Climate model tuning
Climate model tuning
(OP)
http://www.mpimet.mpg.de/fileadmin/staff/klockedan...
"During a development stage global climate models have their
6 properties adjusted or tuned in various ways to best match the known state
7 of the Earth’s climate system. These desired properties are observables, such
8 as the radiation balance at the top of the atmosphere, the global mean tem-
9 perature, sea ice, clouds and wind fields. The tuning is typically performed
10 by adjusting uncertain, or even non-observable, parameters related to pro-
11 cesses not explicitly represented at the model grid resolution."
There's rather a lot in it, I haven't read it through yet. Some of the phrases concerning clouds are 'nicely' phrased.
"During a development stage global climate models have their
6 properties adjusted or tuned in various ways to best match the known state
7 of the Earth’s climate system. These desired properties are observables, such
8 as the radiation balance at the top of the atmosphere, the global mean tem-
9 perature, sea ice, clouds and wind fields. The tuning is typically performed
10 by adjusting uncertain, or even non-observable, parameters related to pro-
11 cesses not explicitly represented at the model grid resolution."
There's rather a lot in it, I haven't read it through yet. Some of the phrases concerning clouds are 'nicely' phrased.
Cheers
Greg Locock
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RE: Climate model tuning
RE: Climate model tuning
Quando Omni Flunkus Moritati
RE: Climate model tuning
RE: Climate model tuning
"The “knobs” are tuned to create a better representation of their specific aspects of the climate system. These adjustments can only be made in the range established by observations or peer-reviewed study." i must read the article to see how this tuning is different to matching the historical record. it'd be interesting reading to see how they address the different combinations of "knob position" that achieve the same match to the observation ...
Quando Omni Flunkus Moritati
RE: Climate model tuning
RE: Climate model tuning
if they're not tuning to match past climate record, how come ... "models are generally able to reproduce the observed 20th century warming of about 0.7 K, and details such as the years of cooling following the volcanic eruptions, e.g. Krakatau (1883) and Pinatubo (1991), are found in both the observed record and most of the model realizations."
"it is usually to be expected that improved performance arises not because uncertain or non-observable parameters match their intrinsic value – although this would clearly be desirable – rather that compensation among model errors is occurring."
this doesn't fill me with confidence about climate models.
Quando Omni Flunkus Moritati
RE: Climate model tuning
You get lucky sometimes.
RE: Climate model tuning
David Simpson, PE
MuleShoe Engineering
Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat
RE: Climate model tuning
I understand that some events can't fit in the model, but how would one know that the knob is not being adjusted for the results that owner wants in the future case?
Even if you think the model is correct, you should be concerned about the tuning going on. This can leave you with a very wrong result.
Question: How many climate models are being used to predict a result? Assuming some of them are wrong, or are being used wring, we should be able to come up with an avreage result. What is the standard devation of those models? What would be a confedence factor in the average results? And who wrong can they be?
I have to question everything, as a leap of faith should only apply to a religon.
RE: Climate model tuning
No, that's actually the easiest thing to account for, since it's a singular delta-function event, composed of a sudden introduction of heat, gases, and particulates, which can be inputted into the model, and the model should respond accordingly. This is not that different than modeling shock events in FEA programs. Pinatubo, in particular, should have been well instrumented and measured, as should have been the resulting climate afterwards, since everyone was looking for the perturbations. Pinatubo would then be input into the model, and the resultant climate effects should be relatively easier to compare against actual data.
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RE: Climate model tuning
also, it shows that the models are compared with the historical record, the inference being that a model that agrees with the historical record is "better".
Quando Omni Flunkus Moritati
RE: Climate model tuning
David Simpson, PE
MuleShoe Engineering
Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat
RE: Climate model tuning
I'm sure what you're getting at. How is a model that disagrees with historical records a good thing? btw, a copy of the article with graphics is here: http://www.readcube.com/articles/10.1029/2012MS000...?
The authors simply state "models are generally able to reproduce the observed 20th century warming of about 0.7 K, and details such as the years of cooling following the volcanic eruptions, e.g., Krakatau (1883) and Pinatubo (1991), are found in both the observed record and most of the model realizations."
Which, if they're supposed to match the historical records, requires that the models must account for the pertubations, particularly since both volcanic events are "natural."
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RE: Climate model tuning
When I said "very heavy hand on the controls" I meant that they put in actual data into the model for the days/weeks/months after the eruption. That is pretty heavy handed. Based on those specific interventions, 108 years after Pinetubo they would have had another similar sized event. If it happens in 5 years or 50 years or 150 years then the data for 2099 will be very wrong. I can simulate the event pretty easily, it is the timing that has me gobsmacked.
David Simpson, PE
MuleShoe Engineering
Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat
RE: Climate model tuning
That would be, at most, a one-time event. There's nothing that says it would, or need to, repeat on its own; that would simply be sophomoric, at best. Timing is simple. You create a time series of inputs that lasts the duration of the event and add them to the flow of the simulation. We do this sort of thing in engineering analyses routinely, to simulate discrete events. There's neither magic nor nefariousness involved; it's purely discrete math.
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RE: Climate model tuning
So for this example, you are trying to match a time series so you either discard the time period where the unusual event occurred from your calibration run before the run or after the run (i.e. discard partial data or partial results). It does no good to "match" history by feeding in the exact answers.
David Simpson, PE
MuleShoe Engineering
Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat
RE: Climate model tuning
But, since clouds are the least-understood meteorological and climactic process, and therefore cannot be managed by basic-physics in the models but rather by heavy-handed tuning, this miss is not surprising.
RE: Climate model tuning
Or maybe they have to have the temperatures drop prior to the activity in order to match the total thermal drop. Heavy-handed knob-fiddling. (All double-entendres intended).
RE: Climate model tuning
i think it shows that models are tuned to the historical record, despite contentions to the opposite.
Quando Omni Flunkus Moritati
RE: Climate model tuning
Granted, models that diverge greatly from historical data are re-examined but, again, the tuning is done to more accurately represent the subsystem, not as a blind attempt to match historical data.
From the paper:
RE: Climate model tuning
how does modelling these isolated events "improve sub-system representation" ?
another day in paradise, or is paradise one day closer ?
RE: Climate model tuning
However, dissipative self-organizing features such as thunderstorms or hurricanes/typhoons are intrinsic to the coupled atmosphere-ocean system and should not be forced but should be allowed to evolve.
One of the fascinating features of vulcanism is that they provide an excellent insight into how the coupled atmosphere-ocean system reacts in the short-term to step changes in incoming solar irradiance (via particulate/aerosol blocking). They provide excellent opportunities to learn about our world.
However, because the models poorly represent regional data (ref. IPCC), it is not surprising that they don't handle these regional effects, which can have global impact, well.