In January, 2014 the American Physical Society (APS) held a one day workshop on climate change and invited six climatologists to participate.  A full transcript of the workshop can be found here. The six speakers are all very eminent climate scientists.  The discussion was limited to the physical basis of climate change and atmospheric physics was the predominant topic.  Three of the speakers lean to the alarmist view. That is they think we are headed toward a climate catastrophe due to man-made Carbon Dioxide. These are Dr. Held, Dr. Collins, and Dr. Santer.  The other three lean to the skeptical view and do not think we are headed to a climate catastrophe. These are Dr. Curry, Dr. Lindzen and Dr. Christy.  Short biographies of each of the speakers can be seen here. Someone new to the climate change debate would have a hard time telling the alarmists from the skeptics from this transcript. They were all very professional and they stuck to the science as their host, Dr. Koonin, requested. Climate science and the debate about it are much more complex than the media, the politicians and public know. This workshop drills down to the root of the disagreements and reading it reveals the considerable uncertainty in estimates of both climate sensitivity to CO2 and the effect of natural long term climate cycles.

The media think of catastrophic anthropogenic climate change or global warming (CAGW) in very simplistic black and white terms.  According to the media and many politicians esteemed scientists all agree we are headed to a world ending catastrophe due to man-made CO2 and everyone who is skeptical of this conjecture is a knuckle-dragging troglodyte, aka a “denier.”  This is in spite of a recent poll that shows CAGW skeptics are better informed on climate science than the climate alarmists.

I will try and summarize the important points discussed in the meeting. Dr. Koonin, the host of the event, has published his own summary in the WSJ. Professor Judith Curry has also written about the meeting here. Another view by Tony Thomas can be seen here and commentary published in Physics Today can be seen here. The Climate Workshop Framing Document was created by the committee after thoroughly reading the AR5 Physical Science Basis Report. It contains the questions that guided the presenters and the discussion. I will only deal with a few of the questions in this summary. In my discussion of the transcript below all page references are to the transcript itself. I use both the transcript page references and hyperlinks to keep this summary complete but brief.

No unsubstantiated appeals to authority were allowed by Dr. Koonin.  Not a single participant mentioned “the 97% consensus!”  Uncertainty and the quantification of uncertainty, particularly of climate forcings, was the topic of the day.

All six were in the room, together with the APS committee on climate change, and all could ask questions.  The Q&A sessions were particularly educational.  The transcript of the meeting is 573 pages long which led to 19 typewritten pages of notes. This is a summary of my notes.

To the best of my knowledge the APS has not issued a new climate change statement, but that doesn’t matter much. This workshop and the transcript are really what we needed. Yet another uninformed political statement by a scientific society, like those from the AAAS or the American Chemical Society or the original statement (now being reviewed) by the APS simply parroting the IPCC is pointless. This transcript is as good at explaining the issues as anything I’ve seen. To quote Professor Curry: “This is a remarkable document… it provides in my opinion what is the most accurate portrayal of the scientific debates surrounding climate change.

The six invited climate scientists were sent a framing document that contained a list of questions about AR5 (the Fifth IPCC Report- Physical Basis).

The hiatus in warming since 1998 or “the stasis”

From the framing document :

While the Global Mean Surface Temperature (GMST) rose strongly from 1980-98, it has shown no significant rise for the past 15 years…[The climate does not track the projections published in the 4th IPCC report, so the framing document asks …]

To what would you attribute the stasis?

How long must the stasis persist before there…[is] a problem with the models?

Dr. Collins thinks the stasis (or hiatus) is due to volcanic aerosols although he admits their effects on climate are not well understood.

Dr. Curry does not think that volcanic and man-made aerosols can fully explain the hiatus. She also believes that natural climatic cycles have “juiced” the warming in the last half of the 20th Century. A natural cooling cycle started late in the 20th Century that is counteracting the warming effect of man-made CO2. She presents a proposed natural climate cycle, astadium wave,” that predicts a natural cooling period over the next twenty years or so. Thus, she believes that the hiatus suggests natural forces (or “forcings”) are powerful enough to counteract man-made forcings.

Dr. Santer also thinks that volcanic aerosols are an important factor in the hiatus, but probably only up to 25%. He acknowledges that natural long term cycles (mainly the AMO and the PDO) may contribute significantly, but these are poorly understood and not in the models. Some of the models do attempt to capture the shorter term ENSO cycle, or parts of it. ENSO is clearly not the cause of the hiatus.

Dr. Lindzen and Dr. Christy do not directly address this question, but Dr. Held is somewhat neutral on it. He says that the warming in the second half of the 20th Century is forced, but he does not know if the forcing is anthropogenic or natural (page 409). Long term climate cycles that are not in the models could be a cause.

A final thought from Dr. Collins (page 92): 

“…if the hiatus is still going on as of the sixth IPCC report, that report is  going to have a large burden on its shoulders walking in the door, because recent literature has shown  that the chances of having a hiatus of 20 years are vanishingly small.”

There seemed to be general agreement at the workshop that if the hiatus lasts 20 years (until 2018), the IPCC and a potential AR6 are in real trouble.

Climate Sensitivity

From the framing document (VI.2)

The estimated equilibrium climate sensitivity to CO2 has remained between 1.5 and 4.5 in the IPCC reports since 1979, except for AR4 where it was given as 2-5.5.

What gives rise to the large uncertainties (factor of three!) in this fundamental parameter of the climate system?

How is the IPCC’s expression of increasing confidence in the detection/attribution/projection of anthropogenic influences consistent with this persistent uncertainty?

Wouldn’t detection of an anthropogenic signal necessarily improve estimates of the response to anthropogenic perturbations?

Sensitivity was defined by Dr. Lindzen and Dr. Collins in this way (page 277):


ΔT0 is the initial temperature at equilibrium and f is the net dimensionless feedback from external forces, for example CO2 concentration, clouds, volcanic aerosols, etc.  “f” ranges from zero to 1, if it is one ΔT is infinite and a plot of “f” (on the x axis) versus ΔT looks like the figure below from Lindzen and Choi (their figure 11).


When “f” is past a certain point it really takes off.  This is what the alarmist contingent of climate scientists are worried about.  So, what is the net external forcing on our climate system, how large or small is it likely to become?  The point of Dr. Lindzen’s talk is that we do not know and cannot accurately measure it at this time.  But, he can see in his data that the anthropogenic contribution is very small.  He also notes that the IPCC estimate of the man-made effect is about 2 Watts/m2 in AR5 and that is much smaller than the Milankovitch effect of 100 Watts/m2 at 65 degrees north, see Edvardsson, et al. The Milankovitch effect causes the glacial periods.  The alarmists disagree that it is small, but they cannot measure it either as noted in Trenberth and Fasullo, 2013 and by Dr. Collins and others in this workshop.

Dr. Lindzen focuses on climate sensitivity in his presentation. He relies heavily on Lindzen and Choi (2011), Spencer and Braswell, 2011, and (oddly) Trenberth and Fasullo, 2013. All of these papers try to use satellite measurements of radiation escaping from the Earth to detect how much solar radiation is being absorbed. The amount of solar radiation entering the Earth’s atmosphere is known fairly accurately and if we see less being emitted into space over time this suggests that increasing levels of Carbon Dioxide in the atmosphere may actually be changing the amount of heat being absorbed by the Earth and its atmosphere as the computer models suggest. Perhaps this is a way to obtain an observational measure of climate sensitivity.

However, while all of the studies suggest that the amount of extra heat being retained is much less than predicted by the models, none of the studies were able to compute climate sensitivity as hoped. Dr. Lindzen’s study found an unambiguous negative longwave feedback in the climate system and a slight positive, but less clear, shortwave feedback. The longwave negative feedback is probably due to water vapor and clouds.

Trenberth and Fasullo also failed to detect a signal in the satellite data, but if there were a signal in the data, it was small.  An interesting thing about Trenberth and Fasullo is that they spend the whole paper showing how natural forces and cycles are contributing to the warming from 1976 to 1998 and the hiatus since 1998 and then conclude “… the veracity of decadal variability in models is an issue. “

So, until the last paragraph they are reasonable in their analysis.  Then, apparently frightened that someone might think their data suggests that natural forces may be equally to blame for recent warming or worse more than the impact of man, they add this bit of obeisance to their climate change priesthood:

 “The analysis in this article does not suggest that global warming has disappeared; on the contrary, it is very much alive but being manifested in somewhat different ways than a simple increase in global mean surface temperature.

Not the first climate alarmist paper I’ve read where the conclusions are at odds with the data and analysis presented in the body of the paper.

Anthopogenic influence

From the framing document

…global radiative balance, with the total downward flux on the Earth’s surface estimated as 503 ± 7 W/m2 [while the] total anthropogenic direct perturbation of this balance to be some 2.3 ± 1 W/ m2 , less than 0.5% of the downward flux.

Many different processes and phenomena will be relevant and each needs to be “gotten right” with high precision if the response to anthropogenic perturbations is to be attributed correctly and quantified accurately. Moreover, there are expected feedbacks (water vapor-temperature, ice-albedo, …) that would amplify the perturbative response. How can one understand the IPCC’s expressed confidence in identifying and projecting the effects of such small anthropogenic perturbations in view of such difficult circumstances?

Why did ‘confidence’ regarding the assertion that human influences dominate the climate system, increase in AR5 when (a) so many of the climate processes are poorly known and modeled, and (b) the global temperature failed to warm as expected?

Dr. Lindzen and others have noted how small the IPCC computed anthropogenic contribution to heat absorption is, roughly 2 Watts/m2. So, the committee reasonably asks how can we be sure it dominates climate change?

Dr. Collins is confident that the warming from 1950 to 1998 is man-made. He admits that there are long term climate cycles that are not taken into account in the models, but he believes their variability is accounted for with multiple model runs using different initial conditions. Dr. Curry calls this simply ignoring the longer term cycles, basically the AMO and the PDO. Dr. Collins acknowledges that there is no “first principles” evidence that the warming in the last half of the last century is man-made, this conclusion is based solely on comparisons between climate models.

Dr. Collins and Dr. Santer present “a dipole” or warming troposphere and cooling stratosphere as evidence that man-made warming is occurring. I find this unconvincing and so did most of the attendees at the workshop. I think it can be safely ignored as speculation from dodgy computer model runs. See Dr. John Christy’s figure on page 352 (reproduced below), the computer climate model’s vertical profile does not match observations.  In the latter half of the twentieth century, one important external force is anthropogenic; I don’t think anyone disagrees with this.  But, what was the total internal forcing?  Have we modeled that accurately?

Dr. Santer believes that man’s influence on the climate is there, he can see a signal, but he does not know how big it is.  Except for the estimate of the forcing due to volcanism, he has not tried to estimate the size of any other external forcings, including man’s. Unlike Dr. Curry or Dr. Christy, he believes the influence of volcanic aerosols is significant, but not the only cause of the hiatus.  The forcing he computes for volcanic aerosols is about 0.2 to 0.3 Watts/m2, a very small number.

While Dr. Santer does no scaling to observations, the IPCC report does scale their short term projections to match observations, then it removes these negative scaling factors (the scaled mean temperature is reduced by 25%) for the longer term projections to the year 2100.  This artificially inflates the estimated temperature in 2100 by 25% or more.  Dr. Koonin asks why should we tune the model to current observations and throw away the tuning for the longer term projections (page 259-260)?

It seems that most of the group agreed that if the IPCC uses scaling factors in their short term projections, they should use them in their long term projections.  Dr. Collins does not agree.  He thinks that if the corrections are needed for aerosols and mankind cleans the air by reducing pollution, then the corrections should be removed.  This does not make a lot of sense to me, since Dr. Santer and the others believe most of the aerosols are due to volcanism, not pollution.  Dr. Santer notes that while a lot of thought has gone into determining parameter uncertainty, little work has been done on the uncertainty in the model forcings.  He believes much more work on forcings is needed (page 274).  There was general agreement on this point.

In answer to the question of “Why has IPCC confidence of man’s domination of climate increased?” Dr. Christy says that the answer must come from the Convening Lead Authors of the IPCC AR5 (page 332) because “I am baffled.”   He then adds “The only way to tell how much is human versus natural is through model simulations.” Dr. Christy also points out that annual mean surface temperature (AMST) is a poor metric to use. The average temperature of the entire troposphere is more important, especially the troposphere in the tropics. The models do an exceptionally poor job of matching the tropospheric temperatures and the vertical temperature profile, suggesting they are fundamentally flawed. He presents some very interesting temperature profiles that I have not seen elsewhere between pages 335 and 352 of the transcript. The one on page 352 is a real shocker. See below:

The vertical axis is in pressure units but goes from the surface of the Earth at the bottom up to the stratosphere.  And, you can see that the models all overestimate the rate of temperature increase significantly.  Dr. Christy wanted this sort of illustration to be in the IPCC report, but it was not put in.

Dr. Held is a physicist by training but works mostly on computer climate models.  Dr. Held is convinced that the warming we have seen over the last 50 to 100 years is forced rather than internal.  This does not speak to man-made CO2 forcing or the sensitivity factor, but regardless of the source, he thinks it is mostly forced.  His point is that because the world ocean is gaining heat, there has to be external forcing (page 409).

Dr. Held tries to back away from the IPCC statement that confidence has increased, from AR4 at 90% to 95% in AR5, that man’s influence caused more than half of global warming since 1951.  He does not believe that (page 418).  The statements he is referring to are in Chapter 10 of AR5 and he thinks the media and the executive summary of Chapter 10 are misinterpreting the contents of Chapter 10.  He sounds embarrassed by the “tizzy” over this.  The discussion is interesting, so I quote part here (page 422):

DR. HELD: I don’t focus that much on 90 versus 95 percent. To me, I don’t get into a tizzy about that sort of thing.

DR. KOONIN: Nobody should, but the media do.

DR. HELD: Yes, they do. Just, I don’t.

I am reminded of the conclusions in Trenberth and Fasullo, 2013. Here the executive summary and the press release of Chapter 10 do not agree with what one of the contributing authors says they wrote and in Trenberth the conclusions do not match the body of the paper. There is a pattern here.

In any case, Dr. Held, one of the chapter authors, backs away from both the executive summary and the press release and sounds kind of embarrassed.

Sea Ice

From the framing document

The long-term decline of [sea ice] in the Arctic and the slight secular increase in the Antarctic are evident. To what extent do you believe the recent Arctic decline to be unusual, given that Section 5.5.2 of the AR5 WG1 report states: “There is medium confidence that the current ice loss and increasing SSTs [sea surface temperatures] in the Arctic are anomalous at least in the context of the last two millennia.”?

Please comment on the ability of the models to reproduce the Arctic trend, but not the Antarctic trend.

Dr. Held discusses the difference between Arctic temperatures and sea ice (receding) and Antarctic temperatures and sea ice (advancing).  He believes that the Arctic and Antarctic are very different and will not behave the same.  But, none of the models show Antarctic ice advancing, which is what is happening.  He claims that the sea ice thickness is very thin and that it is mostly wind-blown ice.  Unfortunately observations do not support this assertion.

Dr. Curry discussed other potential influences from the Sun besides TSI (total solar irradiance).  There are a lot of them, but none are understood very well.  Another poorly understood affect that was discussed a lot was how and how quickly heat is transferred vertically in the oceans (page 134).  It seems to move more quickly than the models predict, heat transfer from the oceans to the atmosphere and back was also discussed a lot.  The idea of “hidden” heat in the deep oceans that will somehow come back to haunt us is pretty silly (page 136).  If the heat is well mixed in the oceans all it does raise the ocean temperature a few one-hundredths of a degree.  The long and short of it, is that the internal climate drivers are very poorly understood.  I do not think any of the climatologists at this meeting believe that that the climate models can represent the true natural forces over a 20 year period.  This alone makes the claim that they have computed the magnitude of the true anthropogenic effect somewhat absurd.

Sea ice was discussed.  While sea ice is retreating in the Arctic, it is growing in the Antarctic, see the figure below.


The Discussion

After all of the presentations there was a panel discussion. They got on the topic of scientific societies making public statements about issues, like climate change.  How far should the APS go in a statement?  Dr. Curry feels strongly that the societies should not be making statements on public policy beyond their particular expertise.  She is not comfortable that the APS has enough expertise to comment on climate change.  The previous statement that this meeting is reviewing was strongly supportive of a major worldwide effort to mitigate climate change.  Was it wise to make that statement?

Dr. Collins would like the APS to make a statement on the obvious things like CO2 is increasing, CO2 affects atmospheric temperature and so on.  Dr. Lindzen points out that the media and the public would take all of this as ominous, when it may not be.  The statement might be correct, but how it is perceived may not be correct.  Dr. Lindzen, Dr. Christy and Dr. Koonin all agreed that given a choice of trying to mitigate man-made climate change or adapting to it, adaptation is better (page 531).

The major theme of the day was the uncertainty in the forcings according to Dr. Koonin.  They are larger than he imagined at first. I think everyone agreed with that conclusion.

I was struck by the level of agreement on several key issues. First there is considerable uncertainty in the forcings, both natural and man-made. This means that the cause or causes of warming in the second half of the 20th Century are not known with any precision. Saying that man is responsible for more than 50% of the warming is not useful or defensible. We simply do not know, there is no observational evidence and the models are not accurate enough to tell us.

There was general agreement that the IPCC press releases and summaries are not an accurate reflection of the body of the IPCC documents, this reflects badly on the IPCC. There was general agreement that the models do not characterize the Antarctic or AMST well. Most of the group also thought that the models do not characterize the troposphere temperature or the vertical temperature profile in the troposphere very well. I don’t think Dr. Collins or Dr. Santer agreed with this, but Dr. Christy’s evidence was persuasive. So there was a consensus at the meeting on some important issues, but not the consensus the media promulgates. All in all, this transcript is a treasure. It is long, but well worth the read.