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Discussion > Sense and Sensitivity

I have a problem with the notion of positive feedback in any system. I learned about positive and negative feedback theories in my, now long forgotten, engineering studies, so when I first read that the IPCC were talking about positive feedbacks that would increase the temperature by between 1.5C and 4.5C, with the probability of 3C being the actual rise it troubled me. This first appeared in the Charney report. Jules Charney because he had two computer models one showing a 2C sensitivity and the other 4C sensitivity had taken away 0.5C from the lowest and added 0.5C to the highest to get this range. I know that there has been a lot of work on sensitivity showing other possible numbers but the IPCC has stubbornly remained at 1.5C to 4.5C, numbers clearly plucked out of the air, 38 years ago that have withstood the test of time, and the $billions thrown at climate science.

It demonstrates, to me at least, that the climate science community don't have a handle on sensitivity, especially in terms of positive feedbacks, but I've remained quiet on the issue, as, not for the first time, I'm not sure I have a handle on it either, so I'm opening up here to be educated. For the purposes of this discussion I'm ignoring the complexity of the atmosphere and using what I understand to be the position of the IPCC on sensitivity.

Here's the theory:

More CO2 -> more heat -> increase in temperature ->more water vapour -> more retained heat ->increase in temperature -> ?

I know at least one of our contributors will see the flaw in the theory as I've presented it. It is the classic destructive positive feedback loop and should continue until the oceans have boiled away. But no one challenges it, it is widely accepted and I don't know of any mechanism put forward by the climate science community which would break that loop at 3C, 6C or any other C, it is clearly something I'm missing. Does anyone know what it is?

Just to give you an update as to where I am. Otto et al 2013 showed a radiation imbalance of 0.6Watts/m^2, with cloud albedo reflecting around 23%, or 77Watts/m^2 of the incoming radiation. We are told that more CO2 will cause more precipitation, I don't know what it says about that on the Met Office web site, but I'm assuming more precipitation is accompanied by more cloud assuming for the sake of this discussion that the cloud cover increases by 1% and the relations ship between cloud cover and reflected radiation is linear the increase in reflected radiation would be 0.77Watts/m^2 giving a radiation imbalance of minus 0.17Watts/m^2. So I can see the possibility of negative feedback, but why is this ignored? Or is it?

This is simple stuff, so I'm assuming everyone understands that and notwithstanding the clear relationships between heat, water vapour, clouds and precipitation, why is the climate science community declare a positive feedback relationship between CO2 and water vapour (true), and what do they think dampens the positive feedback to keep it in the range 1.5C - 4.5C.

It doesn't make sense to me.

Mar 10, 2017 at 4:30 PM | Unregistered Commentergeronimo

There ain't no such thing as climate sensitivity. It's an invalid concept except in the case of models and records. That is, you can look in model output for what the implied CS is for comparison with measurements or other models. You can't use it for prediction. You can't work out the immediate versus the long-term effects of CS.

There is also no real basis for an imbalance of 0.6 watts/ sqm or any other figure. How is it observed? How is it calculated? Is it the usual compilation of averages? Average albedo, average radiation, arithmetically calculated. Or, in other words, bogus.

Mar 10, 2017 at 5:34 PM | Unregistered Commenterrhoda

Mar 10, 2017 at 4:30 PM | geronimo

It would be more honest if ECS was between 1 and 6, that being the number of sides on a dice, used to narrow the range down a bit.

This theory explains why Climate Scientists can not consider the possibility of ECS being less than 1.

Mar 10, 2017 at 5:51 PM | Unregistered Commentergolf charlie

Thanks rhoda you're the "sense" part of the title. You may be right but we'd have a difficult job persuading anyone else as they're accepted by the whole of the scientific community. I've put this out there because I do accept that in a dynamic system like the climate there will be feedbacks, the IPCC say they will be positive feedbacks and (a) I don't see how there can be given the inherent instability of such systems in the absence of a dampener. It's what they think the dampener is, and why they can calculate it's stability value for temperature. I am aware sensitivity using historical data, which is suggesting it's lower than the IPCC is saying, but what I'm trying to understand is what physical mechanisms the IPCC see as stabilising temperature, even at unacceptably high temperatures.

Mar 10, 2017 at 6:11 PM | Unregistered Commentergeronimo

Geronimo, I began a post right here with the same title (it's an episode of Blackadder the third) years ago. I never got to the bottom of it, I remain irritated by the number of assumptions we are expected to take for granted in this game.

Things that way against the use of CS:


Models don't even agree with each other, or observation.

Observations are unable to separate natural variations from CO2 effects. There has been plenty of historical temp change without CO2 variation.

Tipping points, if they exist, make predictions useless.

Emergent phenomena, once a place gets overheated it dumps heat by any means available with timings and amounts not covered by theory.

Mar 10, 2017 at 6:29 PM | Unregistered Commenterrhoda

Mar 10, 2017 at 6:29 PM | rhoda

I agree, with the exception of Computer Generated Models not agreeing with each other. I think they verify one Computer Generated Model, by judging it against it's predecessors, rather than that thing Climate Scientists just don't understand, the Earth and it's real climate. The website known as "Real Climate" is therefore a lie, before anything is written.

Mar 10, 2017 at 6:44 PM | Unregistered Commentergolf charlie

geronimo - If I understand it, you are wondering how positive feedback can operate without getting into a catastrophic cycle?

So long as each time the signal goes round the positive feedback loop, it is reduced in amplitude, the thing will not run away with itself, even though the feedback is positive (rather than negative): 1 + 1/2 + 1/4 + 1/8 + 1/16 +....... = 2.

But if the so called loop gain is greater than one, even by a little bit, the thing will eventually blow up: 1.00 + 1.10 + 1.21+1.33+1.46+1.61+ 1.77+......................= *POOF*.

Feedback control system engineers are very wary of systems incorporating positive feedback - all too easy to get into instability.

The idea that nature has engineered a positive feedback system, with enough loop gain to multlply effects by a significant factor but which has never, in the history of the world, gone into 'thermal runaway' would be a joke except that in "climate science" it is taken, not only seriously, but as a fact.

Mar 10, 2017 at 6:53 PM | Registered CommenterMartin A

The way I read the “theory” is that the heat that is trying to escape to space is being reflected back, thus increasing the down-welling heat by being added to the incoming solar radiation, which heats the Earth more, thus the outgoing radiated heat is even greater, and is only foiled again, being radiated back down, thereby increasing the heat even more, which heats the Earth more, thus the outgoing radiated heat is even greater, and is only foiled again, being radiated back down, thereby increasing the heat even more, heating the Earth… etcetera, etcetera, until we all boil. Simples. We are do-o-o-omed!

Would the world be more dangerous or just more interesting if all laws of nature could be similarly circumvented? At last! We could have perpetual motion!

Mar 10, 2017 at 9:15 PM | Unregistered CommenterRadical Rodent

Mar 10, 2017 at 6:53 PM | Martin A

Thank you for putting that into English. As a country bumpkin who somehow got an O Level in physics, I can sort of understand how "Snowball" Earth could come about with white snow and ice reflecting heat from the sun.

I have never got my head around how a "hotter" earth would not end up with more clouds, effectively "insulating" the planet's surface from the sun, and preventing it getting hotter in some form of feedback loop.

It seems Climate Science might make some sense if all water and biological ife was removed from Earth. I don't recall Trump promising that, so we will have to survive without Climate Science, as we always have done before.

Mar 10, 2017 at 9:21 PM | Unregistered Commentergolf charlie

Yes, GE. That is the converse to the cloudy night, warmer night scenario: cloudy day, cooler day. While water in the atmosphere does give some sort of evidence that there are components of the atmosphere that could have some effect on keeping the atmosphere warm, this same component also helps to keep the atmosphere cool. Oh, dear – balance. The AGW brigades are not going to like this…

Mar 11, 2017 at 12:08 AM | Registered CommenterRadical Rodent

Radical Rodent, The Royal Society has always prided itself on excellence. I wonder how long this page will survive?

https://royalsociety.org/topics-policy/projects/climate-change-evidence-causes/

And where do they source their info from? Mann? Hockey Teamsters? Skeptical Science? Gergis? Karl? Or just The Guardian?

Climate Science is becoming Unsustainable, Scientifically, but it has taken a few Politicians to correct this. The money men are already starting to flee

Mar 11, 2017 at 1:20 AM | Unregistered Commentergolf charlie

I was walking around the kitchen baking a cake for my son's birthday today. Giving this some thought.

As an Engineer, Geromino, like myself I have always been troubled by positive feedbacks. Here is my attempt to simplify the problems I have with climate sensitivity. I had all sorts of ideas, but was strict with myself and came up with something like this.

At this point in creation climate is either sensitive or it isn't, you cannot have it both ways.

So we assume that it is sensitive. But, this is sensitivity in a complex and chaotic system. Linear sensitivity? Hmmmm.

Assume the climate is a Lorenz Water Wheel, but spinning slowly over billions of years. For arguments sake, assume water is Carbon Dioxide.

What climate scientists are saying is that they can accurately model what will happen next from the current state. They are saying what the direction of the wheel will be, the acceleration and the final velocity for the next time period.

And this is a significant change to "recent" previous states. Acceleration is greater, reaching a terminal velocity quicker and the direction will be constant.

But if it is a sensitive system, then it is a sensitive chaotic system. And who is to say that the wheel will not stop and reverse?

Who is to say that at 2 degrees (ignoring that these are just modelling factors) the temperature will not plunge? And continue plunging? past zero?

The fact that we are still here after so many billions of years, indicates the system isn't so sensitive. Ignoring outside or internal influences (impacts and volcanoes etc.) The chaotic system has had numerous opportunities to destroy itself. That one methane bubble just coming to the surface, at the same as a lighting strike occurs, right next to a tree, that catches fire, then sets fire to the grasses that have been dry because of no rain...etc...etc... The earth has seen it all.

You cannot have both ways. it is either sensitive or it isn't. My attempt early on Saturday morning to give it some thought.

Mar 11, 2017 at 8:59 AM | Unregistered CommenterJiminy Cricket

"geronimo - If I understand it, you are wondering how positive feedback can operate without getting into a catastrophic cycle?"

I am, but specifically I was looking to see what the physical mechanism in the climate system is that would limit the positive feedback at a certain temperature, I have never seen that explained. I can see the increase in cloud cover might provide some negative feedback along with the lapse rate, and the black body effect i.e.the Stefan-Boltzmann etc. but I don't have a handle on how the climate scientists put these things together, or why the number has remained stubbornly at 1.5C - 4.5C over such a long period of time. It's inconceivable to me that Jules Charney's finger in the air guess in 1979 could have been right based on two models and that $gazillions have been poured into building new more sophisticated models without modification.

This assumed positive feedback is the cornerstone of CAGW theory, I've no doubt that in a multi-variable dynamic system there will be multiple positive and negative feedbacks, I also have no doubt that if these positive and negative feedbacks weren't in some sort of equilibrium we'd have gone POOF a long time ago. But that assertion doesn't seem to shared by the climate science community, or anyone else for that matter. So where am I going wrong?

Mar 11, 2017 at 11:19 AM | Unregistered Commentergeronimo

So where am I going wrong?

In assuming that the 'climate science community' might be right?

Mar 11, 2017 at 3:06 PM | Unregistered CommenterMartin A

The claimed positive feedback is not inextricably linked to CO2. Any temperature perturbation could kick it off, upwards or downwards. But it doesn't. It doesn't run away, it doesn't run to a limit and stay there. Ergo, there is no overall posiiive feedback. If anybody thinks there is, let them show the measurements, there has been plenty of time to observe them, no need to model if you can look out of the window.

Mar 11, 2017 at 3:45 PM | Unregistered Commenterrhoda

Geronimo

The atmospheric CO2 generates downwelling radiation in the 13-17 micrometre band. Increase the CO2 content and you increase the insulating effect at those wavelengths, leading to a higher surface temperature.

The black body radiation increases with the surface temperature, in a band between 5 and 30 micrometres. Since much of the energy trapped by increasing CO2 escapes at other wavelengths, a runaway positive feedback does not happen.

I don't know why you think that climate scientists do not know about equilibrium. Look in the literature and you will find that the acronym for climate sensitivity is ECS. This stands for Equilibrium Climate Sensitivity.

ECS is the increase in temperature due to increasing the CO2 by a defined amount and then leaving it constant until all the positive and negative feedbacks work through and temperatures stabilise.

Read AR5 and you find an ECS mid-range estimate of 3C.

For example, consider a parallel Earth at an equilibrium surface temperature of 14C for 280ppm CO2. Increase the CO2 to 560ppm and keep it there. 1.3billion cubic kilometres of ocean heat sink will gradually warm to a new equilibrium surface temperature of 17C. This might take a thousand years.

The current Earth system remains out of equilibrium for two main reasons.

Firstly, the increase in CO2 to date has not had time to work through into the equilibrium temperature. The ocean heat sink and feedbacks have not had enough time to warm and stabilise at an appropriate equilibrium temperature for 400ppm.

Secondly, we have not stabilised the CO2 concentration. As long as CO2 continues to increase, temperatures will continue to lag and equilibrium is impossible.

Mar 11, 2017 at 4:52 PM | Unregistered CommenterEntropic man

Golf Charlie: that is a page that is over 3 years old, now (posted 27th Feb 2014), so you would have thought that they would have done something to correct some of the grievously unscientific answers to questions:

6. Climate is always changing. Why is climate change of concern now?
All major climate changes, including natural ones, are disruptive. Past climate changes led to extinction of many species, population migrations, and pronounced changes in the land surface and ocean circulation. The speed of the current climate change is faster than most of the past events, making it more difficult for human societies and the natural world to adapt.
In what way are they comparing it with past events to know that it is faster? That past proxy records show changes of 1°C per century as average, yet over the past 30 years it works out at, say, 1.5°C per century (ignoring that, over the last century, it has risen 0.8°C). Yep – and if you extrapolate the rise from sunrise to midday, it would be 1200°C per century! (Obviously, to do that would be daft – but then so is comparing the apples of a couple of decades with the oranges of centuries!)

Then we have the truly egregious one:

15. What is ocean acidification and why does it matter?

Direct observations of ocean chemistry have shown that the chemical balance of seawater has shifted to a more acidic state (lower pH) (see Figure 7). Some marine organisms (such as corals and some shellfish) have shells composed of calcium carbonate which dissolves more readily in acid. As the acidity of sea water increases, it becomes more difficult for them to form or maintain their shells.

A subject that one would have thought would have been considered comprehensively debunked by the RS by now. This is followed by yet another example of utter tom-foolery:
16. How confident are scientists that Earth will warm further over the coming century?

Very confident. If emissions continue on their present trajectory, without either technological or regulatory abatement, then warming of 2.6 to 4.8 °C (4.7 to 8.6 °F) in addition to that which has already occurred would be expected by the end of the 21st century.

Nope. Those proud members whose noble efforts helped to raise the Royal Society to the esteemed institution it once was must be spinning in their graves.

Mar 11, 2017 at 5:04 PM | Registered CommenterRadical Rodent

Rhoda

Using the IPCC empirical formula 5.35ln(C/Co)/3.7, beloved of all dragon slayers, the direct warming due to increasing CO2 from 280ppm to 400ppm would be 5.35ln(400/280)/3.7 = 0.52C.

Over the period of that change, temperatures have increased from 13.8C to 14.8C , about 1C.

This is twice what one would expect if all the positive and negative feedbacks cancelled out, suggesting a net positive feedback of 0.5C and a climate sensitivity of 1/0.5 = 2.0.

Since this quick concentration ignores the lag, 2.0 may be considered a minimum estimate. The actual figure will be larger.

Mar 11, 2017 at 5:08 PM | Unregistered CommenterEntropic man

EM, that is very simplistic. Any temp perturbation might kick off Why can't you show the actuals? The change in water vapour. Some actual thing, not supposition.

Mar 11, 2017 at 5:24 PM | Unregistered Commenterrhoda

As long as CO2 continues to increase, temperatures will continue to lag and equilibrium is impossible.
What a shame that most of the records of the past few hundred millions of years show that it is CO2 that lags behind temperatures, not the other way round. But… let’s ignore that, shall we? We can’t have facts interfering with beliefs, can we?

Here is a simple proposition to consider: there has NEVER been, and there will NEVER be, any long-term equilibrium.

Mar 11, 2017 at 5:36 PM | Registered CommenterRadical Rodent

Rhoda

Not supposition, but physics. The same physics works in the laboratory and in the field. It is well enough understood that the Sidewinder missile was designed to home on the 15 micrometre radiation from the hot CO2 in a jet fighter's exhaust.

These are the actuals . Look at the graphs here or in more detail here .

The natural positive and negative variables combine to produce a slight cooling trend.The radiative physics of CO2 predicts a warming trend which matches observations.

Mar 11, 2017 at 6:10 PM | Unregistered CommenterEntropic man

Radical rodent

I would agree with you that in most past climate events CO2 lags temperature. For example, for the last 2 million years since the current Ice Age began Milankovich cycles have driven temperature and temperature has driven CO2. The CO2 has acted as a positive feedback.

However, you have fallen into a logical trap. That CO2 SOMETIMES lags temperature does not mean that CO2 ALWAYS lags temperature.

Snowball Earth's were mentioned earlier, and shield volcanoes have in the past produced enough CO2 to drive warming. Then there's the PETM.

The most obvious example of CO2 leading temperature is our current unprecedented situation. Our civilization dug up 300 million tons of fossilised plant material and burned it to increase the atmospheric CO2 content by 40%. The temperature increase then followed.

We are probably the first. The Earth contains enough useful mineral deposits to build one(1) high technology civilization. If someone or something had done it before us, those deposits would have been mined and dispersed.

Mar 11, 2017 at 6:47 PM | Unregistered CommenterEntropic man

EM.
Are you recycling your old posts?
I have the strongest sense of deja vu.

Mar 11, 2017 at 6:58 PM | Unregistered CommenterSupertroll

EM "Using the IPCC empirical formula 5.35ln(C/Co)/3.7, beloved of all dragon slayers, the direct warming due to increasing CO2 from 280ppm to 400ppm would be 5.35ln(400/280)/3.7 = 0.52C."

I think you might find you're out by a factor of 3 there old chap. Try doing the calculation using your equation for a doubling of CO2 the answer should be 3C, no?

Mar 11, 2017 at 7:11 PM | Unregistered Commentergeronimo

EM, I don't think I mentioned the sidewinder missile. But I wonder if that same physics accounts for its 80+% miss rate on its introduction. I observe that you don't provide any acual answers. If there's a positive feedback, why does not any temperature perturbation lead to a run either to a stop or away in either direction? Could it be that the simplistic physics you assert do not take into account MOST of the complex processes which are taking place?

Mar 11, 2017 at 8:22 PM | Unregistered Commenterrhoda