How’s this for “rapid response“? This rebuttal comes out at exactly the same time the press embargo lifts in Science. We were able to obtain advance copies of the Dessler paper, plus Dr. Spencer had seen it as a poster at the recent A-Train satellite symposium. – Anthony
Update: Dessler responds here at Real Climate and makes the full paper available here at his TAMU website.
2PM EST, December 9th, 2010 by Roy W. Spencer, Ph. D.
How clouds respond to warming – the ‘cloud feedback’ problem – will likely determine whether manmade global warming becomes either the defining environmental event of the 21st Century, or is merely lost in the noise of natural climate variability.
Unfortunately, diagnosing cloud feedback from our global satellite observations has been surprisingly difficult. The problem isn’t the quality of the data, though. The problem is figuring out what the cloud and temperature behaviors we observe in the data mean in terms of cause and effect.
So, Andy Dessler’s (a Texas A&M climate researcher) new paper appearing in Science this week is potentially significant, for it claims to have greatly closed the gap in our understanding of cloud feedback.
Dessler’s paper claims to show that cloud feedback is indeed positive, and generally supportive of the cloud feedbacks exhibited by the IPCC computerized climate models. This would in turn support the IPCC’s claim that anthropogenic global warming will become an increasingly serious problem in the future.
Unfortunately, the central evidence contained in the paper is weak at best, and seriously misleading at worst. It uses flawed logic to ignore recent advancements we have made in identifying cloud feedback.
In fact, the new paper is like going back to using only X-rays for medical imaging when we already have MRI technology available to us.
What the New Study Shows
So what is this new evidence of positive cloud feedback that Dessler has published? Well, actually it is not new. It’s basically the same evidence we published in the Journal of Geophysical Research.
Yet we came to a very different conclusion, which was that the only clear evidence of feedback we found in the data was of strongly negative cloud feedback.
But how can this be? How can two climate researchers, using the same dataset, come to opposite conclusions?
The answer lies in an issue that challenges researchers in most scientific disciplines – separating cause from effect.
Dessler’s claim (and the IPCC party line) is that cloud changes are caused by temperature changes, and not the other way around. Causation only occurs in one direction, not the other.
In their interpretation, if one observes a warmer year being accompanied by fewer clouds, then that is evidence of positive cloud feedback. Why? Because if warming causes fewer clouds, it lets in more sunlight, which then amplifies the warming. That is positive cloud feedback in a nutshell.
But what if the warming was caused by fewer clouds, rather than the fewer clouds being caused by warming? In other words, what if previous researchers have simply mixed up cause and effect when estimating cloud feedback?
A Step Backwards for Climate Science
What we demonstrated in our JGR paper earlier this year is that when cloud changes cause temperature changes, it gives the illusion of positive cloud feedback – even if strongly negative cloud feedback is really operating!
I can not overemphasize the importance of that last statement.
We used essentially the same satellite dataset Dessler uses, but we analyzed those data with something called ‘phase space analysis’. Phase space analysis allows us to “see” behaviors in the climate system that would not be apparent with traditional methods of data analysis. It is like using an MRI to see a type of tumor that X-rays cannot reveal.
What we showed was basically a new diagnostic capability that can, to some extent, separate cause from effect. This is a fundamental advancement – and one that the news media largely refused to report on.
The Dessler paper is like someone publishing a medical research paper that claims those tumors do not exist, because they still do not show up on our latest X-ray equipment…even though the new MRI technology shows they DO exist!
Sound strange? Welcome to my world.
We even replicated that behavior see in the satellite data analyzed with phase space analysis — our ‘MRI for the climate system’ – by using a simple forcing-feedback climate model containing negative cloud feedback. It showed that, indeed, when clouds cause temperature changes, the illusion of positive cloud feedback is created…even when strongly negative cloud feedback really exists.
Why Dessler Assumed We Are Wrong
To Dessler’s credit, he actually references our paper. But he then immediately discounts our interpretation of the satellite data.
Why?
Because, as he claims, (1) most of the climate variability during the satellite period of record (2000 to 2010) was due to El Nino and La Nina (which is largely true), and (2) no researcher has ever claimed that El Nino or La Nina are caused by clouds.
This simple, blanket claim was then intended to negate all of the evidence we published.
But this is not what we were claiming, nor is it a necessary condition for our interpretation to be correct. El Nino and La Nina represent a temporary change in the way the coupled atmospheric-ocean circulation system operates. And any change in the atmospheric circulation can cause a change in cloud cover, which can in turn cause a change in ocean temperatures. We even showed this behavior for the major La Nina cooling event of 2007-08 in our paper!
It doesn’t mean that “clouds cause El Nino”, as Dessler suggests we are claiming, which would be too simplistic and misleading of a statement. Clouds are complicated beasts, and climate researchers ignore that complexity at their peril.
Very Curious Timing
Dessler’s paper is being announced on probably THE best day for it to support the IPCC’s COP-16 meeting here in Cancun, and whatever agreement is announced tomorrow in the way of international climate policy.
I suspect – but have no proof of it – that Dessler was under pressure to get this paper published to blunt the negative impact our work has had on the IPCC’s efforts.
But if this is the best they can do, the scientists aligning themselves with the IPCC really are running out of ideas to help shore up their climate models, and their claims that our climate system is very sensitive to greenhouse gas emissions.
The weak reasoning the paper employs – and the evidence we published which it purposely ignores! – combined with the great deal of media attention it will garner at a time when the IPCC needs to regain scientific respectability (especially after Climategate), makes this new Science paper just one more reason why the public is increasingly distrustful of the scientific community when it comes to research having enormous policy implications.
===============================================================
Abstract:
On a global scale, clouds presently influence climate in a way that cools the planet. But, they will lose some of that cooling capacity as climate warms, according to a study that supports current ideas about how atmospheric carbon dioxide affects global temperature. Clouds can potentially have both positive and negative feedback effects on climate, and this is responsible for much of our uncertainty about the amount of warming that will be caused by increasing concentrations of carbon dioxide in the atmosphere. It’s generally agreed that overall this feedback is positive, with warming being exacerbated as clouds trap larger quantities of outgoing infrared radiation, but so far we have only a general idea of this effect. Andrew Dessler has estimated the actual magnitude of the feedback effect by analyzing ten years of satellite data on the flux of radiation through the top of the atmosphere. He concludes that the feedback effect is indeed positive and of a value that agrees with the canonical range of estimates of how much warming will occur for a doubling of atmospheric carbon dioxide.
Article #10: “A Determination of the Cloud Feedback from Climate Variations over the Past Decade,” by A.E. Dessler at Texas A&M University in College Station, TX.
Contact: A.E. Dessler at +1-979-862-1427 (office phone), +1-979-220-4513 (mobile phone), or adessler@tamu.edu (email).
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FTA: “Phase space analysis allows us to “see” behaviors in the climate system that would not be apparent with traditional methods of data analysis.”
Indubitably. Actually, phase space analysis is very traditional in the larger scientific community. Dr. Spencer’s phase plane analysis was elementary for a control systems engineer to read. Assuming clouds drive temperature, the counter-clockwise rotation in the Spencer-Braswell plots immediately indicates negative feedback.
It DOES NOT MATTER if you plot the two items against one another and find that you have a positive or negative slope – that only gives you information on what the relative phase is. You can get either result with positive or negative feedback. This is the gist of Dr. Spencer’s argument, and he is inarguably correct. The weakness of Dessler’s argument is he makes no accounting for phase lead or lag. He treats the data as if the response were instantaneous. His analysis is therefore fatally flawed.
ge0050
Good on you sir. I believe your point is fundamental to understanding cloud feedback and is one of the many issues that continues to confound us when we study climate. Feedbacks are neither temporally nor spatially constant. On a blog post at a neutral site Gavin made the case that the positive feedback could be inferred from back calculating an implied feedback following the Younger Dryas. One of the issues I have with that argument is that it ignores the issue you raised. It would not surprise me at all if net water vapor feedback is positive when exiting an ice age, but this tells us little about what it is NOW.
Incidentally, I posted a link to my post at 5:47 PM at RealClimate. Guess what? It’s gone. What a surprise.
Thanks for you interest in my work. One thing I’d like to comment on is the question of whether clouds warm or cool. Of course clouds cool. That’s not the question. The question is whether clouds cool more or less as the climate warms. A mathematical analogy would be: we know the function is negative, what we’re trying to determine is the sign of the first derivative. What I find is that while clouds cool, and will continue to cool, they will cool less as the climate warms.
Since there’s a bunch of criticism about my methodology, I’d like to point out that Lindzen uses basically the same approach as I do (although there are differences, e.g., he only looks at 20N-20S). Thus, I contend that, if you don’t believe my approach, then you must also not believe Lindzen. In fact, I would go so far as to say that Spencer and Lindzen cannot both be right. So who do people here believe?
Bob Tisdale: You’re probably right about that. I put that into the e-mail without spending much time thinking about it.
I was taking a walk the other morning, it was still foggy out, but I ventured on anyway. Boy did that burn! The IR bouncing back and forth from the ground to the fog was quick and intense!
The guy refers to himself, by name, in his own abstract? What the heck is up with that??
Anyone with any engineering experience would know that the positive feedback hypothesis is junk, as it would mean that the Earth would have fried just after birth. it clearly hasn’t.
Robert of Ottawa says:
December 9, 2010 at 6:24 pm
“…it would mean that the Earth would have fried just after birth. it clearly hasn’t.”
We are wasting too much space on such comments by neophytes – no offense that, I made the same mistake when I was new to the topic, too. It’s meant in a different sense than you are used to. See my comment here.
Robert of Ottawa says:
December 9, 2010 at 6:24 pm
Anyone with any engineering experience would know that the positive feedback hypothesis is junk, as it would mean that the Earth would have fried just after birth. it clearly hasn’t.
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Well, yah, but that’s not what the models told us!!!! Well, ok, it is, but we didn’t have models back then so it didn’t count!
Andrew Dessler says: December 9, 2010 at 6:11 pm
Thanks for the reply, and sorry about the misspelling of your last name in the comment above.
Andrew Dessler says:
December 9, 2010 at 6:11 pm
Dr. Dessler: I am not familiar with Dr. Lindzen’s analysis. But, as I pointed out here, your analysis is flawed. You MUST take account of the phase difference between your variables. As it is, you have produced nothing of a conclusive nature.
Andrew Dessler says:
December 9, 2010 at 6:11 pm
What I find is that while clouds cool, and will continue to cool, they will cool less as the climate warms.
==========================================================
Andrew, that seems to fly in the face of observations and temperature reconstructions.
Most reconstructions show a fairly sharp rise, a peak, and a rapid jagged decline.
If clouds “cool less” as the climate warms, what is your opinion as to why the planet has never had run away global warming before?
Andrew Dessler says:
December 9, 2010 at 6:11 pm
…….. Of course clouds cool. That’s not the question. The question is whether clouds cool more or less as the climate warms. A mathematical analogy would be: we know the function is negative, what we’re trying to determine is the sign of the first derivative. What I find is that while clouds cool, and will continue to cool, they will cool less as the climate warms.
…….. In fact, I would go so far as to say that Spencer and Lindzen cannot both be right. So who do people here believe?
======================================================
Wow, Dr. Dressler, thanks for dropping by with more than a link to a place where we can’t comment. It is greatly appreciated!
Yes, Lindzen and Spencer have different approaches. This is known. The answer to your question, for me, at least, is both and neither. I respect both for their candor and willingness to share, educate and engage. Sometimes I agree, other times, not so much. It isn’t as if people believe either are infallible. As you probably know, Dr. Spencer posts here from time to time. Often, it is simply a report of his satellite data, which is often met with many jeers. It’s natural. He comes here anyway, knowing that he will be challenged and tasked to answer questions.
Skeptics come in all shapes, sizes and colors. For instance, I’m a bemused skeptic. I’m one that believes a bit of warming would be beneficial to the earth, and would be more than happy to show where history tells us it is. I also don’t think we’re effecting the climate much either, but its a bit of a side point for me. I tend to look beyond science but the policies enacted, well, I get a bit animated…..enough of that….
To the science……doesn’t more heat cause more evaporation, which in turn, causes more clouds? (I’m sorry, but I like to start at the start of premises. This way there isn’t much misunderstanding.)
Bob Tisdale says:
December 9, 2010 at 5:23 pm
Andy Dressler: Just in case my comment gets lost over at RealClimate, I’ll reproduce it here.
====================================
Your comments got snarked by one of the mods over there, Bob. I hope you will publish a retort.
Best,
Chris
Andrew Dessler has estimated the actual magnitude of the feedback effect by analyzing ten years of satellite data on the flux of radiation through the top of the atmosphere. He concludes that the feedback effect is indeed positive
============================================================Andrew Dessler says:
December 9, 2010 at 6:11 pm
What I find is that while clouds cool, and will continue to cool, they will cool less as the climate warms.
============================================================
So who do people here believe?
============================================================
You’re making that choice a lot easier………………
In your abstract you claim that the feedback from clouds is positive.
In your words, you say that clouds will continue to cool, only cool less.
Since when is cooling less a positive feedback?
Unless you guys have re-written the English language along with climate science,
positive feedbacks are not what you would call doing negative feedbacks less.
savethesharks says:
December 9, 2010 at 7:34 pm
Your comments got snarked by one of the mods over there, Bob.
========================================================
Shocker. Hard to imagine Bob will get to retort in any manner. Let me know if they let us start playing there, ……..after several years.
So warmer air makes the clouds go away. If we heat the planet too much, it will be like Venus, full of clouds.
latitude: I think Bart gave a good response to your question. While clouds provide a positive feedback that increases climate sensitivity, sigma T^4 is the fundamental stabilizing feedback that keeps the climate from running away. Of course, if a feedback is stronger than sigma T^4, then the climate will indeed runaway, but the feedbacks in our climate system are far weaker than that.
Bart: There are good physical reasons to expect clouds and water vapor to be controlled by surface temperature w/o any lag (in monthly data). Thus, the lag zero correlation is expected to be the most appropriate. In support of this, I’ve looked at other lags and the correlations are all weaker than lag zero.
latitude: If clouds cool less as the climate warms, then that is indeed a positive feedback. Remember, the feedback is a derivative, dR/dT, where R is heat trapped by clouds and T is the temperature. I’m saying the derivative dR/dT is positive … the fact that R is negative does not preclude dR/dT from being positive.
latitude says:
December 9, 2010 at 7:12 pm
If clouds “cool less” as the climate warms, what is your opinion as to why the planet has never had run away global warming before?
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Maybe we’re wording the question wrong. IDK, it seems to me, if his posit is correct, then before we were even imagined, humanity would have long been wiped from the face of the earth. Maybe he doesn’t have an answer to the question or maybe we’re not understanding his posit correctly……….Dr. Dressler?
Andrew Dessler says:
December 9, 2010 at 8:00 pm
“There are good physical reasons to expect clouds and water vapor to be controlled by surface temperature w/o any lag (in monthly data). “
You do not have to go on faith. YOU’VE GOT THE DATA. Go to your control systems department (the best control systems people are typically in EE) and tell them you need to perform a system identification analysis. They will explain it all to you.
Dr. Dressler, what of the antithesis?
Before signing out…
“I’ve looked at other lags and the correlations are all weaker than lag zero.”
I frequently see this. You are using inappropriate analysis tools for a dynamic system. Take my advice, if you want to know the truth. Consult the experts in system ID who have been about it for decades before you climate guys ever came along.
And… I assure you, there are significant lags. All I have to do is look at the Spencer-Braswell plots to see it staring me in the face.
Bart says:
December 9, 2010 at 8:22 pm
Before signing out…
“I’ve looked at other lags and the correlations are all weaker than lag zero.”
I frequently see this. You are using inappropriate analysis tools for a dynamic system. Take my advice, if you want to know the truth. Consult the experts in system ID who have been about it for decades before you climate guys ever came along.
======================================================
Heh, now Bart, as correct as you may be, you know how the “appeal to authority” is viewed. Some, if they can put their personal beliefs aside for a while, can ID systems on their own. Of course, it wouldn’t hurt to ask some experts along the way, but that’s the easy way!