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Discussion > Sense and sensitivity

I commend this lively and provocative new article to all who pass this way: Willis at WUWT

He is challenging presumptions about sensitivity which are at the heart of GCMs. By noting how the climate system seems to respond to volcanoes, he argues that it just does not work along the lines presumed by the models.

In other words, the current belief is that the climate can be modeled as a simple system, whose outputs (global average air temperatures) are a linear function of the SUM of all the various forcings from greenhouse gas changes, volcanoes, solar changes, aerosol changes, and the like. According to the theory, you simply take the total of all of the forcings, apply the magic formula, and your model predicts the future. Their canonical equation is:

Change in Temperature (∆T) = Change in Forcing (∆F) times Climate Sensitivity

In lieu of a more colorful term, let me say that’s highly unlikely. In my experience, complex natural systems are rarely that simply coupled from input to output. I say that after an eruption, the climate system actively responds to reductions in the incoming sunlight by altering various parts of the climate system to increase the amount of heat absorbed by other means. This rapidly brings the system back into equilibrium.

May 25, 2013 at 12:48 PM | Registered CommenterJohn Shade

Well, I thought it was not in dispute that CO2 absorbs radiation in some bands and emits it in another. Where is the trapped heat there. If it is emitted towards the surface, what happens to it then? What proportion of the heat is trapped and how much eventually escapes via radiation?
May 25, 2013 at 12:05 PM | rhoda


I wish I could find Richard Feynman's quotation that, if you oversimplify explanations of phsics, it is a form of lying.

I have the idea that "climate science" is taught in the tradition of geography lessons - you listen and you regurgitate. Rote learning, in other words.

"Carbon dioxide traps heat" "Tyndall (or Fourier) showed that carbon dioxide traps heat" are clearly lines its students are taught to learn by heart.

In trying to visualise what goes on in a climate scientist's mind when they repeat those lines, I imagine that they have some sort of picture of heat trying to get out but being being unable to escape, perhaps a bit like a lobster caught in a lobster pot.

Yet if you take the standard simplistic model for analysing the increase in average temperature due to the greenhouse effect (the Earth as a black body surrounded by a shell of greenhouse gas), there is no heat being trapped anywhere.

Incoming short wave radiation (or what remains after the immediate albedo reflection of a percentage) is absorbed by the Earth, approximated as a black body.

The Earth has, in the past, been raised to a sufficient temperature by incoming short wave radiation so that all is in equilibrium. The surface of the Earth re-radiates a sufficient total power so that the total radiation that emerges from the greenhouse layer exactly balances the incoming short wave radiation.

Everything is in balance (in the ghg model). Nothing is being heated, nothing is cooling. No heat is being "trapped". It's bollocks to say it is.

May 25, 2013 at 5:08 PM | Registered CommenterMartin A

Rote learning, in other words.

Perhaps that explains why a common retort by AGW proponents is "Go and read some science!".

Is that an expression that would be used by someone who has studied some branch of physics?

May 25, 2013 at 7:07 PM | Registered CommenterMartin A

The rather stupid and lazy hypothesis proposed by the AGW proponents links the 22 year period of rising temperature [out of the past 72 years of falling or stable temperature] with increased levels of CO2.

Using that same completely unscientific hypothesis one could claim the past 16 years of non increasing temperatures, with ever increasing CO2 levels, shows that CO2 has a negative effect on temperature by stopping the previous 22 year increase [which obviously was due to some other natural forcing]

Or, of course, one could conclude that CO2 has bugger all effect on temperature but makes a convenient political tool.

May 26, 2013 at 5:07 AM | Registered CommenterRKS

RKS - Yes, completely agree. My comment on Kate Willett's video posted on myclimateandme was:

I think the argument here can be summarised as “we can’t make any measurements that show warming is due to CO2 but the 0.8 degrees rise we have seen must have been caused by CO2, because we don’t know of anything else that could have caused it and it is, after all, a greenhouse gas”.

I understand that there has been no significant warming for 15+ years, although atmospheric CO2 has continued to rise.

Doesn’t it make sense to say now “well, we now see it could not have been that, because the warming has stopped, while the CO2 went on rising it. So it really must have been caused by something we don’t know about”?

Explanations such as “it is still warming but masked by something else we don’t know about” sound hollow. It is one thing without evidence being explained by a second thing without evidence.

I used to think there was at least some science in "climate science".

May 26, 2013 at 9:07 AM | Registered CommenterMartin A

Perhaps I should rephrase the question. How about 'What experimental evidence did you use to come to the conclusion that the whole logical train of CO2 warming is as described in the hypothesis?' And is that the best evidence there could have been?
May 24, 2013 at 5:39 PM rhoda

Well, it was always a forelorn hope that Big Climate Science would pop up and give firm experimental evidence.

I've pointed to the first of the Met Office's two arguments to assure us that CO2 causes AGW. The first was an argument from ignorance. Essentially "We don't know what else could have caused the warming (from 1960-1998) and that proves it was caused by CO2".


The second of the Met Offices's arguments is "Our climate models show that CO2 causes AGW". Some time ago, Richard Betts of the Met Office gave a reference here on BH to a Met Office paper said to confirm the warming effects of fossil-fuel CO2.

(I have stated before my belief that the Met Office models are inherently incapable of being validated in the sense normally applied to simulation models of physical systems. And the viewpoint that an unvalidated model illustrates a hypothesis; it does not provide evidence.)

They ran the simlation with CO2 switched off. Result: the simulated GAT did not track the actual.

They ran the simulation again with CO2 switched on. Result: the simulated GAT tracked the actual.

The result was used by IPCC

And is reproduced on the Met Office's My Climate and Me website:
Climate Change Conclusions

When climate scientists consider all the 'natural factors' that could be affecting our climate, the long-term temperature trend (green line) in the chart below is broadly flat. Introduce the effect of man-made greenhouse gases into the mix and the computer model produces a line that tracks almost directly onto the observed temperature rise.

Rhoda - there is the evidence provided by the Met Office and used to justify the Climate Change Act.

Are you now convinced?

May 28, 2013 at 5:29 PM | Registered CommenterMartin A

One thing I still can't really grasp is why so many people believe in the CO2 AGW hypothesis. From my point of view it falls into the plausible but very weak hypothesis that really needs a lot of supporting evidence before I even start to take it seriously. As pointed out by rhoda and Martin A the theory seems to be:
1) CO2 absorbs IR (I accept that) - 2) This leads to a radiation induced warming in the upper troposphere - 3) You can follow the current lapse rate down to the ground to give surface warming - 4) We don't know what else could cause the warming, and anyway fossil fuels are evil.... That seems to be about it.

In my mind this is weak in so many areas. As I said I except 1) but 2) is really quite flimsy reasoning mainly due to the fact that it isn't radiation that moves heat around the atmosphere but convection. I would at least like to see a basic derivation where convection is included in the model. As also pointed out by geronimo we can clearly see that CO2 is terrible at trapping heat. Just go to a dry hot arid area and feel the temperature drop rapidly when the sun goes down as the CO2 is doing a bad job trapping that heat. As everyone knows water vapour and cloud do a very good job of trapping heat at night. So it is clear to see that the water cycle is the dominant factor in 'trapping' heat in the atmosphere. Also it is clear that deserts (hot in the day and cold at night) with little water don't have the negative feedback caused by water in say Singapore (cooler during the day but warmer at night). To me this clearly shows the negative feedback that the water cycles causes in many ways through water vapour, clouds, rain , evaporation/condensation energy transfer into the upper atmosphere. On an even more basic note that implies negative feedback is the fact that everybody knows that heat rises. So even without other factors heating the air near the ground automatically leads to a situation where it tries to cool itself down. I think 3) is a very tenuous piece of reasoning that would need to be backed up by evidence. As I said convection and latent heat of evaporation/condensation moves a whole lot more energy around than radiation in the atmosphere. There is also the very basic fact mentioned that it is only the 'greenhouse' gases in the atmosphere that radiate in the IR and the do in fact radiate the energy away into space. Therefore it is definitely a correct thing to say, that the greenhouse gases do 'cool' the atmosphere in this way.

4) is a point where the IPCC for example quickly backed themselves into a corner by saying categorically it couldn't be the sun. I think the sun and longer term ocean oscillations can go along way in describing the temperature variations on the Earth. Going back to why do people believe the hypothesis so readily when if I gave that explanation to some scientists they would be highly sceptical without evidence to back it up. I'm not sure why people are so non-sceptical (gullible) but it just seems a huge leap of faith to go from a vaguely plausible hypothesis -> science is settled without any of the bits in between being covered.

Jun 1, 2013 at 11:59 AM | Unregistered CommenterRob Burton

Regarding the question and 'climate sensitivity' it seems a pretty wishy-washy and useless way to regard changes in temperature. Though, many other studies and articles on this site seem to regard it as an important concept. Does anyone know where it originally came from?

I was going to respond to Richards 97% thread but didn't really understand what he meant by it. You could probably stick me in the 3% camp if you wanted as I think it is as close enough to zero to not name any difference even if the basis of the AGW CO2 hypothesis is correct.

Jun 1, 2013 at 12:38 PM | Unregistered CommenterRob Burton

Rob - dunno where the idea of Climate Sensitivity (that, to my surprise, even AGW sceptics seem to take seriously and regard as a well-founded concept) came from.

But I think it is closely bound up with the notion of "forcing" (a term which I have noticed stimulates the gag reflex in some BH commenters). Forcing seems to me a totally concocted notion, capable of existing only in computer models, not in the physical world. Some time back Willis Eschenbach. at WUWT articulated pretty much the same reasons I take exception to it being used as if it were something established by physical measurement and verified experimentally.

Unlike the Dragon Slayers, who believe that radiative physics as taught in the 20th century is baloney, I have no problem with the simple GHE model of the Earth as a black body surrounded by a shell of greenhouse gas. But, as you say, heat is transported by convection (and other mechanisms) and the model involves overwhelming simplifications, so that to me it is nothing more than a plausibility argument at best. Yet an awful lot of people, including Met Office scientists, have learned to say "CO2 traps heats" and they truly believe it.

Judith Curry discussed whether there is a more convincing derivation of the GHE that (say) a physics graduate could make sense of. She concluded that there was the simple black body model and there were GCM's but nothing in between to provide an explanation of the GHE.

Jun 1, 2013 at 1:16 PM | Registered CommenterMartin A

I was going to respond to Richards 97% thread but didn't really understand what he meant by it. You could probably stick me in the 3% camp if you wanted as I think it is as close enough to zero to not name any difference even if the basis of the AGW CO2 hypothesis is correct.

Jun 1, 2013 at 12:38 PM | Rob Burton>>>>>>>>>>>>

I'm in agreement with that.

If the measured effect is indistinguishable from noise it is, in practice, irrelevant and a complete waste of valuable discussion time and effort. It is for that reason I find much of the lukewarm discussions little more than navel gazing. Perhaps, as I don't dispute the basic radiative properties of CO2, I'm a 'minutewarmist' although, as a practical person, I'm probably best described as a 'nonwarmist'.

Jun 1, 2013 at 2:52 PM | Registered CommenterRKS

Thanks John Shade for that reference to Willis at WUWT at the top of the page - very worthwhile. After four billion years I guess a week isn't so long to catch up :)

Jun 1, 2013 at 7:30 PM | Registered CommenterRichard Drake

Bumping this again as there are a couple of posts today to which it is relevant. To those who haven't been here before, I think my top comment here says most of what is still my position.

Jul 18, 2013 at 1:21 PM | Registered Commenterrhoda

My view of climate is that we’ve not yet scratched the surface of the things that make it tick. We’re like that brain surgeon the warmists talk about but we’re trying to make a snap judgement on the patient by looking at them walk into the hospital reception. What's the value of a diagnosis before we’ve even stopped to listen to the patient describe the symptoms? In fact I’m not even sure we’ve been to kiddie school, let alone qualified as brain surgeons.

I can’t judge papers like Scarfetta’s because bits of every paper I’ve read seem plausible but as with the warmist papers, plausible isn’t enough and only time is demonstrating if those theories are right or wrong. As for the statistics… well if I wanted to put that much time in I’d be getting paid for it.

I think the Sun has effects in many more ways than how shiny it is and it has it’s own complicated cycles going on. It may be affected in tiny ways that over millenia produce stuff that we've never even seen. My suspicion is that solar status is more to blame for a loopy jet stream than Arctic ice but that too may add another perturbation. I think that solar activity could vary cloud location as well as quantity and that in turn affects whether heat goes into the ocean or heats up the land. I think we need to be able to predict ocean phases and work out exactly where the heat moves too and from. I wonder if volcanoes vary depending upon latitude, wind direction, time of year, local weather, proximity to the oceans, etc. I think the number and size of storm events act as air conditioning. What is ENSO doing and why is it doing it? I don’t think the final calculation of climate will be a sum of the parts. It could be much more sophisticated with ANDs, ORs, NOTs and non linear relationships.

How many years of observations would be needed to untangle something like that? We haven't even had satellites for the full cycles of ocean phases, let alone a warming and cooling phase like the MWP followed by the LIA. And within all that mess, CO2 might be having an effect so it's too soon to say the effect is zero in the same way it's too soon to say it's large.

I don't blame the scientists for bringing CO2 to global attention. Peak energy concerns were probably valid. Renewables might one day be useful. However mankind isn't ready to give up fossil fuels. We're sitting on a whole heap of low CO2 fuel. The planet isn't co-operating temperature wise. CO2 reduction is hugely unfair on the poor. The science is not fit for the purpose it is being used. That's all the persuasion I need to be sceptical.

Jul 18, 2013 at 11:02 PM | Unregistered CommenterTinyCO2

Anyone like to post a tutorial on climate sensitivity?

It seems to me unvalidated climate sensitivity models are dependent on the results from other unvalidated models (GCMs) which are dependent on the results of other unvalidated models (radiative forcing).

Turtles Models all the way down.

Jul 18, 2013 at 11:08 PM | Registered CommenterMartin A


Damn! You made another superb post there hehe

Jul 19, 2013 at 12:41 AM | Registered CommenterDung

I pretty much agree with everything TinyCO2 said and everything Rhoda has said.
To even start to construct a Climate Sensitivity figure you would need to totally understand how our climate works. Others have already pointed out that we are nowhere near having that knowledge.
Even were it the case that you understood the whole climate system, you would consider a Climate Sensitivity figure to be useless standing on its own.
I do not know (or can not remember) the origin of the belief that the relationship of temperature to CO2 is logarithmic. However if it is logarithmic then the effect of CO2 on temperature would change with every increase in CO2. In addition there is the obvious implication that at some level of CO2 there would be no further warming (Climate Sensitivity is ZERO), did that happen already or if not when will it happen?
Considering the current hiatus in warming there are only two possible explanations:

CO2 is currently having no effect on temperature and all other effects balance out.

CO2 is having an effect but right now it is balanced out by other (so far) unexplained effects.

Since we do not have any evidence that CO2 is having any effect at all, Climate Sensitivity seems to be something that belongs in La La land not science and I am sad that others give it credence.

Jul 21, 2013 at 10:49 PM | Registered CommenterDung

Dung, you (and rhoda and I) are in the 3% of sceptics who think the concept of climate sensitivity is rubbish.

I imagine that the 97% who think it is a meangful concept that can be used to calculate future global temperature would point out to you that it applies when the system has eventually reached equilibrium, so carping on about what global temperature is currently doing does not invalidate the idea of CS.

Jul 22, 2013 at 2:20 PM | Registered CommenterMartin A

The Next Top Model?

"(...) In recent decades, Foreign Affairs' readers (and editors) have seen the nuclear winter melt down, the energy crisis metastasize into an oil glut, and the population bomb implode. This breathtaking string of global systems modeling fiascos leaves some analysts asking why climate models are deemed sacrosanct when variables as critical as the sensitivity of the climate to the doubling of carbon dioxide in the atmosphere have failed to converge on uncontroversial values.

Cambridge, Massachusetts"

Jul 22, 2013 at 2:25 PM | Registered CommenterMartin A


If it only applies when the system has reached equilibrium and they believe that situation has not yet arisen then why are they carping on about it?
By the way Rhoda has not said CS is rubbish, she has simply asked where is the evidence. Hopefully when she receives no evidence she will take the next step ^.^

Jul 22, 2013 at 9:45 PM | Registered CommenterDung

From a different thread:

" I don't see that emerging from the "climate sensitivity is bunk" camp"

I suppose I am a major contributor to that camp. (...)
Jul 22, 2013 at 1:53 PM rhoda

I rest my case.

Jul 22, 2013 at 10:59 PM | Registered CommenterMartin A

I'd say it may be bunk. Or more accurately I'd ask whether it is a valid and useful concept. In fact, that is what I asked in the first post here. It is in the nature of a challenge to those who employ the concept or accept it. Not a single one of them from any side of the debate has ever answered the challenge of explaining WHY it is a valid or useful concept. One has to wonder why that is.

Jul 23, 2013 at 9:57 AM | Registered Commenterrhoda

" One has to wonder why that is."

Well, I think it is because:

- They want it to be thought of as a useful and meaningful concept, so they are disinclined to ask the sort of awkward questions you insist on asking.

- 97% of climate scientists* think it is a useful and meaningful concept.

- That confirms (for 97% of climate scientists) that it really is a useful and meaningful concept.

* 97% of climate sceptics also, it seems.

My general experience in other fields is that anything that comes out of an unvalidated model should be treated as rubbish until such time as the model has been validated.

Jul 23, 2013 at 1:19 PM | Registered CommenterMartin A

Rhoda, I too think it may be bunk, every electrical engineer is taught about positive and negative feedbacks, but both are "controlled" in the sense that there is something in the feedback loop that keeps the feedback to the required level in the case of negative feedback then say 10% of the signal in anti-phase with the input signal. Positive feedback is the nitro-glycerine of the electrical engineering world because of it's tendency to go out of control. Now to climate.

If a rise in temperature causes more water vapour and that water vapour itself causes a rise in temperature I cannot see the mechanism in the climate system that stops that feedback loop, you could speculate there is one, say more water vapour implying more clouds, but at no point do I see anyone being able to say that a doubling of CO2 will give rise to a global temperature increase of 3C, because once that train leaves the station it will go on until it crashes. If there was such a climate sensitivity then records of the crashes would be apparent in the paleoclimate proxies, and there are none. This may, not for the first time, be my ignorance, but I do wish someone would explain to me why they think positive feedbacks will stop at a certain temperature.

Jul 23, 2013 at 2:08 PM | Unregistered Commentergeronimo



Not a single one of them from any side of the debate has ever answered the challenge of explaining WHY it is a valid or useful concept. One has to wonder why that is.

Well at the moment Climate Sensitivity models are giving answers that fit in with the skeptic view that there is no or very little AGW. Our comrades have suddenly ditched all need to stick to the facts and be objective, they are too busy being happy clappy about low CS :(

Jul 23, 2013 at 2:49 PM | Registered CommenterDung

We now know the reason for Uncle Steve's Climate Sensitivity model from the past. The opposition stated that a low CS model could not possibly predict today's climate so Steve gave them a low sensitivity model that did exactly that.
Does Steve think the model is sound? No he specifically states that he is not arguing that is a good model and just for good measure he adds that it is probably just good fortune that it produced the result that it did.
What exactly has Steve gained? A crap low sensitivity model is as useless as a crap high sensitivity model.
All the focus is on CS because the IPCC put CS at the centre of its CAGW claims. However there is a big problem here; the effect of CO2 in the atmosphere has never really been quantified, we do not really know whether it is huge, significant or negligible. We think the relationship with temperature is logarithmic but again that relationship has never been quantified.
There are a lot of theories and a lot of heavy maths flying around but why not look at the empirical evidence?
Even the hard core nuts at RC do not believe that when temperature increases at the start of an interglacial; CO2 is to blame. RC accept that some other effect is the cause and most likely Milankovitch cycles. Then RC claim that during the warming, the effect of CO2 kicks in and it is true that CO2 starts to rise during the warming. RC then go on to say that "maybe" the CO2 completed the job and the original cause fades away (with no evidence or theory to back that up).
Sticking with the RC theory; why is it that the warming ends quite abruptly and plateaus into the relatively steady temperature of the interglacial. Why is it that temperature plateaus when CO2 continues to rise for almost 1000 years? There is no way that CO2 is controlling temperature during this period. What is the Climate Sensitivity figure during this period, it would not be positive ^.^
If there is such a thing as Climate Sensitivity, shouldn't it be constant?
There are at least two explanations here and one of them is that the effect of CO2 is so tiny as to be irrelevant, the other is that at the atmospheric levels of CO2 involved; the effect of CO2 had become saturated.
The current hiatus in warming is again a time when CO2 is rising and temperature is not rising, if it continues then CS will equal zero.
All the empirical evidence points to a level somewhere around 200 ppm as the level above which CO2 has no effect.

Jul 28, 2013 at 9:45 PM | Registered CommenterDung