Another paper for the Copenhagen train. This is an estimate according to the abstract. Here’s the abstract and the supplemental information, of course the publicly funded paper is behind the AAAS paywall.
From UCLA News: Last time carbon dioxide levels were this high: 15 million years ago, scientists report
By Stuart Wolpert October 08, 2009 Category: Research
You would have to go back at least 15 million years to find carbon dioxide levels on Earth as high as they are today, a UCLA scientist and colleagues report Oct. 8 in the online edition of the journal Science.
“The last time carbon dioxide levels were apparently as high as they are today — and were sustained at those levels — global temperatures were 5 to 10 degrees Fahrenheit higher than they are today, the sea level was approximately 75 to 120 feet higher than today, there was no permanent sea ice cap in the Arctic and very little ice on Antarctica and Greenland,” said the paper’s lead author, Aradhna Tripati, a UCLA assistant professor in the department of Earth and space sciences and the department of atmospheric and oceanic sciences.
“Carbon dioxide is a potent greenhouse gas, and geological observations that we now have for the last 20 million years lend strong support to the idea that carbon dioxide is an important agent for driving climate change throughout Earth’s history,” she said.
By analyzing the chemistry of bubbles of ancient air trapped in Antarctic ice, scientists have been able to determine the composition of Earth’s atmosphere going back as far as 800,000 years, and they have developed a good understanding of how carbon dioxide levels have varied in the atmosphere since that time. But there has been little agreement before this study on how to reconstruct carbon dioxide levels prior to 800,000 years ago.
Tripati, before joining UCLA’s faculty, was part of a research team at England’s University of Cambridge that developed a new technique to assess carbon dioxide levels in the much more distant past — by studying the ratio of the chemical element boron to calcium in the shells of ancient single-celled marine algae. Tripati has now used this method to determine the amount of carbon dioxide in Earth’s atmosphere as far back as 20 million years ago.
Aradhna Tripati
“We are able, for the first time, to accurately reproduce the ice-core record for the last 800,000 years — the record of atmospheric C02 based on measurements of carbon dioxide in gas bubbles in ice,” Tripati said. “This suggests that the technique we are using is valid.
“We then applied this technique to study the history of carbon dioxide from 800,000 years ago to 20 million years ago,” she said. “We report evidence for a very close coupling between carbon dioxide levels and climate. When there is evidence for the growth of a large ice sheet on Antarctica or on Greenland or the growth of sea ice in the Arctic Ocean, we see evidence for a dramatic change in carbon dioxide levels over the last 20 million years.
“A slightly shocking finding,” Tripati said, “is that the only time in the last 20 million years that we find evidence for carbon dioxide levels similar to the modern level of 387 parts per million was 15 to 20 million years ago, when the planet was dramatically different.”
Levels of carbon dioxide have varied only between 180 and 300 parts per million over the last 800,000 years — until recent decades, said Tripati, who is also a member of UCLA’s Institute of Geophysics and Planetary Physics. It has been known that modern-day levels of carbon dioxide are unprecedented over the last 800,000 years, but the finding that modern levels have not been reached in the last 15 million years is new.
Prior to the Industrial Revolution of the late 19th and early 20th centuries, the carbon dioxide level was about 280 parts per million, Tripati said. That figure had changed very little over the previous 1,000 years. But since the Industrial Revolution, the carbon dioxide level has been rising and is likely to soar unless action is taken to reverse the trend, Tripati said.
“During the Middle Miocene (the time period approximately 14 to 20 million years ago), carbon dioxide levels were sustained at about 400 parts per million, which is about where we are today,” Tripati said. “Globally, temperatures were 5 to 10 degrees Fahrenheit warmer, a huge amount.”
Tripati’s new chemical technique has an average uncertainty rate of only 14 parts per million.
“We can now have confidence in making statements about how carbon dioxide has varied throughout history,” Tripati said.
In the last 20 million years, key features of the climate record include the sudden appearance of ice on Antarctica about 14 million years ago and a rise in sea level of approximately 75 to 120 feet.
“We have shown that this dramatic rise in sea level is associated with an increase in carbon dioxide levels of about 100 parts per million, a huge change,” Tripati said. “This record is the first evidence that carbon dioxide may be linked with environmental changes, such as changes in the terrestrial ecosystem, distribution of ice, sea level and monsoon intensity.”
Today, the Arctic Ocean is covered with frozen ice all year long, an ice cap that has been there for about 14 million years.
“Prior to that, there was no permanent sea ice cap in the Arctic,” Tripati said.
Some projections show carbon dioxide levels rising as high as 600 or even 900 parts per million in the next century if no action is taken to reduce carbon dioxide, Tripati said. Such levels may have been reached on Earth 50 million years ago or earlier, said Tripati, who is working to push her data back much farther than 20 million years and to study the last 20 million years in detail.
More than 50 million years ago, there were no ice sheets on Earth, and there were expanded deserts in the subtropics, Tripati noted. The planet was radically different.
Co-authors on the Science paper are Christopher Roberts, a Ph.D. student in the department of Earth sciences at the University of Cambridge, and Robert Eagle, a postdoctoral scholar in the division of geological and planetary sciences at the California Institute of Technology.
The research was funded by UCLA’s Division of Physical Sciences and the United Kingdom’s National Environmental Research Council.
Tripati’s research focuses on the development and application of chemical tools to study climate change throughout history. She studies the evolution of climate and seawater chemistry through time.
“I’m interested in understanding how the carbon cycle and climate have been coupled, and why they have been coupled, over a range of time-scales, from hundreds of years to tens of millions of years,” Tripati said.
In addition to being published on the Science Express website, the paper will be published in the print edition of Science at a later date.
UPDATE: Bill Illis add this graph in comments, which brings up the obvious correlation questions.
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Joel Shore :
Be very sure that I know how the word feedback is used .
Please spare me irrelevant examples with converging series which have nothing to do with the issue .
I suspect that you are very confused about equilibrium issues and have probably not understood much of my argument .
.
First you talk about “change in the energy balance … by increasing the level of GHG” .
This is the first confusion because of course there is no change of “energy balance” . The only way to change the “energy balance” is to change the energy output of the Sun and/or the reflectivity . If those don’t change , the Earth system will emit (provided there is equilibrium) exactly the same energy as what it gets from the Sun . The internal energy of the Earth is independent of the CO2 concentration .
.
Second is considering SB as “negative feedback” . I have seen many creative descriptions of the SB equations but “negative feedback” is the first time .
There is no way that SB equation can be even remotely described as “negative feedback” .
If what you want to say is as trivial as “a hotter black body emits more radiation” then say so .
.
Third is that in theory a positive feed back must not NECESSARILY lead to a divergence . But in order to not to do so , severe additionnal constraints are necessary . As it can’t be warranted that such constraints exist , the Nature has apparently preferred to privilege negative feedbacks . That’s why the negative feed backs really dominate the natural processes that are illustrated by the VERY general Le Chatelier principle . Or do you deny this principle ?
.
Fourth is the assimilation of instabilities and feed backs . It is simply not true that an instability is a result of a positive feed back. An instability is the property of non equilibrium systems and all examples you gave are examples of non equilibrium systems . And non equilibrium systems are by definition … not in equilibrium .
.
Fifth .
Please don’t venture in non equilibrium dynamics because you have apparently very much to learn there .
This “If the positive feed back leads to an instability then the system runs off to a part of phase space space with stability is restored ” is not even wrong .
A system out of equilibrium is per definition INSTABLE . All the time and forever . What may be and generally is stable is the invariant sub set of the phase space that is called attractor . But you may not confuse the trajectory (or the state) of the system and the topology of the attractor .
While the attractor may be stable the system is ALWAYS instable and never stays in the same region of the attractor .
What I explained in the first post is that evidence of 3.8 billions years shows that :
a) the Earth attractor is stable (what doesn’t come as a surprise)
b) the Earth is an out of equilibrium (dissipative) system whose trajectories are instable but must stay within the attractor
c) whatever the internals parameters of the system (chemical , radiative , physical) do , it will oscillate among the states that are within the attractor .
d) that excludes “new” Marslike , Saturnlike or Venuslike states at least at scales that are measured in hundreds of millions or billions years .
Tom Vonk says:
No. That is not correct. As you increase CO2 levels, the Earth radiates less heat back out into space because of the increased greenhouse effect. (And, as I’ve noted, the spectrally-resolved changes in emission have even been observed by satellite observations.) The Earth-climate system will, of course, heat up in order to increase its emissions and move toward restoration of the radiative balance. However, because of the thermal inertia of the oceans, the relaxation to the new radiative balance occurs fairly slowly.
Well, that is precisely what I mean, although the S-B Equation puts a quantitative number on what is otherwise simply a qualitative statement. I am not sure why you would find this to be a problem. As for considering, SB to supply a negative feedback, see the discussion in Global Physical Climatology by Dennis L. Hartmann, Section 9.3.1. You can read it online here: http://books.google.com/books?id=Zi1coMyhlHoC&pg=PA231&lpg=PA231#v=onepage&q=&f=false .
Well, it is a principle of chemical equilibrium. I agree that it can be generalized to other places, e.g., it applies to how the changing magnetic field through a coil of wire produces a current that produces a magnetic field that opposes the original change in magnetic field. And, I think the S-B Equation is in essence also a generalization of the Le Chatelier Principle.
However, in the sense that negative and positive feedbacks have been used to discuss the climate system, the Principle does not apply…Or, perhaps it is better to say that it probably does apply to the net feedback when the S-B Equation is included amongst the negative feedbacks but it does not apply when the discussion switches to the level that I explained, namely of discussing how the new equilibrium temperature predicted by the radiative forcing and S-B Equation without considering any feedback processes in the troposphere is changed once those processes are considered.
Well, no system is truly in equilibrium…and, in fact, even when I use the term “equilibrium” above, I am using it in a rather sloppy way. (Sorry about that.) I should really say “steady-state” or finesse it entirely and just talk about what happens once “radiative balance is restored”.
Perhaps we are using terminology in different ways, but to my mind of thinking, an instability is very definitely the result of a positive feedback. For example, the dendritic instability occurs when a small bump in the surface attracts material via diffusion at a higher rate than the surrounding surface and hence that bump grows. To me, that seems like a positive feedback, where an initial perturbation leads to a response that magnifies that perturbation.
However, I agree that a positive feedback won’t necessarily lead to an instability…It has to be sufficiently strong. (This is true at least for positive feedbacks as used in climate science; someone was telling me once that the term is used differently in control theory and I don’t really know enough to comment. Perhaps the control theory usage of the language is closer to what the usage would be in climate science when you count the feedback due to the S-B Equation in the net feedbacks. I’d have to think this through a little more.)
I more-or-less agree with you. I.e., I do think that a runaway greenhouse effect like Venus is unlikely to be in the cards (without a significant increase in solar irradiance, for example). However, I am not sure that I agree that this can absolutely be argued in principle and without a doubt. Jim Hansen thinks that the current “experiment” that we are conducting may be without precedent in that the timescales over which we are releasing large stores of CO2 in the atmosphere may be such that they overwhelm the negative geochemical feedbacks that operate on much longer timescales and thus that it is possible that if we burn enough fossil fuels fast enough, we could really produce a runaway effect. And, it seems to me that while one may be able to argue this is wrong, I don’t think you can simply dismiss it on the basis of phase space attractors and such…Or at least, you would have to refine your arguments.
But, anyway, none of this has anything to say about whether a net positive feedback (in the sense that climate scientists use the term…i.e., not including the negative feedback due to the S-B Eq.) may be operating in the climate system so that it magnifies the amount of warming that we would get if we just calculate the change of radiative forcing due to the increase in greenhouse gases without including any of the feedback processes like changes in water vapor, clouds, ice albedo, etc.
It also has nothing to say in regards to “tipping points”, i.e., pushing the climate system past some point where it runs off to a new state, something like a shutdown of the thermohaline circulation or the disintegration of ice sheets. And, indeed, there is evidence of such behavior in the past.
cba says:
Okay…I just mentioned the desert thing because I didn’t want to be caught overgeneralizing. And, I am not sure whether the source I read that said that deserts could have emissivities as low as 0.7 were talking about the NIR or deeper into the IR. I am happy to simply believe that the Earth’s emissivity can be assumed to be 1.
Well, I encourage you to read the literature on the matter. What seems to be true both in the climate models and in the real world is that averaged over the whole globe, RH tends not to change much as the global temperature changes. However, the RH does go up in some places and down in others.
I would say that the standard is generally roughly that the last digit is uncertain but the second-to-last is not, although this is not strictly true since a value of 3.9 could mean the real value could be 4.0. Better, however, is to give the uncertainty explicitly. As I remember it, the uncertainty in this 3.7 number is estimated to be about +/-10%.
You mean between the SAR and TAR. Yeah…because they apparently went from just talking about the instantaneous forcing, i.e., without allowing for stratospheric adjustment to allowing for stratospheric adjustment.
(1) My point is simply that a 10% change in cloud cover probably doesn’t change the estimated global mean forcing by that much. In particular, it probably changes it by less than the ~10% uncertainty that exists in that number.
(2) However, there are compensating effects due to changes in the escape of longwave radiation. Actually, I just found a nice estimate of the effects of clouds in this paper (p. 196): Clouds in total reduce the absorbed solar radiation by 48 W/m^2 and enhance the greenhouse effect by 30 W/m^2, so their net effect is to cool by an amount of 18 W/m^2. When you compare this to the 4 W/m^2 due to doubling CO2, it means that clouds would have to change by a significant percentage in order to be comparable. I am not saying that clouds are not important, but just that the sensitivity to them is not quite as dramatic as one might think if one doesn’t recognize the partially-compensating effects.
Bah…I’ve seen much worse examples in physics. Peer review is an imperfect filter; that’s just the way it is.
And, frankly, it seems to me that there are people like McIntyre who specialize in making mountains out of molehills. And, they only seem to notice the failures of peer review in one direction. I don’t recall hearing the outcries from skeptics about the fact that lots of errors in Spencer and Christy’s original work resulted in an artificially low temperature trend (in fact, a negative trend in their early work)…and the errors persisted until quite recently, with the last major correction being in 2005, I believe. And, I don’t recall the shouts in the skeptic community when Douglass et al. made the mistake of comparing our single realization of the climate system in the real world to the standard error, rather than the standard deviation, in the predictions of the climate models.
Your last sentence makes the first sort of irrelevant. Sure, it is technically true that one actual contradiction means a hypothesis is not completely correct. However, in practice, for any major scientific theory, you can at any given time find many puzzling contradictions between the theory and the empirical data. Of course, over time one wants to work to resolve these either by modifying (or perhaps eventually discarding the theory) or figuring what is wrong with the data. However, one doesn’t generally just abandon the theory immediately, particularly when it explains a lot of other data. If we did that, we would be back in the Dark Ages with essentially no scientific theories. Skeptics often claim that AGW is held to a different standard than other theories…e.g., that it is not falsifiable. However, in my view, it is the skeptics who want to hold it to a different…higher…standard.
I think there is a lot of verification of the basics going on. And, in fact, I learn about more things all the time. For example, until a few days ago, I wasn’t aware of the work using satellites to look directly at the decreased radiative emission from the earth, spectrally resolved, due to the enhancement of the greenhouse effect.
joel,
perhaps you should interpret the “climate” version of feedback as merely another borrowing of something they have a fundamental missunderstanding of rather than assuming the engineering version is some strange variant that is a little different.
In fact, you might should interpret what is called feedback in climate as being a setpoint with feedback control.
cba,
What matters is the physics. It is not really useful to get in arguments about whose definitions and terminology are better.
Joel Shore (14:32:45) :
Tom Vonk says:
First you talk about “change in the energy balance … by increasing the level of GHG” .
This is the first confusion because of course there is no change of “energy balance” . The only way to change the “energy balance” is to change the energy output of the Sun and/or the reflectivity . If those don’t change , the Earth system will emit (provided there is equilibrium) exactly the same energy as what it gets from the Sun .
No. That is not correct. As you increase CO2 levels, the Earth radiates less heat back out into space because of the increased greenhouse effect. (And, as I’ve noted, the spectrally-resolved changes in emission have even been observed by satellite observations.) The Earth-climate system will, of course, heat up in order to increase its emissions and move toward restoration of the radiative balance. However, because of the thermal inertia of the oceans, the relaxation to the new radiative balance occurs fairly slowly.
That is completely wrong – I don’t care what your satellites say.
There will always be a level in the atmosphere that is radiating back at 241 watts/metre^2 – 255K
This is how the climate scientists always go off track. They think they found something – like 0.8 watts/metre^2 is being absorbed into the ocean so therefore the Earth is only emitting back 240.2 watts/metre^2 to space now.
Obviously wrong. There are still 4 different levels in the atmosphere above 255K – 241 watts/metre^2 emitting back 100.00000% of the solar energy received by the Earth so its time to go back to the drawing board again.
Bill Illis says:
In other words, you believe differently so you ignore both the fundamental physical understanding that has been around for half a century and the empirical data that backs it up.
That is not the point. The point is this: If you are too low in the atmosphere then most of the radiation emitted upward from that level will be absorbed again before it can escape, so the emission to space from that level will be small. If you are too high in the atmosphere, then the atmosphere is so thin that it doesn’t absorb very much of the radiation from below (and also it tends to be cold, which reduces its emission of radiation) and hence emission to space from this level will be small. In between, these two extremes, there is a region from which most of the radiation that escapes to space is emitted. As the concentration of greenhouse gases increases, that region shifts upward in the atmosphere to where it is colder and hence the amount of radiation emitted to space decreases putting the earth out of radiative balance. (It is absorbing more energy from the sun than it is emitting back out into space.) As a result, it warms until the radiative balance is again restored.
See here for a historical discussion of this, which was all settled about half a century ago: http://www.aip.org/history/climate/simple.htm#L_0623
P Wilson:
Could you please tell us how you arrived at the conclusion that precipitation is predicted to increase with heating of the atmosphere by greenhouse gases? That is not the prediction that I have heard.
Could you please provide a cite for the claim that water vapor feedback is only included for water vapor feedback and not for solar forcing? Since it is not true, you might have a hard time.
Could you please provided a cite for this claim? Don’t look too hard though since you won’t be able to, because it is not even close to being true.
You just make it all up as you go along, don’t you?
its quite straightforward. water vapour intercepts c02 where c02 doesn’t – such as ambient temperatures. C02 intercepts heat where is it cold. The higher the temperature, therefore, the less c02 interferes with heat. Given that there 33 times more vapour molecules than c02 molecules, it stands to reason that all being equal -c02 at 357ppm, a temperature of 20C at ground level in the day – the salient characteristic is water wapour, which can be anything from 0-4% of the atmosphere. It is not stable, but varies dramatically. Its what the AGW’s call the multiplier enhanced greenhouse gas runaway notion. Its a good theory, but clearly it doesn’t happen that way, as water vapour condenses to form precipitation in the troposphere, where it is subzero – and this is one of the autonomous cooling events that AGW has difficulty with that results from any warming, as the feedbacks are quite negative. The theory holds that extreme weather events take place – widespread drought punctuated by extreme flooding precipitation, but periods of little precipitation in between.
The enhanced ghg “forcing” would cause precipitation to decrease by creating a dry and arid climate with hot summers and relatively warm dry and sunny winters. Even when oceans absorb heat, they do not necessarily increase in temperature. However, even if this were the case.
http://co2now.org/index.php?option=com_content&task=view&id=79&Itemid=88
contd., got cut there – don’t know why
.. the theory of c02 being t ecause of all calamities has changed a lot – rather surreptitiously and quietly- since this paper in 2001.
Paradigms modify themselves on the basis of changing variables. What was thought in 2001 isn’t what is thought today, yet in 2001 it was held that c02 was the great heat bomb. Given that precipitation is on the increase, thats a position that had to be reversed, and even mainstream climatologist now contend that vapour is the main greenhouse gas
In 5 years from now, it will be interesting to see how different AGW theory is in comparison to the present theory.
joel shore,
concepts & definitions don’t matter, eh? I guess that goes along with the totally insignificant minor problems mckintyre discovered – like inverting proxy data and failing to use statiscally significant sampling.
“If you are too low in the atmosphere then most of the radiation emitted upward from that level will be absorbed again before it can escape, so the emission to space from that level will be small. If you are too high in the atmosphere, then the atmosphere is so thin that it doesn’t absorb very much of the radiation from below (and also it tends to be cold, which reduces its emission of radiation) and hence emission to space from this level will be small. In between, these two extremes, there is a region from which most of the radiation that escapes to space is emitted. As the concentration of greenhouse gases increases, that region shifts upward in the atmosphere to where it is colder and hence the amount of radiation emitted to space decreases putting the earth out of radiative balance.”
If it’s being absorbed, then power is being provided. The reason it’s so cold way up there is pure and simple that insufficient power is being provided for it to maintain a temperature higher than what it is. Also, when there is an increase in ghgs (to utilize your understanding of stefan’s law and single number emissivity), that emissivity increases, causing more radiation to be emitted at a given temperature which means that the conservation of energy will result in a lower temperature for balance to occur.
Another cute bit is that your increase in downward radiation in clear sky conditions is all in the deep IR. Ocean absorption of IR is essentially a surface effect with no penetration – unlike blues and near uV. The notion that oceans are going to heat up with that extra power is a bit amusing. You’ve got radiation, conduction, and convection. Radiation in the relevent far IR through the water is nonexistent. Conduction is quite poor and convection works against the conduction as warmer water will have lower desnsity and tend to rise (for surface water above 4C or so), preventing the conduction. What’s left is radiation outward and evaporation, invoking the extremely powerful water vapor cycle which is already responsible for a significant amount of outgoing power.
cba:
I said that it is silly to argue about who has the better definitions and terminology. As long as one uses the definitions and terminology consistently, one will get the same result.
I’m not sure what your whole point in that paragraph is. Are you saying that the radiation transfer codes are calculating things incorrectly? Are you complaining about the pedagogy? Or are you just being ornery?
What is amusing is the notion that these sorts of considerations will somehow get you around the basic issue of the radiative balance between the earth, sun, and space. As for the mechanism by which the greenhouse gases do heat the ocean, see here: http://www.realclimate.org/index.php/archives/2006/09/why-greenhouse-gases-heat-the-ocean/ Here is the basic idea:
P Wilson: Most of your post is unintelligible. I’ll try to comment on the few things that I can parse.
Warming increases evaporation. Why would that lead to less precipitation overall? There certainly can be changes in patterns so that some places get less…and there can be more drying in summer due to the greater heat. But, I don’t think I have seen any predictions of precipitation decreasing on the global scale.
Man, I have no clue where this stuff comes from. I am reading the book “Global Warming: The Hard Science” by L.D. Danny Harvey which was published in 2000. And, in that book he certainly talks about the fact that the no-feedback response to doubling CO2 is about 1 C and that the biggest feedback is water vapor. The only difference that I can detect from current thinking is that there was less direct evidence that the mid- and upper-troposphere was moistening as expected back then (although there was already some), so it was harder to dismiss the notions of Richard Lindzen that the upper troposphere would not moisten.
You not only have no real sense of the science; you have no sense of the history of the science.
“You not only have no real sense of the science; you have no sense of the history of the science.”
Those words will come back to haunt you, Joel Shore.
I’m aware you have little clue Joel
You ask:
Warming increases evaporation. Why would that lead to less precipitation overall?
The IPCC maintained that warmer air temperatures caused by ghg forcing are likely to lead to lower precipitation and heat waves as warm air is able to hold more water vapour than cold air.
“..in a warmer world, precipitation tends to be concentrated into more intense events, with longer periods of little precipitation in between. Therefore, intense and heavy downpours would be interspersed with longer relatively dry periods…”
So I get it from the IPCC. Perhaps you could re-direct your vituperations back to the source
Here’s a compilation of “Errors covertly corrected by the
I.P.C.C. after publication”
http://ff.org/centers/csspp/pdf/20070226_monckton.pdf
just a sample
However, if you’re interested in a discussion of Kelvin or radiation, heat emission and absorbtion – even the physical properties of molecules under heat stress then feel free
My God Joel! You call my posts unintelligible, then you quote RC. The irony
oops. Not being simple enough. If c02 were heating the atmosphere more than the oceans (which it necessarily doesn’t anyway), less precipitation would occur.
joel,
your reference didn’t seem to come through on the clouds where you stated 30W /m^2 positive and 48W/m^2 negative effect.
Clouds do vary from very low albedo to rather high, 10% to 90% (or 0.10 to 0.90), depending upon their nature. Single numbers as your’s must be
some sort of average value. Some other factors that should not be controversial are that there is 62% average cloud cover and that there is about 0.31
average Earth albedo. Of that 0.31, about 0.23 is caused by atmospheric effects, such as cloud albedo and scattering – which is mostly towards the blue
and represents a small amount of total power. A rough power estimate is visible light accounts for 42 – 44 % while IR accounds for a few percent greater and
the uV and above amounts to perhaps 7%. Another factor is the averaged (over position and time) incoming solar power is about 342w/m^2 and the
albedo reflection is about 105.
Applying these values (back of the envelope style) suggest that cloud albedo (plus atmospheric factors) results in 342*0.23 = 79W/m^2 and all the blue /uV power amounts to about
24w/m^2. The difference provides a net of 55W/m^2 assuming 100% of that uV/blue is scattered away which is clearly not the case. It would be closer to a
far closer to 50%, leaving 79-12=67w/m^2 for cloud albedo which is substantially more than attributed by your article. This too is an averaged value.
By using the averaged incoming solar, one can get an idea of what’s going on. However, for outgoing IR, it’s a totally different matter in that clouds
may not be around 24 hrs per day (and it doesn’t matter for incoming solar whether there are clouds present at night). Clouds in the areas of high solar
incoming power tend to form in the morning and dissipate in the evenings, leaving clear sky for the night times. Examples are the afternoon thunderstorms.
This doesn’t mean all clouds disappear at dusk but it does point to the dangers of too much generalities being toss into the mix. Having not seen your
referenced paper, I have no idea whether they included the fact that some albedo contributing clouds are not present at night to cause a full effect of an
averaged power blocking.
to get an idea of cloud emissions, assume a T of around 273K or 220K and compare to 288K, the average surface temperature.
emissivity can assumed to be 1 and stefan’s law can be asssumed to be reasonably correct considering we have solid and or liquids rather
than merely gas. The sigma constant is 5.67E-8.
T Emitted power w/m^2
220 133 approximately at tropopause
273 315 at freezing
288 390
Average balance is 235 (with 107W/m^2 albedo and 342W/m^2 average incoming)
This according to stefan’s law corresponds to about 254 K and average atmospheric lapse rate is around 6.5K. Going to averages, one has 288-254 = 34K
which corresponds to a height of 34/6.5 = 5.2km or around 17,000 feet which is above about 1/2 of the atmosphere. This reduces the total path length by
merely a fraction since it is a log function. However, the line widths are reduced due to less pressure broadening. As I recall, this is a linear function wrt
pressure and the narrower line widths seriously reduce the absorption effects as pressure diminishes.
A question arises as to the nature of the second number you gave, 30w/m^2, cloud absorption of outgoing IR. Considering cloud cover is around 62%, then that
indicates 30/0.62 = 48 w/m^2 outgoing IR cloudcover blockage – assuming there is no day/night time variation in cloud cover fraction which would make
that number even greater. Using a really rough number as I don’t have time to look up the details, clear skies result in around 160w/m^2 ghg absorption. With an
average of 390 w/m^2 surface output, stefan’s law for 288K, that leaves about 230W/m^2 surface radiation that radiates to space. When the
averaged cloud gets in the way, then some or all of that is blocked as well but the top of that cloud will effectively radiate a continuum based upon
its temperature at that altitude. Lower down, you get more power radiated due to higher temperatures while higher up you get less absorption from above
due to less material and lower pressures (less broadening) and lower temperatures.
Comparing this to the surface radiated power absorption, remember the little number in question about 3.5 or 3.7 W/m^2 for a doubling of CO2?? The CO2 absorption
is going to predominate above the clouds due to very low absolute humidity – right? (at least according to conventional ‘wisdom’). If you double
or halve the optical path you add (or remove) that 3.5 or 3.7W/m^2 increment of power. That means that for ground radiated power, removing the
atmosphere above the 5 or 6km level (optically) would result in only an increase of this 3.5 or 3.7 W/m^2 power amount. That is simply
because the vast bulk was already removed way below near the surface. When you radiate a new continuum at this cloud height, it has no component
already removed so it starts from scratch. Ultimately, if it were all at the same concentrations, constant pressure and temperature, the result would be that the same amount
of power would be removed by the time it reached the sky – minus that pesky 3.5 or 3.7 W/m^2 from the last doubling. Using 160 W/m^2 for the total
minus the last doubling or halving of CO2, we get about 156.5 W/m^2.
However, we do not have constant pressure, constant temperature, nor do we have constant concentrations. In fact, we have very little
water vapor which is the dominant absorber at lower altitudes. Remember, lower pressures mean narrower line widths so there is less area under the
curves over wavelengths – or fewer photons get captured because they must be at the right wavelengths. Also, the temperatures have resulted
not only in absorption variations but also in the peak power wavelengths – stefan’s law’s cousin – wein’s displacement law. This is a shift of
the peak wavelength. The absorption line wavelengths have virtually not shifted at all – except due to slight pressure shifting and a miniscule reduction
in the index of refraction of air. The net result is that we are nowhere close to to absorbing another 156.5 W/m^2 in the 2nd (upper) half of the
atmosphere. In fact, over 90% of the h2o vapor is below this level so the dominant atmospheric effect of water essentially no longer applies at 5km and
above (using the 1976 US Standard Atmosphere).
If we take the clear sky contributions for co2 and h2o as essentially being the total of 160 w/m^2 and that co2 contributes about 20% of this
total – leaving h2o to about 80% (and ignoring minor contributors) – we get 32 w/m^2 and 128W/m^2 for co2 and h2o total. Note that the 32
corresponds to around 10 or 11 doublings (or halvings) which is not all that bad an estimate (since additional halvings drop each effect to around 2.x to 3W/m^2)
Also, for 5km altitude, the h2o has around 90% or what’s left above is around 9% of the h2o left. That means that if we start with the 9% as one
path length, we have about 11 path lengths below and 8 would be 3 doublings, 16 would be 4 doublings. Taking the conservative estimate that
there are 3 doublings for h2o over the top half of the atmosphere, each doubling would be 128/4 = 32W/m^2 for absorption above this altitude.
That leaves our total absorption at 32 + 3.7 w/m&2 = 36 w/m^2 for cloud emitted radiation – assuming the same effects as the lower atmosphere and
the same effects upon the blackbody distribution for the lower temperature.
So we are emitting 235W/m^2 from clouds at 5km, we are losing 36 w/m^2 from higher altitude absorption and the claim from your paper appears
to be that the clouds are absorbing about 48W/m^2 of outgoing IR where present. Considering that all the ignored corrections are going to be to reduce
that 36 w/m^2 further, it would seem that the cloud number of 48 is somewhat exagerated if your original number is to be taken as an average overall value
rather than an average for cloudy only conditions. Actually, it would seem that the 48w/m^2 is averaged over clear & cloudy skies as it is somewhat lower
than the more common 77 to 79 W/m^2 values. It also seems that the 30 W/m^2 number would be more in line with what an actual absorption
for cloudy only effect would be.
P Wilson says:
I don’t see anything there where the IPCC is saying that precipitation will decrease globally. In fact, I see nothing that contradicts what I said, which I will repeat again for your convenience:
P Wilson says:
I don’t find RC posts to be unintelligible. Furthermore, you quote Christopher Monckton. Do you think we should compare Monckton’s standing in the field to that of any of the contributors to RealClimate? For example, we could look at papers published in refereed journals.
Joel, you wouldn’t happen to know about ol’ Albert’s story about publishing in a peer reviewed journal would ya?
cba: Sorry that I forgot to put in the link. Here it is: http://www-ramanathan.ucsd.edu/RamAmbio.pdf (see in particular p. 196 and Figs. 8 & 9). It looks like References [33] and [34] would give more detail although I haven’t actually looked them up.
Joel Shore (12:42:34) : I don’t find RC posts to be unintelligible. Furthermore, you quote Christopher Monckton. Do you think we should compare Monckton’s standing in the field to that of any of the contributors to RealClimate? For example, we could look at papers published in refereed journals.
The gang at RC “referee” each others journals in an old boys network.
We have seen their quality of refereeing and how much they are to be trusted.