*I have read of recent work in which historical temperature and forcing data are sued to constrain the value of climate sensitivity. Considering ” you can get different N-S solutions for identical “forcings”. The “forcings” alone don’t allow to find solutions” what is the practical utility of these studies? They develop a value for one solution but could there be other solutions with entirely different values.*

*Again jsut a layman’s question so please excuse it if it is merely a distraction.*

No yours is a very relevant question. It is actually at the center of the discussion and it is also exactly there that difficulties lie.

I will try to explain that in “layman terms”.

The studies you mention do not solve N-S equations. Actually they don’t solve any equations at all. They use an extremely simplified **equilibrium** model similar to the one in this thread where the variable is the GMT (global mean temperature).

In such models GMT directly depends on forcings so it is not really surprising that the conclusion is that …. GMT depends on forcing (only).

You will measure the huge difference between a realworld physical model and these simplifications when you note that :

– realworld model gives the fields (temperatures f.ex) in every point at any time. Simplified model gives only a global average with no way to verify if that average is right or not because the correspondence between fields and their averages is not one to one. In other words for an infinity of different fields (e.g for an infinity of different dynamics) there is the same average.

– realworld model focuses on the transport of energy (oceanic oscillations and currents) because this is the engine of the climate. Simplified models have no energy transport at all because spatial averaging erases any spatial variabilities. There is no Gulf stream and no POD in simplified models.

– realworld model is never in equilibrium. The energy balance is permanently overshooting and undershooting what provokes oscillations on all time scales (f.ex ENSO). Simplified models are (per definition) at or near equilibrium and never oscillate.

So why they do it, ask you.

Frankly I don’t know.

Perhaps simply because they can – it is easy and there is always a set of hypothesis where it works (like epicycles). It provides for infinite opportunities of publishing.

Or perhaps because (some) believe that energy transport doesn’t matter and the dynamics are uniquely determined by spatial averages.

Or perhaps because (some) make a bet of “all things being equal” and hope that the dynamics are all clustered in a small region of the attractor so that the averages don’t vary much.

There has been historically an irrational cult of GMT since the beginning – perhaps because it is easy to communicate and (supposedly) easy to measure. It is probably very hard to get out of this dead end and take the non linear dynamics of the real climate seriously.

]]>Carrick,

Isn’t this simple model suggestihg you don’t need cycles that things can adequately be explained by external forcing alone. The irony is that the GCM’s that try to include internal variations (arguably badly) actually make things worse! If you go with the idea that this simple model has some merit then it would seem that it strengthens the idea that internal variation is NOT contributing greatly to decadal+ variations. The shape of the 20th century temperature graph is well explained by the response to RCP4.5 external forcings alone.

]]>Could I ask a layman’s question.

Tom Vonk writes

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The exact “path” (the right word is the field which is a function f(x,t) defining a value of a parameter in every point and at any time) definitely matters for everything – both for local/instantaneous values and for any transformations thereof like f.ex averages..

It matters even more because the system is NEVER in any kind of equilibrium.

There are no “stochastical internal fluctuations” – the system is fully deterministic with a unique solution for the 5 equations.

The proof thereof is, like David Young also said, that you can get different N-S solutions for identical “forcings”. The “forcings” alone don’t allow to find solutions

====================

I have read of recent work in which historical temperature and forcing data are sued to constrain the value of climate sensitivity. Considering ” you can get different N-S solutions for identical “forcings”. The “forcings” alone don’t allow to find solutions” what is the practical utility of these studies? They develop a value for one solution but could there be other solutions with entirely different values.

Again jsut a layman’s question so please excuse it if it is merely a distraction.

]]>And the implications for GCMs are?

]]>This is not correct and my post was precisely designed to show why it was not correct.

Let’s restrict just to Navier Stokes which is the largest and most important part of climate dynamics.

N-S is a system of 5 non linear coupled PDEs that fully describes the dynamics of the system given some initial and boundary conditions.

3 for momentum conservation

1 for mass conservation

1 for energy conservation

Like David Young is rightly saying, energy conservation alone can give nothing because it is only 1 out of 5 equations.

Because 5 are necessary, talking only about GMT while neglecting the coupled momentum equations can give no solution or an infinity of solutions or anything in between.

The exact “path” (the right word is the field which is a function f(x,t) defining a value of a parameter in every point and at any time) definitely matters for everything – both for local/instantaneous values and for any transformations thereof like f.ex averages..

It matters even more because the system is NEVER in any kind of equilibrium.

There are no “stochastical internal fluctuations” – the system is fully deterministic with a unique solution for the 5 equations.

The proof thereof is, like David Young also said, that you can get different N-S solutions for identical “forcings”. The “forcings” alone don’t allow to find solutions.

The right way to analyse such systems are attractors.

]]>Craig, I think the problem here is that conservation of energy by itself is a weak constraint. There is also conservation of mass and momentum. These are the source of interesting nonlinear behaviour. It’s I think quite possible to get 2 different climates with identical forcings. We see this in solving the Navier-Stokes equations all the time. Adding complexity as would be required for climate usually makes things less well posed.

]]>fstembridge Posted Jul 31, 2013 at 11:56 AM:

CC writes: “We have increased our planet’s atmospheric insulating ability by over a third”

Really? got a cite for that?

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fstembridge, good catch,

my bad – I misspoke – sorry, let’s try that again.

I meant to say:

“we have increased our atmosphere’s insulation ‘medium’ by over a third.”

For our planet’s atmosphere 280 to 400ppm is a radical increase in such a short time span.

~

Exactly what that translates to in actual increased heat retention down here within our global heat distribution engine remains to be seen.

What the last few decades have taught us – is that this increasing matrix of insulating GHG components has produced an increase in temperatures/energy. Exact number is ?, so what?

Even the little warming we have experienced these past few decades has already resulted in a radical upswing in extreme infrastructure and food-supply damaging, people killing/dispossessing weather events. Who cares about exactly what speed it’s going, we already know it is going way the blazes too fast.

And why that attitude implying every scientist is trying to scam us?

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Greenhouse gases are for real; and scientists do have a detailed and reasonable understanding. Nothing totally exact, fuzzy edges for sure, but that’s how the real world and real life are. That’s why I believe what I see around here at CA is quite disingenuous… and a disservice to your/our children.

What is the point of the endless hostile contrived picking apart of inconsequential details while ignoring the gorilla in the room?

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PS.

CO2 a greenhouse gas is roughly analogous to “insulation” cloaking our planet. Or do you reject that? Sources?

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THE NOAA ANNUAL GREENHOUSE GAS INDEX (AGGI)

NOAA Earth System Research Laboratory

http://www.esrl.noaa.gov/gmd/aggi/

… “An externally imposed perturbation in the radiative energy budget of the Earth climate system, e.g. through changes in solar radiation, changes in the Earth albedo, or changes in atmospheric gases and aerosol particles.” …

The perturbation to direct climate forcing (also termed “radiative forcing”) that has the largest magnitude and the least scientific uncertainty is the forcing related to changes in long-lived and well mixed greenhouse gases, in particular carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and halogenated compounds (mainly CFCs).”

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https://www2.ucar.edu/climate/faq/how-much-carbon-dioxide-and-other-kinds-greenhouse-gas-already-atmosphere

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“We have increased our planet’s atmospheric insulating ability by over a third”

Really? got a cite for that?

]]>Funny, Craig, I was just now cross posting about a 2007 remark of yours (my last comment, on the Callendar thread) before seeing this comment of yours on GCMs. That is a remarkable coincidence….

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