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Discussion > Sense and sensitivity

Apologies to Blackadder III from whom I stole the title.

Climate Sensitivity. Well, the issue about clmate sensitivity is, just how much is it? Is it a dangerous 6 degrees, or a benign 1 degree. That's the question, is it not? One which has taxed the minds of the team, the IPCC and the sceptics for a couple of decades now. Scarcely a day passes without a new paper or a rebuttal or a Press Release giving a new figure, or at least a refinement of the old. The climate sensitivity has become the battlefield of the clmate wars, the salient feature of the struggle between the warmists and the lukewarmers.

My object here is to pose a question. Is there really a meaningful figure for the expected temperature rise of the Earth for a doubling of CO2 in the atmosphere? Is it even a useful concept in our understanding of the climate? (I can see how useful a concept it is for the science policy folks, and for the sky-is-falling crowd.)

What's the problem? Anybody can see that if an increase in CO2 warms the planet then there must be a way of getting a handle on that in terms of numbers. Ditto for all the other players in the forcing canon. Aerosols, soot, non-radiative effects of H2O, solar and so on. Every one of them has a forcing in degrees per..well.. something or other, and when you sum the forcings you get a result which you can use to predict what is going to happens to temperatures. conversely, if you have a rough handle on what you think are the major forcings but not CO2, you can subtract the known from the measured trend to deduce the climate sensitivity due to CO2 and its feedbacks.

That last is the stuff of much debate right now. Should AR5 acknowledge a lower figure for CO2 based on newer observations and better data on other forcings? Are better statisitical interpretations of the evidence, more enlightened bayesian approaches, giving us a CS figure which is low enough for AGW not to be a concern but possibly even a net benefit? Well, they may be, but what if the concept is nothing more than just that?

But we've measured it, haven't we? We are only arguing about the magnitude, aren't we? Not in my view. What have we done when we have subtracted the known from the measured? Well, what we have left is not the bit we knew we didn't know, it is the sum of all the things we didn't know, whether we knew about them or not. It is expressed in terms of cliimate sensitivity to CO2, but all it really is is a part of a trend which might not BE a trend less a lot of other forcings none of which are definitely known to act on a straightforward non-interacting basis. The whole idea of cumulative forcings is suspect. OK, fine as a concept, but should that concept not need to be shown to be a valid way of looking at things before it is used to inform us?

Here is my null hypothesis. Each and every influence on temperatures acts at a point in time and space. It has immediate effects in terms of temperature and other non-temperature responses. What happens at one point affects what happens at others. There is no basis for assuming any sort of linear response without confirming observations. There is no basis for assuming that any observed linear response will be the same outside the observation space. You can have your forcings, but each will act only at a local level. There is no basis for assuming you can just sum them and get anytihng other than a transient effect on any observed parameter. What they integrate into is a global effect but it is only instantaneous. It has the effect of moving your long-term measure (eg. 'global average temperature') in a very short timescale. There is no basis for assuming any sort of long timescale, much less the century-scale periods we are talking about with a doubling of CO2. What you have may well be a random walk. Going up and down as the influences take it, each day influenced by the one before and serving only to set the start point for the one following. That's what you have, in your time series. Look for trends and you will find them. Apply forcings and you will see what looks like a response. But it is all an illusion.
You can see cycles? Well, of course you can. Humans are programmed to see patterns and persist in doing so when they are not there. But perhaps even the cycles and the correlations with this that or the other variable are no more than illusion themselves. Maybe nothing actually repeats. Except possibly onions.

Feb 4, 2013 at 2:43 PM | Registered Commenterrhoda

given that the Gavster has at least 4 definitions for sensitivity:

In practice, people often mean different things when they talk about sensitivity. For instance, the sensitivity only including the fast feedbacks (e.g. ignoring land ice and vegetation), or the sensitivity of a particular class of climate model (e.g. the ‘Charney sensitivity’), or the sensitivity of the whole system except the carbon cycle (the Earth System Sensitivity), or the transient sensitivity tied to a specific date or period of time (i.e. the Transient Climate Response (TCR) to 1% increasing CO2 after 70 years). As you might expect, these are all different and care needs to be taken to define terms before comparing things (there is a good discussion of the various definitions and their scope in the Palaeosens paper).

I am tempted to say that sensitivity is the equivalent of what mediaeval geographers wrote on maps - Here Be Dragons. In static terms, an injection of a GHG would result in a temperature rise....eventually. in a dynamic system such as the atmosphere, when these injections of gases are continual, in different places and lots of other unmodelled processes are going on...who knows what the outcome will be? Is sensitivity an absolute constant? Does it change over time and why?

it is just the scientific version of "something that is too complicated to measure or compute takes place". Zorita on jeff Id's blog said much the same thing a few years ago when he said that no one could model precisely what happened in the 1930s to make it such a hot decade. I do not understand why BBD and Rabett and Tobis and Pierrehumbert and other warmistas cling so hard to CO2 warming and high sensitivity.

Feb 4, 2013 at 6:54 PM | Unregistered Commenterdiogenes

Is there nobody to defend the idea of a universal CS and the validity of adding forcings arithmetically? We have all been taking the idea seriously for a good decade, but where is the justification? Why debate the value of CS when it may be an entirely hypothetical concept?

Feb 6, 2013 at 11:38 AM | Registered Commenterrhoda

You have to take the battle to where they want to fight it. Even if you think CS is meaningless, if they are using its magnitude as a weapon to beat you, it is tactical to take on that battle on their ground - even if you think it's pointless.

Feb 6, 2013 at 11:51 AM | Unregistered CommenterTheBigYinJames

Well, I'd say 'Show me' and they would have to come to my battlefield. But if we don't, if we take the position of so many on our side of accepting bad terms and trying to ameliorate them, like that economist bloke (Tim Worstall, just slipped my mind there) who accepts carbon tax and argues about the rate then we have given away most of our position first. Reminds me of Michael Foot's defence policy in the 1983 suicide note, let them invade and fight as a resistance.

Feb 6, 2013 at 12:16 PM | Registered Commenterrhoda

Well, I'd say 'Show me' and they would have to come to my battlefield.

Good luck with that.

This debate is typified by them NOT coming to your battlefield. So we have to take it to them, or not fight.

Feb 6, 2013 at 12:17 PM | Unregistered CommenterTheBigYinJames

Well, I can't play the dead bat if they won't bowl to me. but their entire schtick is NOT to argue with us but to tell us there is no debate or we are not qualified to be in it because we are not circularly-defined climate scientists. No tactic adopted by us has pinned the other side into backing up their assertions, they merely bypass us with their helpful media fellow travellers.

But that doesn't answer the question of the validity of CS. Someone who first mooted it must have justified it? No? Twice in the last week I'v heard people harking back to Arrhenius. Is that really the answer? Has nobody looked at it critically since?

Feb 6, 2013 at 12:35 PM | Registered Commenterrhoda

I'd be happy to have any of you come an join me over at Deltoid, where we've been having a long running discussion about 'ocean acidification' and the proof or otherwise thereof.

There are a few waverers there who are just beginning to wonder if their visceral 100% wholehearted belief in everything they are told by 'climate scientists' is correct. And that maybe 99.5% is the right number.

Others, however, are still wedded to the idea that the Living Saints from Climatology are perfect in every way, their every pronouncement is infallible and that anybody daring even to question their conclusions should be burnt at the stake - but in a carbon neutral way.

It is hard to imagine Phil Jones and Mike Mann having groupies .. but Deltoid is where they hang out. Eat your heart out Mick and Keef.

Feb 7, 2013 at 5:06 PM | Unregistered CommenterLatimer Alder

I'm bumping this in case anybody has found a real argument to justify using past CS as a value useful in predicting the future. I've heard nothing yet, but I may be too stubborn to see it.

Mar 17, 2013 at 8:58 PM | Registered Commenterrhoda

" justify using past CS as a value useful in predicting the future."

Scuse my ignorance but aren't past values of CS simply a matter for speculation?
If someone claims to have computed a value for past CS, in view of the complexity of the system and our ignorance of it, and our inability to validate such an estimate, aren't they just deluding themself? Is a prediction computed from a delusion anything other than a delusion squared?

[Quite apart from the point you have made that CS may well vary in time and space in unknown ways so that even if we had today's value it might not tell us much about next year's value.]

Mar 17, 2013 at 10:38 PM | Registered CommenterMartin A

I don't think there is any evidence for a long term climate sensitivity. We can see historical records showing increased temperatures of 1C, and there is no follow-on catastrophic rise in temperaturs. Hence the need to "get rid of the MWP". That there is some sensitivity is without doubt, because rising temperatures will cause more water vapour, which, as my live experiment shows keeps heat in the atmosphere ("live experiment" is sleeping in a tent overnight in the desters (no water vapour) and a beach in Thailand (lots of water vapour)). However, over a short period of time my hypothesis is that the sensitivity is reduced rapidly keeping the energy budget balanced. The most likely reason for this is nimbus clouds. The Met Office seem to want to have it all ways they tell us that we're going to have more rain because of global warming (true) but that the climate sensitivity is 433C and we're all going to fry (false because rain clouds cause negative feedbacks).

I agree with TBYJ though, stating there isn't any feedback will simply mean you're left out of the conversation there must be feedback, there is in all forms of life, the question is why climate scientist believe that, unique in all forms of surviving life, the climate has feedbacks which will destroy life as we know it. Since we've had a climate for 4.5 bn years or so it's not stupid to believe that it's feedbacks are benign.

Mar 19, 2013 at 6:05 AM | Unregistered Commentergeronimo

Can I give this one a bump? We have RB driving us down the deadend street of 97%, we have Kevin Anderson on another thread putting turbine techology into some daft time series whereby the rate of past efficiency improvements is somehow relevannt to future tech and THAT proves something or other about whether windmils will..well, I lost the will to live along with the thread of his argument.

So, while the warmists are here, would they like to read the thread above and put me right? Or the one about best evidence or experimental proof? Nothing but unanswered questions, and if you can't answer the questions of an Oxfordshire housewife how ever do you think you have a handle on GW, AGW or especially CAGW?

May 18, 2013 at 5:01 PM | Registered Commenterrhoda


Have you ever received even a partial answer to any of your questions?

If they cannot be answered, then, so far as I can see, there are large swathes of climate science that cannot make any realistic claim to be based on reality.

I think it would be quite useful to have all of your questions collated in a single posting.

May 18, 2013 at 10:36 PM | Registered CommenterMartin A

After a quick trawl for rhoda's questions, here are her BH discussion questions that I found. (most recent first, oldest last)

Can there be a positive water vapour


An experimental demo of GHE.

Much ado about nothing much

CO2 theory question

Best evidence: The story so far.

Where's my best evidence?

May 19, 2013 at 10:07 AM | Registered CommenterMartin A

Here be dynamite, if only we could find a way of igniting it.

Well done rhoda for all your work, and Martin A for that handy list.

I think I too am in the camp of nothing much is going on. But what a hard camp it is to win attention for!
- Not much chance of headlines in the mass media.
- Not an appealing basis for winning research grants.
- No scope for wowing and cowing audiences with tales of doom and gloom.
- No edge for the leftie to attack capitalism with, nor the greenie to denigrate technology.
- No consultancy opportunities to take advantage of the new and little known

Just a so far fruitless search to find any clothes on the emperors of alarm!

May 19, 2013 at 11:17 AM | Registered CommenterJohn Shade

I'm going to review all the questions Martin helpfully listed, but on this thread rather than bump all of them. First, positive water vapour feedback. There just was no argument proposed to support it. In fact we all missed the undisputed fact that in the absence of H2O, in dry places, diurnal temperature variations are rather lager than in wet places. Hence the presence of water does not enhance the signal. Pretty much QED, unless someone can propose a mechanism which explains that and gives a positive feedback but magically does not lead to a runaway.

First finding: There is no positive water vapour feedback. There is a high probability that there is a negative feedback.

May 20, 2013 at 6:09 PM | Registered Commenterrhoda

" First, positive water vapour feedback."

Of course!

We were so busy looking for evidence of +ve feedback that we never paused for a moment and said "OK, is there any evidence for negative feedback?" on the basis that if the feedback is -ve, that rules out it being +ve.

Maybe there is a lesson to be learned here.


"...unless someone can propose a mechanism which explains that and gives a positive feedback but magically does not lead to a runaway."

Moderate amounts of +ve feedback can enhance an effect without leading to runaway. But, as soon as you get even moderate amounts of enhancement of an effect, it then takes only a modest further increase in the +ve feedback to nudge the thing into instability.

Anyone who has played with systems involving positive feedback is painfully aware how easy it is for the slightest change to push the thing into instability. The idea of Nature engineering a system of positive feedback giving significant enhancement of an effect (greenhouse heating, in this case) but never overstepping the limits of stability, equates to essentially an impossibility to such people.

May 20, 2013 at 11:34 PM | Registered CommenterMartin A

It is true that there is a large diurnal drop in temperature in deserts and the like, but in my view that's evidence of CO2 having no effect because the CO2 ppm is as likely the same, or thereabouts in all regions of the world. However if you live in the tropics, which I occasionally do, where there is a large amount of water vapour in the air the night time temperature barely drops. Which in my view makes the case for water vapour retaining the heat. At least at the superficial level.

However when the sun comes up and starts to heat the tropics if the feedback was truly positive then we would expect the temperatures to rise above the night time level, and they don't, well not very much. The main lesson from this observation is that where there is no water there is no heat retention. I have difficulty with the term "feedback" in this context having studied in feedbacks in the electrical engineering sense where they can be positive i.e they add to the input, or negative i.e. they reduce the input. In other disciplines they seem to use the terms positive feedback for anything that makes something bigger, but as we see in the tropics water vapour retains the heat, but doesn't seem to make the temperatures significantly bigger when the generator is turned on.

A further mystery, at least to me, maybe Martin can conmment. Positive feedback is the nitro-glycerine of the electrical engineering world, and has to be handled with kid gloves to get the required effects. If it is not carefully dampened it spirals out of control. I have tried asking Richard Betts and others what dampens the feedback at 3C for a doubling of CO2 and far from receiving a satisfactory answer I've received no answer at all. It may be that my question is so incredibly stupid that they don't want to embarras me. But here's the issue in the theory:

1. Tempeature rises and causes the oceans to warm;
2. The oceans give off water vapour, and CO2;
3. This causes the temperature to rise;
4. Go back to 1.

What magically breaks that cycle when the temperatures get to 3C because of a doubling of CO2?

The final point is that we've had temperatures at 1C above the present in the past, why is there no evidence of positive feedback and the IPCC-like catastrophes in the past records?

It would be an absolute disaster for climate science if they've got feedback theory wrong, but they're lucky in the fact that they use "feedback" in a very loose sense and may be able to weasel their way out of it.

May 21, 2013 at 7:44 AM | Unregistered Commentergeronimo

I see Martin A has made my point with much more eloquence than I could muster.

"The idea of Nature engineering a system of positive feedback giving significant enhancement of an effect (greenhouse heating, in this case) but never overstepping the limits of stability, equates to essentially an impossibility to such people."

I suppose my rambling post might give some background as to why we think the way we do, but Martin has articulated the problem in one sentence.

May 21, 2013 at 7:52 AM | Unregistered Commentergeronimo

OK, not so much as an indication that there is a positive WV feedback. The next on the list is the experiment question. Can we postulate an experiment to show the claimed radiative effect is present in the lab? Can we show it happening in the outside world? You know, I didn't think this was a hard question. Anybody who hypothesises that a given phenomenon can lead to a global catastrophe can be asked to show his working, can't he? And to back that up with a demonstration that his theory works in practice, and that it can be seen to be working. It is no good at all saying simultaneously the the effect has far-reaching global effects and that you can't actually show it happening. If every proposed experiment cannot sort the signal from the noise, wouldn't you want to carry on with better and better experiments until you can? What in science gives someone the enitilement to skip that bit and go straight to the answer? Hubris, sheer hubris.

May 21, 2013 at 1:33 PM | Registered Commenterrhoda

I thought I'd posted this before....

> Can we postulate an experiment to show the claimed radiative effect is present in the lab?

Is it good enough to show that CO2 will slow the cooling of a heated mass?


May 23, 2013 at 9:27 PM | Unregistered CommenterNial

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 | Registered Commenterrhoda

rhoda - I think I found your answer. Dr Kate Willett of the Met Office states: Unfortunately it's not possible to conduct a laboratory experiment to conclusively test whether climate change is caused by man or not.

Video: OK the earth is warming, but how do we know it’s us?

If the Met Office, which presumably knows about these things, concedes that experimental evidence cannot be produced, why spend time looking further?

Kate goes on to explain the reason why we can be sure that global warming is man made. Here is my summary of her proof. (Transcription of video below)

1. We have produced more and more CO2 since the late 1700's
2. CO2 has risen to 392 ppm
3. CO2 traps heat
4. We don't know anything else could have caused the 0.8 °C rise since 1850
5. That's it

Transcription of video:

Unfortunately it's not possible to conduct a laboratory experiment to conclusively test whether climate change is caused by man or not.

However, we do understand the natural factors that affect global temperatures; things such as volcanoes or solar variations or variations in the earth's orbit. These natural factors are not sufficient to cause the 0.8 °C rise in temperatures that we've seen since 1850.

We also know the properties of greenhouse gases such as carbon dioxide. Way back in 1859, British scientist John Tyndall showed that carbon dioxide could trap heat. So the physics is actually quite simple. CO2 is actually incredibly effective at trapping heat compared to another other gases in the air so if we increase the amount of carbon dioxide in the atmosphere, then we are trapping more heat in it. This has the effect of warming the earth.

Since the industrial revolution began in the late 1700's we've been steadily increasing our output of carbon dioxide. In 2012 we reached a concentration of 394 parts per million of carbon dioxide in our atmosphere

This represents a 25% increase since 1960 and is the highest level of carbon dioxide in our atmosphere for at least 800,000 years. Over the same period, we have noticed a 0.8 degree rise in global average temperatures.

The special increase in global temperature since 1850 can only be explained if we include the effect of increased greenhouse gas levels in particular carbon dioxide produced by us in burning fossil fuels.

May 25, 2013 at 10:44 AM | Registered CommenterMartin A

MartinA. Was that rhoda's question? That's always been the case, and recently more so. The lack of experimental evidence aligned with the impossiblilty of a controlled experiment allows the climate science alarmist to, as you said, "Make it up as they go along." And they continue to do so, and be believed because they're in the only group of people universally respected by politicians, "scientists". They are respected because politicians see them as being "above the fray" and very clever. We know otherwise, but we're not respected. The only solution will be time, because they cannot keep making forecasts that persistently don't come true indefinetely.

May 25, 2013 at 11:22 AM | Unregistered Commentergeronimo

"We also know the properties of greenhouse gases such as carbon dioxide. Way back in 1859, British scientist John Tyndall showed that carbon dioxide could trap heat. So the physics is actually quite simple. CO2 is actually incredibly effective at trapping heat compared to another other gases in the air so if we increase the amount of carbon dioxide in the atmosphere, then we are trapping more heat in it. This has the effect of warming the earth."

CO2 can trap heat? That is a given, is it? 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? Does 400ppm really trap twice as much as 200ppm? When the amount intercepted changes, does the proportion that ends up as heat change? If you think you know the answers to those questions, how? Where is the experimental backup? And of course, if the physics is oh so simple, why no experimental demo?

May 25, 2013 at 12:05 PM | Registered Commenterrhoda