What follows is a mini-debate by e-mail during the last 3 weeks between myself and Andy Dessler over the question of whether cloud feedbacks in the climate system are positive or negative.

Last night, Andy Revkin suggested that I post it. I believe this e-mail exchange is rather unusual during a time when scientists arguing over global warming more often spar with sound bites in the popular press rather than personally between themselves.

This was partly the result of my somewhat scathing post on December 9, 2010 regarding Science recently publishing Andy’s paper claiming positive cloud feedback. (I was not asked to peer review Andy’s paper even though I have published the most recent and directly comparable paper on the subject.)

The e-mail debate, which is still in progress, has been cc’d to a variety of people, the more recognizable addresses being: mann@meteo.psu.edu; gschmidt@giss.nasa.gov; trenbert@ucar.edu; jgillis@nytimes.com; rkerr@aaas.org; santer1@llnl.gov; revkin@optonline.net; rlindzen@mit.edu; olivermorton@economist.com; ekintisch@aaas.org; p.campbell@nature.com; john.christy@nsstc.uah.edu; mlemonick@climatecentral.org; eric.berger@chron.com; jhalpern@howard.edu.

The exchange of e-mails is listed in chronological order, following an initial e-mail alert from Scott Mandia of the Climate Science Rapid Response Team of my blog post on Andy’s paper. I am not posting Scott’s e-mail in respect of his privacy.

I entered the e-mail discussion after Scott criticized my my blog post implying that Andy’s paper being published by Science on the last day of the Cancun climate conference was motivated by more than just science. I have italicized where one of us quotes from an earlier e-mail.

SPENCER (11 December, 2010, #1 of 2):
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.
-Roy

SPENCER (11 December, 2010, #2 of 2):
…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 (11 December, 2010):
Roy-

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?
Thanks!

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.

Regards,
Andy Dessler

SPENCER (13 December, 2010):
Andy:

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).

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:

[PLOT OF CNRM-CM3 TIME SERIES}

A scatter plot of the data is next:

[CNRM-CM3 SCATTER PLOT]

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:

[LAG CORRELATION PLOT]

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).

-Roy

DESSLER (14 December 2010):
Roy-

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.

Thanks!

SPENCER (15 December 2010):
Andy:

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.

-Roy

DESSLER (18 December 2010):
Roy-

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?

Thanks!

SPENCER (20 December 2010):
Andy:

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.

-Roy

DESSLER (21 December 2010):

Roy-

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!

SPENCER (22 December 2010):
Andy:

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.

-Roy

DESSLER (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.

Thanks!

SPENCER (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.)

-Roy

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.

Today’s my first full day in Cancun at COP-16, and as I emerged from my hotel room I was greeted by a brisk, dry, cool Canadian breeze.

It was 54 deg. F in Cancun this morning — a record low for the date. (BTW, Cancun is nowhere near Canada).

Al Gore is not supposed to be here…but it could be that the Gore Effect has announced his secret arrival. We will check into this.

The following pic I took pretty much sums up what some are trying to accomplish here:

You might recognize this organization:

Does this photo say something about the future of wind power in Europe?

Even the ghost of John Lennon is here — Give Peas A Chance:

YR MON GLOBE NH SH TROPICS
2010 1 0.648 0.860 0.436 0.681
2010 2 0.603 0.720 0.486 0.791
2010 3 0.653 0.850 0.455 0.726
2010 4 0.501 0.799 0.203 0.633
2010 5 0.534 0.775 0.292 0.708
2010 6 0.436 0.550 0.323 0.476
2010 7 0.489 0.635 0.342 0.420
2010 8 0.511 0.674 0.347 0.364
2010 9 0.603 0.555 0.650 0.285
2010 10 0.426 0.370 0.482 0.156
2010 11 0.381 0.513 0.249 -0.071

The tropical tropospheric temperature anomaly for November continued its cooling trend, finally falling below the 1979-1998 average…but the global anomaly is still falling slowly:+0.38 deg. C for October November, 2010.

2010 is now in a dead heat with 1998 for warmest year, with the following averages through November:

1998 +0.538
2010 +0.526

December will determine the outcome, but remember that the difference between the two years is not statistically significant.

For comparison, here are the monthly anomalies for 1998:

YR MON GLOBE NH SH TROPICS
1998 1 0.582 0.612 0.552 1.097
1998 2 0.753 0.857 0.649 1.291
1998 3 0.528 0.655 0.401 1.025
1998 4 0.770 1.014 0.525 1.059
1998 5 0.645 0.685 0.606 0.885
1998 6 0.562 0.635 0.490 0.536
1998 7 0.510 0.659 0.362 0.442
1998 8 0.518 0.544 0.492 0.447
1998 9 0.458 0.571 0.345 0.312
1998 10 0.416 0.519 0.312 0.339
1998 11 0.192 0.272 0.113 0.130
1998 12 0.277 0.416 0.138 0.073

FOR THOSE TRACKING OUR DAILY TEMPERATURES: Since I’m getting many e-mails about quirks in the daily channel 5 temperature updates at the Discover website, here are a few tips to keep in mind:

1: The Discover website is an automated process and there is little quality control.

2. A few of the orbit files end up coming in several days late, in which case some day’s averages can be missing for several days. We fix it manually as time permits.

3: If a daily temperature difference between this year and last year is 100’s of degrees, it’s because one of the days has missing data. It’s not because we’ve been hacked by Earth First! Check out the text data…you’ll figure it out.

4. During spring there can be strong warming trends, and (as has happened in the last couple of weeks) in the fall there can be strong cooling trends. This is partly because the seasonal cycle has not been removed from the data. Click the “Average” box and “Redraw” to see how what’s happening compares to what’s normal for that time of year.

[note: These satellite measurements are not calibrated to surface thermometer data in any way, but instead use on-board redundant precision platinum resistance thermometers (PRTs) carried on the satellite radiometers. The PRT’s are individually calibrated in a laboratory before being installed in the instruments.]