Sunday, January 23, 2011

Dr. Why vs. Commander Coincidence

UPDATE 28 Jan 2011: By popular demand Eli has added the front end of the discussion so the entire correspondence is in one place

Those of you who follow Roy Spencer's blog are aware of a discussion between him and Andy Dessler on cloud feedback. Richard Lindzen chimed in about half way through. This has been copied to a number of bloggers (thanks), and the first part of the interchange can be found on Spencer's blog, much of the second part can be found on Dessler's, but the formatting, forgive Eli, leaves much to be desired.

Eli's POV, and the bunnies are quite free to have their own, is that this is another case of the phenominologists vs. the physicalist. One the one side, Lindzen and Spencer, (of Spencer and Lindzen YMMV) are saying, hey more clouds. On the other Dessler is screaming, why are there more clouds.

For the concern trolls out there, the snark (mostly at the end when everyone gets impatient) is shown in red. Avert your eyes. More seriously as Andy Dessler says, this is an example of how scientists communicate with each other. It can get rough in the tea room, something that the stolen UEA emails showed and which led to a huge amount of tutt-tutting.

To keep things clear Eli has added siggies where the actual Emails did not have them.


SPENCER Email to Dessler 11 December 2010:

In retrospect, my questioning of the timing has distracted from the central science issues, and was a bad move on my part. My apologies to Andy.



ER NOTE: This correspondence was copied to about 25 people, scientists, bloggers, journalists and various thereofs.


SPENCER Email to Dessler 11 December 2010:

...but I stand by my assertion that Andy’s paper is a step backwards for science. I would debate him or anyone else on this issue in a public or professional forum at any time.

I would be happy to submit a response to Science if I thought it had “a snowball’s chance”, but many of us have learned over the years that the editorial process there is quite biased on the subject of anthropogenic global warming.

BTW, I have stopped corresponding with Andy after he made public our e-mail exchange without asking me.

Roy Spencer


DESSLER Email to Spencer 11 December 2010:


I certainly accept your apology.

…but I stand by my assertion that Andy’s paper is a step backwards for science. I would debate him or anyone else on this issue in a public or professional forum at any time.

I ACCEPT! Let’s start immediately. Since you’re willing to do this essentially anywhere and anytime, I say we do this via e-mail. And since you want this to be public, I pledge to post the entirety of all of our e-mail correspondence on a blog that everyone can read (and since you also have copies of our correspondence, you’ll also be free to post it).

If you accept (and I don’t see how you can refuse given your statement above), then you can begin by answering this e-mail I sent to you yesterday:

Hi Roy-
I wanted to follow up on our interesting discussion. My main question involves your theory of cause-and-effect for an ENSO. During our first e-mails it seemed you were saying it was caused by clouds, but then things seemed to change. Could you send me a short summary of what’s driving the temperature changes during those cycles?

I look forward to a renewed and energetic discussion of these issues. After all, this is how science is supposed to operate.

And to the reporters on this e-mail, I hope you all see that the mainstream science community is pushing to engage the skeptics. I hope Roy shows that skeptics are similarly willing to engage.

Andy Dessler


SPENCER Email to Dessler 13 December 2010:


Sorry about the late reply…I wanted to get to the office to look at some IPCC model output that might help shed light on this.

So, since you want to talk about ENSO, let’s do that.

Of all the IPCC AR4 climate models, the one that has the best match to observed sea surface temperatures (SST) related to ENSO is CNRM-CM3 (see Fig. 8.13 from the IPCC AR4 Report).

Figure 8.13. Maximum entropy power spectra of surface air temperature averaged over the NINO3 region (i.e., 5°N to 5°S, 150°W to 90° W) for (a) the MMD at the PCMDI and (b) the CMIP2 models. Note the differing scales on the vertical axes and that ECMWF reanalysis in (b) refers to the European Centre for Medium Range Weather Forecasts (ECMWF) 15-year reanalysis (ERA15) as in (a). The vertical lines correspond to periods of two and seven years. The power spectra from the reanalyses and for SST from the Hadley Centre Sea Ice and Sea Surface Temperature (HadISST) version 1.1 data set are given by the series of solid, dashed and dotted black curves. Adapted from AchutaRao and Sperber (2006).

The first attached plot shows 20 years (1980-2000) of monthly anomalies in global radiative flux and surface temperature from that model’s 20th Century runs:


A scatter plot of the data is next:


See the spirals? Thats due to radiative forcing of SSTs. How do we know? Because there are only two possibilities: radiative changes (directly or indirectly) causing temperature changes, or temperature changes (directly or indirectly) causing radiative changes (by definition, feedback). The reason the spirals appear is that the radiative forcing is proportional to the CHANGE of temperature with time…not the temperature directly. Feedback is essentially instantaneous with the current radiative state of the armosphere and surface.

This is shown in the following lag correlation plot for the entire 20th Century:


That atmsopheric circulation changes alone can cause ENSO-typ behavior was also demonstrated by this paper in GRL, The Slab Ocean El Nino.

AGAIN I want to emphasize…the evidence for the direction of causation is whether a lag exists or not.

The NEXT question is to what extent this de-correlated behavior affects the regression slope…this was a subject of our 2010 JGR paper. All I know so far is that, on average, it biases the regression slope toward zero (which could be misinterpreted as a borderline unstable climate system).



DESSLER Email to Spencer 14 December 2010:


Thanks for your message … I knew you couldn’t stay mad at me ;)

Before I get into the details of the correlation, I’d like to get one thing straight: you’re arguing that the warming during an El Nino is caused by radiative heating by clouds. Right?

Once you confirm that, we can move on with the discussion. If you’re not saying that, then I’m confused by your message — in that case, I’d appreciate it if you could please explain the role of clouds in driving surface temperatures variations during ENSO.


Andrew Dessler


SPENCER Email to Dessler 15 December 2010:


Feedbacks and forcings involve *temperature* changes, not abstract concepts like “El Nino”. Thus, your question is a bit of a red herring.

What I *AM* saying is that the time-evolving nature of the temperature and radiative flux anomalies is consistent with a significant, non-feedback cloud-induced temperature change. That is what the phase space analysis reveals.

Now, what all of this might mean for how El Nino & La Nina evolve over time is an interesting question, I agree,…I’m just trying to make sure we don’t lose sight of the quantitative evidence. Whether the evidence I am talking about necessarily implies a non-feedback role for clouds in how El Nino and La Nina evolve over time, that is a separate question.



DESSLER Email to Spencer 18 December 2010:


Thanks for your response. I would have gotten back sooner, but I was at the AGU meeting.

What I *AM* saying is that the time-evolving nature of the temperature and radiative flux anomalies is consistent with a significant, non-feedback cloud-induced temperature change. That is what the phase space analysis reveals.

The problem here is that correlation is not causality: if I beat a drum during an eclipse, the Sun will return 100% of the time. You could claim that the time-evolving nature of the drum beating and return of the sun is consistent with a causal mechanism, and you’d be right. It is indeed consistent. But it’s also wrong — we both know that the drum does not make the Sun return.

The existence of a correlation does not mean that there is a causal link — so we cannot conclude that the correlation you’ve identified tells us anything about the role of clouds in generating ENSO surface temperature changes.

Rather, we have to look at the energy budget of an ENSO event. Those data contradict the idea that clouds are important in ENSO: analyses of the heat budget of ENSO (e.g., Trenberth et al., 2010: Relationships between tropical sea surface temperatures and top-of-atmosphere radiation. Geophys. Res. Lett., 37, L03702, doi:10.1029/2009GL042314 and references therein) don’t show a role for clouds.

In fact, the original Cane and Zebiak model of ENSO does not really even have clouds in it

So my question to you is whether there exists any physical evidence (beyond just the correlation) that clouds play any role at all in generating ENSO temperature variations?


Andrew Dessler


SPENCER Email to Dessler 20 December 2010:


OK, I think now you are raising the possibility that what I am calling a “non-feedback radiative forcing” was at some previous time itself a feedback upon temperature. If that were the case, then there would be a lagged correlation, and you would then need to do your feedback parameter diagnosis at some time lag between the radiative flux and temperature data…not simultaneously. This is what Lindzen has been trying to get published, and is another way of getting a feedback estimate.

But it is not what you did in your Science paper. When I do it with the same 10-year CERES dataset you used, I get a very different result…outside the range of most if not all climate models.



DESSLER Email to Spencer 21 December 2010:


Let me be clear: I am not “raising any possibilities” here. What I am trying to do is get you to articulate YOUR THEORY of ENSO causality. I’ve been trying to do this since our initial e-mail and trying to get a straight answer is beginning to feel like eating jello with chopsticks.

So let’s get back to the issue at hand: Do you have any physical evidence that clouds are playing a significant role in causing temperature variations during ENSO (besides the correlation, which (I think) we agree does not prove causality)? If so, what is it? If not, do you concede that I have the correct direction of causality in my paper?

After we resolve this, we can start talking about lags, etc.

Thanks again for your willingness to engage in discussions on this issue!

Andrew Dessler


SPENCER Email to Dessler 22 December 2010


How can you insist I answer a question, the answer to which would not refute (or prove) what we demonstrated in Spencer & Braswell (2010 JGR) anyway?

You can ask me, “Do you still beat your wife?”, and I’m not going to answer yes or no to that one either.

Remember, it is not me, but YOU who is claiming our results necessarily imply that clouds are part of the forcing of ENSO-related temperature changes…and you might well be right. If so, congratulations on your finding.

And I would say this interpretation IS entirely reasonable: that a change in the trade winds associated with the initiation of El Nino causes a change in cloud cover, which then is part of the forcing of El Nino-related temperature changes. THAT sounds entirely reasonable to me, and is consistent with the evidence we presented.

But that does NOT mean “clouds cause El Nino”.

Don’t confuse qualitative statements like these with what we showed QUANTITATIVELY in Spencer & Braswell, which was a simple statement of the CONSERVATION OF ENERGY:

The satellite data show radiative imbalances causing temperature changes with time.

That’s just a statement of the 1st Law of Thermodynamics. Are you claiming the 1st Law didn’t apply during 2000-2010?

Maybe YOU should answer THAT question before we continue the discussion.

But if you continue to insist on me answering “yes or no” to a question that is not relevant to what we are debating, I suggest we end this now.



DESSLER Email to the list 26 December 2010:

For those not following closely, let me recap the argument that Roy and I are having. In my research paper, I showed that the energy trapped by clouds increases as the surface temperature increases, and concluded that there is a positive cloud feedback acting. Roy objected to this saying that clouds are actually causing the surface temperature change, so I have cause and effect backwards. My response to this is that the temperature variations over the last 10 years are primarily driven by ENSO, and we know that ENSO is not caused by clouds.

This is the crux of our disagreement. In his last e-mail to me, Roy said, “The satellite data show radiative imbalances causing temperature changes with time” and “Our analysis shows that non-feedback cloud variations do cause large amounts of temperature variability during the satellite data period in question.”

But neither of Roy’s claims seem correct to me. I do not think he’s actually demonstrated that clouds are causing temperature changes.

To resolve this, I pose the following question to Roy: can you summarize for everyone on this list the evidence that clouds are affecting surface temperature over the last ten years. And can we quantify how much are clouds affecting the surface temperature? Are they responsible for 1% of the variance, or 99% of the variance, etc.?

And to show you that I am willing to answer your questions, I will answer the question you posed to me in your last e-mail: “Are you claiming the 1st Law didn’t apply during 2000-2010? Maybe YOU should answer THAT question before we continue the discussion.” The answer is that I do not dispute that the first law applies. I agree that energy is always conserved.

Happy holidays.


Andrew Dessler


SPENCER Email to Dessler 30 December 2010:

OK, let me see if I can briefly summarize my side of this…

The evidence that clouds cause a substantial portion of the temperature changes during the ten-year period in question is twofold:

(1) the temperature changes tend to lag the radiative flux changes, something that is revealed by “connecting the dots” in the scatterplots of radiative flux-vs-temperature, and

(2) this lagged behavior strongly decorrelates the temperature-versus-radiative flux variations (as is seen in Andy’s, and virtually all previously published, scatter plots of this type).

This poorly-correlated behavior is consistent with the short-term behavior of most if not all of the AR4 climate models, and was mimicked by our simple forcing-feedback model, both of which we published in JGR earlier this year.

In contrast, feedback (temperature causing cloud changes, which is what Andy believes is going on) is much closer to simultaneous, which would lead to strongly correlated data (which is seldom observed…except on month-to-month time scales).

Our JGR paper also demonstrated that this decorrelation was not simply due to noisy data…”connecting the dots” (phase space plots) shows looping and spiral patterns, rather than the zig-zag patterns one gets with random noise.

In the big picture, what the satellite data suggest is a sort of meandering of the climate system through varying states of radiative IMbalance, with the temperature changes always trying to play catch-up with the radiative flux changes, …but then the atmospheric circulation causes another change in cloudiness, and the temperature then has to slowly respond to that, too, …etc. Radiative equilibrium is never actually reached.

Regarding Andy’s question of just what percentage of all of the variability is due to “forcing” versus “feedback” is still an open question. All I know is that the “forcing” so strongly decorrelates that data that doing linear regression to get a feedback estimate is going to result in a regression slope approaching zero, which is then commonly misinterpreted as strongly positive feedback.

(We also showed in our JGR paper that short satellite periods of record can even lead to a bias in the direction of NEGATIVE feedback…but this is much less likely than a bias in the direction of positive feedback.)



Dessler e-mail to Spencer 3 January 2011


Happy new year!

Thanks for your response. I do think we are making progress now.

In your last message, you confirm that the only evidence supporting your hypothesis is the observed correlation between surface temperature and cloud radiative forcing as well as what you refer to as "decorrelation" of the data.

Because of the complexity of the Earth, there are always multiple hypotheses for every correlation. For the observed correlations you note, I have a competing hypothesis which I think explains the data better than yours.

Here is mine: the heating the surface is caused by energy stored in the ocean. This drives changes in atmospheric circulation, which change clouds. Clouds play a very small role in the surface energy budget during ENSO.

There are several strong pieces of evidence that support my point of view:

  • (1) Climate models successfully simulate the same lead/lag relationship -- see my attached figure. This suggests that correlation you identified is just normal ENSO physics.
  • (2) Energy budgets of the surface also suggest virtually no role for clouds during ENSO (e.g., see Trenberth publications).
  • (3) As far as the decorrelation of the data goes, I have not looked at this in the climate models. However, I think you sent a figure a few e-mails ago showing a climate model that reproduced that. Again, this suggests that it's normal ENSO physics. In addition, I note that the models generate about the same r^2 as the data.
Finally, you have no evidence supporting your hypothesis beyond the mere existence of the correlation. Because of that, your theory explains nothing (e.g., you cannot tell me what percentage of all of the variability is due to "forcing" versus "feedback") and makes no testable hypotheses.

  • So here are my questions for you:
  • (a) Do you have any evidence that my proposed hypothesis is wrong?
  • (b) Does your hypothesis make any testable predictions that would allow it to be falsified? If so, what are they?
  • (c) Does your hypothesis explain anything that my theory does not?


Andrew Dessler

[Figure caption: The slope of the regression of energy trapped by clouds vs. surface temperature, as a function of the lag between the time series. Negative values indicate that changes in clouds lead changes in surface temperature. The black line is calculated from observations cited in Dessler [2010] and the red lines are the climate models from that same paper.]


Spencer e-mail to Dessler 7 January 2011

Happy New Year Andy,

I've been catching up this week after having last week off for the holidays.

The evidence I presented you was NOT just the decorrelation of the data, as you I mentioned in my previous e-mail , it was TWO-fold: It is also the lagged relationship, with radiative flux changes preceding the temperature response, then the temperature changes either simultaneous with (as as we will see with ENSO, preceding) the radiative feedback response. The phase space plots we published are one way of revealing the lagged relationship.

Without taking this time lag into account, you will get correlations -- and thus regression slopes-- close to you do, even in the climate model matter what the feedbacks are. We demonstrated this in Spencer & Braswell (2010).

Now, let's look at the oceans, since you want to emphasize the signature of ENSO during the period of record....

By far the most precise measurements of global SST variations come from AMSR-E on NASA's Aqua satellite and, as you know, a CERES radiation budget instrument also flies on that satellite. I did a calculation with these data somewhat similar to the one you did.

Attached find a plot somewhat analogous to yours, but from Aqua SST versus radiative flux....As you can see, the radiative feedback response occurring AFTER the temperature changes suggest strongly negative feedback. Also shown in the same plot AR4 climate model results from their 20th Century runs on the same plot.

The peak correlation of the satellite data in the plot was 0.68, at 11 months lag. At zero lag, the correlation is only 0.27. (What was the correlation of the data you showed in Fig. 2 of your Science paper? I did not see one listed.)

Clearly, there are cause-effect things going on here that cannot be revealed in plots like your Fig. 2, unless these time lags are taken into account.

As a result of our discussion, I've decided that we should do another publication, focusing on the lag relationships seen in the Aqua data and what they might mean for feedback and climate model validation.



Dessler e-mail to Spencer 10 January 2011

Hello, Roy.

If you don't mind, I'm going to keep after you on one important point.

In these e-mails, we have discussed two hypotheses for the observed lead/lag relation and decorrelation. My hypothesis is that all of the observations are due to canonical ENSO physics --- not clouds causing temperature changes. The fact that climate models get these relations supports this, and it is consistent with the surface energy budget.

Your hypothesis --- clouds cause temperature changes --- has no supporting data (beyond just the correlation & decorrelation) and it is not consistent with the surface energy budget.

Here's my question: Why would anyone (including you) accept your hypothesis when the mainstream view fits the data better.

I'm interested in your thoughts.


Andrew Dessler

Enter Richard Lindzen

Lindzen e-mail to Dessler 11 January 2011

Dear Andy,

I find this exchange a little peculiar in that you never seem to address what I understand Roy's main points to be.

First, Roy notes that outgoing radiation (especially in the visible) varies for many reasons of which feedback to surface temperature is but one. Other obvious examples range from volcanic aerosol production to cloud triggering by Kelvin-Helmholtz instabilities. I know of no one who really questions that surface temperature is not the only or even the main source of fluctuations in visible radiation.

Second, any changes in outgoing radiation will also cause changes in surface temperature. This is simply a matter of elementary thermodynamics. For non-feedback changes in radiation, the temperature changes will follow rather than lead temperature changes.

Third, because of the first two points, simple regressions of outgoing radiation on surface temperature will not be a useful measure of feedback. Spencer and Braswell illustrated this in their paper. There are, of course, other problems with the use of simple regressions as well.

It would be interesting to see your response to these points.

Best wishes,



Dessler e-mail to Lindzen on 14 January 2011


Your question gets to the same issue that I am after: what is the cause of the temperature variations over the last 10 years. If it turns out that clouds are responsible, then that would indeed challenge my feedback estimate.

However, I suggest that ENSO is responsible for the temperature variations. I've repeatedly asked Roy for evidence that clouds are responsible, and he cannot provide anything beyond some ambiguous correlations. The problem with that of course is that correlations do not tell us causality.

If you have evidence that the variations over the last decade are caused by clouds, then please let me know what that evidence is.


Andrew Dessler


Spencer e-mail to Dessler on 14 January 2011


I cannot believe you keep saying "correlations do not prove causality", when you yourself have used a (near-zero!) correlation in your paper to support causality in only one direction!

But we (including Lindzen) are claiming that relatively LARGE correlations, with a clear lead-lag relationship, DO strongly suggest causation.

I do not know how you can, in all honesty, continue this mantra of yours...oversimplifying our position into something like "clouds cause El Nino", or some such thing.

After all, the Southern Oscillation Index is an ATMOSPHERIC index, and for you to claim that changes in the trade winds DON'T cause a change in cloud cover, which can in turn affect ocean temperatures, is treading on thin ice.

And if, perchance, Kevin Trenberth is coaching you on these talking points, I wish he would just come out and defend them himself.


Lindzen e-mail to Dessler 14 January 2011

Dear Andy,

It is clear where you are going wrong. You are confusing changes over long periods during which equilibration can occur with fluctuations from which feedbacks can be determined. Note that in order to measure feedbacks from outgoing radiation, one must look at time scales that are short compared to equilibration times (years) but long compared to the action of feedback processes (days). That fluctuations in clouds, volcanos, etc. occur over the relevant time scales is obvious as is the fact that such fluctuations must, of necessity, cause changes in surface temperature. The issue of whether clouds can cause El Nino is a red herring. Incidentally, we have looked at your data. If you restrict yourself to relevant time segments, your r-square goes up greatly, and if you perform an analysis of leads and lags, you too get a negative feedback from fluctuations in outgoing radiation that lag SST (whether you choose segments or your entire record -- though again, r square is much larger for segments). The ambiguities in the choice of segments in Lindzen-Choi 2009 disappear when one uses 2 or 3 month smoothing.

Best wishes,



Dessler e-mail to Spencer on 17 January 2011


Correlation does not prove causality. Period. I honestly cannot believe you want to argue this point. The fact that you do lays bare the intellectual bankruptcy of your “clouds cause climate change” hypothesis. It’s now evident that there really is no actual physical evidence to support it.

In science, correlations allow you to construct hypotheses, which then must be tested with physical arguments. The history of science is littered with the corpses of high r squared correlations that fooled people into assuming causality. I’m afraid you’re another victim.

I would NEVER assume correlation proves causality. My cloud feedback calculation is supported by a firm causal link: ENSO causes surface temperature variations which causes cloud changes. This is supported by the iron triangle of observations, theory, and climate models.

As to your comment:
“After all, the Southern Oscillation Index is an ATMOSPHERIC index, and for you to claim that changes in the trade winds DON'T cause a change in cloud cover, which can in turn affect ocean temperatures, is treading on thin ice.”

Of course changes in trade winds can change clouds.

But what causes changes in the trade winds during ENSO?

It’s the changing SST distribution. Get it? Surface temps drive clouds. QED.

Thanks for this interesting discussion. Believe it or not, I think we’ve actually reached closure. I have no more questions for you.

To the reporters/bloggers on this list: I would encourage you to write/blog about this exchange. I think that this was an unusual and frank exchange of views that people would be interested in. FYI, I’m also archiving these e-mails on my previously dead blog,


Andrew Dessler


Dessler e-mail to Lindzen on 17 January 2011


First, I’d like to comment on your statement that, “The issue of whether clouds can cause El Nino is a red herring.” I agree, and I assume from this that you also have no physical evidence that clouds are causing surface temperature changes. If you did, you would be advancing it as a fatal flaw in my paper.

What’s puzzling is that I just re-read the comment you submitted to Science about my paper. In it, your first and main point is: “These results imply that [Dessler’s results are] ... not indicative of the cloud feedback, but is largely a consequence of the temperature changes induced by non-feedback cloud variations.” That sure sounds like “clouds cause ENSO” to me.

So have you concluded that your comment to Science is now a “red herring”? Are you going to withdraw it?

OK, now on to the meat of your e-mail. You make the argument that there are certain time scales over which the feedback must be calculated.

To be honest, I simply don’t follow the logic of your argument. Luckily, it sounds like this is really point number 2 from your Science comment, which is reasonably clear: “A second problem arises from the use of regression over the whole record. The problem here stems from the fact that feedbacks introduce temporary imbalances to the radiative budget (over time scales of hours to months), but over longer periods (years to decades depending on climate sensitivity), the system equilibrates so as to eliminate these imbalances (6). Using the whole record acts to distort the feedback estimates by including equilibration as well as feedback. More accurate estimation of feedback requires the isolation of the specific feedback signals (5, 6).”

I have two responses. First, as I wrote in my response to the Science comment, “Their second criticism indicates confusion between forcing and feedbacks. It is forcing (e.g., an increase in greenhouse gases, a brightening Sun) that generates imbalances in the Earth’s radiative budget. This radiative imbalance then causes the planet to warm, restoring equilibrium. Feedbacks do not create a radiative imbalance — they simply change the magnitude of the warming necessary to restore radiative balance. When estimating the magnitude of a feedback, there is no requirement that the Earth’s surface temperature be either in or not in equilibrium.” Clearly, as articulated in your Science comment, this argument is fundamentally wrong.

Second, I wonder what the source is of the claim that we must consider equilibrium time scales in our analyses of feedbacks. It appears to be reference 6, which is Lindzen and Choi 2009. But the claim is not proven in that paper --- it is simply assumed (in paragraph 5 of that paper). Can you provide a reference where some evidence is presented in support of this claim?


Andrew Dessler

Lindzen e-mail to Dessler on 17 January 2011

Dear Andy,

You really do seem seriously confused. Since when does one need proof that clouds can change for many reasons other than changing temperature? Since when does one need proof that changes in the radiative flux associated with non-feedback changes in cloud will inevitably cause changes in surface temperature? Moreover, given that radiative balances are restored over the equilibration time, how in the world would one deduce feedbacks over such time scales using TOA fluxes? These are elementary textbook issues.



Dessler e-mail to Lindzen 19 January 2011


It seems that your argument about time scales interfering with feedback calculations is predicated on clouds causing climate change (i.e., clouds acting as a non-feedback radiative forcing).

I had previously asked you if you had any evidence that clouds were actually causing temperature variations over the last 10 years, and you dodged it.

So, let me ask you again, do you have any evidence that clouds are causing any of the temperature variations over the last 10 years?


Andrew Dessler

Lindzen e-mail to Dessler 19 January 2011

At 04:22 PM 1/19/2011, Andrew Dessler wrote:
It seems that your argument about time scales interfering with feedback calculations is predicated on clouds causing climate change (i.e., clouds acting as a non-feedback radiative forcing).

Not at all. It is based on the fact that radiative processes act to reestablish equilibrium.
I had previously asked you if you had any evidence that clouds were actually causing temperature variations over the last 10 years, and you dodged it.
Changes over a ten year period are irrelevant. That changes in clouds must cause changes in temperature is simply basic physics.

Richard Lindzen


Andy Revkin e-mail to the list 19 January 2011

Hi all,

I've pared down the list here for the moment.

I haven't had time to keep track of every back-and-forth here, but I'd like an assessment - particularly from Andrew and Roy but also any other scientists on this list - as to whether this conversation has revealed any points of agreement or simply hardened areas of disagreement?


Spencer e-mail to Revkin 19 January 2011

I don't see any convergence here.


Dessler e-mail to Revkin
19 January 2011


I agree with Roy that there was no convergence in our discussion. However, I did not initiate the exchange in order to try to convince Roy Spencer and Dick Lindzen that my theories about the cloud feedback are correct—I am not that naive.

Rather, I wanted to have a public discussion between the scientists, where we really focused on science, and no one could avoid the hard questions. I hoped people would be able to tell who was doing real science and who wasn't.

In that sense, I think that my exchange was a success. While it took a while, I was able to finally get Roy to admit that his cloud feedback theory is based on the idea that "correlation proves causality". And Dick responded to my requests for confirming evidence with the argument that his point of view is so obvious that he need not provide any evidence to support it.

While I don't think that many non-scientists can understand the fine points of climate science, my hope is that anyone can read these e-mails and say to themselves that Roy and Dick's responses don't look terribly credible or scientific.

On the other hand, I'm not sure how many people will wade through these e-mails carefully. That's why I hope journalists like you, Andy, can write a good story on this and encourage people to go read the e-mails themselves, particularly the last few. If you write about this, you may want to ask other scientists, particularly non-climate scientists, to read the e-mails and get their views on which of our positions appears most reasonable.

Let me know if you have any additional questions.


Andrew Dessler

Lindzen e-mail to Dessler
20 January 2011

Yup, Andy. You did get me to admit that the first law of thermodynamics no longer needs proof. You also got me to admit that clouds change for many reasons other than the surface temperature. There are several text books devoted to this. Finally, you never explained how one could use imbalances in outgoing radiation once the system has time to equilibrate. What you have admitted is that you have been grandstanding.

Best wishes,


Spencer e-mail to Revkin
20 January 2011

Since Andy (Dessler) has editorialized on his view of the mini-debate we have been having, I will too.

The only thing Andy has offered to refute our published work in this field is that "clouds don't cause El Ninos", or something similar.

We have shown with a simple, physical model that we can match the behavior that the satellite observations display. In contrast, Andy has only *assumed* that his observed relationship (with a near-zero correlation!!) is consistent with causation in only one direction! On this subject, Andy is accusing me of claiming something (inferring causation from correlation) he himself is doing!

It is terribly frustrating that with all of the evidence in Spencer & Braswell (2010), Andy thinks it can all be swept away with his claim that we have not demonstrated that clouds cause temperature changes during the ten year period in question. Yet this is EXACTLY what we demonstrated!

I can only conclude Andy does not understand the evidence we presented.



Dessler e-mail to Lindzen
20 January 2011


Climate science is quantitative. When you prove clouds are important, then we'll talk. Simply proving it is not prohibited by the first law is not proof of anything. I see now why you can't get your work on this published in peer-reviewed journals.


Andrew Dessler


Dessler e-mail to Spencer
20 January 2011


This discussion has the capacity to quickly turn personal and ugly. I'm not going to engage in that kind of exchange. I will simply encourage everyone to read the entirety of the e-mail exchange and you'll get a good idea of where the science of cloud feedback stands, and how credible the skeptical point of view is.


Andrew Dessler

Spencer e-mail to Dessler
20 January 2011

Andy, by "ugly" I assume you are referring to the comment you just made to Dick Lindzen?

"I see now why you can't get your work on this published in peer-reviewed journals"


Lindzen e-mail to Dessler
20 January 2011


Why do you insist on what simply isn't true. Note that while clouds are a likely suspect because small changes can lead to large changes in the radiative budget, we are working with observed changes in the radiative imbalance, and the numbers are such that one can expect changes in SST. The questions are how much and with what lead or lag. Those are questions that you fail to address.



pedant 278 said...

I think the email header is wrong for the email beginning, "Since Andy (Dessler) has editorialized on his view of the mini-debate we have been having, I will too."

Two groups of people talking past each other. Dessler's pretty acidic, though tone counts for nothing unless you're a skeptic and want to play the civility card.

willard said...

These emails were not hacked. They are worthless. Except perhaps for the sake of an amusing title.

A travesty, I dare say.

Pinko Punko said...

It seems clear that there is quite a bit of avoidance here on one side (Spencer and Lindzen), though this is also the first where I've ever seen Dessler lose his cool. He seems to have had the patience of a saint for the most part.

Arthur Smith said...

The first thing they should have done (and Dessler's at fault here) is agree what they were debating. Rational debate is impossible without at least some agreed base context. Were they talking about regional, or global average effects? Were they talking about hourly, daily, monthly or annual averages of temperature, cloudiness, or some other statistical properties? Without an agreed base context, S and L can say whatever they feel like and it may well be true in some different context than what Dessler was talking about.

Given the public nature of this discussion I think Dessler should have spent a lot more time trying politely trying to state in his own words exactly what Roy Spencer claimed, in a way Spencer could agree to (or demonstrate he really was avoiding something)

Magnus Westerstrand said...

One thing to do when you engage in thees kind of things is ask some one outside the specific area to read an comment. Think much clarity could be added e.g. what more could make Spencer correlation then what he is suggesting... point out again that Dessler actually are trying to test a physical mechanism... and just trying to stick to the point...

(you got one heading wrong, Dessler e-mail to Revkin on 1/20/11 should be Spencer?)

Rocco said...

Okay, could somebody who understands this stuff explain to me what exactly is it that S&L are claiming?

- clouds cause enso
- clouds cause temperature change, enso is irrelevant
- something else


Anna Haynes said...

> "Given the public nature of this discussion I think Dessler should have spent a lot more time trying politely trying to state in his own words exactly what Roy Spencer claimed, in a way Spencer could agree to"

Agree with Arthur. To an outsider the exchange was not clear.

Anonymous said...

Dessler has every right to be terse and frustrated-- Lindzen has after all been slandering climate scientists for years now, and is an arrogant SOB which makes sincere and clam dialogue difficult. Here he just keeps dodging the questions and referring to his debunked 2009 paper. Lindzen made also several unsupported statements. Roy seems caught up about his stupendously marvelous paper with Braswell (get off your high horse Roy, remember how you screwed up the MSU data?). Roy seems very confused, but tries to hide it with bluster.

Andy failed to throw I knock-out punch (maybe I missed it?), and naughty of him to accuse others of being personal after taking a swipe at Dick. I am willing to bet that it is Andy's work which stands the test of time; not Roy's and not Lindzen's.

That all said, what a mess, they really were talking past each other, and because the rules of engagement were not specified, or the actual objective, so the well-intentioned exercise failed IMHO. Both Lindzen and Spencer failed to sell their ideology/science.

Really, all the lay person sees is "the science is not settled". Sad fact is that Lindzen and Spencer are most likely wrong about low climate sensitivity. That is what is at issue here and what counts ultimately.
But Dick and Roy want us all to wait 50-100 years to find out who was right. No thanks fellas.

EliRabett said...

Lindzen is doing his Bill Gray act.

jakerman said...

"what a mess, they really were talking past each other"

Isn't that the only way that Spencer's and Lindzen's claims survive? They don't survive peer review, instead Spender puts them in book claiming that:

"climate researchers are rather myopic. They think that the only way for global-average temperatures to change is for the climate system to be forced ‘externally’…by a change in the output of the sun, or by a large volcanic eruption. These are events which occur external to the normal, internal operation of the climate system.

But what they have ignored is the potential for the climate system to cause its own climate change. Climate change is simply what the system does, owing to its complex, dynamic, chaotic internal behavior.

As I travel around the country, I find that the public instinctively understands the possibility that there are natural climate cycles. Unfortunately, it is the climate “experts” who have difficulty grasping the concept. This is why I am taking my case to the public in this book. The climate research community long ago took the wrong fork in the road, and I am afraid that it might be too late for them to turn back."


"The experts have simply mixed up cause and effect when observing how clouds and temperature vary. The book reveals a simple way to determine the direction of causation from satellite observations of global average temperature and cloud variations. And that new tool should fundamentally change how we view the climate system."

Sure sounds like Andy was nailng Spencer on his core claim. Spencer was running from this, keeping discussion away from science and "taking [his] case to the public" instead.

EliRabett said...

Turned AD to RS where needed. Thanks

Ron Broberg said...

Good grief. This exchange has actually *increased* my respect for blogs as a medium of communication.

Jakerman said...

Aurthur sensibly writes:
"The first thing they should have done (and Dessler's at fault here) is agree what they were debating. Rational debate is impossible without at least some agreed base context."

Here was Dessler on the 14th Dec:

"DESSLER (14 December 2010):

Thanks for your message … I knew you couldn’t stay mad at me

Before I get into the details of the correlation, I’d like to get one thing straight: you’re arguing that the warming during an El Nino is caused by radiative heating by clouds. Right?

Once you confirm that, we can move on with the discussion. If you’re not saying that, then I’m confused by your message — in that case, I’d appreciate it if you could please explain the role of clouds in driving surface temperatures variations during ENSO.


Anonymous said...

One of the resident non-scientists here. As I understand it:

1. Clouds come from the sun evaporating water.
2. A warmer atmosphere holds more water.
3. But the cloud, when it forms, shades the water underneath it, reducing the rate of evaporation.
4. So in general, figuring out the role of cloud cover in global climate models is a hard problem.

5. All that being said, Spencer and Lindzen believe that the shading of clouds can drive major ocean currents, specifically the ENSO. Going by what's been written at Science of Doom, the decrease in incoming solar radiation (at a specific wavelength?) is setting up a complex response in the ocean that leads to the formation of an ENSO current.

6. Dessler believes, by contrast, that S&L have no plausible physical model by which the change in cloud cover over portions of the Pacific can lead to the formation of the ENSO current.

Do I have that right?

Lawyer mouse

Rocco said...

Lawyer mouse: Nope. S&L seem to be claiming that they never said that clouds cause ENSO.

EliRabett said...

For completeness, should Eli put the beginning part of the back and forth here also???

Steve Bloom said...

For a modest sum, I would be happy to expound on my new hypothesis that planetary atmospheres are caused by the surrounding vacuum. :)

It somewhat sounds as if the rework of Lindzen & Choi may have failed of publication. Does anyone know? Also, does anyone know about any comment(s) on Spencer & Braswell?

IMHO Andy did a fine job here, but it's certainly true that anyone not reasonably familiar with the long history of this "debate" wouldn't be able to tell. It's also true, I suppose, that a specified cloud oscillation in principle *could* drive something like ENSO (although that would fall apart on examination of the details, as Andy noted), but, in addition to the three points Andy made, that rather begs the questions of a) a driver for the postulated cloud behavior and c) why we don't see similar things happening all over the planet. Andy seems to want to win the debate in what might be called a "pure" form, without resorting to either those questions or paleoclimate (e.g changes in ENSO during glaciations).

Revkin is useless.

BTW, whoever thinks Andy got snippy first must have missed Spencer's comment about Trenberth.

Steve Bloom said...

Yes, please, Eli, plus red highlighting for Spencer's Trenberth jab.

Vaughan Pratt said...

While I don't see any mention of global warming on this page, the extensive commentary on the Dessler-Spencer debate on Spencer's blog included 14 references to global warming. Apparently the commenters there are under the impression that this debate has some bearing on global warming. Are they simply confused, or is there a global warming subtext underlying the discussion on this page that the discussants here (Dessler, Spencer, Lindzen, etc.) are tiptoeing around?

(And on a separate note, why does the previewer here work on Firefox but not Chrome?)

silburnl said...

"Yes, please, Eli, plus red highlighting for Spencer's Trenberth jab."

I think there's a case to enredden the bit earlier in the same email about how Dessler can't honestly be advancing such an oversimplified version of Spencer's position as well. That's where I thought the gloves started to come off.

From which I must assume that Spencer's answer to Dessler's question in the 14th Dec email was "No". Were they able to frame a mutually agreeable position in the period leading up to the new year exchanges? I suppose I could go to Spencer's blog and look but I'd rather not give him the pageviews. Also I'm lazy.


Vaughan Pratt said...

Absent any response to my question about the relevance of this debate to global warming, I'd like to suggest that there is none.

El Nino events and episodes occur on a time scale of three to seven years. I would therefore have expected them to be irrelevant to global temperature smoothed to a running mean of 12 years. This is the red curve here.

At a 12-year scale, there would seem to be only four relevant terms.

1. The 56-year Atlantic Multidecadal Oscillation or AMO.

2. The 75-year or so Pacific Decadal Oscillation or PDO.

3. CO2 as per Tyndall and Arrhenius.

4. "Everything else."

On the URL above these are plotted in blue for 1 and 2, green for 3, and black for 4 (labeled Residue).

Over the 160 years of data the residue (black) does not seem to be going anywhere, but just fluctuates about its mean. I'm imagining that a substantial portion of those fluctuations might be attributable to aerosol cooling from e.g. volcanoes and perhaps World War 2, which must have put up a lot of dust from all the bombing of cities that went on.

The violet curve represents 1, 2, and 4. It rises sharply after 1980 just as does the observed or red curve, the HADCRUT3 data.

One would automatically assume that the violet curve took the last thirty years of HADCRUT3 and CO2 data into account.

One would be wrong.

Using only the CO2 and temperature data up to 1981, the parameters for 1, 2, and 4 above are almost identical to those obtained with the additional 30 years of data. The predicted global temperature based only on the data available up to 1981 is shown here.

The two parameters for Hofmann's formula for CO2, namely 1790 for onset and 32.5 years for each doubling of anthropogenic CO2, are due to Hofmann for the full-data curve, and are obtained using Hofmann's methodology (fitting to the Keeling curve assuming 280 as the natural base) for the 1850-1981 curve. The remaining parameters minimize the squared error (i.e. the sum of the squares of the values of the residue curve).

The climate sensitivity as determined by this fit is either 1.84 C per doubling of CO2 if the temperature is taken immediately, or 2.22, 2.69, or 3.28 according to whether one postulates a 10, 20, or 30 year delay after adding the CO2 for it to take effect, modeled naively by using 1800, 1810, and 1820 respectively in place of 1790 for Hofmann's date of onset of anthropogenic CO2, defined as when it was 1 ppmv.

Vaughan Pratt said...

Sorry, the two occurrences of the phrase "1, 2, and 4" should have been "1, 2, and 3" (forgot to change them when I reversed the order of 3 and 4 in the list). That is, the violet curve estimates the contributions of the ocean oscillations and CO2.

Flavius Collium said...

Hmm, to me it seems possible that Spencer indeed is claiming with the correlation graph that the climate models suck with the ocean and that their other explanation just might have something to it - which Dessler bastardized into "clouds cause warming" or some such - where Spencer's frustration seemed very genuine. But I don't know the subject area.

But just look at that graph. I'm not entirely sure but it looks interesting!

(I don't read Lindzen's stuff.)