Climate Audit

Reference

Warning spoiler!

20. Conclusions

• All examined long records demonstrate large overyear variability (long term fluctuations) with no systematic signatures across the different locations/climates.
• GCMs generally reproduce the broad climatic behaviours at different geographical locations and the sequence of wet/dry or warm/cold periods on a mean monthly scale.
• However, model outputs at annual and climatic (30 year) scales are irrelevant with reality; also, they do not reproduce the natural overyear fluctuation and, generally, underestimate the variance and the Hurst coefficient of the observed series; none of the models proves to be systematically better than the others.
• The huge negative values of coefficients of efficiency at those scales show that model predictions are much poorer that an elementary prediction based on the time average.
• This makes future climate projections not credible.
• The GCM outputs of AR4, as compared to those of TAR, are a regression in terms of the elements of falsifiability they provide, because most of the AR4 scenarios refer only to the future, whereas TAR scenarios also included historical periods.

Vic Sage

To take Government (or any) money for climate models, on the basis that they work, while knowing that they don’t work is ……

Actually if the modelers weren’t using the models to make indefensible clams, it wouldn’t be a problem. Trying to develop climate modeling programs is a reasonable scientific endeavor. As long as:

1. They admit when they are wrong
2. Are actively and properly trying to validate their results
3. Don’t make strong positivist claims until the models are proven to work
4. Stay out of the political realm

Ivan

Maybe I missed something but in presentation observed temperatures are in principle much higher than in model simulations. That would mean that models systematically underestimate rate of warming. Am I wrong?

Declan O'Dea

#7, Ivan: Yes, you are wrong. Your first observation is about the absolute levels of temperature, and then your inference relates to the rate of warming. Not logical. Look at the rates of warming in the various graphs, and you’ll see that, relative to reality, the models show rates of temperature change that are broadly similar (Alice Springs, Khartoum, Matsumoto, Aliartos, Colfax), higher (Manaus), or much higher (Albany, Vancouver), not lower. But it really doesn’t mean anything anyway. Given the very poor predictive power of these models, the outcomes from such comparisons are basically random.

Smokey

It’s beginning to look like GIGO means not only “garbage in, garbage out,” but regarding climate models: “garbage in, Gospel out.”

Sam Urbinto

I don’t know, it’s all Greek to me. 😀

Do the models account for things like this?

Paul Linsay

Apropos of the disagreement of the Hurst exponents between models and data, I remember that there was a paper several years ago that pointed out the the GCMs did not have the same fluctuations as the actual climate over a very large ranges of time scales.

John A

Can I also add that I remain baffled by the notion that climate models are highly innaccurate in the short term but become increasingly accurate as the time horizon increases and as more climate models are combined.

That seems to me to encapsulate the entire problem I have with the credibility of climate models and the people who swear by them.

Richard Feynman called it a disease in science.

Geoff Sherrington

Re # 17 John A

Can I also add that I remain baffled by the notion that climate models are highly innaccurate in the short term but become increasingly accurate as the time horizon increases and as more climate models are combined.

This is an analogy for stockmarket prediction, where from day to day some people have poor scores, some have good scores, but the hustlers say that over the term of decades, (and as more players have joined), the market has always risen after a fall. If the observation is correct, it is useless. Also, if it is wrong it is useless.

Texas Aggie

RE #17 John A:

“Can I also add that I remain baffled by the notion that climate models are highly innaccurate in the short term but become increasingly accurate as the time horizon increases and as more climate models are combined”

Koutsoyiannis appears to be saying the opposite. The further into the future, the less correlation to reality, to the point of uselessness.

hswiseman

OUCH! Thats going to leave a mark.

Ok, now that we have settled this, can we get down to some real science on what impacts we might expect from increasing CO2 concentrations?

Pete

RE #2 and “systemic source of error”.

1. I had done CFD modeling of 2-D turbulence over a corner using the K-E turbulence model many moons ago (1981). As I recall the need for the K-E method was to get the number of variables to solve for equal to the number of equations. There were 1 or 2 “fudge factors” that you had to guess at and these would be based on a trial and error where you see if the results compare closely to the output. Isn’t that basically what they have to do in the GCMs and isn’t that a systematic source of error?

2. Also, if you had the full accurate profile of all the initial conditions (velocity, pressure, temp, etc) of the entire calculation field (or maybe it was just the grid boundaries-I don’t recall), you didn’t need the K-E simplification, but you couldn’t feasibly get this profile for real world situations. Lets say you could get all the initial conditions of the atmosphere at the start of a run, you’d still have shortfalls in the modeling of the physics, and shortfalls in the modeling of the coupled ocean and land as well as pure calculation rounding and grid size issues.
All systematic sources of error.

3. I assume the GCMs are basically trying to solve Navier-Stokes equations mixed in with volume distributed “generation” terms (like cosmic ray based cloud formation (are they in yet?, condensation, aerosols, etc). Are the Navier-Stokes existence and smoothness problems discussed in the following wikipedia excerpt a potential “systematic source of error” or is it a different animal of a category?:

“The Navier-Stokes equations are also of great interest in a purely mathematical sense. Somewhat surprisingly, given their wide range of practical uses, mathematicians have not yet proven that in three dimensions solutions always exist (existence), or that if they do exist they do not contain any infinities, singularities or discontinuities (smoothness). These are called the Navier-Stokes existence and smoothness problems. The Clay Mathematics Institute has called this one of the seven most important open problems in mathematics, and offered a $1,000,000 prize for a solution or a counter-example.”

Ivan

Those are interesting results, but I suppose that people on RC or similar would argue that authors use only 10 stations or something like that. Although spatially dispersed all around the world and climatically diverse, they amount to small fraction of overall number of stations, probably even stations with long temperature records. Additionaly, we already know that stations with strange, counterintuitive temperature trends do exists everywhere in the world. Some of the station used by Koutcoinas et al, also are strange, (eg Karthum excibit cooling trend in 1920s and 1930s when world passed through large warming, and then the same station shows strong warming trend 1945 onward, although much of the world (and logically most of the other stations) exhibit cooling trend 1945-1975). I wonder to what extent exercise like this with probably cherry-picked (or randomly chosen, whatever) stations with non-representative trends could be taken as model testing procedure? I suppose a larger number of stations should be picked, or at least stations with trends similar to global.

Steve Geiger

32 Ivan, yes. That was the first thing that occurred to me as well….seems like a method ripe for cherry picking (although I did not read all of it, and maybe he lays out a tenable method by which individual comparison points were chosen (?). And yes, Gavin has already dismissed it based on the very limited coverage and using single points to compare to entire model grid cells (he recommended a different study which ostensibly used some sort of regional averages of station data to compare to the model output…and surely got more favorable results).

Demetris Koutsoyiannis

Thanks Steve for the posting and the comment, also on behalf of my co-authors. Thanks Spence_UK for drawing attention to this presentation. And thanks to all discussers for the comments. I am impressed by the number of downloads of the presentation file from our repository, which was triggered by this posting. 2500 downloads in two days! More than the annual number of downloads of our most popular papers.

This was in fact a poster paper in the EGU session “Climatic and Hydrological Perspectives on Long-term Changes” (see information in http://www.cosis.net/members/meetings/sessions/information.php?p_id=322&s_id=5262) organized by Manfred Mudelsee, Kosta Georgakakos and Harry Lins (Vienna, April 2008). I think it was a great success and it was decided to reorganize a similar session in 2009, again in Vienna.

The session organizers had invited climatologists, hydrologists, mathematicians and other scientists to discuss together their different perspectives on long-term changes. I think the target was achieved. For instance, Rasmus Benestad, who had criticized the idea of Long Term Persistence (LTP) in climate a couple of years ago in RealClimate (http://www.realclimate.org/index.php?p=228) expressed a vivid interest on LTP in the morning oral block; by the way this block was chaired by Alberto Montanari, the president of Hydrological Sciences of EGU. I had an oral presentation there, jointly with Tim Cohn, on LTP and climate (The Hurst-Kolmogorov pragmaticity and climate, available on line, http://www.itia.ntua.gr/en/docinfo/849). Benestad who spoke later said that LTP is fascinating. He presented the history of climatic changes of Northern Europe, and replying my question, agreed that many factors that have driven or affected these climate changes are unpredictable. He has reported about the EGU session in RealClimate (http://www.realclimate.org/index.php/archives/2008/04/egu-2008/).

That’s about this EGU session – I look forward to an even greater success in 2009.

Coming back to the discussion in this thread, I have a couple of comments. I see that confidence on GCMs is deeply rooted, so any falsifying results, like ours, must be attributed to manipulations such as cherry picking. No, we did not do any cherry picking. We retrieved long data series without missing data (or with very few missing data) available on the Internet. We had decided to use eight stations and we retrieved data for eight stations, choosing them with the sample size criterion (> 100 years – with one exception in rainfall in Australia, Alice Springs, because we were not able to find a station with sample sizes > 100 years for both rainfall and temperature) and also a criterion to cover various types of climate and various locations around the world. Otherwise, the selection was random. We did not throw away any station after checking how well it correlates with GCMs. We picked eight stations, we checked these eight stations, and we published the results for these eight stations. Not even one station gave results better than very poor. Anyone who has doubts, can try any other station with long observation series. Our experience makes us are pretty confident that the results will be similar with ours, those of the eight stations. And anyone who disagrees with our method of falsification/verification of GCM results may feel free to propose and apply a better one. What we insist on is that verification/falsification should be done now (not 100 years after) based on past data. The joke of casting deterministic predictions for hundred years ahead, without being able (and thus avoiding) to reproduce past behaviours, is really a good one, as things show. But I think it is just a joke.

In this respect, I do not think that the uncertainty of future climate can be eliminated with more petaflops in computers. Have we understood everything on climate, so that our problem is just the increase of computational speed and accuracy? Even if this were the case, it is known from dynamical systems that a fully understood system with fully known dynamics (even simple – but nonlinear) is unpredictable for long time horizons. For instance in my Toy Model of Climatic Variability (http://www.itia.ntua.gr/en/docinfo/648 or http://dx.doi.org/10.1016/j.jhydrol.2005.02.030) I have demonstrated that a caricature 2-dimensional climatic model with fully known extra simplified dynamics is unable to reproduce even its own “climate change” trajectories given slight uncertainty of initial conditions.

steven mosher

RE 32. Dr. K. Thank you for your work. SteveMc, on a few occasions we have had threads
that touch on Hurst and LTP. do we have specific thread dedicated to either. It would be
a nice place for Dr. K to drop and chat?

UC

#32

I had an oral presentation there, jointly with Tim Cohn, on LTP and climate (The Hurst-Kolmogorov pragmaticity and climate, available on line, http://www.itia.ntua.gr/en/docinfo/849). Benestad who spoke later said that LTP is fascinating. He presented the history of climatic changes of Northern Europe, and replying my question, agreed that many factors that have driven or affected these climate changes are unpredictable.

Excellent presentation. From engineer point of view, the paper by Richard Voss,

1/f (Flicker) Noise: A Brief Review, 33rd Annual Symposium on Frequency Control. 1979, page(s): 40- 46

is also a good read on this topic. 1/f makes predictions (given the observations) for distant future quite inaccurate, and makes forcings and ‘weather noise’ difficult to separate. Hockeystick shows no 1/f behavior ( http://www.climateaudit.org/?p=483#comment-208708 ) , but the connection between hockey stick and reality is questionable.

Eric (skeptic)

I guess I don’t get the obsession with “initial conditions” by both the modelers and the critics. In the long run (anything longer than a week) those should not matter. For example, I could drop a foot of snow here in Virginia (an impossibility this time of year), and in a week or even just a few days, the climate will be back to normal. The comment about turbulence makes a lot more sense. In general the chaotic elements of weather are the problem, perhaps “initial conditions” is a euphamism for that?
The biggest problems I see with modeling (and the entire AGW movement) is oversimplification. Above that is alluded to by lack of cosmic ray cloud formation. The resolution of models is very poor as well. An MCS can have a notable climate impact in the short and medium run, but would normally be left out or parameterized. The general problem with parameterizing is that the parameters are valid for current climate but not for altered climates. More valid parameters can be determined from higher resolution submodels.
If I am not mistaken the modeling problem will be solved within 20 years or so. The “initial conditions” or chaotic effects problems will not (IMO) affect the average climate provided weather is modeled with full fidelity (adequate resolution and comprehensive inputs).

John A

For those interested, there is a very good webpage on Hurst exponents and autocorrelation in time series (such as stock market indices) at this link

Its not quite as scary a topic as you’d think.

The practical example of the Hurst exponent is trying to estimate the minimum size of a reservoir so that it never runs dry (which is what Hurst studied with the Nile). This is discussed here

Jaye

I guess I don’t get the obsession with “initial conditions” by both the modelers and the critics.

chaotic effects problems will not (IMO) affect the average climate provided weather is modeled with full fidelity (adequate resolution and comprehensive inputs).

Read up on simple non-linear systems like the Lorenz attractor. As for the second comment, in the 19th century many scientist thought that they had everything they needed with enough data and PDE’s.

Bob Hawkins

“So far modellers have failed to narrow the total bands of uncertainties since the first report of the Intergovernmental Panel on Climate Change (IPCC) in 1990.”

Actually, not since the first (USA) National Academy of Science review of the brand-new topic of global warming in 1979.

The NAS review put the climate sensitivity at 1.5C to 4.5C per doubling. The latest spread from IPCC in AR4 is 2.0 to 4.5, immediately followed by the statement that “values less than 1.5C are highly unlikely.”

Think about what computers were like in 1979 compared to today. Thinking that the next increment in computer power will make a difference does not fit the historic trend.

Kenneth Fritsch

Re: #41

PS. you don’t need climate models to know we have a problem. – gavin]

The take away line in that thread might be Gavin Schmidt’s comment excerpted above. It gets beyond the science but explains much with regards to policy related issues and motivations.

Jaye

eric,

As somebody said, just finding the attractor is the tough part.

As for the second, are there any systems that can’t be described with sufficient data and PDE’s?

Most natural processes would qualify. For instance, the time interval series between drips from a dripping faucet is chaotic.

Gerald Browning

I posted the following two comments on Real Climate. The first one went thru, the second is “awaiting moderation.” 🙂

Might I suggest that the commenters on this thread read the article by Pat Frank that recently appeared in Skeptic for a scientific (not handwaving) discussion of the value of climate models and the errors induced by the simplifications used in the parameterizations. That article, along with the mathematical discussion of the unbounded exponential growth (ill posedness) of the hydrostatic system of equations numerically approximated
by the current climate models should mathematically clarify
the discussion about the value of the models.

Jerry

[Response: That’s funny. None of the models show this kind of behaviour, and Frank’s ludicrous extrapolation of a constant bias to a linearly growing error over time is no proof that they do. That article is an embarrassment to the otherwise reputable magazine. – gavin]

Gavin,

Before so quickly dismissing Pat Frank’s article, why don’t you post a link to it so other readers on your site can decide for themselves the merits of the article? What was really hilarious was the subsequent typical hand waving response that was published by one of the original reviewers of the manuscript.

I also see that you did not disagree with the results from the mathematical manuscript published by Heinz Kreiss and me that shows that the initial value problem for the hydrostatic system approximated by all current climate models is ill posed. This is a mathematical problem with the continuum PDE system .
Can you explain why the unbounded exponential growth does not appear in these climate models? Might I suggest it is because they are not accurately approximating the differential system? For numerical results that illustrate the presence of the unbounded growth and subsequent lack of convergence of the
numerical approximations, your readers can look on climate audit under the thread called Exponential Growth in Physical Systems.The reference that mathematically analyzes the problem with the continuum system is cited on that thread.

Jerry

shs

49, On the contrary, Douglass et al has shown climate models fail to show we have a problem, with re to AGW.

Gerald Browning

Responses from Gavin and me

[Response: I have no desire to force poor readers to wade through Frank’s nonsense and since it is just another random piece of ‘climate contraian’ flotsam for surfers to steer around it is a waste of everyones time to treat it with any scientific respect. If that is what he desired, he should submit it to a technical journal (good luck with that!). The reason why models don’t have unbounded growth of errors is simple – climate (and models) are constrained by very powerful forces – outgoing long wave radiation, the specific heat of water, conservation of energy and numerous negative feedbacks. I suggest you actually try running a model (EdGCM for instance) and examining whether the errors in the first 10 years, or 100 years are substantially different to the errors in after 1000 years or more. They aren’t, since the models are essentially boundary value problems, not initial value problems. Your papers and discussions elsewhere are not particular relevant. – gavin]

Gavin,

It is irrelevant what journal the article was submitted to. The scientific question is does the mathematical argument that Pat Frank used stand up to careful scientific scrutiny. None of the reviewers could refute his rigorous mathematical arguments and thus the Editor had no choice but to publish the article. Pat has used a simple linear formula to create a more accurate climate forecast than the ensemble of climate models (the accuracy has been statistically verified). Isn’t that a bit curious given that the models have wasted incredible amounts of computer resources? And one only need compare Pat’s article with the “rebuttal” published by a reviewer to see the difference in quality between the two manuscripts.

The mathematical proof of the ill posedness of the hydrostatic system is based on rigorous PDE theory. Please feel free to disprove the ill posedness if you can. However, you forgot to mention that fast exponential growth has been seen in runs of the NCAR Clark-Hall and WRF models also as predicted by the Bounded Derivative Theory. Your dismissal of rigorous mathematics is possibly a bit naive?

If any of your readers really wants to understand if the climate models are
producing anything near reality, they will need to proceed beyond hand waving arguments and look at evidence that cannot be refuted.

Jerry

Sam Urbinto

At least Gavin realizes that there is “outgoing long wave radiation, the specific heat of water, conservation of energy and numerous negative feedbacks.”

How one models those, well, that’s another story, as is what the results mean.

The hydrosphere wants better representation in all this atmospheric stuff. I hear it’s ready to go on strike.

Raven

#55 (Pat Frank)

Pat, I was confused by the ranges you presented because I interpreted them as the 95% confidence interval. This would make the results clearly wrong because they were way outside any physically possible outcome (i.e. the probably of a 100 degC cooling in the next 100 years is effectively zero). However, your text seemed to indicate that these unrealistic ranges indicate that the models are unstable and that you are not claiming that the model 95% confidence intervals are +/- 100 degC.

However, I am not certain. Could you please clarify the meaning of those ranges?

Gerald Browning

Hi Pat (#55),

It never ceases to amaze me how people like Gavin are able to use verbiage in order to circumvent the logic of a rigorous mathematical argument. The quote at the beginning of your manuscript says it all. These people should spend the time they waste on verbiage learning some scientific skills.

Note that when I pointed out that exponential growth has been shown in NCAR’s own well posed (nonhydrostatic) models as proved by mathematical theory, Gavin did not respond. Unphysically large dissipation can hide
a multitude of sins and is a common tool misused in many numerical models in many scientific fields.

If you look at the derivation of the oceanographic equations, they are
derived using scaling for large scale oceanographic flows (similar to how the hydrostatic equations of meteorology are derived). The viscous terms
are then added to the hydrostatic oceanographic equations in an ad hoc manner. There is no guarantee (and in fact we were unable to prove) that this leads to anything physically realistic. A better method starts with the NS equations and subsequently to a well posed system.

Jerry

Curt

Like Frank K in #57, I’m scratching my head trying to figure out what Gavin means by “errors”. What is he comparing these model results to? And if he knows what the values should be, why is he running the models at all?

Scott-in-WA

This leads (past Lovelock and past DNA) to the question, does climate have inbuilt feedbacks that prevent tipping point and runaways? Plants like this broc cauli have been around for long periods by geological criteria and the subsistence of life implies control, replication and stability rather than runaway and extinction.

Those pesky geologists seem to believe that for the major portion of the last hundred million years of earth’s history, the earth’s average temperature has been from five to ten degrees centigrade warmer than it is today. Whatever the reasons, life on earth has managed, somehow or other, to survive the experience.

Craig Loehle

Consider a chaotic system but one that has an orbit, let’s say the orbit looks like when you try to draw a circle over and over so the orbits are bounded (close to a circle) but never quite repeat. The initial value problem diverges exponentially, but the solution always stays near the circle orbit. Thus divergence of the solution does NOT mean runaway behavior like going to infinity. It means that small errors in initial values lead to unpredictable (but bounded) trajectories. Translated to the climate system, failure of the initial value problem means that you can’t predict the weather, but does NOT mean that the model predicts 200 deg C temperatures in New York at some point because the system is bounded by the inputs of energy at all times, which are also being dissipated. Koutsoyiannis results mean that the local scale orbits of the weather are wrong, and thus you should not use the models for forecasting long term impacts of the climate in Arizona or Calcutta. It does not prove that the long-term 100 year climate projection of GMT is wrong–but neither has anyone proved that this is right either.

Frank K.

Re: 66 and 67

Hi Craig,

Given your comment above, why then do most (perhaps all) climate models have an “Eulerian core” which is essentially solving the atmospheric initial value problem? If climate is indeed a “boundary value” problem, then I would think that simpler models for the “weather noise” would suffice.

Of course you can’t get those colorful fluid dynamic (CFD) plots and animations without the chaotic atmosphere in the solution somewhere…

Craig Loehle

I believe it is both an initial value and boundary value problem. The initial value problem is needed to get it started. With a completely random initial state, it would eventually settle down to a realistic climate, but you might have to run it for thousands of (simulated) years to get the ocean to spin up correctly (with proper currents etc). In that sense it is feasible as a boundary value problem, but wastes resources to run it that way. The boundary value problem is because the system constantly loses heat and without the constant input of solar energy (make it a pure initial value problem) it quickly would go to absolute zero temperature as heat was radiated away. The claim that the system is unstable — goes out of control with an input of CO2– is implausible though Hansen pushes this. One can’t argue it is impossible, because the system was not designed per se for stability. But the earth has been through a lot over billions of years and life is still here, so negative feedbacks seem more plausible than positive.

Gerald Browning

Technically the (unmodified) continuum weather and climate systems of dynamical equations are initial-boundary value problems. The initial part is the data that are used to start up the system. The boundary values are, for example, the constraint that the vertical velocity at the surface vanish. If the systems were strictly hyperbolic (no dissipation) then the initial values would play a crucial role in the long term evolution of the systems. But fluids are not inviscid and so over longer periods the physical dissipation that drains energy from the systems and the
forcing that provides energy input can become the dominant components of the long term solutions. The real problem is that the dissipation used in climate models is unphysically large and the associated parameterizations of the forcing terms are then necessarily inaccurate. Of course there is the more insidious problem with the ill posedness of the hydrostatic system and the fast exponential growth of the nonhydrostatic system, i.e. numerical methods will never converge to the solutions of the real systems.

Jerry

Paolo M.

Craig Loehle #66,
you say that Koutsoyiannis results do “not prove that the long-term 100 year climate projection of GMT is wrong–but neither has anyone proved that this is right either”.

Climate is not just T2m and even less is not GMT.
Climate must be regarded as the ensamble of all meteorological, oceanic, etc. variables for each point (3D) of the globe and what AOCGMs are required to do is not merely a projection of GMT but to correctly forecast the multidecadal distribution of each meteorological (etc..) variable.
So, if you prove that a model cannot forecast the distribution of just one or two variables in a station to station approach (I think more then 8 stations are required), then you proved models are wrong.
The position of who says that models can correctly simulate just one unphysical variable (GMT) dosn’t hold.

By the way, regarding current climate models, which are a boundary condition problem, whereas the climate system, at least in a multidecadal time frame, is a non linear system, Roger Pielke has a related thread in today’s weblog.

Frank K.

Re: 70

I agree that the climate system is driven by boundary conditions and various “forcings”, and thus over long time periods responds as a boundary value problem (i.e. initial conditions become less relevant as time proceeds). However, one problem I see with this in a numerical context is that many of the boundary conditions are themselves functions of time, and worse yet functions of the dependent variables you are solving for (particularly temperature). Will perturbations in the boundary conditions or numerical errors in the solution grow non-linearly and cause the solution to wander unpredictably? I have noticed that many of the models employ spatial filters, “mass fixers”, “energy fixers” and the like to keep the solutions stable. How do these adhoc treatments affect temporal accuracy over long integration times? Maybe there’s enough numerical diffusion in the algorithms to keep them from becoming unstable regardless of the initial or boundary conditions!

Frank

Sam Urbinto

Danged unions. Them and their lack of reconcilliation with the models.

😀

Craig Loehle

Paolo M.: let me give an example. Forest growth simulators model many species, with birth, growth, and death of individual trees. Even with exact initial conditions, the composition of trees on any individual plot of ground can’t be predicted, but over long time periods the average tree mass and species assemblage often can. Thus just because you can’t predict the weather (local tree composition) does not mean the long-term aggregate behavior can’t be predicted. Same with climate, as defenders of GCMs argue, such as Gavin (hear that Gavin?). However, if your model for clouds is wrong (e.g., positive feedback instead negative), then that is a different matter altogether.

dover_beach

Pat, I’m sure research funding agencies might be interested in the implications of H. Halide and P. Ridd (2008) but those directly involved in the operation of GCMs won’t.

BTW, I very much enjoyed your most recent Skeptic article.

Geoff

There is a big push going forward to get funding for supercomputers for climate forcasting as you can see in today’s Nature editorial:

Nature 453, 257 (15 May 2008) | doi:10.1038/453257a; Published online 14 May 2008

The next big climate challenge

Governments should work together to build the supercomputers needed for future predictions that can capture the detail required to inform policy.

and

Now that that consensus is all but universal, climate modellers are looking to take the next step, and to convert their creations from harbingers of doom to tools of practical policy. That means making their simulations good enough to guide hard decisions, from targets for carbon dioxide emissions on a global scale to the adaptations required to meet changing rainfall and extreme weather events on regional and local scales.

Today’s modelling efforts, though, are not up to that job. They all agree on the general direction in which the climate will move as greenhouse gases build up, but they do not reliably capture all the nuances of today’s climate, let alone tomorrow’s. Moreover, each model differs from reality in different ways.

Perhaps most importantly:

Meeting this need is not just a matter of buying a supercomputer. It means moving climate modelling up the petaflop pecking order for a sustained period of time.

Why do I get the feeling the edtorial writer has not read Halide and Ridd (2008)?

anna v

Pat Keating
May 14th, 2008 at 12:52 pm 73

Are you aware of the paper :

” A new dynamical mechanism for major climate shifts.

Anastasios A. Tsonis, Kyle Swanson, & Sergey Kravtsov

Department of Mathematical Sciences, Atmospheric Sciences Group, University of Wisconsin-Milwaukee, Milwaukee WI 53201-0413

Abstract We construct a network of observed climate indices in the period 1900–2005 and investigate their collective behavior. The results indicate that this network synchronized several times in this period. We find that in those cases where the synchronous state was followed by a steady increase in the coupling strength between the indices, the synchronous state was destroyed, after which a new climate state emerged. These shifts are associated with significant changes in global temperature trend and in ENSO variability. The latest such event is known as the great climate shift of the 1970s.

We also find the evidence for such type of behavior in two climate simulations using a state-of-the-art model. This is the first time that this mechanism, which is consistent with the theory of synchronized chaos, is discovered in a physical system of the size and complexity of the climate system.”

They use a neural net on coupled atmospheric and ocean circulations .

bender

Interesting.

maksimovich

re 86

Tsonis et al is an interesting paper.The velocity inversion (v > -v )has the same effect as time inversion (t>-t).

We see this also as in Ghil et al (2008)

The natural climate variability induced by the low-frequency variability of the ocean circulation is but one of the causes of uncertainties in climate projections. The range of these uncertainties has barely decreased, or even increased, over the last three decades. Another major cause of such uncertainties could reside in the structural instability |in the classical, topological sense of the equations governing climate dynamics, including but not restricted to those of atmospheric and ocean dynamics

The Shilnikov phenomena is a problematic issue for the GCM as they stand.

Pat Keating

86, 87 anna v

No I wasn’t aware of the Tsonis et al paper. Thanks for citing it.

Craig Loehle

Sam: thanks. Paolo: I am NOT defending the models. Certainly when you see results like Douglass et al and many other results that don’t match, it is no longer obvious that the models work, I am just saying that if GMT trends over 100 years is all you want, the models could miss el ninos and local weather badly and still average out ok globally. the MIGHT do this, but it has not been proved that they do it properly in the case of adding GHG & land use change in.

Paolo M.

Sam Urbinto #93
I think you missed what I said, i.e. I mentioned “multidecadal distribution of each meteorological variable”, that is the definition of climate. I’m not dealing with weather, so I agree with Gavin too.
I don’t agree with modelists and those of you who endorse modelist reasoning when they say that, by using numerical modeling (AOCGMs), they were able to correctly simulate GMT during the last few decades and, therefore, models are skillfull or, simply, good in their prediction.
But the climate system is not GMT and you can’t choose the physical variable you pretend being correctly predicted and dismiss the others.
A model predicts all variables of your physical system and your climate model is good if all “multidecadal distributions of each variable” are well simulated.
Would you accept a weather man that does good predictions of wind direction only and is wrong for precipitation, temperature, wind speed, cloud cover and type, etc…?
Or what about a weather model doing good prediction of fog only?
And what about a climate model that predicts GMT? Do you have to look at the other variable or don’t?
If the climate community wants to use AOCGMs (whose atmospheric part is represented by common weather models), all variables (their multidecadal distribution) must be correct and on a local scale.
I’m not really impressed by how good models predict GMT.

Sam Urbinto

Paolo:

I promise you that the climate in August 1930 in Havana Cuba was about the same as it was in August 2005 give or take a few degrees. And that it probably didn’t snow either of those months. The tricky thing is getting any more specific than that.

Gerald Browning

Pat Frank (#83),

There is an attack on your manuscript by Anthony Kendall (#127)
on real climate. I am responding, but thought you might also want to reply.

Jerry

Gerald Browning

Pat (#83)

My original post on RC disappeared so I reposted and it seems to have disappeared. Isn’t that cute. If the post doesn’t appear, it tells me
quite a bit about the “scientists” at RC .

Jerry

ianl

#103,

http://www.realclimatesecrets.org/

just returns “cannot be found”

Gerald Browning

Pat (#83),

Do you want to respond to the nonsense?

Jerry

PaddikJ

[Response: No. There is no lag to the forcing and it would only look good in the one case he picked. It would get the wrong answer for the 20th Century, the las glacial period or any other experiment. – gavin]

Interesting. Assume he’s referring to model runs when he says “experiment.”

What’s this Realclimatesecrets.org? I get the “can’t display this page” message, even when I enter it manually.

John A

Re #108:

I think the suggestion of a “realclimatesecrets.org” was tongue-in-cheek to suggest a place where deleted comments from realclimate.org should go.

The real reason for the disparagement is that Gavin is too lazy to construct a proper argument and relies on “voice of god” symbolism and short putdowns to get his own way.

It doesn’t wash.

Pat Frank showed me his proposed manuscript a few months ago and I grasped the point he was making about error-propagation immediately, but I’m not a PhD so who knows what appalling process happens to them that they cannot understand simple well-posed arguments any more?

The climate models are beguiling because of the human belief engine that gives massive positive feedback to random data that “looks” or “smells” correct, and because climate modellers spend about five minutes considering errors before deciding that they’re too trivial to be concerned with.

What Pat Frank has shown in a simple, comprehensible way is that the growth of errors beyond a few months are so large that the projection is literally meaningless – there is no information in that curve. It’s then a belief system to credit that curve with predictive power, not mathematical rigor.

The climate models do to the future what the Hockey Stick does to the past, produce a beguiling picture of curve while hiding the fact that the errors in the calculation are so large that the curve means literally nothing.

Has anyone asked Gavin about Koutsoyiannis et al? That should be entertaining.

PaddikJ

human belief engine

Memorable phrase, but maybe a bit harsh? “Human pattern recognition engine” might be closer to the mark in the present context. It’s extremely powerful, very useful most of the time, but also extremely seductive.

I thought all Science majors had to take the “Guarding Against Pseudo-Patterns 101” course. Maybe not Climatology majors.

Aaron Wells

Michael Tobis at initforthegold:

I’m not sure whether Pat Frank willfully misunderstands my position in order to mislead others, or simply displays his incapacity for understanding the topic at hand. The last comment leans rather in the direction of deliberate obfuscation. As usual, it is difficult to be sure.

I refer the interested reader to these two attempts of mine to elucidate the present matter.

part 1

part 2

With that, comments are closed on this thread.

It would appear that Michael has taken his ball and gone home.

UC

John A,

I think the suggestion of a “realclimatesecrets.org” was tongue-in-cheek to suggest a place where deleted comments from realclimate.org should go.

yes. The problem would be to prove that the comment in question was really submitted to RC, but gavin could always correct erroneous posts. Or someone could try to re-submit the comment, if he/she thinks that this kind of comment will not be deleted. Blog-format would be needed, naturally.

Gerald Browning

My response (#182) to a hand waving argument by Ray Ladbury (#178) on RC.

Hank,

I would like to comment on Ray’s lack of understanding of mathematics
in his following comment.

Hank, I’m aware of Browning, and what he has cannot be correctly characterized as understanding. I notice that he scrupulously avoided the issue of whether CO2 is a greenhouse gas–and all the other physics. The issue is not whether the models work–their success speaks for itself. The thing that bothers me about Browning et al. is that they completely lose sight of the physics by getting lost in the details of the models.If you are a “skeptic,” the models are your best friends–they’re really the only way we have of limiting the risk we face. That the planet is warming is indisputable. That CO2 is behind that warming is virtually beyond doubt. What is open to dispute is how much harm will come of that. If we were to limit ourselves to the worst-case from paleoclimate, the damage to human society is effectively unlimited. The models tell us where to worry. They give us ideas of how much we have to limit emissions and how long we have to do it. They make it possible to go from alarm to cost-effective mitigation. If the models were to be demonstrated unreliable, they are more likely to err on the conservative side. We still have large risks, but now they are unquantifiable. Ask Warren Buffet if he’d prefer a risk that is imperfectly bounded to one that is unbounded and see which one he’ll take.
I’m sorry, but I don’t attach a lot of value to technical prowess when it is divorced from the context (physical and societal) of what is being modeled.

It is well known in mathematics that if an initial-boundary value problem
for a time dependent partial differential equation is not properly posed,i.e. it is ill posed, then there is no hope to compute the solution in the continuum and certainly not
with any numerical method. The reasons that the ill posedness of the hydrostatic system that is the basis of all the atmospheric components of the current climate models has not yet been seen are as follows.

The climate models are only resolving features greater than 100 km in size, i.e. they are not resolving mesoscale storms, hurricanes, fronts, etc. These are certainly important to any climate. How is it possible that the climate models are able to run when not resolving these features. The answer is by using unphysically large dissipation that prevents the small scale features from forming. Thus the model is not physically realistic as claimed by Ray and the forcing terms are necessarily inaccurate in order to overcome the unphysically large dissipation (energy removal). Runs by Dave Williamson at NCAR have shown the inaccuracy of the spatial spectrum when using unphysically large dissipation and have also shown that the forcing terms (parameterizations )are not physically accurate (references available on request). Thus the models are not accurately describing the continuum dynamics or physics (forcing), i.e. the numerical solutions are not close to the continuum solution of the hydrostatic system.

Runs by Lu et al of the NCAR Clark-Hall and WRF models have also shown that as soon as finer numerical meshes that resolve the smaller scale features are used, fast exponential growth appears even in the well posed nonhydrostatic models (reference available on request). In the case of the hydrostatic system, meshes of this size will show the unbounded exponential growth typical of ill posedness (see numerical runs on Climate Audit under the thread Exponential Growth in Physical Systems).

Thus hydrostatic climate models are currently so far from the real solution of the hydrostatic system that they are not showing the unbounded exponential growth. And the numerical gimmick that is used to run the models unphysically removes energy from solution at too fast of rate, i.e. it is not physically accurate.

So CO2 has increased, but climate models are not close to reality so adding forcing terms (physics) at this stage or later when the unbounded exponential growth appears is nonsense.

Climate audit has shown that the global measurement stations are questionable (to say the least) and the numerical climate models are inaccurate and always will be. So the arguments for AGW are not scientific, but hand waving. I have nothing to gain in this argument (I am retired), but RC has lots to lose in terms of funding.

Jerry

maksimovich

RE 118 (gerry)

It is well known in mathematics that if an initial-boundary value problem for a time dependent partial differential equation is not properly posed,i.e. it is ill posed, then there is no hope to compute the solution in the continuum and certainly not with any numerical method.

This from Dymnikov (2006)(Mathematical problems of climate)

It is necessary to prove some statements for the system of partial differential equations describing the climate system’s model.

I. The global theorem of solvability on an arbitrarily large time interval t.

Unfortunately, there is presently no such a theorem in a spherical coordinate system with “correct” boundary conditions. This is not a consequence of the absence of such theorems for three-dimensional Navier–Stokes equations. The equations of the state of-the-art climate models have a dimension of 2.5 because the hydrostatic equation is used instead of the full third equation of motion.

maksimovich

Koutsoyiannis et al bring questions on the uncertainty of GCM to match the reality of obsevables,both in predictabilty,and retrodiction (hindcasting)

The divergence from reality(from unknown quantities of ‘natural variation”) at present being one level of uncertainty.

The level of mathematical skill from the “proprietors” of “state of the art gcm” being another as Dymnikov observes.

It should be emphasized that most of the scientific community concerned with climate models are generally not interested in mathematical problems and treat a model as a specific finite-dimensional construction with a specific description of physical processes, thus reducing the study of the model’s quality to a numerical experiment alone.

Another problem area is the parametrization of external forcing,from what id the “normal mean climatic state’ and what is an “abnormal state”

Ghil et al also bring some interesting questions.

As the relatively new science of climate dynamics evolved through the 1980s and 1990s, it became quite clear from observational data, both instrumental and paleoclimatic, as well as model studies that Earth’s climate never was and is unlikely to ever be in equilibrium….

…The difficulty in narrowing the range of estimates for either equilibrium sensitivity of climate or for end-of-the-century temperatures is clearly connected to the complexity of the climate system, the multiplicity and nonlinearity of the processes and feedbacks it contains, and the obstacles to a faithful representation of these processes and feedbacks in GCMs. The practice of the science and engineering of GCMs over several decades has amply demonstrated that any addition or change in the model’s parametrizations” i.e., of the representation of subgrid-scale processes in terms of the model’s explicit, large-scale variables may result in noticeable changes in the model solutions’ behavior.

Near and far-from equilibrium states and phase transitions from LTP regimes are significant(non trivial)mathmatical problems for ezternally forced GCM.

Ruzmaiken puy this quite succinctly.

Linear and non-linear systems respond differently to external forcing. A classical example of a linear system response is the Hooke’s law of elasticity that states that the amount by which a material body is deformed is linearly proportional to the force causing the deformation. Earlier climate change studies used this linear approximation to evaluate the sensitivity of the global temperature change caused by external forcing. However the response of non-linear systems to external forcing is conceptually different; the issue is not a magnitude (sensitivity) of the response. Non-linear systems have internally defined preferred states (called attractors in mathematics) and variabilities driven by residence in the states and transitions between them. The question is what is the effect of an external forcing: change of the states, residence times or something else?

Answer to this question is critical to our understanding of climate change.
Based on the model studies mentioned above we can formulate the following, updated conjecture of the climate system response to external forcing: external effects, such as solar, the QBO and anthropogenic influences, weakly affect the climate patterns and their mean residence times but increase a probability of occurrence of long residences. In other words, under solar or anthropogenic influence the changes in mean climate values, such as the global temperature, are less important than increased duration of certain climate patterns associated say with cold conditions in some regions and warm conditions in the other regions

We saw an early response from HADCRU in updating the ensemble(sample)sst due to more accurate data from the Argo project(late last year),and in other papers published this year.(This is a correct methodology as the extrapolation of historical sst ensembles have high levels of uncertainty and inaccuracies)

On the other side of the table Humbert is arguing there must be a problematic issue with Argo as yet unidentified and similar to initial issues with MSU,nut these are unimportant as he says

This calculation differs from the usual climate calculation, which basically assumes that the climate evolution “forgets” the initial condition after a relatively short time, or at best treats the part remembered through using an ensemble of initial conditions rather than trying to figure out which initial condition is closest to reality.

A statement that will probably “keep the poets happy” but notwithout problems as Jaynes notes.

But in a well{known work on statistical mechanics (Penrose, 1970) it is stated that …”the letters of the alphabet can be arranged in 26! ways, of which only one is the perfectly ordered arrangement ABC… XYZ, all the rest having varying degrees of disorder.” To suppose that Nature is influenced by what you or I consider “orderly” is an egregious case of the Mind Projection Fallacy.

bender

#122 Does Ghil read CA?

maksimovich

It seems RC agrees,there is no consensus with enso variability.

Given that ENSO is the dominant source of variability on interannual timescales, it is likely that future changes in ENSO (more specifically, the mean state of the climate and whether it is more “El Nino” or “La Nina” like, i.e. is there a strengthened or weakened ‘Walker Circulation’) could have a profound influence on Atlantic TC frequency. Although the IPCC models project overall a more El Nino like mean state with a weakened Walker circulation, there is far from a consensus among the models. Several credible state-of-the-art coupled models project precisely the opposite. And all of the models used in the IPCC assessment suffer to a varying extent from certain fundamental biases (the inability to produce a realistic ‘ITCZ’ over a large part of the equatorial Pacific ocean–the so called ‘split ITCZ problem’).

Indeed the reality is quite observable in slide 21 of the Ghil Lorenz lecture,where overall the CS returns to its previous state.

Neil Haven

Re 127
If the post-Pinatubo behavior of the climate system over a period of approximately three years is evidence for the models, is the current stable or declining temperature trend of five to eight years evidence against the models?
I wish the modellers would be explicit about their claims, the sands do shift so…

Gerald Browning

Neil (#128),

I looked at the first reference that Gavin cited (Hansen et al. on Pinatubo). I have never seen more caveats in a manuscript.
After reading it I was uabale to conclude anything. Note that I had asked for a very specific info on how Pinatubo was simulated. This did not provide it.

Jerry

Tom Vonk

#130

I looked at the first reference that Gavin cited (Hansen et al. on Pinatubo). I have never seen more caveats in a manuscript.
After reading it I was uabale to conclude anything. Note that I had asked for a very specific info on how Pinatubo was simulated. This did not provide it.

That is the key point Jerry .
I do not know if you will be able to get the complete and accurate information about what the models did and I doubt it .
My take on it would be that a simple 2 D variationnal model (remember we are only talking about some 3 values of delta T where delta T is a difference between a yearly average integrated over the whole sphere and some reference value) would only consider the change in overall average albedo and adjust the energy balance accordingly .
Then as the time is too short to perturbate the oceans’ systems , only the atmosphere and the surface would be perturbated .
From there one can get an order of magnitude of the global perturbation (“cooling”) that would surely be the right order of magnitude of the observed average temperatures .
An independent but not really necessary sophistication could be to connect the albedo and optical thickness variation to the properties of the aerosols (quantity , size distribution , speed of propagation etc) .
One could hope that a multimillion GCM can get at least energy conservation over a very short period (a couple of years) right .
As those are short signals , the problem can be solved by a perturbation method where more or less everything can be considered constant and it wouldn’t imply anything about the skill to predict absolute values or variations over periods of hundreds of years when oceans , sun and ice cover kick in .

So if you get the information , I am ready to bet that it doesn’t contain much more than what I sketched above , envelopped in fancy vocabulary like spectral absorptivity and such .

steven mosher

BENDER,

I have another for the list

http://www.statslab.cam.ac.uk/Reports/1996/1996-18.ps

Regression in Long-Memory
Time Series
Richard L. Smith, Cambridge University and
University of North Carolina
Fan-Ling Chen, University of North Carolina
ABSTRACT
We consider the estimation of regression coecients when the residuals
form a stationary time series. Hannan proposed a method for doing this,
via a form of Gaussian estimation, in the case when the time series has
some parametric form such as ARMA, but we are interested in semipara-
metric cases incorporating long-memory dependence. After reviewing re-
cent results by Robinson, on semiparametric estimation of long-memory
dependence in the case where there are no covariates present, we propose
an extension to the case where there are covariates. For this problem it
appears that a direct extension of Robinson’s method leads to inecient
estimates of the regression parameters, and an alternative is proposed. Our
mathematical arguments are heuristic, but rough derivations of the main
results are outlined. As an example, we discuss some issues related to cli-
matological time series

…..

Our interest in this problem was motivated, in part, by the problem of
estimating trends in climatological time series, and of obtaining associated
standard errors and signicance tests. For discussion, see Bloomeld (1992)
and Bloomeld and Nychka (1992). It is a well-known phenomenon that
time series of global average temperatures exhibit a steady increasing trend
over most of the last 150 years, but it is still a point of debate whether such
trends are real evidence of an enhanced greenhouse eect due to human
activity, or are simply long-term fluctuations in the natural climate….

Neil Haven

Jerry (#128) and Tom V. (#132)
With the caveats, approximations, and gross simplifications in Hansen’s treatment, including the admitted inability to predict regional facts based on Pinatubo’s eruption, one wonders why the 1992 Hansen paper is seen as a test of numerical climate models at all, rather than as a test of the much simpler proposition “big volcanic eruptions that change albedo make the global average temperature go down for a while”.

bender

I have complained bitterly in the past about getting no response (other than denial) from RC on the topic of the structural stability of EOF-derived “circulatory modes”. I have suggested these are just “eigenthingies”.

I now ask why RC (Schmidt, Roberts, Ladbury) did not point me toward Zwiers & von Storch (2004) who state:

“Exploratory analysis is a valuable aid that may lead to recognition and idetification of dynamical mecahnisms of variaiblity. One should however, keep in mind that the patterns obtained from methods such as EOF analysis are not a priori constructed to extract information about dynamical behaviour; they simply provide an efficient representation of variability. There is no guarantee that the often tacitly made assumption that EOFs represent dynamic ‘modes’ of variability will hold.”

From: Zwiers & von Storch. 2004. On the role of statistics in climate research. Int. J. Climatol. 24: 665-680.

Funny how these authors not only understood and anticipated my question, but answered in the affirmative. (Not only that, they quote the word ‘modes’ the same way I do.)

It is against blog rules to speculate why RC might have failed to point out this paper. But the paper says a number of intersting things that sounds a lot like Wegman.

The relevance to Koutsiyiannis thread is: internal LTP noise and the problem it causes for attribution exercises.

In keeping with the auditing function of CA, one wonders if this paper was cited in the IPCC docs, and if so, in what context.

Ian Castles

Re #138. Bender, A search of all chapters of the 2007 Report of WGI (“The Physical Science Basis”) shows that this 2004 paper by Zwiers and von Storch was NOT cited in that document. It would be surprising if there was any reference in the Reports of the other Working Groups.

Gerald Browning

All,

Pat Frank has decided to post a response on RC to address the less than scientific comments on RC about his manuscript that appeared in Skeptic. Note that some of those comments came from Tapio Schneider. After reading Tapio’s comments on the history of his participation in the review process,
you might want to read my response and, of course, eventually Pat’s
response.

Also note that my list of issues has been dismissed by Gavin
without him ever adressing them quantitatively.

Jerry

Geoff

Bender (#138),

I also like the preceding sentences from the same paragraph as your quote:

The danger with ‘blind’ techniques, such as canonical correlation, EOF, POP and other types of analysis, is that they deliver dynamically interesting looking numbers and patterns, but reliable problem-independent tests are unavailable. Confirmatory analysis, whereby one tests a specific hypothesis developed from exploration with such techniques on independent data, is hardly possible in this context.

Gerald Browning

>Regarding the articles in Skeptic Magazine and claims made by Browning
(e.g., #91, #152) and others, some (late) comments to clarify the
history and some of the science.

> In September 2007, Michael Shermer, the publisher of the magazine,sent me Frank’s submitted article (an earlier but essentially similar version
thereof), asking me what I think of it. This was not a request to
review it but an informal email among acquaintances.

Are articles submitted to Editors suppose to be sent out to random people or only to the intended reviewers? This seems like a breach of publication rules.
What is the difference between the copy you saw and the final published article so we can make sure that the two contain the same scientific information before proceeding.

>I pointed Shermer
to some of the most glaring errors in Frank’s article. Some of these
have come up in posts and comments here.

I will address the “glaring errors” mentioned in this comment and then we can proceed to any other glaring errors.

> For example, Frank confuses
predictability of the first kind (Lorenz 1975), which is concerned
with how uncertainties in the initial state of a system amplify and
affect predictions of later states, with predictability of the second
kind, which is concerned with how (possibly chaotic) internal dynamics
affect predictions of the response of a system to changing boundary
conditions. As discussed by Lorenz, even after predictability of the
first kind is lost (”weather” predictability), changes in statistics
of a system in response to changes in boundary conditions may be
predictable (”climate” predictability).

You call this a glaring error when Lorenz has not proved anything. In particular you are very careful to say “may be predictable”. That is not a rigorous proof, nor even a rigorous statement.

> Frank cites Matthew Collins’s
(2002) article on limits to predictability of the first kind to infer
that climate prediction of the second kind (e.g., predicting the mean
climate response to changing GHG concentrations) is impossible beyond
timescales of order a year; he does not cite articles by the same
Matthew Collins and others on climate prediction of the second kind,
which contradict Frank’s claims and show that statistics of the
response of the climate system to changing boundary conditions can be
predicted (e.g., Collins and Allen 2002). After pointing this and
other errors and distortions out to Shermer–all of which are common
conceptual errors of the sort repeatedly addressed on this site, with
the presentation in Frank’s article just dressed up with numbers
etc. to look more “scientific”–I had thought this was the last I had
seen of this article.

Is there a mathematical proof in Collins second manuscript or is it just a run of a climate model? As a mathematical friend of mine clearly stated, a model is not a proof of anything. That is especially true when the model is closer to a heat equation than the system with the correct Reynold’s number. In fact there have been many blind alleys in science because of exactly these type of assertions.

>Independently of Michael Shermer asking my opinion of Frank’s article,
I had agreed to write an overview article of the scientific basis of
anthropogenic global warming for Skeptic Magazine. I did not know that
Frank’s article would be published in the magazine along with mine, so
my article certainly was not meant to be a rebuttal of his
(#91). Indeed, I was surprised by the decision to publish it given the
numerous errors.

It has yet to be shown that there are any mathematical errors in Pat’s
manuscript. In fact when the reviewers are unable to present any rigorous arguments in rebuttal, the Editor is required to publish the article.
The Editor told Pat that someone would write a rebuttal in the same issue.
So would the questionable arguments above be your rebuttal?

>Regarding some of Browning’s other points here, the ill-posedness of
the primitive equations means that unbalanced initial conditions
excite unphysical internal waves on the grid scale of hydrostatic
numerical models, in lieu of smaller-scale waves that such models
cannot represent. This again limits predictability of the first kind
(weather forecasts on mesoscales with such models) but not necessarily
of the second kind. Browning is right that the models require
artificial dissipation at their smallest resolved scales.

The problem has nothing to do with unbalanced initial conditions. The problem will arise from rounding errors and does not go away over a longer time period. It is only hidden by the poor resolution and unphysically large dissipation. Does this have something to do with the “glaring errors” in Pat’s article or is it just another random potshot.It certainly not rigorous.

If the numerical solution is not even close to approximating the continuum solution, nothing can be stated about the results. And very few modelers have shown that reducing the mesh size leads to the same or even a similar solution. In fact Dave Williamson has shown just the opposite result.

>However,
from this it does not follow that the total dissipation in climate
models is “unphysically large” (#152) (the dissipation is principally
controlled by large-scale dynamics that can be resolved in climate
models).

This is pure nonsense. Dave Williamson has shown that the cascade of vorticity happens in a matter of days and is very different when too large of dissipation is used (in fact smaller than in current climate models).
And he reduces the hyperviscosity coefficient by orders of magnitude when reducing the mesh size (but leaves the sponge layer coefficient near the top the same). You might try reading the scientific literature in your own field.

>And it does not follow that the “physical forcings are
necessarily wrong” (#152). Moreover, the “forcing” relevant for the
dynamical energy dissipation Browning is concerned with is not the
forcing associated with increases in GHG concentrations, but the
differential heating of the planet owing to insolation gradients (this
is the forcing that principally drives the atmospheric dynamics and
ultimately the dynamical energy dissipation). As Gavin pointed out, many aspects
of anthropogenic global warming can be understood without considering
turbulent dynamics.

We are not talking turbulent dynamics. We are talking about a numerical solution that is not even close to the solution of the continuum system
for scales less than 100 km (mesoscale storms, fronts, hurricanes).
What prevents these from forming? Too large of dissipation. If the correct dissipation were used, the forcings would be quite different. Have you heard of microphysics for smaller scales of motion?

Jerry

Geoff

Re: Comment 84 and others on throwing more petaflops at climate models (without waiting for better understanding):

The scientists at the NCAR are actively getting more “flops” Here’s the story on their new 76-teraflop supercomputer, said to be one of the world’s 25 fastest. They only need 13 more to reach their first petaflop. I wonder how much one of those babies costs?

Hoi Polloi

The scientists at the NCAR are actively getting more “flops” Here’s the story on their new 76-teraflop supercomputer, said to be one of the world’s 25 fastest. They only need 13 more to reach their first petaflop. I wonder how much one of those babies costs?

Can’t help imagining Mother Nature smiling in the background about them human beings trying to fathom her antics…

Raven

#151 (Jerry) says:

And it is clear from comments made by RC that they don’t even know the difference between a well posed and ill posed system. Pathetic.

Would it be possible to give us non-modellers a layman’s summary of the difference?

Gerald Browning

Raven (#152),

There are many references that discuss properly posed problems.
I will quote the definition from the book “Difference Methods for Initial-Value Problems” by Richtmyer and Morton. And then I will try to explain in simpler terms.

From page 39:

The problems we consider can be represented abstractly, using Banach space terminology. One wishes to find a one-parameter family u(t) of elements of B, where t is a real parameter, such that

(3.1) d over dt u(t)= A u(t), 0

bender

ampersand lt semicolon, Jerry:
<

Gerald Browning

Hoi Polli (#150),

The computing rates are always cited in the best scenario, i.e. single processor peak rate times the number of processors. The problem was always that the processors got bogged down in communications between processors
so the actual rate was considerably less, e.g. as little as 10 % of peak.
So the extra processors did not increase the computing in a linear fashion
as the number of processors increased. I assume that this is still true? In any case, when the basic dynamical system has serious problems
the claimed increase in forecast or climate model accuracy is nonsense.

Jerry

Raven

#157 – Thanks – that is the level of explanation I was looking for.

Gerald Browning

Well it seems that RC has also edited Pat Frank’s rebuttal to Tapio.

Jerry

Pat Frank

Here’s my original response to the relevant portion Tapio Schneider’s comments at RC. Gavin edited out the first bit, but I can fully document it.

It’s interesting that Tapio, Gavin, and A Kendall all missed the point that the cloudiness error tested out as systematic, consistent with theory-bias. If that error is indeed from theory-bias, it will play havoc with the position that all climate prediction needs is a bigger, faster computer.

Anyway, here’s the original post. May it make it through the discretion filter at CA. 🙂

———————————-
Re #206, only one of the two climate scientists recruited by Dr. Shermer at Skeptic referred to type 1 and type 2 errors. That particular reviewer prefaced his remarks to Dr. Shermer with an attempt at character assassination; see SI Section 1.2 for a more discrete paraphrasing of the accusation and a discussion of it.

I cited Collins’ 2002 article (Skeptic ref. 28) merely to show from a different perspective that GCM climate projections are unreliable. Likewise Merryfield, 2006 (ref. 29). Citing them had nothing to do with validating my error analysis.

Collins and Allen, 2002, mentioned by Schneider, tests the “potential predictability” of climate trends following boundary value changes. E.g., whether a GCM can detect a GHG temperature trend against the climate noise produced by the same GCM. This test includes the assumption that the GCM accurately models the natural variability of the real climate. But that’s exactly what is not known, which is why the test is about “potential predictability” and not about real predictability. Supposing Collins and Allen, 2002, tells us something about the physical accuracy of climate modeling is an exercise in circular reasoning.

The error relevant to uncertainty propagation in the Skeptic article is theory-bias. Schneider’s claim of confusion over type 1 and type 2 errors is both wrong and irrelevant. Of the major commentators in this thread, only Jerry Browning has posted deeply on theory-bias, and his references to the physics of that topic have been dismissed.
—————————–

RomanM

#165: Pat

Apart from the politically correct initial endorsement of the IPCC AR4 with no indication of having done any analysis themselves, it appears to me (reading the bold text, in particular) that the ASA leadership is advocating – and rightly so – that there is a need to involve more statisticians in the climate science process. This is basically the same conclusion that most of us on CA have come to independently.

Gerald Browning

Well Real Climate has started to selectively edit my responses. Would the readers on this site want me to post them here?

Jerry

Steve: Sure.

Jim Arndt

Roger Pielke Sr. responded to Ray Pierrehumbert

“In this simple case, where the model noise and SST forcing matches satellite-observed statistics from CERES (for reflect SW) and TRMM TMI (for SST), a positive feedback bias of 0.6 W m-2 K-1 resulted (the specified feedback, including the Planck temperature effect, was 3.5 W m-2 K-1)……to the extent that any non-feedback radiative fluctuations occur, their signature in climate data LOOKS LIKE positive feedback. And when modelers use those relationships to help formulate cloud parameterizations, it can lead to models that are too sensitive.”
http://climatesci.org/2008/05/22/a-response-to-ray-pierrehumbert%e2%80%99s-real-climate-post-of-may-21-2008-by-roy-spencer/

Gerald Browning

Steve (#168),

Thank you.

RC actually posted links to four of the references I gave them ( Comment #284 – the two Williamson manuscripts, the Lu manuscript, and the book reference that contains the ill posedness proof of the hydrostatic equations).
When I provided the references, I expected them to try to find some weakness in the manuscripts. Gavin immediately picked out one line of the conclusion of the Jablonowski and Williamson
manuscript saying it showed the numerical models converged and that I was wrong (see exchange #294 below).

# Gerald Browning Says:
22 mai 2008 at 1:30 PM

Gavin (#291),

And you claim I am rude. Only in response to your insults. Williamson’s tests show very clearly the problem with inordinately large dissipation, i.e. the vorticity cascade is wrong and the parameterizations necessarily inaccurate exactly as I have stated. Anyone that takes the time to read the manuscripts can see the problems and can judge for themselves.

Jerry

[Response: Presumably they will get to this line in the conclusions of J+W(2006): “In summary, it has been shown that all four dynamical cores with 26 levels converge to within the uncertainty … “. Ummm…. wasn’t your claim that the models don’t converge? To be clearer, it is your interpretation that is rubbish, not the papers themselves which seem to be very professional and useful.- gavin]

I responded (and it actually went thru) with #295

# Gerald Browning Says:
22 mai 2008 at 1:49 PM

Gavin (#294),

And what is the uncertainty caused by and how quickly do the models diverge? By exponential growth in the solution (although the original perturbation was tiny compared to the size of the jet) and in less than 10 days. Also note how the models use several forms of numerical gimmicks – hyperviscosity and a sponge layer near the upper boundary) for the “dynamical core” tests, i.e. for what was suppose to be a test of numerical approximations of the dynamics only. And finally, the models have not approached the critical mesh size in the runs.

Jerry

There was no response to this.

Earlier Ray Ladbury had made a rather uninformed statement about the ill posedness and that is where I called the scientists on the site
pathetic (on CA comment above) for arguing about this issue when they clearly did not know the difference between a well posed and ill posed system. So they evidently called in an applied mathematician to try to counter my arguments because they could not handle them. Now the applied mathematician did not use his real name, but I have a guess who it might be. Anyway here is his first substantive comment (#285) and my response.

Gerald #281

No Gerald, I have not missunderstood the definition of a well posed problem. In order to be well posed a problem should
a) Have a solution at all
b) Given the initial/boundary data that solution should be unique.
c) The solution should denpend continuously on the given data

Your comment have focused on point c) but the other two are also part of the definition of well-posedness.

In fact if you are going to object to simulations knowing that the problem is well posed isn’t even the best thing to complain about. Even if the problem is well posed it is far more important to know if the problem is well-conditioned. Just knowing that the solution depends continuously is is of little value.

Even for problems which are not well posed we can often do a lot. If you talk to the people doing radiology you will find that they have to compute inverse Radon transform, and that problem is known the be ill-posed. However there are ways around that too.

For something like a climate model you probably don’t even need to looks for classical solutions, since one is interested in long term averages of different quantities. Knowing that e.g. a weak solution or a viscosity solution exists, together with having an ergodic attractor in the phase space of the model would give many correct averages, even if the system is ill-conditioned and chaotic within the attractor.

I had a look at what you wrote over at Climate Audit too, and calling the people who are writing at RC “pathetic” for for knowing the definition of a well posed problem in mathematics isn’t exactly in the spirit of the good scientific discussion you claim to want.
While I’m at it I can also let you know that the performance of a modern supercomputer is not given as the single processor flops times the number of processors. It is based on running a standardised set of appliction benchmarks. Take a look at http://www.top500.org if you want to get up to date on the subject.

# Gerald Browning Says:
22 mai 2008 at 12:41 PM

Jonas (#285),

You seem to conveniently have forgotten the interval of time mentioned in Peter Lax’s original theory. You might look in Richtmyer and Morton’s classic book on the initial value problem on pages 39-41.

Jerry

Note that the above reference is exactly the one I cited here.
Because you never know what will be allowed, I did not respond any further
to Jonas’ remark But I will here.

Ill posedness is a very local phenomenon and will appear if the time dependent differential system is (nearly) hyperbolic or parabolic. Nonlinearity will not change the result. That has been illustrated by (non) convergent numerical examples on this site.

Well posedness is defined for linear variable coefficient hyperbolic and
(incompletely) parabolic systems. Extensions to nonlinear equations can and have been made for finite periods of time. For a rigorous treatment of the nonlinear incompressible Navier-Stokes equations, see the miminal scale estimates by Henshaw, Kreiss, and Reyna.

Tomography (MRI’s) use a circular device to take multiple scans of the object (e.g. the brain) and the amount of X-rays is quite large. The reason for this is that the mathematics is trying to invert an integral and this process is known to be ill posed. The problem reduces to
inverting an ill conditioned matrix, but this is an entirely different problem than an ill posed time dependent PDE. And even in this case only the largest features can be determined because smaller scale features are even more ill conditioned.

The benchmarks used to test the parallel computers, the so called linpack series, are a special set of routines developed for parallel computers to perform linear algebra.
That does not mean that a climate model will run as efficiently as the benchmarks because of nonlocal communications. So this statement is misleading. In fact a number of models have reverted to finite difference methods instead of spectral methods because they employ more local communications.

AT #300 Jonas commented

# Jonas Says:
22 mai 2008 at 2:58 PM

Gerald #292.
Lax is a great mathematician but his original papers are not among my readings. R&M I have on the other hand read, some time ago. Unless my memory is wrong(I’m at home and don’t have the book available here) the initial part of the book covers linear differential equations and the Lax-Richtmyer equivalence theorem for finite-difference schemes.

So, if by “the interval of time” you refer to the fact that this theorem only assumes that the solution exists from time 0 up to some time T and that for e.g Navier-Stokes it is known that such a T, depending on the initial data, exists then I understand what you are trying to say. However the problem with this is that unless you can give a proper estimate of T you can not know that the time step you choose in the difference scheme is not greater than T. If that is the case the analysis for small times will not apply to the computation. So long term existence of solutions is indeed important even when using the equivalence theorem.

Furthermore, the equations used here are not linear and for nonlinear equations neither of the two implications in the theorem are true.

There is no doubt that there are interesting practical and purely mathematical, questions here, but if you are worried about the methods used try to make a constructive contribution to the field rather than treating people here like fools and calling them names at other web sites. I’m not working with climate or weather simulation but I have doubts about something I read outside my own field I will politely ask the practitioners for an explanation or a good reference rather than trying to bully them.

And my response at #301

# Gerald Browning Says:
22 mai 2008 at 4:16 PM

Jonas (300),

I am willing to continue to discuss well posedness, but ill posedness of the hydrostatic system is the problem and the unbounded growth shows up faster and faster as the mesh is reduced (more waves are resolved) exactly as predicted by the continuum theory in the above reference by Heinz and me. There are computations that show this on Climate Audit under the thread called Exponential Growth in Physical Systems.I ran those tests just to illustrate the theoretical results.

I cannot here explain the connection between linear and nonlinear theory,
but there are theorems discussing this issue, especially for hyperbolic and
parabolic systems. See the book by Kreiss and Lorenz on the Navier-Stokes equations.
For some beautiful nonlinear theory on the NS equations, look at the minimal scale estimates by Henshaw, Kreiss and Reyna and associated numerical convergence tests.

Jerry

I tried to respond to the bullying comment but it disappeared.

Tom Vonk

#172
“For something like a climate model you probably don’t even need to looks for classical solutions, since one is interested in long term averages of different quantities. Knowing that e.g. a weak solution or a viscosity solution exists, together with having an ergodic attractor in the phase space of the model would give many correct averages, even if the system is ill-conditioned and chaotic within the attractor.”

Huh ??
What might he be possibly meaning with this garbage ??
Classical solution of what ? Classical as opposed to what , non classical ? What makes a solution classical ?
How does he know that a weak solution (of what ? Of N-S ?) exists ? And how weak anyway ?
How does he know that there is an attractor in the phase space of the model ? Of course that he doesn’t know that and it is even impossible to prove that there is one .
Besides even if there was one , the phase space of the model is dramatically smaller than the phase space of the real Earth and would be irrelevant .
What is a “viscosity” solution ?
What has ergodicity to do with attractors ? What would be “non ergodic” attractors ?
“A system chaotic within the attractor” . God ! A system is chaotic or isn’t . If it is , it may have an attractor but it has not to . But saying that a system is chaotic within an attractor is like saying that bubbling water has bubbles in it .

If I hasard a translation of this garbage in semi understandable terms , it gives something like that .
“As we use (temporal) averages , there is a magic that makes the behaviour of the system independent of the number of dimensions of the phase space .
This magic warrants that by using a crude model with a very low number of dimensions , if a finite number of numerical runs with a finite time horizont appears bounded (e.g the trajectories of the modelled system lie all within a subspace of the model phase space that we call attractor for no particular reason other than because we can), then the same result and the same bounding applies to the real system with infinite phase space dimension and infinite time horizont .”

Now despite the fact that the person obviously has no understanding of the chaos theory , there is not an embryo of beginning of a stability theory of the trajectories of the climate system in the phase space .
There is a powerfull theorem , the Kolmogorov-Arnold-Moser theorem , that has been used to study the stability of the planet orbits .
Indeed while it is known that the orbits are chaotic it doesn’t necessarily imply that they are unstable .
The Kolmogorov-Arnold-Moser theorem says that if and only if the system can be represented by a perturbation Hamiltonian then under suitable conditions the effect of the perturbation Hamiltonian is to only deform the attractor but not to destroy it .
In other words the system is chaotic but stable (within certain bounds) .
An analogous approach to the climate would be to find an integrable system that would be an idealisation of the climate and then prove that the difference between the real climate and the idealised (modelled) climate is a perturbation .
Perturbation meaning in that context that the perturbation Hamiltonian is small and stays small .
Applying KAM theorem would then prove that the attractor can (or can not) be destroyed by the perturbation .

And it is at this point that the problem even if formulated in the frame of the chaos theory meets Jerry’s issues .
To apply such methods to a known chaotic system , it is necessary that its idealisation be INTEGRABLE .
Numerical methods qualify only insofar that it can be proven that they converge to the continuous solutions of whatever system of equations is chosen .
Climate models fail already at this stage as Jerry shows .
Even if somebody found this idealised converged system which would be clearly completely different of the current climate models , there would be a second much more formidable task – prove that everything that is not contained in the idealised system constitutes a “perturbation” .
This task , supposing that the first has been solved , is way beyond our current state of knowledge and it is not excluded that actually the perturbation method doesn’t apply at all .

What stays ?
Evidence over the last billion of years suggests that some dimensions in the infinity of dimensions of the phase space (temperature , pressure etc) are bounded .
This suggests that there indeed might be an attractor for the climate .
However evidence also suggests that despite rather “narrow” bounds on some dimensions (air and water velocities , solar irradiation , temperature) the attractor is sufficiently vast that it allows extremely different dynamic states (ice Earth , tropical Earth , stormy Earth etc) with fast transitions between them .
Looking at that attractor with a 10 years scale would be at best useless and at worst ridiculous .

Neil Haven

That was a fantastic rant Tom V. Thanks sincerely for the tour of K-A-M.

This seems strange, though:

Evidence over the last billion of years suggests that some dimensions in the infinity of dimensions of the phase space (temperature , pressure etc) are bounded . This suggests that there indeed might be an attractor for the climate .

Why should boundedness imply the existence of a dynamical attractor, rather than simply bounded responses to bounded perturbations?

Neil Haven

Jerry, Tom V, Dan, et al.

I note that the budget for the U.S. Climate Change Science Program is a bit over $2B per year. I also note that the strategic plan for U.S. climate research does not even mention research into the mathematical foundations of climate models (see particularly Chapter 10 “Modeling Strategy”). I was particularly surprised to see that NSF’s program statement in Chapter 16 does not even use the word ‘mathematics’.

I realize this is a very broad question to which a comprehensive answer in a blog is impossible, but do you have any thoughts on how we should be spending the research dollars? What research questions are being overlooked? How do you think the program for climate modelling research could be recast or modified?

Steve M. has mentioned adding an independent oversight/auditing function to the funding mix; Dan H. has emphasized software verification and validation for code used to drive policy; etc.

Gerald Browning

Neil,

Note that there are no numerical analysts or continuum PDE scientists
on the IPCC. An oversight board that included some independent specialists (no funding attachments to the game) would be very appropriate. But it might be difficult to find a specialist in these areas that could stay awake during all of the unsubstantiated hand waving.

Jerry

steven mosher

bender UC, you will like this.

I’m digging into the attribution studies. Why? because the huge spread in the model outputs in forecasts made me wonder how in gods name they ever did and attribution study. with ensembles that wide lots of observations fit the data.

so, chapter 9 of Ar4. figure 9.5

Comparison between global mean surface temperature anomalies (°C)
from observations (black) and AOGCM simulations forced with (a) both anthropogenic
and natural forcings and (b) natural forcings only. All data are shown as global
mean temperature anomalies relative to the period 1901 to 1950, as observed
(black, Hadley Centre/Climatic Research Unit gridded surface temperature data
set (HadCRUT3); Brohan et al., 2006) and, in (a) as obtained from 58 simulations
produced by 14 models with both anthropogenic and natural forcings. The multimodel
ensemble mean is shown as a thick red curve and individual simulations are
shown as thin yellow curves. Vertical grey lines indicate the timing of major volcanic
events. Those simulations that ended before 2005 were extended to 2005 by using
the fi rst few years of the IPCC Special Report on Emission Scenarios (SRES) A1B
scenario simulations that continued from the respective 20th-century simulations,
where available. The simulated global mean temperature anomalies in (b) are from
19 simulations produced by fi ve models with natural forcings only. The multi-model
ensemble mean is shown as a thick blue curve and individual simulations are shown
as thin blue curves. Simulations are selected that do not exhibit excessive drift in
their control simulations (no more than 0.2°C per century). Each simulation was
sampled so that coverage corresponds to that of the observations. Further details of
the models included and the methodology for producing this fi gure are given in the
Supplementary Material, Appendix 9.C. After Stott et al. (2006b).

Now, you can go look at this graphic, but basically what you see is two chart.
In one chart you have the Observation surrounded by spaggitti. 14 models, 58 runs. this is basically the hindcast experiement. and you see the observation
falls within the swath of the 14 models. In this experiement GHG are modeled.

Now comes the second chart. where GHG are not modelled and you have only “natural” forcings.

Do they use 14 models? Nope. they use 5. why? to reduce the spread? do they use
58 runs? nope only 19. Do they run every model? nope. only those that have no drift in the control runs.

So for “forecast” they use a whole host of models. they dont throw out those with drift in control runs, the drift gets transported into forecast uncertainity. Makes it harder to falsify. But when the want to do an attribution study, you get 5 models 19 runs, and the less reliable models tossed off the island.

Interesting.

Kenneth Fritsch

Re: #182

So for “forecast” they use a whole host of models. they dont throw out those with drift in control runs, the drift gets transported into forecast uncertainity. Makes it harder to falsify. But when the want to do an attribution study, you get 5 models 19 runs, and the less reliable models tossed off the island.

Interesting.

Is that “interesting” nuanced or hyperbole? More questions: How would this analysis have been handled if it were strictly a scientific endeavor? Or if it were marketing immediate mitigation for AGW? Does AR4 follow the RC line of “reasoning” or is it vice versa?

Neil Haven

steven m

FWIW, IMO this is a brilliant idea. Revisiting the attribution studies in light of the currently-convenient criterion for what is consistent with what should be worth a raft of publications. Hoist, meet Petard.

steven mosher

re 183, 184, 186 and 187.

It’s funny when the douglas thread got going and I what there notion of
“consistent” was it got me thinking about the attribution studies.
Partly because I was also looking at the modelE response for GHG forcing.
Hoist and petard, exactly

Then Gavin showed the huge spread of forecasts for the next twenty years.
I asked a simple question. Do you use the bad hindcasters to forecast?

Yup. hmm.

where’s beaker?

Anyways more sources to dig through. Chatper 9 AR4. interesting reading

Sam Urbinto

188 steven mosher says:

where’s beaker?

He got tired of saying ‘SD fits anything, SEM fits nothing’ instead of ‘you can’t compare a model ensemble with observations’

But of course, if I remember correctly, he (she, it) had a problem with the observations being acceptable. Which I agree to, but satellite is more trustworthy than air/water thermometer readings, so take that FWIW.

But, hey.

Dan Hughes

re: #178

A very, very short summary:

1. Documentation, documentation, documentation … document everything in all models, methods, and software.

2. Verification that the coding is correct.

3. Verification that all numerical solution methods are performing with expected theoretical characteristics.

4. Development of Validation plans, procedures, and processes.

5. Carry out Validation processes. A continuous activity. It’s a process.

6. Develop and implement an approved Software Quality Assurance Plan for maintaining the production-level code.

Geoff Sherrington

Re larger computers

Is this exchange (slightly modified for typos, clarity and spaces) of any interest to you math people? Are CPUs these days big enough to avoid precision loss if interim storing on disc is needed? Is the carrying of enough significant figures in calculations and constants like pi a source of error for climate modellers? Try seeing how many sig figs you get for pi in Excel. (This part of note by Geoff Snr.)

From: support@graphpad.com
Sent: Thursday, 22 May 2008 1:53 AM
Subject: Precision and Accuracy [CASE#233853]

Prism does calculations in double precision, but only stores data and results in single precision. We don’t generally share information about how it was programmed. Why are you asking?

Harvey

On 2008-05-20 23:30:03.0 you wrote:
Precision and Accuracy

How many significant figures can your software carry?
What language was it written in?
Who wrote the compiler and linker?
Do you use their compile, link and runtime libraries?
Have your team written any math or statistical routines?

Sincerely
Geoffrey James Sherrington (Geoff Jnr)

John F. Pittman

http://www.iac.ethz.ch/people/knuttir/papers/tebaldi07ptrsa.pdf

The use of the multi-model ensemble
in probabilistic climate projections
BY CLAUDIA TEBALDI
1,* AND RETO KNUTTI
2
1Institute for the Study of Society and Environment, National Center for
Atmospheric Research, PO Box 3000, Boulder, CO 80304, USA
2Institute for Atmospheric and Climate Science, Swiss Federal Institute of
Technology, Universita¨tstrasse 16 (CHN N 12.1), 8092 Zu¨rich, Switzerland
Recent coordinated efforts, in which numerous climate models have been run for a common set of experiments, have produced large datasets of projections of future climate for various scenarios. Those multi-model ensembles sample initial condition, parameter as well as structural uncertainties in the model design, and they have prompted a variety of approaches to quantify uncertainty in future climate in a probabilistic way. This paper outlines the motivation for using multi-model ensembles, reviews the methodologies published so far and compares their results for regional temperature projections. The challenges in interpreting multi-model results, caused by the lack of verification of climate projections, the problem of model dependence, bias and tuning as well as the difficulty in making sense of an ‘ensemble of opportunity’, are discussed in detail.

Parameter uncertainties… stem from the fact that, mostly for computational constraints, smallscale processes in all components of the climate system cannot be resolved explicitly, and their effect on the large-scale climate response must be parametrized with bulk formulae that depend on large-scale variables available in the model… While many processes behind the parametrization are well understood, or observational or theoretical arguments exist, there are cases where the evidence is rather circumstantial and values are often chosen simply because they seem to work.

bender

#196 Looks like a must-read. Might need a new thread for this one.

John F. Pittman

#197 You mean “no drift GT 0.2C”?

Simulations are selected that do not exhibit excessive drift in their control simulations (no more than 0.2°C per century).

I wonder if the quote should actually read “(no more than a positive 0.2°C per century”?

steven mosher

re 200. ya sorry. GT.

Pat Frank

My last reply to criticism has been deleted from the, “What the IPCC Models Really Say” thread at RC. I know the comment made it onto the board, so I guess the moderator found it offensive. Here it is, in its entirety.
——————————————–
# Pat Frank Says: Your comment is awaiting moderation.
23 May 2008 at 6:25 PM

Re. #310 — B. P. Levenson wrote, “Frank’s article assumes that global warming goes away if you take out the models.”

It assumes no such thing.

“But in a larger sense Frank’s argument is ridiculous.”

You’ll have to demonstrate that on the merits. Unsupported assertions won’t do it. GCMs may have a million floated variables. John von Neumann reportedly said that he could model an elephant with 4 adjustable parameters and with 5 could wave the trunk. With a million variables, GCMs can be tuned to match any past climate, and that doesn’t mean anything about predicting future climate.

“Frank’s article amounts to a lengthy argument that something we can see happening isn’t happening.”

The article says nothing about climate as such. It’s about error assessment and model reliability; nothing more.

#311 — Ray Ladbury, your supposed “insidious motives” are products of your mind, not mine.

#312 — Dan, for proof see article references 13 and 40.

Other examplpes:
M.L. Khanekar, T.S. Murty and P. Chittibabu (2005) “The Global Warming Debate: A Review of the State of the Science” Pure appl. geophys. 162, 1557-1586; L. C. Gerhard (2004) “Climate Change: Conflict of observational science, theory, and politics” AAPG Bulletin 88, 1211-1230; V. Gray (1998) “The IPCC future projections: are they plausible?” Climate Research 10, 155-162; W. Soon and S. Baliunas (2003) “Global Warming” Prog. Phys. Geog. 27, 448-455.

See also Hendrik Tennekes’ “A Personal Call For Modesty, Integrity, and Balance by Hendrik Tennekes” here: http://tinyurl.com/2jxqgs

These are far from exhaustive. Were any of them picked up by news media for public re-broadcast?
——————————————–

Honestly, I don’t see anything offensive there, unless it’s straightforward self-defense that offends.

dover_beach

You miss the point of RC, Pat. They’re a support group; not a discussion group. But I will say I’m glad Jerry and yourself are cross-posting your responses to comments on RC here. Its instructive, for instance, that Levenson’s deceptive misrepresentation is permitted but your reply is not.

Mosh, continue picking that scab you’ve found re attribution studies; I think there might be an infection underneath.

John F. Pittman

Gerald Browning and Gavin’s responses #203 CA, #324 RC:
Gavin’s responses
1.>[Response: Your (repeated) statements do not prove this to be the case. Climate models do not tune the radiation or the clouds or the surface fluxes to fix the dynamics – it’s absurd to think that it would even be possible, let alone practical. From http://www.iac.ethz.ch/people/knuttir/papers/tebaldi07ptrsa.pdf

Parameter uncertainties… stem from the fact that, mostly for computational constraints, small scale processes in all components of the climate system cannot be resolved explicitly, and their effect on the large-scale climate response must be parameterized with bulk formulae that depend on large-scale variables available in the model… While many processes behind the parametrization are well understood, or observational or theoretical arguments exist, there are cases where the evidence is rather circumstantial and values are often chosen simply because they seem to work.

Gavin 2. >Nonetheless, the large scale flows, their variability and characteristics compare well to the observations. From http://www.iac.ethz.ch/people/knuttir/papers/tebaldi07ptrsa.pdf

While many processes behind the parametrization are well understood, or observational or theoretical arguments exist, there are cases where the evidence is rather circumstantial and values are often chosen simply because they seem to work.

Emphasis mine.

John F. Pittman

Gavin #3: The only conclusion that one can draw is that the equations they are solving do have an affiliation with the true physics and that the dissipation at the smallest scales does not dominate the large scale circulation…

What is an affiliation, you join the Hansen-AGW club??? Satire intentional. Not that they are the “true physics”, but that they just kinda hangout with true physics, you know AGW-physics homies.

NOT TRUE. Another explanation quoted below from http://www.iac.ethz.ch/people/knuttir/papers/tebaldi07ptrsa.pdf

Parameter uncertainties… stem from the fact that, mostly for computational constraints, small scale processes in all components of the climate system cannot be resolved explicitly

(this is the physics that can’t)
,

and their effect on the large-scale climate response must be parameterized with bulk formulae that depend on large-scale variables available in the model…While many processes behind the parametrization are well understood, or observational or theoretical arguments exist, there are cases where the evidence is rather circumstantial and values are often chosen simply because they seem to work.

emphasis mine

It is apparent that it is not the physics but that “they seem to work”. Cherry Picking may be more appropriate term.

Warning, Block quotes may be off.

Gerald Browning

And Gavin actually responded to this remark:

# Gerald Browning Says:
24 mai 2008 at 8:00 PM

Gavin (#330)

So you don’t know the answer for the need to resolve the mesoscale storms, fronts and hurricanes, but then you state that a climate model is accurate without resolving them. Is there a contradiction here? Wouldn’t a good scientist determine the facts before making such a statement?

Jerry

[Response: But the fact is that climate models do work – and I’ve given a number of examples. Thus since those models did not have mesoscale circulations, such circulations are clearly not necessary to getting a reasonable answer. I’m perfectly happy to concede that the answer might be better if they were included – but that remains an open research question. – gavin]

Gerald Browning

John (#210),

Thank you. I know that the amount of water fallout is chosen as some fraction of the size of a mesh rectangle. This is clearly not based on any physical principle, but on what works exactly as you state. And that affects radiation and many other things.

Jerry

John F. Pittman

http://www.realclimate.org/index.php/archives/2008/05/freeman-dysons-selective-vision/langswitch_lang/tk

I addressed this from an engineer of 20+ years expierence. But it got lost, I assume. As I stated on RC “I would rather be made a fool than censored.” I am posting a synopsis of what I posted on RC.

This is what I had severe problems with accepting.

Economic estimates of the costs of cutting CO2 emissions are huge. In an absolute sense, this is true, it would be a lot of dollars, but it comes down to a few percent of GDP, which, in an economic system that grows by a few percent per year, just puts off the attainment of a given amount of wealth by a few years.

There is a rule for engineers, without contrary evidence, when using gross as in Gross Domestic PRODUCT, one uses a factor of 10. As in, a computer board costs you a gross of $1, one needs to make the consumer pay $10 in order to make a profit.

A few tranlates to about 33%. Using economic multiplier effect, this translates to 44%. (0.33 + 0.33 * 0.33+…. expressed as percentage). Note the consintancy of the following significant figure.

So…in the USA…46% average taxes of gross, 44% cost of CO2, the most liberal of estimates of real disposable income after paying for food, gas, religion, retirement plan of the 54% after taxes (100 – 46) is 30%, depending on taxes, government subsidies and actual taxes…we obtain 46+44+30=120%. This means that unless the US can provide 20% subsidy above GROSS domestic product (a trivial impossibility) we cannot afford cuting CO2 emmissions all things being equal (120%=100% only happens in GCM’s as far as I know). Satire off.

Gerald Browning

Tom Vonk,

You might be interested in this reply.

# Gerald Browning Says:
24 mai 2008 at 7:49 PM

Gavin (332),

Please cite a reference that contains a rigorous mathematical proof that the climate is chaotic. As usual you make statements without the scientific facts to back them up. I suggest that the readers review Tom Vonk’s very clear exposition on Climate Audit in response to this exact claim on the thread
called Koutsoyiannis 2008 Presentation in comment #174 if you want to know the scientific facts.

Jerry

[Response: No such proof exists, I never claimed it did, and nor do I suspect it is. However, NWP models and climate models are deterministic and individual realisations have an strong sensitivity to initial conditions. Empricly they show all the signs of being chaotic in the technical sense though I doubt it could be proved formally. This is a different statement to claiming the climate (the attractor) itself is chaotic – the climate in the models is stable, and it’s certainly not obvious what the real climate is. (NB Your definition of ‘clear’ is ‘clearly’ different to mine). – gavin

Gerald Browning

All,

Note that the reference that Gavin cites is not very rigorous and if anything supports my arguments more than his. I can pull out the relevant statements by Lynch if desired.

Jerry

Raven

#219 (Jerry)

Would this be a reasonable layman’s summary or your criticisms of the models:

There is no mathematical evidence that the GCMs used to model the climate actually solve the physical equations that they are claiming to solve. If they did they should be able to reproduce a number of critical climate features such as weather fronts and cyclones. This means that any success at hindcasting is most likely the result of parameter tuning and not because they correctly model the physics. For this reason, any predictions made by these models must be treated with extreme caution.

gb

John,

The authors refer to verification and validations studies, so people are working on it! Furthermore, they discuss the usefulness of ensemble simulations which implies that they think that predictability of the second kind is possible and that the internal variation is not arbitrary large. And when they talk about comparisons with observations they say ‘… all those activities have helped in improving the models, and have greatly increased our confidence that the models capture the most relevant processes …’ Nowhere they say that climate models are unphysical!

It is a good article and I recommend reading it. It points out that validating and verifying climate models is not trivial and should be done carefully (not like Douglass and Koutsoyiannis). But they don’t endorse Jerry’s and Tom’s view in any way!

gb

Bender,

These are issues that you don’t understand yourself.

bender

#226
Prove it.

kim

226 (gb) That he could make such a marvelously pertinent list argues some understanding.
===================================

Scott-in-WA

Bender #227: What this is about is vertical convection & cloud formation. Anything meso-scale that could act as a powerful negative feedback that might over-ride many or all of the positive feedbacks we hear about continually in the media. IMO this is about ocean-atmosphere convection especially in the tropical S. Pacific in DJF. Internal variability and trends in cloudiness vs. external forcing via GHG trend……. Even if GCMs correctly reconstruct the past, they do not necessarily predict the future. Especially if there are unphysical dissipations that are poor approximations to reality.

After spending a year reading the arguments and counter-arguments concerning the validity and usefulness of the GCMs for climate prediction, I have reached the conclusion that without having a significantly better understanding of the actual physical processes operating within their actual physical systems, the modelers are simply chasing computational rainbows.

What kinds of field experiments and field observations are necessary to gain a significantly better understanding of the actual physical processes operating within their actual physical systems? How much data, and of what kind, must be collected in the field, and how? What will this cost, and how much time will be needed to collect the data, to process it, and to interpret it?

bender

#226 = Driveby shooting with blanks.

kim

Actually, his car stalled as he essayed the getaway and he’s out there, mute and mortally wounded.
===========================================

bender

#235

It is possible that the models are a useful approximation

Slight reword:
It is possible that the models are a useful approximation of the PAST.

Q: Is it possible that the models are a useful approximation of the FUTURE?

This depends on whether or not a powerful negative feedback from ocean clouds kicks in at higher GMT. Do the GCMs simulate such a “mesoscale” processes? No. However this “mesoscale” process has global-scale consequences.

The best way to deny this possibility is to deny funding to those wishing to study it.

John F. Pittman

from http://www.iac.ethz.ch/people/knuttir/papers/tebaldi07ptrsa.pdf emphasis mine

The predictive skill of a model is usually measured by comparing the predicted outcome with the observed one. Note that any forecast produced in the form of a confidence interval, or as a probability distribution, cannot be verified or disproved by a single observation or realization since there is always a non-zero probability for a single realization to be within or outside the forecast range just by chance. Skill and reliability are assessed by repeatedly comparing many independent realizations of the true system with the model predictions through some metric that quantifies agreement between model forecasts and observations (e.g. rank histograms). For projections of future climate change over decades and longer, there is no verification period, and in a strict sense there will never be any, even if we wait for a century. The reason is that the emission scenario assumed as a boundary condition is very likely not followed in detail, so the observations from the single climate realizations will never be fully compatible with the boundary conditions and scenario assumptions made by the models. And even if the scenario were to be followed, waiting decades for a single verification dataset is clearly not an effective verification strategy. This might sound obvious, but it is important to note that climate projections, decades or longer in the future by definition, cannot be validated directly through observed changes. Our confidence in climate models must therefore come from other sources. Our confidence in climate models must therefore come from other sources.

The judgement of whether a climate model is skilful or not does not come from its prediction of the future, but from its ability to replicate the mean climatic conditions, climate variability and transient changes for which we have observations, and from its ability to simulate well-understood climate processes. For example, climate models are evaluated on how well they simulate the present-day mean climate (e.g. atmospheric temperature, precipitation, pressure, vertical profiles, ocean temperature and salinity, ocean circulation, sea ice distributions, vegetation, etc.), the seasonal cycle and climate variability on various time scales (e.g. the North Atlantic oscillation, ENSO, etc.). Their response to specified forcing is compared to the observed warming over the industrial period. They are evaluated against proxy data from past climate states, e.g. the Last Glacial Maximum, the Mid-Holocene, the last Interglacial period, or even further back in time (e.g. Kiehl & Shields 2005; Otto-Bliesner et al. 2006a,b). Further, individual processes in the model are studied in detail and evaluated against both theory and observations. While all those activities have helped in improving the models, and have greatly increased our confidence that the models capture the most relevant processes, simulating the past and present correctly does not guarantee that the models will be correct in the future. In other words, while there is a lot of circumstantial evidence for the models to be trusted for the future, there is no definitive proof for model skill in projecting future climate. In fact, most models agree reasonably well with observations of the present-day mean climate and simulate a realistic warming over the twentieth century (of course, the specific performance depends on each model/ metric combination), yet their predictions diverge substantially for the twentyfirst century, even when forced with the same boundary conditions.

From gb

It points out that validating and verifying climate models is not trivial and should be done carefully (not like Douglass and Koutsoyiannis).

In what way should have Douglass and Koutsoyiannia have proceeded? If a model’s predictive skill is usually measured by comparing the predicted outcome with the observed one; that atmospheric temperature, precipitation, pressure, vertical profiles, ocean temperature, etc. can be used through some metric, what metric do you advise?

Our confidence in climate models must therefore come from other sources.

I agree with the comments about the statistics that Becker posted. However, I was left somewhat taken back in that using such a strict method basically meant that model skill could vary from a minus correlation to a near perfect correlation and not be inconsistant with the model…that it “paid” to have as many poor or exaggerated models such that the probability distribution was as large as possible. Where is the predictive usefulness or skill of such an ensemble? And does not such an ensemble invalidate the proof?/assumption noted below of

given model errors tend to cancel

?

And since

The reason is that the emission scenario assumed as a boundary condition is very likely not followed in detail, so the observations from the single climate realizations will never be fully compatible with the boundary conditions and scenario assumptions made by the models.

shouldn’t Jerry’s and Tom’s comments such as

If the models do not resolve the basic features (easily proved just by their crude mesh), then it is clear that the model solution is not near reality or even the solution of the differential equation. And given that fact,the dynamics is wrong and then necessarily the physics.

be addressed in a form where temperature and pressure profiles match the independent realizations of the true system with agreement to boundary conditions without an aphysical forcing by the models(modellers)?

The difficulty in quantifying model performance for future climate can be circumvented using two approaches. The first approach may be to ignore model performance altogether. As criticizable as this should be, it is in fact the case that multi-model simple averages are widely used, for example in the IPCC (2001) report. While this is likely to improve the best guess projections because model errors tend to cancel, it hardly makes optimal use of the information available.

If multi-model simple averages are widely used, what is it that makes say Douglass in particular wrong? Especially given model errors tend to cancel. Is this, model errors tend to cancel, an assumption, has it been proven? If it has been proven, how and where? What metric did they use and should we not take, say, Douglass and use the same metric if possible, or at least as a starting point for our measurement of predictive skill?

aurbo

Re garbled French in #241,

That should have been:

Plus ça change, plus c’est la même chose.

My bad HTML.

Geoff Sherrington

Re # 238 bender

Q: Is it possible that the models are a useful approximation of the FUTURE?

Answer: Unequivocal NO, on logic grounds. There is nothing known to which to compare their performance.

If you think these models have utility, why not adapt their useful components and apply them to trading in stocks and shares? That way you might lose money more rapidly. Also, the chances of calibration by hindcast are better.

I have yet to see a set of objectives for modellers, a structured design for investigation, a placement of resources to lessen replicative effort, the objectives of review points along the way, the criteria that allow continuation or cause termination of effort. In all, as the history of science has shown, an unplanned approach is less effective than a planned one and serendipity, though sweet when it occasionally happens, cannot be built into requests for more funds.

As before: What is the question, what is the acceptable answer and what is the path mapped between them?

Tom Vonk

#218

# Gerald Browning Says:
24 mai 2008 at 7:49 PM

Gavin (332),

Please cite a reference that contains a rigorous mathematical proof that the climate is chaotic. As usual you make statements without the scientific facts to back them up. I suggest that the readers review Tom Vonk’s very clear exposition on Climate Audit in response to this exact claim on the thread
called Koutsoyiannis 2008 Presentation in comment #174 if you want to know the scientific facts.

Jerry

[Response: No such proof exists, I never claimed it did, and nor do I suspect it is. However, NWP models and climate models are deterministic and individual realisations have an strong sensitivity to initial conditions. Empricly they show all the signs of being chaotic in the technical sense though I doubt it could be proved formally. This is a different statement to claiming the climate (the attractor) itself is chaotic – the climate in the models is stable, and it’s certainly not obvious what the real climate is. (NB Your definition of ‘clear’ is ‘clearly’ different to mine). – gavin

I never doubted one second that Schmidt’s definition of clear was special and he’d probably give mud as an example of clear water .
I have also noticed that he equates chaos to sensibility to initial conditions what shows that he has , let’s say , a rather naive vision .
Indeed sensibility to initial conditions is a necessary but not sufficient condition for chaotic behaviour (a^x is very sensible to initial conditions but not chaotic) .
He also associates chaos to randomness (you know , statements like “small scale things cancel out”) what is not only naive but wrong .
One can especially appreciate the use of the word “technical sense” – as there is no definition of chaos in a “technical sense” , it is just a convenient buzzword trying to vehiculate the notion that the author is a “technician” what he clearly is not .
Indeed the deterministic chaos is a PROPERTY of a set of differential equations .
The existence or non existence of chaotic behaviour depends not only on the form of the differential equations but also on the numerical values of the parameters appearing in the said equations .
There is a whole field of study called “transition towards chaos” that shows that continuous variation of some parameters (f.ex the Reynolds number) will lead a perfectly deterministic non chaotic system described by the same equations towards different chaotic behaviours .
In this sense one doesn’t need to “doubt” the possibility to prove chaotic behaviour , the impossibility of such a proof is directly related to the fact that the climate is NOT described by a set of differential equations and as , per definition , it will never be the case so it will never be possible to prove anything about the properties of unknown solutions to non existent equations .

Now the second part shows clearly (in a non Schmidtian sense) that he doesn’t know what he is talking about .
So the statement about the existence of chaos is “different” from a statement if “the attractor itself is chaotic” … one has difficulty to not burst out laughing .
What is an attractor (and I remind again that an existence of an attractor is NOT necessary for a chaotic system) ?
When it exists it is a sub space of the phase space that contains all the dynamical states of the system .
It is unique and well defined by its topology .
That this topology may be complex (f.ex fractal attractors like the Mandelbrot’s set) is interesting but irrelevant .
In any case an attractor is never “chaotic by itself” , it is just an invariant set of points for a given dynamical system that is itself chaotic under certain conditions .
Talking about “attractors chaotic by themselves” is about as nonsensical as nonsensical goes .

Back to the climate .
Let’s suppose that God provides us with 3 456 266 coupled differential and algebric equations and gives us the insurance that that is exactly everything that is needed to completely describe the climate for eternity .
He might give us only 77 777 equations and warn us that it will reasonably approximate the system for no more than 130 years and as he is infinitely good , He would give us the error bars .
Let’s suppose farther that we are able to study the behaviour of the solutions of this system and prove that it presents an attractor .
When I am talking about “solutions” , I mean of course continuous solutions in Jerry’s sense .
This attractor being an invariant of the climate system we have now the certainty that ANY possible climate will be somewhere inside the attractor .
Of course given an initial condition we will not be able to select the trajectory of the system among the infinity of possible trajectories but we’ll know that it will be continuous and stay inside the attractor .
The question would be now if the perfect knowledge of the attractor is useful for something .
Well it depends .
If its topology is simple and its volume small (like a very thin hypertorus f.ex) then yes .
Indeed while the exact evolution of the system would be unknown , it would stay during short times in relatively small volumes of the phase space where the dimensions of the volume would give the uncertainty of the parameters .
If its topology is complex (f.ex fractal) and its volume large then no .
Indeed such a system would present many bifurcations and fast transitions from large volumes to other large volumes of the phase space .
In other words the spectrum of possible states would be so large that it would be of no practical use .

As the past data show us that the real case is the second one , even if there was an attractor and we knew it , this knowledge would be useless because knowing that the real Earth is somewhere between an ice ball and a desert ball (not mentionning jungle and water balls) and going unpredictably to the one or the other , is of no practical value .

kim

Sun’s output, over million year timescales, is pretty steady and very gradually rising.

H/t LS.
====

John F. Pittman

I guess gb took a day off. I will try to answer one of the questions I asked.
1. The nature of skill…the answer (emphasis mine)

Our confidence in climate models must therefore come from other sources. The judgement of whether a climate model is skilful or not does not come from its prediction of the future, but from its ability to replicate the mean climatic conditions, climate variability and transient changes for which we have observations, and from its ability to simulate well-understood climate processes.

The most telling points are “mean climatic conditions” and “simulate well-understood processes”. If skilful is the ability to predict mean and simulate, then Douglass and Koutsoyiannis need to be evaluted wrt this statement from The use of the multi-model ensemble in probabilistic climate projections BY CLAUDIA TEBALDI 1,* AND RETO KNUTTI 2.

Indications that Douglss approach should be considered as a correct approach

The idea that the performance of a forecast can be improved by averaging or combining results from multiple models is based on the fundamental assumption that errors tend to cancel if the models are independent, and thus uncertainty should decrease as the number of models increases…

Indeed, models are developed relatively independently by different groups around the world. However, models are also similar in many respects. All models have similar resolution, and thus can or cannot resolve the same processes. It is probable that the errors introduced into the models by the parametrization or the unresolved processes are similar across models. Models often use the same theoretical arguments for their parametrizations…The random errors will tend to cancel, while the ones common to many models will not. There might also be ‘unknown unknowns’, i.e. misrepresentations of processes, missing processes or uncertainties in processes that we are not aware of.
The problem gets worse when the datasets which are used to tune the model are identical to those used later to evaluate the performance of the model and derive model weights in multi-model averages. Model evaluation should ideally be performed on independent datasets. Otherwise, the possibility of circular reasoning arises: a model can agree well with observations simply because the very same observations have been used to derive or tune the model…

Model tuning is often a subjective process…Despite those difficulties, objective tuning methods, data assimilation and model evaluation on seasonal forecasts or in the context of weather prediction provide promising areas of research that have barely been explored with climate models so far…Fortuitous agreement of climate models with reanalysis products might therefore result to some degree from common biases in both climate models and reanalysis models.
Finally, some models are known to ignore certain processes. For example, in the most recent collection of simulations of the twentieth century, several models do not include variations in the solar and volcanic forcing, and therefore should not reproduce the observed warming trends and patterns correctly. Nevertheless, they are usually evaluated against the observed trends.

The real question is if Koutsoyiannis, can be ignored or assumed relevant.

gb said:

The authors refer to verification and validations studies, so people are working on it! Furthermore, they discuss the usefulness of ensemble simulations which implies that they think that predictability of the second kind is possible and that the internal variation is not arbitrary large. And when they talk about comparisons with observations they say ‘… all those activities have helped in improving the models, and have greatly increased our confidence that the models capture the most relevant processes …’ Nowhere they say that climate models are unphysical!

They are working on it. SO in this sense, Douglass’s methodology represents the science in its current state. And since we are “improving” our confidence about relevant processes then that whether the models are not falsifiable or verifiable, as in Koutsoyiannis, would be a direct counter to the claim that the models have captured enough of the relevant processes.

Douglass used the accepted methodoly for climate models…ensemble mean. Gavin’s response bounded this methodolgy when used by Douglass to any and all models, indirectly proving Koutsoyiannis’s point. The real argument by Gavin and stated in TEBALDI, AND KNUTTI, is simply that they seem to work. This is a shamanistic approach to the natural world, not the scientific approach.

The result of accepting such utterances means that climate models are without known skill, in the scientific sense…i.e. they just seem to work, but not necessarily too well as shown by Douglass.

Gerald Browning

Mr. Pete(#245),

I am using SUSE Linux with Konquerer as my web browser and the link seems to work?

Jerry

Scott-in-WA

There was this:

Scott-in-WA, #232: — After spending a year reading the arguments and counter-arguments concerning the validity and usefulness of the GCMs for climate prediction, I have reached the conclusion that without having a significantly better understanding of the actual physical processes operating within their actual physical systems, the modelers are simply chasing computational rainbows. ….What kinds of field experiments and field observations are necessary to gain a significantly better understanding of the actual physical processes operating within their actual physical systems? How much data, and of what kind, must be collected in the field, and how? What will this cost, and how much time will be needed to collect the data, to process it, and to interpret it?

And then there was this:

Tebaldi Paper (see Pittman #240): — For projections of future climate change over decades and longer, there is no verification period, and in a strict sense there will never be any, even if we wait for a century. The reason is that the emission scenario assumed as a boundary condition is very likely not followed in detail, so the observations from the single climate realizations will never be fully compatible with the boundary conditions and scenario assumptions made by the models. And even if the scenario were to be followed, waiting decades for a single verification dataset is clearly not an effective verification strategy. This might sound obvious, but it is important to note that climate projections, decades or longer in the future by definition, cannot be validated directly through observed changes.…….In fact, most models agree reasonably well with observations of the present-day mean climate and simulate a realistic warming over the twentieth century (of course, the specific performance depends on each model/ metric combination), yet their predictions diverge substantially for the twentyfirst century, even when forced with the same boundary conditions.

If I interpret the Tebaldi/Knutti paper correctly, then it will not be possible twenty years from now to use actual field observations of actual physical processes to validate the predictive skill of today’s climate models, including today’s prediction datasets for future climate behavior.

If this is indeed the case, then it raises the most obvious and tortuous questions, the most important being, “Is this really science?”

It is safe to say that as far as the world’s carbon growth scenarios go, the rate of growth will likely continue at current rates and will probably even accelerate.

So in reality, the Great Experiment will go forward, C02 levels will continue to rise, and now we have to ask the question, what constructive role will the GCMs play twenty years from now in explaining what actually happened over that two-decade timeframe?

I think we would be just as well off today in the year 2008 if we recognize that the creators of these models have become, for all practical purposes, programmers for a new class of pseudo-scientific video game.

Here is what we should do. We should combine all the existing code from all the most popular GCMs into one large, graphically-driven modeling program, one with numerous parameter and pathway options which the user can choose at various critical points in the program.

What should it be called? How about ….. Grand Theft, Climate.

Neil Haven

Jerry

re: Lynch & Clark

I stepped through the Lynch & Clark energy and enstrophy slides that Gavin suggested. Perhaps you or someone more familiar with these things than I am could help me understand a little better?

As best I can tell from the slides, the 2D turbulence theory they reference predicts that injected energy should cause an *energy* cascade in the atmosphere upward to larger scales (smaller wave numbers) according to a power law with an exponent of -5/3. Injected energy should also (theoretically) lead to an *enstrophy* cascade to smaller scales with a rate of fall-off proportional to k^(-3).

However, actual observations (which were made more than 25 years ago!) show a -5/3 exponent at scales 600 km and below, indicative of an energy cascade dominating at smaller scales, and a -3 exponent at scales above 600 km, indicative of an enstrophy cascade dominating at larger scales (for east-west winds). This phenomenon they call a ‘kink’. The kink for north-south winds is at a scale an order of magnitude smaller. (Presumably due to disruptions by a more severe north-south temperature gradient?)

Questions: I am confused by the distinction here between energy and enstrophy. Isn’t enstrophy the energy in vorticity? By ‘energy’ do they mean the energy in irrotational velocity?

The model they reference (the ECMWF model) does not reproduce this kink. Lynch & Clark attribute this to excessive damping of energy. Thus, the model has too little energy at small scales.

They point to baroclinic instability as the energy-driver for the cascades and conjecture that below 600 km the k^(-5/3) slope is caused by a downscale energy cascade, probably augmented by an inverse energy cascade from storm-scale phenomena. Above 600 km scales the k^(-3) slope is dominated by an inverse enstrophy cascade.

Question: How similar is the atmospheric physics modeling in the ECMWF model to GCM models? Surely ECMWF (being used for weather modeling) is no worse than that of an average GCM?

Assuming the GCM and ECMWF models are similar in relevant respects, the significance of the Lynch and Clark discussion is that

A, Even a finely resolved weather model gets the gross energy spectrum of the atmosphere wrong;

B, Excessive damping at small scales contributes to the inaccuracy of the models;

C, The main driver for the shape of the energy spectrum occurs at a scale (baroclinic instabilities) which is below the resolution of current global climate models;

D, Energy and enstrophy cascades are operating in both downscale and upscale directions, and switching dominance, at scales which are not resolved by current global climate models.

If I have read this presentation correctly, the Lynch & Clark presentation does not seem to support the idea that the global climate models are rendering atmospheric physics with high fidelity. Nor does it seem to support the notion that Jerry is wrong to emphasize the unphysical nature of the energy damping in current models.

I would very much appreciate any corrections.

Neil Haven

gb,
Thank-you for the observations. By ‘rotation’ you are referring to coriolis forces? Are you saying the shape of the larger scale spectrum is determined by ‘quasi geostrophic turbulence’ *not* by inverse enstrophy cascade? Did I misread the presentation, or is this a point of disagreement? [Apologies for the elementary questions, but this is obviously not my bailiwick.]

Gerald Browning

Neil Haven (#256),

>Jerry
re: Lynch & Clark
I stepped through the Lynch & Clark energy and enstrophy slides that Gavin suggested. Perhaps you or someone more familiar with these things than I am could help me understand a little better?

I will give it a try.

>As best I can tell from the slides, the 2D turbulence theory they reference predicts that injected energy should cause an *energy* cascade in the atmosphere upward to larger scales (smaller wave numbers) according to a power law with an exponent of -5/3. Injected energy should also (theoretically) lead to an *enstrophy* cascade to smaller scales with a rate of fall-off proportional to k^(-3).

Recall that I provided a simple proof that one can obtain any solution one wants by an appropriate choice of forcing, even for an incorrect time dependent system. Thus one must be very careful with forcing, especially when model results are quoted. There are some very nice mathematical
results called the minimal scale estimates by Henshaw, Kreiss, and Reyna for the nonlinear, incompressible 2D and 3D NS equations (reference available on request). These estimates state how many spatial waves must be resolved in order to correctly compute the continuum solution for a given kinematic viscosity coefficient.
Numerical convergence spindown tests of these estimates in 2D and 3D have shown that the estimates are bang on (references available on request). The interesting thing about these convergence tests is that once the correct number of waves is resolved by a numerical model, additional resolution provides the same solution as predicted by the theory. And incorrect size or type (e.g. hyperviscosity) of dissipation provides a different solution.
I would at least peruse these articles (especially the numerical results) to gain a good understanding of these issues.

>However, actual observations (which were made more than 25 years ago!) show a -5/3 exponent at scales 600 km and below, indicative of an energy cascade dominating at smaller scales, and a -3 exponent at scales above 600 km, indicative of an enstrophy cascade dominating at larger scales (for east-west winds).

Note Lynch is very clear about the sparsity of observations, especially around the equator and in the Southern Hemisphere. This problem is also mentioned in Roger Daley’s text. Given such sparsity, I must admit that I am somewhat skeptical of any claims about a global spectrum or one at smaller scales.

> This phenomenon they call a ‘kink’. The kink for north-south winds is at a scale an order of magnitude smaller. (Presumably due to disruptions by a more severe north-south temperature gradient?)
Questions: I am confused by the distinction here between energy and enstrophy. Isn’t enstrophy the energy in vorticity? By ‘energy’ do they mean the energy in irrotational velocity?

Enstrophy is an integral of the square of the vorticity and this quantity is discussed in detail in the Henshaw, Kreiss, and Reyna manuscript.
Energy usually refers to the total energy, kinetic plus potential,
and is a conserved quantitative of the inviscid system of Eulerian equations (essentially the inviscid compressible NS equations).

>The model they reference (the ECMWF model) does not reproduce this kink. Lynch & Clark attribute this to excessive damping of energy. Thus, the model has too little energy at small scales.

Of course the excessive damping comes as no surprise to me. The amusing thing is that they talk about a random backscatter approach to pump energy into the spectrum near the bottom. I don’t find this very scientific.
Also note the resolution of the ECMWF model, i.e. T799 – the highest of any weather or climate model. But the forecast accuracy is barely better than models with much less resolution (see error plots on Canadian Meteorological site).

>They point to baroclinic instability as the energy-driver for the cascades and conjecture that below 600 km the k^(-5/3) slope is caused by a downscale energy cascade, probably augmented by an inverse energy cascade from storm-scale phenomena. Above 600 km scales the k^(-3) slope is dominated by an inverse enstrophy cascade.

Note that these are only theories with very little supporting evidence.
But if there was not an insertion of energy from some source at some scale, then the system would spin down. Thus this is the real scientific question. If there is a reverse cascade that is important and it is coming from scales less than 100 km that are not resolved by climate models, the whole current effort is nonsense.

>Question: How similar is the atmospheric physics modeling in the ECMWF model to GCM models? Surely ECMWF (being used for weather modeling) is no worse than that of an average GCM?

The ECMWF physics (tuning) is considered to be the best in the world.
The climate models must necessarily use cruder parameterizations because they cannot resolve the smaller scale features as in the ECMWF model or use smaller dissipation coefficients. Actually the dynamical core of the NCAR atmospheric component of the NCAR climate model was originally obtained from ECMWF, but ECMWF would not give out their physics. Thus the only difference is in the resolution and physics.

>Assuming the GCM and ECMWF models are similar in relevant respects, the significance of the Lynch and Clark discussion is that
A, Even a finely resolved weather model gets the gross energy spectrum of the atmosphere wrong;
B, Excessive damping at small scales contributes to the inaccuracy of the models;
C, The main driver for the shape of the energy spectrum occurs at a scale (baroclinic instabilities) which is below the resolution of current global climate models;
D, Energy and enstrophy cascades are operating in both downscale and upscale directions, and switching dominance, at scales which are not resolved by current global climate models.

Neil, I think you have a very good understanding of Lynch’s slides!
Certainly much better than Gavin. 🙂

>If I have read this presentation correctly, the Lynch & Clark presentation does not seem to support the idea that the global climate models are rendering atmospheric physics with high fidelity. Nor does it seem to support the notion that Jerry is wrong to emphasize the unphysical nature of the energy damping in current models.

Obviously I agree.

Jerry

John F. Pittman

Jerry you said in #260

But if there was not an insertion of energy from some source at some scale, then the system would spin down. Thus this is the real scientific question. If there is a reverse cascade that is important and it is coming from scales less than 100 km that are not resolved by climate models, the whole current effort is nonsense…and… Of course the excessive damping comes as no surprise to me. The amusing thing is that they talk about a random backscatter approach to pump energy into the spectrum near the bottom. I don’t find this very scientific.

To make sure I did not misinterpret Lynch or your remarks, when I read these two, this is what I conclude: If there is not an insertion of energy from some source at some scale, the system energy in the system will spin down. Because of excessive damping, causing a spin down, to get the model to come in agreement with the data, Lynch pumped energy into the system. Is this correct?

Gerald Browning

Raven (#222),

Sorry I missed your comment earlier. Your summary is in agreement with my
arguments.

Jerry

Tom Vonk

#260

Note Lynch is very clear about the sparsity of observations, especially around the equator and in the Southern Hemisphere. This problem is also mentioned in Roger Daley’s text. Given such sparsity, I must admit that I am somewhat skeptical of any claims about a global spectrum or one at smaller scales.

This was the part that really impressed me .
I never imagined that so little has been done and achieved about this major problem .
– the data is 23 years old and covers only a part of the 30°N – 55°N band .
– the data is coming from commercial flights so without any validation and controlled experimental setting
– the basic theory is 30 years old , the only “progress” seems to be this cryptical “stochastic backscattering” process that is supposed to heal the unrealistic overdamping at small scales
– the “kink” is not yet well understood

Perhaps the strangest thing is that both theory and models that are supposed to have universal validity are tuned to match data that covers only a small band of the Earth atmosphere .
It clearly must be extremely different in the tropics and as for the S hemisphere , all bets are on .
Where did all that research money go ?

gb

Tom Vonk,

These are measurements taken during 6000 flights over long distances at a height of 10 km. Can you imagine that it is extremely expensive to repeat them?

There is no reason to believe that the spectra are different on the S hemisphere.

What kind of controlled experiments are you proposing? It is not possible to create the same conditions in a lab.

Many rather smart people have been working on this problem in the last 30 years. It is not an easy one!

Please, tells us how we should solve the problem or what the solution is. You seem to think that it is easy to address.

John F. Pittman

Jerry #263
Yes, it helps. The statement where you talk about lifting up the spectrum is where I want to have a clear understanding, because my understanding is that this is a central idea to deciding about the whether the model is correct in physics or ill-posed.

Now Lynch said that Schutt recommended inserting energy at high wave numbers in a random backscatter approach to lift up the spectrum in the ECMWF model because it was losing too much energy due to unphysically large dissipation .

Gerald Browning

There has been considerable progress both in the understanding of turbulence (see above references)and in the understanding of balanced atmospheric flows. Not from numerical models, but from rigorous mathematics
and careful numerical convergence tests.

Jerry

John F. Pittman

Thanks Jerry.

The current ECMWF spectrum is thought to be wrong and the pumping of energy into the high wave numbers of the spectrum is just another attempt to make the spectrum look more “realistic”. There is no theory behind the method.

Confirms what I am trying to make sure that I understand.

Craig Loehle

Even ecosystem models, which are rather kludgy, never get negative animals in a patch…I am proud to say! I love how they call it “unphysical” instead of “wrong”.

Gerald Browning

Willis (#278),

Gavin always has some dodge for any rigorous scientific question.
And if not, RC selectively edits out comments or parts of comments that it does not want to address or to be seen. I have been banished from the site
and will state here that I have never seen such nonsense from people who are suppose to be scientists in my entire career.

Just to confirm my suspicions, I started to read the GISS ModelE manuscript. If any numerical analyst saw the kluges that are endemic
in this manuscript, they would die laughing. And isn’t it interesting that
no one has the computer resources to answer some very basic questions about the impact of these games? Pathetic.

Jerry

P.S. When heating caused a model to become nonhydrostatic due to overturning, the models arbitrarily would redistribute the heat
and reset the flow to be hydrostatic. Now there is a real scientific technique. I see that in the GISS model they now have used turbulence
(diffusion) to “solve” the problem. I cannot believe that Gavin can make the statements that he does knowing full well the GISS model is a complete
joke.

Andrew

I find the comparison with data from Albany, Florida to be quite interesting as a Floridian. May I offer the hypothesis the sharp cooling there is a land use effect? I got the idea from this presentation and talk by James J. O’Brien. He says “Florida is cooling and…this cooling is man-made.”

Gerald Browning

John F. Pittman (#280),

I will elaborate a bit more. When physical parameterizations that are not physically accurate are used in a model that must be kept in hydrostatic
balance, i.e. the model is based on a system that is not the correct system to describe the atmosphere for all scales of motion, the forcing can lead to overturning in a column. In other words, the parameterization would
lead to mass that is heavier above than below in the column. In order to prevent this from happening, the forcing, e.g. latent heating in the column, is arbitrarily redistributed to keep the overturning from occurring. This is clearly an ad hoc fix because in the real atmosphere such overturning, if it were to occur, would be handled by small scale turbulence that is not resolvable in a large scale model. Let me know if this helps.

Jerry

Gerald Browning

John F. Pittman (#284),

>Another question, is this re-distribution, the same part of the kinetic energy as when you responded to Gavin
Since this is about half the forcing for a doubling of CO2,
or is it another error?

I don’t believe this was a response by me? If you do a google search on convective adjustment you obtain

convective adjustment-A method of representing unresolved convection in atmospheric models by imposing large-scale vertical profiles when convection occurs.
As originally developed, convective adjustment was applied when modeled lapse rates became adiabatically unstable. New temperatures were calculated for unstable layers by conserving static energy and imposing an adiabatic lapse rate. If, in addition, humidities exceeded saturation, they were adjusted to saturation, with excess water removed as precipitation. A related adjustment, (stable saturated adjustment), for stable layers with water vapor exceeding saturation, returned them to saturation, also conserving energy. More recently, convective adjustments have been developed that adjust to empirically based lapse rates, rather than adiabatic lapse rates, while still maintaining energy conservation. Convective adjustment is generally applied to temperature and humidity but, in principle, can also be applied to other fields affected by convection.

>How is this energy, or forced hydrostatic balance related to the “sponge layer” or
excessive damping
, I believe you named it.

The excessive damping is a horizontal dissipation operator (many times hyperviscosity) typically applied at all grid points. The sponge layer is another type of dissipation applied near the upper lid of the model to artificially damp outgoing gravity waves. High wave numbers of the spatial spectrum are also chopped (set to zero) to stabilize the pseudo spectral method. The can considerably lower the stated accuracy of the pseudo spectral method.

>Is the hydrostatic klug factor related to
divergence along a particular direction might lead to temporarily negative gridbox masses
?

This sounds like it is due to horizontal advection that is a different mechanism.

Do you begin to get the feeling that the modelers resort to a myriad
of games in order to extend the period of integration beyond a
reasonable length of time, i.e. beyond a short term forecast?

Jerry

John F. Pittman

Jerry said:

Do you begin to get the feeling that the modelers resort to a myriad of games in order to extend the period of integration beyond a reasonable length of time, i.e. beyond a short term forecast?

Yes, that is why I wanted to as specific in my understanding as I could reasonably be. Any one of these “games” by itself is enough to raise serious counter arguments to say what Gavin has been stating. Thank you for your help.

It was W.E. that said

> 4. What is the usual reason for the energy imbalance?

Any decrease of KE in the dynamics goes to heat. It’s a very small
term but at the global scale it’s an energy term that needs to be counted.

It seems Willis has a few points about kludge factors.

I can only sympathize with Pat’s comment. I have found the CA folks rough but attentive. The RC folks seem to be pernicously hard-headed about straw-man and irrelevant side track arguments. Though I would hope that Pat adds to CA’s “Lost at Sea” and other threads as to whether his model will be more accurate without adjustment with the temperature corrections going on. A number of CA posters are wondering about the impact to the aerosol question.

John F. Pittman

Pat #288. I once got in a discussion with Ray Ladbury about the precision and accuracy of what IPCC had in their reports, and what could be attributed to natural and manmade causes. Ray believes that the signal is detectable and is manmade. That there is a clear confirmation, not derivation, the models represent confirmation of the signal. I do not see that the signal has been confirmed one way or the other. But I note that Ray has on several occasions worded his responses to indicate that the signal is known and has been measured, despite the possible inaccuracies or imprecisions, which is what I made a mistake of trying to learn on RC. The folks here on CA actually discuss thoughts with each other.

Andrew

288 (Pat Frank): Don’t be surprised if that’s the last comment your allowed to make. If it gets through at all. You should never suggest that the Iris Hypothesis may be correct!

289 (John F. Pittman): I suspect many RC commenters are scientists in other fields who have no understanding of the science what-so-ever, but merely put there faith in their fellow scientists, no matter how counterintuitive the statements they make are. Sure, a thermometer can’t distinguish between mankind and nature, but if scientists say they can, well, scientists would never lie! Then, of course, is the feeling that if your up against the “bad guys”, the right wingers, the corporations, big oil, you can’t be wrong (or it doesn’t matter if you are) becuase you are morally right. For myself, I find this to be an attitude that makes a mockery of science. I firmly stand by the old saying “Extraordinary claims require extraordinary evidence.”

James

#290 (Willis)

“…In other words, despite the fact that their cloud representation is way off (59% areal coverage modeled, 69% measured) and is parameterized (by specifying ad-hoc the conditions at which clouds are supposed to form), their model is still accurate in measuring the difference in forcing between say, a run with CO2 doubled and a run with CO2 held steady.”

Can you please clarify Gavin’s claim for me? Is it:

a) Cloud formation doesn’t change in the presence of an external forcing from CO2.

b) The CO2-induced changes in cloud formation from a base of 59% are equal to the change(s) from a base of 69%. And since the incremental changes are the same in either case, the absolute error in baseline doesn’t matter.

c) Other?

Also, if possible, could you please post a link to the source(s) for your comparison of Planet Earth vs Planet GISS. I know you’ve posted it before, but one was a dead link, and I’m having trouble finding the other occurences.

Best,

James

Willis Eschenbach

I think you want “Present day atmospheric simulations using GISS ModelE: Comparison to in-situ, satellite and reanalysis data”, available here

My understanding of what Gavin said is like your “b”. It was that, although things are in error in absolute terms, they are correct in relative terms. For example, suppose you want to model a car, and see what happens when you increase the fuel by some amount. Now, the exact modeled value for the car speed given a certain amount of fuel might be off.

But my understanding of the processes, my calculation of the conversion process of fuel to MPH, might be good enough so that the various changes from a given change in fuel would be reasonable, even though some absolute values might be off.

And in fact every model runs on just this assumption, that there are things that we can safely ignore and things that we have to pay close attention to.

I’d need a lot of supporting evidence, however, before I’d believe that a climate model with parameterized cloud formation could properly model the result of a given change in forcing. There are too many interactions, too many feedbacks, to just assume that. You’d have to prove that before I’d buy it.

Gavin, of course, says something like “But look at how well our model handles Pinatubo”, which is true. But he thinks that means something. Me, I think that the ability to correctly represent transient events is a much simpler problem than representing long-term evolutions in what I see as a naturally equilibrated system.

w.

Gerald Browning

Willis (#295),

Satellite data is not in situ and neither is reanalysis data.
The former is a blend of surface info (if it exists) and satellite radiance info. The accuracy of the transformation of radiances to model variables is
a very questionable procedure, especially in the presence of clouds.
The latter is a blend of model and observational data and can be completely in error, especially near the equator where there are few obs and the physics is not understood.

Note that GISS receives money from NASA. I was once told that anyone that
criticized NASA would have their funds chopped. I doubt that GISS is going to criticize the satellite data altough there has been an extensive discussion of its poor quality on this site.

Jerry

Willis Eschenbach

Jerry, Gavin doesn’t deny that the models are tuned … he just claims that there’s not many tuning knobs. Six, if I recall correctly. Riiiiiight …

See the discussion on the Briggs site.

w.

PS – I love their statement about albedo. The model is more than “somewhat” tuned for albedo, it is entirely tuned for albedo and for global radiation balance … the report sez:

The model is tuned (using the threshold relative humidity
U00 for the initiation of ice and water clouds) to
be in global radiative balance (i.e., net radiation at
TOA within 0.5 W m 2 of zero) and a reasonable
planetary albedo (between 29% and 31%) for the control
run simulations. In these experiments we use U00
0.59, 0.57, and 0.59 for ice clouds and 0.82, 0.82, and
0.83 for water clouds in M20, F20, and M23, respectively.

The interesting part to me is that when their clouds are tuned for the proper albedo (about 30%) and to achieve global radiation balance, the cloud cover is way low (58% vs 69%, see Table 3, p 159). If that were my model, I’d be disassembling it to see why the huge error … but they just carry on as if everything were just fine.