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Discussion > Can there be a positive water vapour feedback?

A persistent positive water vapour feedback on a long timescale or a widespread basis?

Well, can there?

Mar 21, 2013 at 2:04 PM | Registered Commenterrhoda

Please clarify the question. I know a lot about feedback (studied/practised electronic feeback amplifier design and control engineering) but I'm not sure what you are asking.

That when it gets hotter, that puts more water vapour into the atmosphere, which makes it get hotter still?

If you look at very long term temperature trends , there seems evidence of things flipping between two states. As SandyS implicitly pointed out on another thread, if things flip state quickly (as in a Schmidt trigger circuit) it is often because positive feeback is involved.

Mar 21, 2013 at 3:48 PM | Registered CommenterMartin A

What I mean to say is if there were a positive feedback (of any kind, not just H2O) wouldn't there be a fingerprint in the way temperatures move? Yes, probably more like a flip flop. Now, we can see climate as bistable, but it does not seem to flip like that. It can hover in between for centuries if not millennia. That doesn't look like positive feedback to me. The warmists need there to be positive feedback. How could we check to see whether they are right? Would not any forcing get a similar H2O effect, so if it is three or more times the forcing as the CO2 CS case requires, is not every trend we see tripled by H2O? Up or down? Does it reinforce itself, or does it have a top limit?

Oh, and my usual why can't it be measured or shown in a lab or outdoors?

Mar 21, 2013 at 5:19 PM | Registered Commenterrhoda

Feedback in the traditional electrical engineering sense is when a system takes some of the output and puts it back into the input. This can be done negatively and positively. Negative feedback is almost wholly beneficial and occurs in nature, because it has a stabilising effect. As the input for our ecosystem is almost exclusively the sun it's difficult to see how feedback works in climate science what I think they mean is that heat is retained while the input that caused it continues so it gets hotter. I have little doubt that water vapour retains heat, I said on one of your threads before, if you go into the desert where there's carbon dioxide as soon as the input (the sun) goes down you can get a 30C change in temperature. On a beach in Thailand the temperature barely drops, while in Hong Kong, very humid, it sometimes doesn't drop at all. So humidity holds heat. Having said that, the next morning when the sun starts shining again the temperatures don't double, so there's something going on which isn't the understood feedback mechanisms of the electronic engineering world.

Mar 21, 2013 at 6:09 PM | Unregistered Commentergeronimo

OK, off the top of my head, here goes. I fear the following will seem obvious and not helpful....

Let's imagine you understand the dynamics of the system you are studying in the absence of any feedback eg with the feedback disconnected. Then you connect up the feedback and compare the dynamic behaviour of the system to its behaviour without feedback. Comparing the two can tell you a lot about the feedback - how strong it is and whether positive or negative.

[I'm using terms associated with electrical/mechanical systems but the principles apply to all physical systems. I may be in danger of using terms that are very familiar to me but may sound like gobbledygook to someone not familiar with the terminology.]

When you then connect up the feedback, you can tell if it is positive or negative and quantify it. For example, if:

1. The system's response to a suddenly applied step function stimulus is more rapid in the presence of feedback, but reduced in amplitude, then you have negative feedback.

2. If the systems response to a step function stimulus is larger with feedback than without, you have a moderate amount of positive feedback.

3. If the system starts to oscillate from extreme to extreme with no input signal, you have strong positive feedback (at least at the frequency at which it is oscillating - you may still have negative feedback at other frequencies).

4. If you connect up the feedback and the system than bangs over to one extreme and sticks there, that's a pretty good clue you have strong positive feedback. - and right down to zero frequency. I think this would correspond to the "tipping points" beloved of CAGW proponents.

[Things can be quite complicated and difficult to understand because the feedback can be negative at low frequencies but become positive at high frequencies because of delays within the system. A large part of the science of control system engineering involves analysing and overcoming this problem.]

What does the foregoing tell us in terms of climate, H2O, CO2 etc? NOT A LOT, I am afraid.

There are at least two problems:

- we can't switch off the feedback system and make measurements with and without it.
- the dynamics of the climate system, so far as I can make out, are simply not understood. (General circulation models seem to me a confirmation of this.)

However, the fact that the climate has never

- whacked over to one side, hit the stops and stayed permanently there

- gone into large oscillations for no obvious reason

seems pretty conclusive evidence that if there is any positive feedback, it is not strong in its effects. Plus "tipping points" don't seem to come into the picture.

Does the foregoing make any sense? I rattled it off while taking a short break from real stuff

Mar 21, 2013 at 6:32 PM | Registered CommenterMartin A

I think what I said about "tipping points" (™Climate Science) is wrong - I think a "tipping point" is something nonlinear, where a system previously stable with little or no positive feeback has a change in its mechanisms and internal feedback becomes large and positive.

I find it hard to imagine such effects existing in reality - although that does not prove they are not possible.

Mar 21, 2013 at 9:01 PM | Registered CommenterMartin A

Martin, you say that, "...that the climate has never... gone into large oscillations for no obvious reason". How do you know that exactly? Is there some proxy reconstruction that you believe in sufficiently to prove that? Or (heaven forbid) a model?

Don Keiller's graph of temperature, which I haven't noticed you disputing, purports to show bistable behaviour. That sort of implies tipping points, don't you think?

Mar 21, 2013 at 10:44 PM | Unregistered CommenterBitBucket

"However, the fact that the climate has never

- whacked over to one side, hit the stops and stayed permanently there

- gone into large oscillations for no obvious reason

seems pretty conclusive evidence that if there is any positive feedback, it is not strong in its effects. Plus "tipping points" don't seem to come into the picture."

Agreed MartinA, there is no historical evidence for tipping points, or even for a sensitivity of 3. I tried to make this point to Richard Betts the other day asking why we'd never seen the sensitivity show up in the past when temperatures reached 1C, the supposed tipping point.

Another thing that puzzles me is that the Earth is unaware where the heat comes from i.e. if it warms and it has a sensitivity of some sort, maybe not 3, then there should be positive feedbacks associated with the warmth. So are we looking at a temperature rise of 0.75C caused entirely by CO2 or are we looking at a temperature rise of. say 0.375C with a sensitivty of 2 bringing it up to 0.75. And why then doesn't it spiral out of control like any other uncontrolled positive feedback?

As you say typically feedback occurs when some of the output is fed back into the input. With the climate that's not happening, all that happens is that some of the heat is retained in the system, but as I pointed out before in warm wet climates, in the tropics, the overnight temperature barely drops, but when the Sun comes up it doesn't rise dramatically, begging the question why the sun doesn't simply add heat to what's already there and giving huge rises in temperature. In dry areas, deserts etc; it's brass monkey's cold at night and goes into the 30s during the day in the summer. The conclsion is that somehow or other the water vapour, far from acting as a positive feedack (in the climate science sense of the word) is actually keeping the temperatures fairly constant.

So we so have presence and absence of water vapour to observe, and the higher the water vapour the closer the night and day temperatures. I'm sure someone can provide an explanation for this, but it's not positive feedback.

Mar 22, 2013 at 5:46 AM | Unregistered Commentergeronimo

To attempt a partial answer to Rhoda's question (can we infer the presence of feedback from observations).

If you have a passive (ie no energy sources) system consisting of resistances and capacitances )electrical system), frictional devices and inertias (mechanical) then its response to an impulse will be non-oscillatory. But if you see oscillatory behaviour in such a system, then you know there is an energy source somewhere and there is feedback if you look for it.

Equivalently, if you drive the system with white noise (flat power spectrum) and you observe a peak in the spectrum of the resulting response, this means there is a resonant frequency and, if the system consists solely of friction+inertia then there has to be an energy source and feedbackl to produce the resonant peak. This ***might*** be a way to detect feedback in a climate system... But I wouldn't count on it.

Mar 22, 2013 at 8:50 AM | Registered CommenterMartin A

If I were to say 'If you don't know whether you have positive feedback in a record of operating a system, you haven't got it.' would I be far wrong? Under what circumstances could the climate not show positive feedback at the kind of levels required for a runaway to the stops?

OR: Is the positive feedback of H2O in fact only local if it exists at all, and ends in a tropical afternoon thunderstorm after a couple of hours?

Further: If it does exist, show me. In a lab, or outdoors. Don't ask me to believe in a bogeyman which cannot be seen or measured.

Mar 22, 2013 at 9:21 AM | Registered Commenterrhoda

Rhoda, you almost certainly would find evidence of "positive feedback" in the biological and engineering sense of the word. However, like all thing climate science they have appeared to use the word "feedback" to illustrate something, which in my view at least, isn't feedback at all. It's heat retention and rejection at the speed of light, or nearly anyway. As with all things in the non-debate the climate scientists aren't having with anyone we appear to have accepted the word feedback so we can move on. MartinA will, I hope, agree with me that if you have a system with positive feedback it is likely to self destruct unless you can introduce damping factors. Clearly there are no signs in the records of widespread destruction caused by high temperatures, and given the tool human ancestors had to deal with changes in their environment it is highly likely we wouldn't be here now. The rule of thumb is that positive feedback systems are inherently unstable, while negative feedback system are stable.

I don't believe you can do an experiment in the lab because there are too many parameters that interact together in complex ways and we would be unable to replicate that in the lab. Not least because there are clearly unknown parameters reacting with all the known parameter in non-linear fashion.

I also don't believe the feedback, if that's what it is, is positive, it is an artifact of the modellers' imaginations.

Mar 22, 2013 at 1:51 PM | Unregistered Commentergeronimo

Well, I was hoping somebody would be able to put the case for positive feedback. Seems not. All the SkS cut-n-pasters must have missed this one.

About the lab though, why would there not be a way to show water vapour feedback if it exists? You may say it is too difficult. That's what you'd say if you were trying to demonstrate ghosts or the tooth fairy.

(Oops, apologies to the tooth fairy, who at least delivers.)

Mar 22, 2013 at 2:40 PM | Registered Commenterrhoda

Don Keiller's graph of temperature, which I haven't noticed you disputing, purports to show bistable behaviour. That sort of implies tipping points, don't you think?
Mar 21, 2013 at 10:44 PM BitBucket

Bit -

In normal writing, perhaps especially on a blog, where one dashes off thoughts as they come, one assumes a level of goodwill and comprehension on the part of readers.

One expects that the context will be inferred, and that there is no need to qualify every statement to the nth degree. It's different from writing patent applications or legal contracts that might eventually be subject to minute examination by a team of hostile legal experts, keen to light on the slightest ambiguity or lack of precision.

In this case, I was talking about the climate on the same sort of time scale as the span of human existence, not what has happened over timescales of 100's of megayears where I think there have been events and physical effects not relevant to climatic changes over the last or the next 0.01 megayear.


Mar 22, 2013 at 6:24 PM | Registered CommenterMartin A

So we have established that positive feedback has some distinctive characteristics. If it is a duck, what we can see happening to the climate neither walks nor quacks like positive feedback. It may still be a duck but why would you think it was?

Mar 22, 2013 at 8:47 PM | Registered Commenterrhoda

Martin, I do not lack goodwill towards you or Rhoda and I have no reason to doubt my comprehension skills.

Why the sensitivity? If the climate can behave in a bistable manner (for which there may or may not be evidence - but some sceptics seems to believe) that implies tipping points, like the Schmitt triggers you and I once used. The conventional meaning of 'never' is not, "not in the time-frame that I feel comfortable talking about", but 'not ever'. I see no evidence that Rhoda was asking about feedback only in modern times...

Like Don Keiller, you seem to want to make unequivocal statements, are then reluctant to provide proof and get upset when challenged. What is so difficult about it? Have there ever been large oscillations or not? And where is your proof. It is okay to say, "I don't really know". You would expect no less from a warmist making such assertions than I am asking of you.

Mar 22, 2013 at 10:06 PM | Unregistered CommenterBitBucket

Here's the difference for me. In electronic series the feedback is always controlled by an attenuator, in the feedback loop, so that the feedback is controlled to provided the desired response at the output.

Now climate science theory:

1. Extra CO2 in the atmosphere causes an increase in temperature (based on the physical hypothesis and the 1980 tt 2000 correlation, nowhere else has this relationship been established);
2. The temperature rise causes a rise in temperature in the oceans increasing the water vapour AND the CO2 in the atmosphere (centuries after the rise in water vapour as I understand it);
3. The increased water vapour increases the temperature;
4. This in turn increases the temperature which releases more water vapour AND CO2 into the atmosphere;
5. The increased water vapour increases the temperature.
6. It's now can't stop if the sun keeps pumping 350 watts/M^2 into the Earth.

By that logic we could not have passed any point in history where the world started warming without experiencing catastrophic global warming. So what has stopped this happening now, and in the past? There has to be something in the natural cycles that keep the warming from running out of control, be it the Oceans, the Orbital path, gamma rays from outer space or, most likely of all, the clouds that form with the extra water vapour. It's a lot more complicated than the climate scientists seem to think, the biosphere. At least to me.

Mar 23, 2013 at 8:02 AM | Unregistered Commentergeronimo

I'm going to have to declare my own discussion thread closed for lack of opposition. The positive feedback doesn't walk or quack. If it's a duck, it's a dead duck.

If though there are forces which can cause a rapid (geologically rapid, I suppose) flip flop between ice and fire it is unlikely that they can be staved off by me switching off standby devices at night. Might as well get rich and adapt.

Mar 23, 2013 at 11:26 AM | Registered Commenterrhoda

I was in the process of trying to translate electronic terminology into Climate Science™ terminology but perhaps it's a futile effort. It's basic stuff - any fule kno.

In electronic terminology the voltage gain with feedback = A / (1 - AB)
A = the gain = (output voltage) / (input voltage) without feedback
B = the fraction of the output voltage added to the original input voltage without feedback to give the new input voltage with feedback.

If it is added, as here, it is *positive* feedback.

[I assume A and B are both positive numbers.]

So if AB is greater then zero and less than one, the feeback increases the overall gain by a finite amount. For example, if A = 1 and B = ½, then the gain with feedback is doubled.

If AB is one or greater, the system is unstable.

So positive feedback does not automatically imply runaway instability.


The Climate Science™ community would dearly love to demonstrate a positive feedback CO² -> H²O effect. The fact that they have not done so (so far as I can make out) surely tells you all you need to know.

Mar 23, 2013 at 11:48 AM | Registered CommenterMartin A

Martin, I think you are wrong. Scientists love their children too. I imagine most would be delighted to find that there is no positive feedback.

Mar 23, 2013 at 12:32 PM | Unregistered CommenterBitBucket

BB, in the absence of the fingerprints of feedback, why would they think it was there? Why can't they demonstrate it or observe it? Why do they believe it in the absence of proof? Models?

If any of them could be persuaded to come here and explain why they think there is pervasive positive feedback, that would be welcome. Why do they leave it up to you?

Mar 23, 2013 at 12:38 PM | Registered Commenterrhoda

@BitBucket "Scientists love their children too. I imagine most would be delighted to find that there is no positive feedback". Activists love their children too. I imagine most would be appalled to find that there is no positive feedback. So, who is scientist, who activist? Hard to tell, eh?

Mar 23, 2013 at 12:49 PM | Unregistered Commentersimon abingdon

@BitBucket "Scientists love their children too. I imagine most would be delighted to find that there is no positive feedback". Activists love their children too. I imagine most would be appalled to find that there is no positive feedback. So, who is scientist, who activist? Hard to tell, eh?

Mar 23, 2013 at 12:53 PM | Unregistered Commentersimon abingdon

I respect science absolutely. I am in awe of the insights of Copernicus, Galileo, Newton, Maxwell and Bohr/Einstein. But their legacy deserves better than the current pretence of "climatologists" who it seems have no useful additional new insights whatsoever. Nevertheless, they are well on the way to wrecking our civilisation by managing to demonise Carbon, yes you heard correctly, Carbon. Carbon? It's what all living things are made of. What on earth are we signing up to?

Mar 23, 2013 at 1:21 PM | Unregistered Commentersimon abingdon

Rhoda, flattering though it might be, I don't think the world's scientists are collectively saying, "its okay, BitBucket's got that covered on the Hill". I imagine the answer is that they don't know. That's okay too. We'd all like certainty, but maybe there isn't any.

Simon, why should activists or activist scientists be appalled? Do you think they get worked up about AGW for some ulterior motive or because they are worried about it? The latter seems most likely. I'd imagine they too would welcome a lack of feedback. As for wrecking civilization, do you think that a society organized around non-carbon-based fuels cannot still be civilized?

Mar 23, 2013 at 5:38 PM | Unregistered CommenterBitBucket

BB, they ain't saying BB's got that covered, because you patently have not. If they don't know, that's fine. I don't know either. But why don't they either find out or stop making predictions which assume this effect which is not in evidence? I really don't care how many kids they have or how good-hearted and human they are. I care that they are spreading alarm without a proper scientific foundation.

Of course, they don't answer to me. But why is it that a simple Oxfordshire housewife can ask so damn many questions that they just can't answer? I don't ask them to do my ironing, why can't they do a little of their own job for me?

Mar 23, 2013 at 6:55 PM | Registered Commenterrhoda