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.
“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.”
As always, well said.
Chris
Norfolk, VA, USA
“… without any objections from the scientists who should know better.”
Porque no? Because a global decrease in economic activity is seen as good (or at least prudent) in itself even if based on scientific malpractice?
What? We have scientists who think they are economists too? “Convenient Lies” or “Convenient Silence”, both should be punished where applicable.
Climate sensitivity cannot be measured directly but estimates can be made by observing climate change in the past or from short-term changes caused by volcanic eruptions. Knutti & Hegerl (2009) and IPCC (2007) conclude that various observations show a climate sensitivity value of about 3oC, with a likely range of about 2 – 4.5oC.
See: http://www2.sunysuffolk.edu/mandias/global_warming/images/climate_sensitivity_lg.gif
Furthermore, the lower value of climate sensitivity of 2oC is fairly well constrained which means that if emissions are not stabilized very soon, significant global warming is inevitable. According to Synthesis Report from the Climate Change Congress – University of Copenhagen (Richardson et al., 2009):
“Recent observations show that societies and ecosystems are highly vulnerable to even modest levels of climate change, with poor nations and communities, ecosystem services and biodiversity particularly at risk. Temperature rises above 2oC will be difficult for contemporary societies to cope with, and are likely to cause major societal and environmental disruptions through the rest of the century and beyond.”
Knutti, R. & Hegerl, G. (2008). The equilibrium sensitivity of the earth’s temperature to radiation changes. Nature Geoscience, (1), 735 – 743.
Richardson, K., Steffen W., Schellnhuber, H., Alcamo, J. Barker, T., Kammen, D., et al. (2009, March). Synthesis report. Retrieved July 8, 2009, from Climate Change Congress – University of Copenhagen Website: http://climatecongress.ku.dk/pdf/synthesisreport/
This is a very fundamental issue that lies at the basis of catastrophic projections/claims. Excellent to keep people focused on this most basic of as-yet “unsettled” aspects of the science.
Bravo, Dr. Spencer.
Now, can you dumb down the central part of this discussion so that, say, a second grader or a US Senator from either coast can understand the scientific argument? Then republish this or present it at the upcoming hearings on “AGW”, making sure to emphasize that great ending. “You’re preparing to spend how many trillions, perhaps even destroying the economy, on these guesses, Senator?”
It is interesting that we can’t really measure the effect yet.
Why would we be spending billions on the research yet not be able to measure the fundamental basis of the theory.
I’ve always considered global warming to be a theoritical concept (that could still turn out to be accurate) but it is so complicated (trillions of photons interacting with trillions of molecules every nanosecond) that we have to prove/disprove/fine-tune it with factual evidence of what actually occurs.
I saw the Crucible last night. I wish I could say that statement was O/T but unfortunatly the themes in the play hit a little too close to this topic than I would have liked. Particularly about jumping from victim to witch without any EVIDENCE.
The atmosphere is a blanket. No blanket can trap heat the way the UN IPCC modellers predict, especially a gas blanket.
And we hate politicians and economists faux scientist spretending to science is one translation.
The science remains unsettled.
Thanks Doc.
This gets into the feedback, which is the process control engineers’ domain.
A noted process control engineer, Dr. Pierre Latour, had something to say on the subject. I added a few words of my own.
http://sowellslawblog.blogspot.com/2009/02/chemical-engineer-takes-on-global.html
Here is a radical approach:
Fix the dishonest/unstable banking and money system that is causing all kinds of environmental damage and then quit worrying. It is called repentance.
Or assume capitalism is flawed, apologize to Russia, and establish the USSA.
This arcane debate is only important if one wishes to justify, or expell, the AGWERs’ temperature predictions for the next 100 years.
Because, since temperatures have, at best, remained static for the last 11 years, whilst CO2 climbed, the theory demanding these future predictions is demonstrated wrong.
I admire Pielke’s patience in playing the Lysenkoist game.
Thanks Roy. Look forward to your presentation when available.
Some amateur thoughts:
Can these be distinguished by different phase, timing or trends between external and internal forcing?
Richard Lindzen in Climate Change Deconstructed
October 26, 2009, discusses positive feedback from global warming models (slide 46) vs negative feedback from ERBE and CERES on (slide 47).
How definitive is this?
Dr. Habibullo Abdussamatov in The Sun Defines the Climate – an essay from Russia shows a TSI graph
The 0.1% short-term excursions in TSI and 0.1% long term solar cycle excursions provide external variations in forcing with differing frequencies.
Satellites measure TSI, outgoing short wave (albedo) and long wave radiation as well as water in the atmosphere. Argo network measures sea temperatures. Cosmic rays are monitored.
Ferenc Miskolczi predicts about constant global optical depth.
I would be interested in comments on how useful these are in measuring the change in optical depth (water vapor + CO2), albedo and outgoing long wave radiation, vs the external forcing from the difference in TSI less reflections, and cosmic rays modulating clouds, relative to the uncertainties involved.
Are the uncertainties in satellite measurements are still so high that it is difficult to measure the response to these variations?
Nir J. Shaviv addresses The oceans as a calorimeter and solar amplification
The temperature lapse rate vs altitude, height of the atmosphere, height of the troposphere, and water content of the atmosphere would seem to be other parameters that could be useful in evaluating the system.
I would be interested in any comments on these vs the feedback parameters.
How much do uncertainties need to be reduced to quantitatively evaluate the parameters? e.g. How much would it help to reduce uncertainties in measuring global water vapor to 0.1% or to 0.01%?
What is extraordinary is that the IPCC projects 4 to 5 times the warming of the 20th century and the great majority of that is supposedly to come from positive feedback.
Scott Mandia: “Furthermore, the lower value of climate sensitivity of 2oC is fairly well constrained which means that if emissions are not stabilized very soon, significant global warming is inevitable.”
Circular reasoning at its best.
Chris
Norfolk, VA, USA
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
Says who? This is an inverse problem. Complicated? Yes. Possibly the system, if it were linear, would be ill-conditioned; or perhaps it is non-linear, and in either case one would find an “ensemble” of systems, but wouldn’t that be more interesting than ensembles of these wearying and predictable simulations?
RE: Scott A. Mandia (18:18:54);
Your first paragraph seems to have been made in contradiction to what the article is saying. Did you read it? Or ignore it in favour of posting your rebuttal? The article is describing the issues relating to lack of certainty and estimates involved in climate modelling. Your first paragraph implies that climate forcings can be estimated – using the models that were described in the article as being based on estmates and not necesarily reliable… I am going in circles. Was there a point beyond agreeing with the article you were trying to make?
Additionally, recent satelite data, included in Richard Lindzen’s latest paper, linked on this website and located here http://www.leif.org/EOS/2009GL039628-pip.pdf show that the estimated climate sensitivity, used in the models currently predicting high sensitivity are in fact suggesting low sensitivity and fall outside of the estimates given to models. All evidence I have seen in models suggesting high sensitivity are based on “best guess” (educated guesswork) and on the hope that as many climate variables as possible are included. Direct observations are showing the opposite to models, at the very least you must concede that there is an issue with the models (and not link back to models to prove the observable evidence incorrect..).
As for the rest of the post you went on to discuss climate sensitivity on a small scale, such as a river network, or coral reef etc – comparably small in relation to a global scale. You cannot make an argument that says “the frogs in my local pond will go extinct if the temperate around the pond increases 2 degrees” and then raise that to “and therefore climate sensitivity on a global level is high” (which to be fair you did not explicity state that, but you did use local variability and estimates on climate sensitivity as an example following a speil about global climate which begs the inference).
What I found to be a more striking admission on the part of the IPCC was in the Summary for Policymakers, which conceded that the question of whether anthropogenoic greenhouse gasses were responsible for most of the observed warming was purely a matter of opinion, rather than scientific procedure. They couched this admission in terms of “expert judgment” but that just begged the question of how those offering their opinon have demonstrated their expertise at attributing causation to an observed climate effect. If causation cannot be verified through measurments, then how can anyone claim actual expertise at attributing causation? It’s a cart-before-the-horse issue.
Like David L. Hagen (19:20:09), I’m also curious about the relationship of Spencer’s remarks with Lindzen & Choi (2009)[1]. It seems that Spencer’s statement is in conflict with Lindzen & Choi, no?
[1] Lindzen, R.S. and Y.-S. Choi, 2009: On the determination of climate feedbacks from ERBE data, accepted Geophys. Res. Ltrs.
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?
Isn’t this in contradiction to Professor Lindzen’s work which shows negative feedback?
Roger Sowell (18:49:41) :
This gets into the feedback, which is the process control engineers’ domain.
Interesting post. I’ll head off to read Dr. LaTour’s comments, but you mentioned that The steady-state gain (dt/dCO2) therefore is 0.0182 degrees C/yr, or almost zero.
Shouldn’t the sensitivity value be in degrees C per quantity of CO2 rather than time? The temperature trend figure you quote is very small, almost zero in fact, but it is nonetheless the staff on which the AGWers hang their standards. The CO2 sensitivity is something we all wish we knew.
If the climate really is a closed loop system, it is almost impossible to measure the feedback. You cannot determing the transfer equations without “opening” the loop. Since we have limited, perhaps zero, control over the input to the system, just looking at the output doesn’t reveal much.
I suspect the ‘values’ for A and B vary with time and physical conditions, variations in orbit, small changes in TSI, etc. So we have a system better described by chaos theory than control theory.
I’ve built a lot of closed loop systems. They had few inputs, few outputs, and not overly complex transfer functions. Still took a long time to wring out all the bugs. With climate, the variables far exceed the known equations, so finding the scale factors (and powers) is not much better than looking at tea leaves and animal entrails.
Well done, Dr. Spencer. Someone has to address this issue. Perhaps a few people will listen to what you have to say.
Jim F: Comparing a second grader to a U.S. Senator does a disservice to the kids in second grade. Most of them want to learn something.
“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”
But isn’t the IPCC case that the second statement is not true? As I understand their position, an increase in T causes evaporation to increase leading to higher atmospheric water vapor, which then end to increase T further due to its greenhouse gas properties. That is, an increase in T leads to a decrease in outgoing energy flux. This is my understanding of what they mean by “positive feeback”. Isn’t it enough to observe outgoing flux to be higher at higher T to refute this assumption? Not to say that you understand how, or can quantify a feedback parameter, but just whether feedback is positive or negative.
It seems to me that the satellite data is enough to say the assumption is busted. Have I missed the point?
Every now and then, one comes across someone who asks a question that pierces the fog of unreason. The importance of the issue raised by RS is self evident. My hat off in recognition of his clear thinking.
A bit off topic, but is there any movement to counter the following alarmist approach to Rudd to influence his actions in Copenhagen ?
http://www.dirtykev.org/letter/letter.php