Bishop Hill Uncertain uncertainty
Mar 13, 2012 Climate: Models Richard Rood's article about uncertainty in climate projections is a few weeks old now, but I came across it only today after someone tweeted a link to it. Rood is trying to make the case that:
the uncertainty in climate projections associated with the physical climate model is smaller than the uncertainty associated with the models of emission scenarios that are used to project carbon dioxide emissions.
His argument seems to rest partly on the fact that climate models include well-understood physical laws at their heart, while economic models are much more empirical. This argument seems to me to be somewhat spurious. The fact that an aeroplane includes a number of transistors, whose behaviour is well-understood, does not make it necessarily more likely to fly than one that doesn't.
He argues that the spread in the models would be much less if it were not for the different economic scenarios that feed them. This seems flawed to me. Rood argues that the spread in the models represents "simple estimate of uncertainty". I'm not sure this is right. To the extent that the models make the same erroneous assumptions and have the same unknown unknowns, surely the climate model uncertainty is much larger?
Reader Comments (58)
"By “physical climate model” I mean a mathematical representation based on the laws of physics. Most simply, in this case, how is solar energy absorbed by the Earth, redistributed, and then emitted back to space? More generally, laws that govern physics, chemistry and biology are incorporated into climate models."
"Based on the laws of physics" is deliberate use of ambiguity. Does "based on the laws of physics" mean "based on textbook expositions of the laws of physics" or " "based on rigorously formulated physical hypotheses that have been selected for the specific purposes of climate science and that have been well confirmed?" If it means the latter then the rigorously formulated set of hypotheses can be presented to us apart from computer code and we can pass judgement on them. Given that set of hypotheses, I am sure that we would gravitate to those that express relationships between rising CO2 concentrations and the behavior of clouds. If it means the former then it means nothing. Climate scientists always wrap themselves in the good name of physics even though they do not employ genuine physical hypotheses at all. If they had them, they would have put them on the table long ago. In climate science, models are an excuse for using the honorific "scientist."
The models are prisoners of the assumption made by the IPCC that the global temperature increase in the late 20th Century was very probably a result of increasing atmospheric CO2. This forces all models to concentrate on radiative heat transfer as the major driver of heat loss from the planet and overlooks the enormous impact of atmospheric conduction and convection in the process of transporting heat to the TOA, from where radiation is the driver. Whilst the behaviour of CO2 as an absorber (and quantised emitter) of thermal radiation in a closed system is well known, it is by no means clear that its behaviour in an open system is understand.
This is compounded with a poor, probably incorrect, treatment of cloud albedo in limiting incoming energy, little or no consideration of the impact of the oceans or the vast refrigeration systems associated with the polar regions and no appreciation of the role the sun itself plays in all this, the models are thus little less than imaginative playthings and no amount of running and re-running a variety of multi-adjustable- constant- containing 'scenarios' provides any guide to future reality. It is simply delusional.
The behaviour of CO2 in a closed system is not well known. I suspect most thermalisation is probably heterogeneous and the experiment absolutely to disprove this is extraordinarily difficult. Until it is done, you can't assume direct thermalisation.
Some top minds are investigating this. Nahle is reportedly concentrating on van der Waals interactions. Happer, an IR specialist, warned in 1993 not to assume direct thermalisation when he resigned as Director of research of the US DoE so he did not have to lie about this basic bit of physics..
Billy Liar; thank you for the Laven paper. The Glory is caused by internal reflection, no dispute in that. One question is why does it only appear from clouds when the observer is observing it as part of the shadow of observer or a structure within which the observer is placed? Another question is why does such backscattering increase when you have strongly bimodal droplet size distributions?
The latter is my input and it's why rain clouds are dark underneath, not the climate science explanation of small droplets and surface reflection which is the Hansen justification that present net AIE conveniently cancels out all present net AGW so as to explain no atmospheric temperature change.
I just hope climate scientists who read this Hansen statement realise how unlikely it is to be true.
sHx said:
"I instantly thought of my good professor who was the only -and very lonely- epistemologist at the university."
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Nice. Getting a Roy Orbison reference into a discussion on models is uber cool!
Rumsfeld is not my favourite person, but being pilloried for stating the obvious about knowledge was unfair. In fact, it made me realise that he is a lot smarter and more humble than his public persona suggests.
As several PPs have eloquently demonstrated, averaging is mostly bunkum. It goes back to the old example of having one hand in ice and the other in fire to produce a temperature comfort figure.
Having worked with economic models quite often over the years, I dispute that they are completely useless. But, the way to make them useful is to exercise serious quality control (i.e., only even consider the best of the best); know what the parameters are; keep the variables to a minimum of measurable inputs/outputs; and constantly do reality checks against the real world. It is feasible to model what an increase or decrease in interest rates will do in a closed system, for example. Going beyond those parameters is straight into Apache Territory.
"we averaged from the models, but the A1F1, the "we all get rich" scenario, goes to 4.45,"
That's not quite right. A1F1 is notthe "when we all get rich" model.
A1 is that model,. All of the variations , F1, T and so on, are descriptions of the way in which we get rich.
F1, for example, assumes that we base our economy on coal. T that we end up using much more hydro, solar etc.
Note, none of these models, none at all, include any mitigation attempts. No carbon taxes, planning, subsidies, FITs etc. The difference between the different A1 s is very much just which turn technology takes quite naturally.
Further, note that A1T produces one of the lowest emissions and thus temperature outcomes. Essentially, globalised capitalism plus low (not no, but low) carbon energy solves the problem.
One of the remarkable features of the dramatic influence of CO2-based political campaigns is how little resistance and vetting their assertions and foundations have received from governments. Despite declaring the issues to be important, nay crucial, they seem only to have funded reiteration of the tenets, exploration of the effects, and sundry carbon-related financial and energy ventures. A new headache tablet brought to market would have had more government-mandated examination and hurdles to pass.
Pielke Snr and Wilby have been pursuing the pharmaceutical analogy. Here is one of their suggestions for a sign to be prominently displayed, I presume, whenever the referred-to climate model outputs are published:
'“The multi-decadal regional climate model results presented in this paper have not shown skill at predicting changes in multi-decadal climate statistics. The model results in our study should not be used to quantify the envelope of the risks from climate to societal and environmental resources in the coming decades. Our model sensitivity results are provided only to assist in improving our understanding of climate processes. ”
http://pielkeclimatesci.wordpress.com/2012/03/14/climate-science-malpractice-the-promotion-of-multi-decadal-regional-climate-model-projections-as-skillfull/
Tim Worstall, thank you for the correction. I plead tiredness :)
I was going to write "the better living through Coal scenario", thought that was too flippant, intended "we all get rich burning carbon scenario", and omitted the method.