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Posted by Jeff Id on December 11, 2010
Judith has yet another nice post on CO2 sensitivity. Her blog has quickly gained celebrity status although I’ve heard complaint that too may ‘skeptics’ are visiting. I’m not sure why a questioner is a bad thing.
My guess is that several here could add to the conversation. It will be interesting to see how this thread will develop.
Brian H said
It all circles back around to the implicit/explicit invoking of “radiative equilibrium”. No matter how many times people like G&T and everyone else with a grain of sense reminds them that their “energy equation” has lots of other terms in it, this keeps coming back.
Tweets that mention Judith Curry on CO2 « the Air Vent -- Topsy.com said
[…] This post was mentioned on Twitter by Science Blog News, C Jenkins. C Jenkins said: Judith Curry on CO2 http://goo.gl/fb/AOZxr […]
Steve Fitzpatrick said
Judith raises interesting questions… which seem to me impossible to answer. There is, and can never be, a no “no-feedback case”. Tilting at windmills, Donna Quixote.
DeNihilist said
Has anyone looked at the IR absorbtion from a quantom angle? ie – could be a wave or a particle. It seems that only particles are being addressed.
Carrick said
Steve Fitzpatrick:
Just because it’s not a direct observable doesn’t mean it’s not a useful quantity. It’s calculable from first principles using measurement.
As Judith says:
Steve Fitzpatrick said
Carrick #5,
I just don’t see how the no-feedback sensitivity is terribly useful in determining the net sensitivity, even if the no-feedback sensitivity could be accurately calculated. The typical estimated values of 1C – 1.2C per doubling are probably as good as needed, in that they set a reasonable lower bound for net climate sensitivity. Whatever the correct hypothetical value is, it is far less important than the size of feedbacks. I disagree with Judith about “can presumably be calculated with certainty”; convective transport has to be important, but any estimate of convective transport that does not include condensation/cloud formation will be way off.
kim said
I think I’ve never heard so loud
The quiet message in a cloud
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Mark T said
Steve,
FYI: not that this what Carrick is getting at, but, to determine closed-loop gain of a feedback system yyou first calculate the open-loop gain.
Mark
Carrick said
Mark T, that was the generally direction I was heading…
If you know the “no feed back” sensitivity (has to be calculated, not measured) and “environmental” sensitivity (this is either modeled or calculated), then the ratio of these is the net gain G = 1/(1-f) where f is the net feedback of the system.
Steve F, I’m pretty sure clouds and their response to changes in CO2 are considered part of the feedback system. You can bring that issue up on Judith’s blog if you already haven’t.
Carrick said
gr…
Meant to say “this is either modeled or measured.
Steve Fitzpatrick said
Carrick,
“I’m pretty sure clouds and their response to changes in CO2 are considered part of the feedback system.”
Yes, for certain, but that is my point. The heat transported by convection can only be accurately estimated in the case that the convection is driven in large part by latent heat. But that means clouds form, which are considered a source of multiple feedbacks. I suppose you could make believe that you have a driving force for convection equal to that for moist convection, but that clouds do not form and added water vapor doesn’t absorb infrared; I’m not sure how useful that is.
Knowing (roughly) the top of troposphere temperature increase for a doubling of CO2 seems to me enough.
Howard said
Carrick:
If the increased heat from increased CO2 results in work being performed, does the portion of that work not being converted back into heat constitute a negative feedback?
Thanks
Carrick said
Steve F:
Nor could it be considered a feedback. Cloud formation certainly would be considered a feedback, because it affects the Earth’s albedo (negative feedback), and because it can block infrared (positive feedback).
Howard:
Not in my language anyway (I realize different fields use the terms slightly differently). You might ask that on Judith’s blog, see what they say.
Steve Fitzpatrick said
Mark T,
“FYI: not that this what Carrick is getting at, but, to determine closed-loop gain of a feedback system you first calculate the open-loop gain.”
Sure, but it is not so simple as a control loop. Judith points out that heat leaves the surface in a number of different ways (radiation, convection, evaporative cooling/latent heat), which varies a lot based on local atmospheric and surface conditions. The problem is that a large portion of total transport (evaporative cooling and the strong convection driven by condensation along the moist adiabat) inevitably cause to the formation of clouds…. that is, feedback. In other words, to calculate the ‘open loop’ processes, you have no choice but to cause cloud and water vapor feed-backs. You can arbitrarily choose to exclude processes like condensation and generate what you then define as ‘the no feedback case’, but excluding physical processes which are an inevitable consequence of the processes you want to include in a hypothetical ‘no feedback’ heat transport seems to me, well, just silly, and certainly irrelevant to the real issue: what is the net sensitivity? IMHO, tilting at windmills.
Carrick said
Steve F, remove the water vapor and the cloud feedback is not inevitable. How useful the metric is may be a point of debate, but the fact it can be calculated to reasonable accuracy, I don’t think can be disputed.
The ultimate judge of its utility would be the people in the field, and not onlookers like ourselves.
TGSG said
“”Steve F, remove the water vapor and the cloud feedback is not inevitable. “”
You mean here on Mother Earth, or in a pretend universe?
Carrick said
TGSG:
It’s the same universe, silly-type person, whether or not the Earth has water vapor. You can do the calculation using the same laws of physics that govern our universe with or without water vapor. Not any different really than assuming circular planetary orbits (then computing the perterbation on that to give the real orbit) or a host of other approximations that get used as an intermediate to a more exact result.
chris y said
re 36, Steve Fitzpatrick- “The typical estimated values of 1C – 1.2C per doubling are probably as good as needed, in that they set a reasonable lower bound for net climate sensitivity.”
It is a lower bound only if the net feedback is assumed to be positive. If the net feedback is negative, then the no-feedback sensitivity is an upper bound.
Mark T said
I never said it was easy or even possible, I just said that is what is necessary to do the actual calculation, which was what Carrick was referring to.
That’s something that needs better exposition, IMO: the fundamentals of feedback control systems.
Mark
Shub Niggurath said
When studying a complex system containing emergent phenomena, how is it useful to start off with imaginary concepts and assume them to be building blocks?
Carrick said
Shub:
We do it all the time of course sometimes it can end up with misleading results (spherical Earth vs spherical cow).
For a particular quantity, the question of utility is better left to the people who are using that quantity than to try and guess.
Shub Niggurath said
He he. What is ‘useful’ at a given point in understanding something does not have to bear any relation to whether such a concept is truly a facet of reality.
Brian H said
Chris Y;
Yes, algebra must be honoured:
if f=-x
then
G = 1/(1-f) = 1/(1+x).
If x is about 100, then f = -100, and then G is about .01.
Or if f >1, then sensitivity is negative. If x = -2, then G = 1/-1 = -1.
😉
Carrick said
Shub:
Shub, I beg to differ.
Even spherical cows are very useful (that is they perform a function). They make us chuckle.
Useful is a different question than meaningful and/or misleading. I admit that I’m not qualified to have an opinion on how meaningful or misleading it is, though I can at least imagine a way one can compute it using atomic physics measurements and a simple moist-air convective 1-layer model.
I will say that there is lot of terminology, as it gets used in climate, that seems like an abuse of language to me. Not only is that confusing, it could end up being misleading.
(In my parlance, CO2 is a “parametric forcing”… the physics of which are very different than an external forcing, even though climate scientists appear to treat them all the same.)
Shub Niggurath said
Carrick,
When we make useful approximations (spherical cow), we implicitly declare we are doing so to gain understanding that can be obtained due to the approximation, but do not care for knowledge to be gained beyond that frontier, at least for the moment.
So, we know spherical cows do not exist. We still use it as a construct. But we do not delude ourselves into thinking actual spherical cows exist.
Does a ‘no feedback sensitivity’ exist?
kim said
Yep, S, it’s basic physics, demonstrable in the lab. Some ol’ fart named Arrhenius made a stab at it back in the day in his thoroughly modern laboratory. Modern climatologists have just imagined what it is outside the laboratory, though. They, nor we, know, alas, and alack.
==================
kim said
er, don’t know. Or something.
==============
Kan said
Lacis et.al 2010 tried, what appears to me, to be a half-baked test of H2O sensitivity (tiny feedbacks), using the GISS GCM. They removed all the CO2 to see what happens.
I would love to see them run a 2xCo2 with no atmospheric H2O (none) test in the GISS model.
Spen said
Kim – the ‘ol fart Arrhenius’ also thought the sun was powered by coal!
stan said
Jeff,
Steve has another post about the team and how it had a climate journal in the back pocket. I suspect that the biggest impact of posts such as these are the effect they have on people like Curry. I wonder if we will ever get to a point where the team’s credibility will have taken so many hits that no reputable scientist will regard any of their work as reliable.
In climate science, more and more the team is beginning to resemble the stuxnet virus in the Iranian nuke facilities. The only way to move forward may be to tear down everything, throw it all out and start clean from the beginning.
Mark T said
I don’t know of any reputable scientists that regard their work as reliable now. Certainly not any engineers.
Mark
Geoff Sherrington said
Re Kim at 7, recalls Ogden Nash
I think that I shall never see a billboard lovely as a tree.
Perhaps, unless the billboards fall I’ll never see a tree at all.
I think I’ve never heard so loud, the quiet message in a cloud.
Perhaps, with thunderstorms allowed, the message will inform the crowd.
kim said
Like thunderclaps the
Audience applauds the truth.
Lightning Steve Mac strikes.
============
Nick Stokes said
“I think I’ve never heard so loud”
I had some fun googling that phrase.