In Their Own Words: The IPCC on Climate Feedbacks
by Roy W. Spencer, Ph. D.
Despite the fact that the magnitude of anthropogenic global warming depends mostly upon the strengths of feedbacks in the climate system, there is no known way to actually measure those feedbacks from observational data.
The IPCC has admitted as much on p. 640 of the IPCC AR4 report, at the end of section 8.6, which is entitled “Climate Sensitivity and Feedbacks”:
“A number of diagnostic tests have been proposed…but few of them have been applied to a majority of the models currently in use. Moreover, it is not yet clear which tests are critical for constraining future projections (of warming). Consequently, a set of model metrics that might be used to narrow the range of plausible climate change feedbacks and climate sensitivity has yet to be developed.”
This is a rather amazing admission. Of course, since these statements are lost in a sea of favorable (but likely superfluous) comparisons between the models and various aspects of today’s climate system, one gets the impression that the 99% of the IPCC’s statements that are supportive of the climate models far outweighs the 1% that might cast doubt.
But the central importance of feedbacks to projections of future climate makes them by far more important to policy debates than all of the ways in which model behavior might resemble the current climate system. So, why has it been so difficult to measure feedbacks in the climate system? This question is not answered in the IPCC reports because, as far as I can tell, no one has bothered to dig into the reasons.
Rather unexpectedly, I have been asked to present our research results on this subject at a special session on feedbacks at the Fall AGU meeting in San Francisco in mid-December. In that short 15 minute presentation, I hope to bring some clarity to an issue that has remained muddied for too long.
To review, the feedback measurement we are after can be defined as the amount of global average radiative change caused by a temperature change. The main reason for the difficulty in diagnosing the true feedbacks operating in the climate system is that the above definition of feedback is NOT the same as what we can actually measure from satellites, which is the amount of radiative change accompanied by a temperature change.
The distinction is that in the real world, causation in the opposite direction as feedback also exists in the measurements. Thus, a change in measured radiative flux results from some unknown combination of (1) temperature causing radiative changes (feedback), and (2) unforced natural radiative changes causing a temperature change (internal forcing).
The internal forcing does not merely add contaminating noise to the diagnosis of feedback – it causes a bias in the direction of positive feedback (high climate sensitivity). This bias exists primarily because forcing and net feedback (including the direct increase of IR radiation with temperature) always have opposite signs, so a misinterpretation of the sum of the two as feedback alone causes a bias.
For instance, for the global average climate system, a decrease in outgoing radiation causes an increase in global average temperature, whereas an increase in temperature must always do the opposite: cause an increase in outgoing radiation. As a result, the presence of forcing mutes the signature of net feedback. Similarly, the presence of feedback mutes the signature of forcing.
The effect of this partial cancellation is to result in diagnosed net feedbacks being smaller than what is actually occurring in nature, unless any forcing present is first removed from the data before estimating feedbacks. Unfortunately, we do not know which portion of radiative variability is forcing versus feedback, and so researchers have simply ignored the issue (if they were even aware of it) and assumed that what they have been measuring is feedback alone. As a result, the climate system creates the illusion of being more sensitive than it really is.
One implication of this is that it is not a sufficient test of the feedbacks in climate models to simply compare temperature changes to radiation changes. “This is because the same relationship between temperature and radiation can be caused by either STRONG forcing accompanied by a large feedback parameter (which would be low climate sensitivity), or by WEAK forcing accompanied by a small feedback parameter (which would be high climate sensitivity).”
Only in the case of radiative forcing being either zero or constant in time – situations that never happen in the real world – can feedback be accurately estimated with current methods.
Our continuing analysis of satellite and climate model data has yet to yield a good solution to this problem. Unforced cloud changes in the climate system not only give the illusion of positive feedback, they might also offer a potential explanation for past warming (and cooling). [I believe these to be mostly chaotic in origin, but it also opens the door to more obscure (and controversial) mechanisms such as the modulation of cloud cover by cosmic ray activity.]
But without accurate long-term measurements of global cloud cover changes, we might never know to what extent global warming is simply a manifestation of natural climate variability, or whether cloud feedbacks are positive or negative. And without direct evidence, the IPCC can conveniently point to carbon dioxide change as the culprit. But this explanation seems rather anthropocentric to me, since it is easier for humans to keep track of global carbon dioxide changes than cloud changes.
Also, the IPCC can conveniently (and truthfully) claim that the behavior of their models is broadly “consistent with” the observed behavior of the real climate system. Unfortunately, this is then misinterpreted by the public, politicians, and policymakers as a claim that the amount of warming those models produce (a direct result of feedback) has been tested, which is not true.
As the IPCC has admitted, no one has yet figured out how to perform such a test. And until such a test is devised, the warming estimates produced by the IPCC’s twenty-something climate models are little more than educated guesses. It verges on scientific malpractice that politicians and the media continue to portray the models as accurate in this regard, without any objections from the scientists who should know better.
If one takes an IPCC moel with positive feedback and runs it out a couple hudred years… do the seas boil?
A sympathetic write up of the Climate Fools Day in The Register:
http://www.theregister.co.uk/2009/10/30/climate_fools_day/
Dr A Burns (20:40:57) :
Hmmm I read that and my first take was exactly the opposite of what the authors intended… I assumed signing a treaty at Copenhagen was the “dirty deal.” All a question of perspective.
I wonder how much clout pathetic webtitions like this have to be honest, but a few to the contrary can’t hurt.
Scott, I think you are putting the cart before the horse. There is no proof that this current warm spell is that much different from others, much less CO2 is the culprit.
You say look at past climate change. OK, look at the temp rise in the early 1700’s (E. England, De Bilt, Uppsala, Berlin), that was not much different from the last 30-40 years.
Or why the current global temps are have fattened out over the past 8-10 years, when the “models” predict they should be going up? If these basic questions cannot be answered, one runs the risk of doing more harm then good.
I think that the recent deconstruction of Lindzen posted here previously stands by itself in refuting the models, because it uses the same definition for models and data of what “change in radiation” and “change in SST”. The models are glaringly inconsistent with the data.
The nit picking comes if the sensitivity measured Lindzen’s way takes into account the objections raised by the present paper on whether what is purported to be sensitivity is the real sensitivity to a specific forcing, but is irrelevant to the scrapping of the models.
Bulldust (21:16:18): If one takes an IPCC moel with positive feedback and runs it out a couple hudred years… do the seas boil?
They most certainly do, according to Dr. James Hansen. The Venus Effect. The seas will boil away and all Life on this planet (and in the Universe as far as we know) will be kaput.
http://wattsupwiththat.com/2008/12/21/jim-hansens-agu-presentation-hes-nailed-climate-forcing-for-2x-co2/
All because you drive an SUV and use more electricity than a Pribilof Islander, you bounder.
But then, looking at the last billion years or so, runaway global warming has not occurred, the proof being we are having this conversation. The End of Life hasn’t happened, yet.
But I do expect boiling seas any day now. The consensus of dependent scientists (CODS) is that we passed the tipping point, in fact quite a few tipping points, years or months or weeks ago. So get out the tea bags and the sunscreen and try to make the best of it.
Second grader? US Senator?
..
What’s the difference?
Well said….
Retired Engineer (19:53:38) :
BINGO! Thank you for this sanity.
I suspect there are way more gains than just A and delays than just B, but you state the same in one of your later sentences (which I have not included).
Indeed. Multiple input, multiple output (MIMO) systems are difficult to analyze by themselves, feedback complicates this.
Mark
Mike D. (21:59:16) :
How do you refer to the individual scientists that make up the CODS? CODs pieces?
Mark
Kevin Kilty (19:52:21) :
You are correct, and thank you for pointing that out. The steady-state gain dt/dCO2 should indeed by in units of degC / pct CO2. The fact that change in CO2 is very small over time also complicates the matter, which is one of Dr. Latour’s points.
I also discuss this issue in my speeches to engineering groups, and stress that the inconsistency in response between temperature and CO2 (dt/dCO2) proves without any doubt that manipulating CO2 will not affect global temperature.
As the available temperature and CO2 charts show, sometimes temperature falls, sometimes remains steady, and sometimes increases for decades, all the while CO2 increases. When a candidate manipulated variable (CO2) has those characteristics, it cannot be used to control the system.
If only the world’s politicians understood process control fundamentals, all this nonsense of controlling global temperatures would cease.
this is an astonishing quote from the ipcc report.
in this context, there is another important issue revealed by mcintyre, where he demontrates how the ipcc report manipulated scientific results. a must read, and – implying rational thinking – suitable to convert agw believers to sceptics.
http://www.climateaudit.org/?p=6590
Yes, Watts up with that?
Noblesse Oblige (19:41:44) :
Lindzen and Choi (GRL to be published, I think) use ERBE and CERES radiation
measurements in concert with sea surface temperature changes to infer a net feedback. This inferred feedback is overall net negative, giving rise to a net climate senitivity that is vastly smaller than the IPCC central tendency of 3 degrees for CO2 doubling and substantially smaller than even the 1 degree calculated for zero net feedback. Presumably by examining a large number of events, the noise due to random unforced changes is averaged out, and any net bias would tend to reduce the climate sensitivity even further.
What’s wrong with this conclusion?
Mark T 22.46.06
Mike D 21.59.16
Perhaps the clout exercised by the CODS could be referred to as CODSWALLOP.
“It verges on scientific malpractice that politicians and the media continue to portray the models as accurate in this regard, without any objections from the scientists who should know better.”
…Well, scientists have bills to pay too, you know. And let’s not forget if they dare speak the truth they’ll be ridiculed by their colleagues, and when they can’t publish their papers any more their research grants will dry up. I mean would you speak out under these circumstances or just keep quiet and save your job/reputation/lifestyle/mortgage/marriage?
Come to think of it, the 20,000 politicians and global warming worshipers looking forward to their gangfest in Copenhagen are not going to take kindly to any scientist pointing out what a load of hogwash it all is. And so-called “Carbon Trading”? You might as well trade in pixidust and moonbeams for all the good it will do the environment.
Dr. Spencer;
Or anyone else here who can help me with a question that’s been nagging me for a couple days. The other day, in the comments for the first post about Monckton’s appearance on Glenn Beck’s show, I got into a tete a tete with another commenter about a study that utilized spectral analysis to separate the contributions of the various GHGs to the greenhouse effect. In googling about on the topic I came across another paper which covered the same ground from a slightly different perspective
http://ams.confex.com/ams/Annual2006/techprogram/paper_100737.htm
Evans and Puckrin 2006 Measurements of the Radiative Surface Forcing of Climate
The link is to the abstract, you need to click the Extended Abstract link to access the pdf of the whole paper.
The experiment in the paper utilized the spectral analysis technique to measure the downward LW radiative flux to the surface of the various GHGs. Since the paper is couched in the usual AGW blather, my first inclination was to doubt its qualities and indeed as a work of science I didn’t find much to recommend it. But, though their conclusions seemed fairly illogical, their experimental techniques seemed reasonable and the data in the their tables is what has had me ruminating. Particularly their Tables 3a and 3b which list respectively their seasonal observations for winter and summer. The readings for the cold dry air of winter show downward LW flux to the surface from CO2 at 30-35W/m2 and from H2O at 95-125W/m2 in line with the approx. 25% contribution of CO2 to the greenhouse effect. What’s shown in the summer readings is what has had me thinking. The H2O numbers went up to 178-256W/m2 in the warm humid air of summer, but the CO2 numbers went down, not just in relative terms but in absolute terms to 10.5W/m2, a third of the winter rate, and bringing the contribution of CO2 to the total GE to 3-4%, a much smaller value than I’ve usually seen quoted. this phenomenon was so obvious that even the clearly warmist authors commented on the higher H2O flux suppressing the flux from the other GHGs. Since this study was done in Canada and most heating of the planet occurs in the Tropic and Subtropic latitudes, which are presumably warmer and more humid than even the summer in Canada and would probably have even levels of H2O flux, if this phenomenon is real and consistent it would seem to me to indicate that contribution of CO2 at those latitudes would be an even smaller percent.
I guess my first question is does any of what I’ve said make sense or am I completely misunderstanding this? If not, has anyone ever attempted these type of measurements in the tropics and if so were the results similar?
typo;… have even higher levels of H2O flux,..
…to indicate that the contribution of CO2 at those latitudes…
fixed a typo I had:
“This is because the same relationship between temperature and radiation can be caused by either STRONG forcing accompanied by a large feedback parameter (which would be low climate sensitivity), or by WEAK forcing accompanied by a small feedback parameter (which would be high climate sensitivity).”
to Scott A. Mandia:
The estimation of feedback from volcanic eruptions depends upon knowledge of the radiative forcing with time, and the heat capacity of the system, both of which have considerable uncertainty on the time scales involved. A wide range of values result depending upon those assumptions.
Dave Wendt (03:36:31)
I think I followed that. The observation which you highlight would be consistent with H2O and CO2 competing for the same or overlapping bandwidths so that with more H2O in the air as water vapour there is less bandwidth available for CO2 to absorb.
With such a large effect as shown by those figures the ability of more CO2 to absorb and re-radiate when there is more H2O in the air seems to be grossly overstated.
Dave Wendt
Interesting link. H2O dominates, contributing 67% to 90% of the radiation, yet all the hoopla is over CO2. If H2O could be quantitatively measured would that not provide a critical measure of probably the most important parameter?
This begs for the application of Ferenc Miskolczi’s quantitative comprehensive line by line HARTCODE radiation transfer program to evaluate the total optical depth. See Miskolczi’s 2008 PHYSICS OF THE PLANETARY GREENHOUSE EFFECT presentation slide 20 of variation in optical depth with latitude, which I infer to be equivalent to the variation in optical depth from summer to winter.
The quantitative validation of LBL codes are discussed in: An inter-comparison of far-infrared line-by-line radiative transfer models David P. Kratz, Martin G. Mlynczak, Christopher J. Mertens, Helen Brindley,
Larry L. Gordley, Javier Martin-Torres, Ferenc M. Miskolczi, David D. Turner, Journal of Quantitative Spectroscopy & Radiative Transfer 90 (2005) 323–341
More importantly, the focus on radiative transfer of minor gases ignores the major effect of convective and latent heat transfer, and of the gross average optical depth. Miskolczi’s evaluations and models suggest that the global optical depth may be constant from energy minimization principles.
Note the reduction in humidity over time. See: ‘Trends in middle- and upper-level tropospheric humidity from NCEP reanalysis data’ by Garth Paltridge, Albert Arking and Michael Pook
journal of Theoretical and Applied Climatology
michael (02:09:05)
I’m relieved to hear you say that because my thoughts have led me to infer a zero effect from more GHGs on the basis that a change in the speed of the hydrological cycle produces an equal and opposite value to the initial forcing.
As long, that is, as the initial forcing does not inject extra energy into the oceans which is why I am somwhat exercised by the significance or otherwise of the so called ocean skin effect as proposed by AGW supporters.
I am pretty sure that the ocean skin effect has been given the wrong sign as suggested by me here:
http://climaterealists.com/index.php?id=4245&linkbox=true&position=12
If I’ve got it all wrong then the sooner someone demonstrates that the better even if I have to amend or even pull the article.
some of the recent posts got me to thinking about our magical feedback force from h2o vapor. Claims I’ve seen are a rather fixed RH as temperature changes and it’s all about h2o vapor increasing with T. Going to the charts for absolute humidity I discovered that a 2 deg C rise with fixed RH achieves only a 1.1 x increase in the h2o vapor amount while a 5 deg C rise with fixed RH achieves a 1.3 x increase. In neither case does that translate into an increased forcing greater than that of the original co2 doubling according to a 1-d radiative model.
The other generally acknowledged factor is that co2 doubling along contributes no more than 0.7 to 1.0 deg C rise and that the rest is all due to h2o vapor. It seems that the h2o vapor increase (in the basic statics case) combined with the co2 doubling is missing a full 3 deg C of additional warming with an assumed 5 deg C rise. It would seem also that the constant RH and absolute humidity constraints create a problem for the 2 deg C rise assumption as well in that the result is in the vacinity of 1 deg C for the combined effect of the increase in h2o vapor and the doubling of the CO2 and hence is missing almost a full deg C of forcing. Of course the second biggest assumption in this is going to be totally ignoring convection which, last time I looked, is going to reduce the effect further. The biggest assumption is the clear sky one which ignores clouds all together along with the water vapor cycle.
Net result is that the RH constraint combined with the basic nature of water vapor means that it’s effect in the forcing is going to be much smaller than the CO2 even though the effect for an h2o doubling is equal to or greater than that of CO2. After all, the ipcc claims that 1W/m^2 of forcing is 1 W/m^2 regardless of the cause or specifics in how it affects.
Do clouds on net increase or decrease T? Albedo is responsible for the averaged 107w/m^2 removal of power from the system. of the 0.3 Earth albedo, the dividing line between surface and atmosphere contribution is considered to be 0.22 for atmosphere (primarily clouds) and 0.08 for surface which is that low due mostly to oceans. If all the clouds suddenly dissappeared, the 239 W/m^2 radiative balance average would increase to over 313 w/m^2 and that corresponds to a stefan’s law increase of almost 10 deg C when the clear sky radiative efficiency of 70% is considered (only about 70% of the radiated surface emissions escape in clear skies). In my book, a 10 deg C increase needed to maintain balance with the removal of all clouds strongly indicates that the net effect of the present cloud cover has to be to reduce the temperature, regardless of which type makes up what % and how much CAGW types whine about it.
Stephen,
there is another tidbit. More trace ghgs in the atmosphere have an effect of increasing the emissivity of the atmosphere (in terms of stefan’s law concepts). That means one radiates more energy down at a given temperature for a chunk of gas and also that one radiates upward that same amount, requiring that the chunk of gas must become cooler as it is receiving an increase absorption that’s about half of the increase in emission – at least as one heads towards the boundaries. I don’t think this can actually result in a cooling but it certainly seems to indicate a lesser warming effect.
Your referenced article was way too long for my reading time today so I only briefly skimmed it. That I didn’t see any glaring problems is a good thing but definitely nothing definitive. It did look reasonable.
Regarding Spencer typo:
I was confused by the first iteration and now also by the second. I was expecting that the same relationship between change in temp and radiative could be maintained by strong internal forcing with weak feedback (low sensitivity) or weak internal forcing with strong feedback (high sensitivity).
Am wonderning now if I have failed to understand the terminology and relationships?
Mark, having also been involved in the design of thermal process control systems, for many years, I agree with your comments on the time delay and MIMO. If you add to that non-linear effects in the forward and feedback loops, it takes a long time to work out the total system dynamics. In a sense there are loops within loops, within loops. All of which takes time to sort out. If I recall correctly we used Kalman filtering in a few cases, to help converge on models and solutions.
Roger Sowell (23:25:11) :
I agree entirely with you on the topic of controlling climate via CO2. By the way, I read the reply to the Letters in HP by LaTour, and not only was it a good read, but a first rate thumping, a polite thumping to be sure, for the fellow who wrote two ill considered letters in that issue. I was surprised, frankly, of the poor quality of thinking expressed in a couple other letters as well.