same effect because someone doesn’t know the difference between absorption (of energy) and absorbance (a neg log eq)
How ever the article calculations seem off to me as the author may have looked at the central portion of the absorption band instead of the “wings” where the absorption is less saturated!
Simple explanation.
1/ There is only a certain amount of energy emitted from the planets surface that CO2 can absorb, aka the saturation point is when all if it is absorbed.
2/ The 50% point on this curve occurs at about 30ppm (IPCC) which represents a 50% probability of photon not being absorbed, ie, transmitted.
3/ When you double the concentration of the absorbing substance, you halve the probability of a photon being transmitted, ie 0.5 X 0.5 =0.25
4/ double again (0.5)^4 =0.125
5/ as you can see each doubling has half the effect of the previous, It basically absorbs 50% of the remaining energy in the spectrum.
For CO2 this is (% saturation)
30ppm = 50%
60ppm = 75%
120ppm = 87.5%
240ppm = 93.75%
480ppm = 96.875%
The hard part is then figuring out how much effect it has directly since water vapour overlaps with two of the CO2 bands and we have an convecting atmosphere at all different temps!

Kev-in-Uk

just a thought. what is the maximum energy density of the atmsophere ? By that, I mean the maximum thermal capacitance of a given zone of the atmosphere (LT, UT or whatever) based on its current composition? Surely, a fixed composition of N2/O2/Co2 has a fixed thermal capacitance? Does the actual thermal capacitance change much by the slight variation in CO2 ? because if not, then the transfer of the thermal energy (as absorbed by the CO2) must dissipate after it reaches the thermal capacitance (at relevant pressures) into adjacent material? This is obviously related to lapse rate – but I would have thought that a given cubic metre of ‘air’ has a fixed thermal capacitance at normal pressures – and therefore what is the change in that thermal capacitance when CO2 concentration is changed – for the life of me, I can’t see it being very much? It’s getting late, I may be missing something…..

Lester Via

CO2 absorbs certain wavelengths in the IR spectrum. At any given wavelength there is some concetration of CO2 that will absorb half the energy at that wavelength. Lets say that is X ppm. Doubling that concentration to 2X ppm will absorb half of what remains or 75% total. Each time the concentration is increased by Xppm, half the energy remaining will be absorbed.
Since CO2 is virtually tranaparent to much of the IR spectrum, it cannot block all IR radiation at any reasonably conceivable concentration that could exist in our atmosphere. Take the planet Mars for example – if you look up into space from any point on mars that is anywhere near the average elevation of the planet’s surface (there isn’t any sea level to use a reference), you will be looking through approxmately 20-30 times the amount of CO2 that now exists in the earth’s atmosphere and it still only blocks part of the IR spectrum. This relatively large amount of CO2, by the way, only causes a minimal rise in Mar’s surface temperature.