The positive feedback factor of CO2

[Andre]

In the other thread we / errm I discussed that theories cannot be proven but they can be falsified.

The theory in question is that doubling CO2 in the atmosphere will cause a global temperature increase in the range of some 2-4 degrees Celsius. There is also some pretty common idea that under primary conditions, without feedback, the temperature increase would be in the order of magnitude of one degree, too insignificant to worry about. Hence we need "positive" feedback to attain those "dangerous" temperature increases.

Actually, without positive feedback, more CO2 is merely a mild friendly climate alleviator at the most

So the issue here is the positive feedback factor of CO2 on the termination of ice ages. It is exhaustively discussed that in the ice cores we see the oxygen isotope (d18O) spikes rise before the CO2 does (d18O is assumed to be temperatures). As the CO2 is lagging 600+/- 400 years, normally this would refute the idea that CO2 causes temperature rise, instead temperature rise seems to rise the CO2.

But there is always a remedy, positive feedback. So some trigger (earth -milankovitch wobbles are assumed to trigger a first faint warming, which induces CO2 increase with some delay, probably because of warming oceans and as soon as CO2 rises, positive feedback kicks in, increasing the warming, which increases the CO2 etc etc a strong positive feedback loop. Case solved.

However, if that is a hypothesis, where are the studies that test it? I haven't seen one. Why are the warmers not pointing at any scientific substantiation when talking about positive feedback?

because it's not true?

So I used this high resolution graph of Antarctica's EPICA Dome C ice cores during the last glacial temination between 20,000 and 10,000 years ago, to demonstrate that there is no positive feedback because the typical behavior of positive feedback is not seen.

Data here: Stenni et al 2001 for the d18O and monnin et al 2004 for the CO2

http://home.wanadoo.nl/bijkerk/epica5.GIF

more to follow

 

[William Astley]

Is there Correlation of Planetary Temperature & CO2 Levels!

Certainty or Uncertainty Concerning whether CO2 Climatic Forcing is Real?:

http://www.geosc.psu.edu/~kump/KumpCommentary.pdf

The following is an excerpt from the above linked paper that notes there have been periods in the Earth's history when the planetary temperature has been high and CO2 levels have been low and periods when the planetary temperature has been low when CO2 levels have been high. The paper is curiously titled "Reducing the Uncertainty of CO2 level and Climatic Change".

"Despite these successes in linking variations in greenhouse gas concentrations (What successes! My comment.) to climate change in the geological past, from 600 Myra ago to the present presents notable intervals for which inferred temperatures and CO2 levels are not correlated (Vetzer, Francois, Evidence for decoupling of atmospheric CO2 and global climate during the Phanerozic eon" Nature 408, 698-701 (2000). ... One of these occurred during the early to middle Miocene (about 17 Myra ago) at a time well established as a warm period (i.e. No ice sheets, my comment) with proxy data for low CO2 levels (260 ppm, same as today before industrial increases. My comment.) (Pagani & Freeman, Micocene evolution for decoupling of CO2 and global climate change during the Phanerozoic eon.)

I have not heard any discussion in the press concerning the lack of correlation between CO2 levels and planetary temperature, in the geological past. The discussion has been centered on the 20th century where there has been rising global temperatures and rising CO2 levels.

Also I have not heard any mention in the press that the sun is at its highest activity level in 8000 years or any mention of the specific mechanism that high solar activity can cause the planetary temperature to be high.

As I have noted in this forum (with links to the relevant papers) there is satellite data and data from observation of the Earth'shine on the moon, to support the assertion that the majority of the 20th century warming is due to the extraordinary 20th century increased in solar activity, which reduces low level planetary cloud cover and hence causes the planet to warm, not due to an increase in CO2 levels. Also as noted, the 20th century period of very, very, high solar activity appears to be ending. Based on proxy climatic data, the sun will now start a very low activity stage and the planet will severely cool. i.e. This is a recurring phenomenon, not a weird event, which has never happened before.

In my opinion, the true problem (i.e. Why we are not talking about climate change, global cooling.) appears to not be not scientific, but rather political. The recent very strong support to eliminate global warming is an indirect method to protect the environment and reduce obvious egregious consumption.

Climate change - global cooling not warming - is based on the facts, a very, very important problem which the majority appears to not be aware of.

 

[Andre]

Thank you for your contribution, William, I concur in general.

On the topic of strong positive feedback of CO2 during the glacial transitions, I made a very rudimentary basic excel model of a strong positive feedback here

http://home.wanadoo.nl/bijkerk/positive-feedback.xls

So let's have a look at the results of one run (attached).

So, the thin black line is simulating the natural forcing or the natural climate variability down the ages. I shaped it with an initial increase followed by a retreat and then resuming the increase, all with a random riple to let it look more natural. Then we add the CO2 reacting linear with the temperatue on a certain delay. This value is added to the black line to get the thin blue line as the total forcing of natural + positive CO2 feedback. The fat red line is the assumed temperature response on the total forcing, closing the positive feedback loop.

As I mentioned, positive feedback systems are bistable, all or nothing, therefore I limited temperature response to an artificial -stable- value of 15 plus random ripple.

Now you see the essential difference between the ice core proxies and the positive feedback model, as soon as CO2 kicks in, the temperature response accelerates and continues all the way to the high stable position, seemlingly rather independent of the natural climate variability, the downward natural trend only delays the accelleration of increase in the output somewhat and that's the big difference, the reason why we don't see a strong positive feedback in the ice cores, to explain the alleged strong sensitivity of climate to changes in CO2

Of course you can get response to natural variability back by downplaying the positive feedback factor, but that would also downplay the role of CO2 in climate with the same amount.

I'd appreciate possible comments of engineers on the system response issues.

 

[Andre]

In the run here, the positive feedback is tuned down 35%. We see the return to response to natural variation, but with a considerable lag. The response of the "temperature" is counteracted by the positive feedback of the CO2, which we don't see in the original reaction of the proxies in the opening post where a sharp trend change is showing against the rising CO2.

So when that CO2 was unable to counteract that as seen in this run, it simply shows that there was no positive feedback of any significance.

The alleged temperatures fluctuated wildly but CO2 did neither cause it nor enforced it with positive feedback.

And that falsifies anthropogenic global warming as in CO2 causing a strong greenhouse effect.

 

[inol]

The ice core records show CO2 increasing by about 50% during interglacial warmings, therefore assuming a 3C increase per doubling the CO2 amplification should be about 1.5C in all. Ie the amplification should be less than 20% of the total forcing. In the examples above the amplification is a lot higher than that. The above really falsifies anthropogenic global warming causing a greenhouse effect stronger than anyone proposes.

 

[Andre]

If we go with the current scholar views, Ice core proxies are really comparing a global CO2 signal with a local "temperature" 10-15 degrees variation or is it really?

http://www.phys.uu.nl/~helsen/PDF/Helsen06JGR.pdf

Anyway, many other proxies elsewhere (sea surface temperatures, pollen etc) give some range of 0-5 degrees temp changes between cold stadials and interglacials. I'll flood you with refs if so desired, but I'm pressed at the moment. This would have to increase the positive feedback range relative to the other leading variation factors, the higher this factor, the stronger the typical positive feedback characteristics, which as said could only be a very weak factor when considering the typical system response.

Personally I think that we are looking at something completely different but that's another matter.

 

[J77]

Please could you summarise...

What is meant by, and what is the nature, of this "positive feedback"?

 

[Andre]

What is meant by, and what is the nature, of this "positive feedback"?

I'll try, I'm afraid conveying complicated procedures in a simple way is not one of my best talents.

So we have the Pleistocene ice ages, most notably since the last million years. It is thought that several long cold glacial periods have been interrupted by shorter interglacials in irregular cycles each about 100,000 years in duration, some 80-90,000 years for the glacials and some 20-10,000 for the mild periods in between.

This information is inferred from many geologic proxies. These are chronologic sequences of data on which conclusions are inferred. For instance the deep ice cores of Antarctica can be analysed on CO2 content and water isotope ratios. And after lots of complicated processing these kind of graphs are produced:

http://www.climateactionnetwork.ca/images/charts/vostok-ice-core.jpg

It's clearly visible that the isotope 'temperature' and the 'atmospheric' CO2 are very closely related and here you're looking at the pre-Hockeystick convincing evidence that CO2 causes global warming.

There was a nagging problem however, air in the air bubbles is younger than the surrounding ice because the fresh snowy ice remains open for the air to circulate in it. Trapping of the air happens some 80 meters down the ice due to the increasing pressure, but that's trapping of air of today. Now there have been libraries written how to tackle this problem and it's still ongoing but meanwhile it became clear that the CO2 spikes were in fact lagging the isotope (temp?) spikes. Therefore, the ice cores disappeared out of the limelight of global warming, instead the hockeystick was created.

So if temperature rises first at the end of the glacial period, apparently it causes the CO2 to increase. A possible scenario would be warming of the oceans, warmer oceans can hold less CO2.

But if you advocate that more CO2 causes increased warming and more warming causes increased CO2 then you have a positive feedback system, the both elements stimulating each other to much higher levels than without positive feedback and this is where the explanation of the global warmers stops, without any closer study.

Now positive feedback systems are very well studied, your computer contains billiards of them, each memory bit is a positive feedback system, knowing only two stable conditions at the extreme ends, on or off, 1 or 0.

So if we know how positive feedback works then we can observe the proxy data and see if it behaves as that kind of system response, knowing how output and input of systems relate. However I have never seen anybody considering that in geologic proxies.

Now it has been 30+ years ago when I struggled with system response on the academy with Laplace, Fourier, S-domains and what not, but I still recognise from the high resultion ice core data that there cannot be a positive feedback at work there, resuming:

1: As the CO2 starts to rise 600 years after the isotopes at about 17,000 years ago, in a positive feedback, there is an enhanced of whatever cause of the warming, hence the warming should accelerate. It does not, so an enhanced working of CO2 greenhouse effect cannot be seen.

2: There is a strong abrupt reaction to natural variability halfway, which is impossible with strong positive feedback, where the feedback takes over the (natural) system input and steers it all the way directly to the system limit, like the status "one" in the computer memory bits.

With the much weaker positive feedback in the last XLS run we still see a considerable delay and a smooth leveling off transition of the signal output, as the CO2 fights against the natural input, wanting to continue up where the variability pulls it down. We see it clearly in the rudimentary simulation but this effect is completely lacking in the ice cores. This is possibly the strongest clue that there is very little feedback going on if any.

So, we can safely conclude that we see no strong positive feedback. Instead the CO2 curve just show passive response to temperature

So if the rising CO2 was unable to boost the "temperatures" during the glacial transitions, why would we think it does it now?

Now, if we dare to think Popperian fasification philosophy, we cannot but conclude that CO2 cannot be a strong climate factor, not then, hence not now.

I hope it helps.

 

[inol]

Perhaps CO2 could be a strong climate factor today simply because there hasn't been much warming. Perhaps important is a better word than strong though in this case. Certainly CO2 could be a weak climate factor on geological scales but recent warming is <1C so there doesn't seem to be a contradiction.

 

[Andre]

Well finally I got the critique I was looking for, allbeit in another thread, burried under a deluding deluge of fallacies,

...

You are claiming that there is no net positive feedback evident in the ice core data. I don't believe you to be qualified to make that claim.

So you are qualified to disqualify me? What difference would that make to reality. Are only the taylors qualified to judge the new clothes of the emperor? Isn't the little kid not qualified to exclaim that the emperor wears no clothes?

I found your analysis of the date to be amateurish and biased.

Where is the analysis that would lead to such a conclusion? How can you be biased with numbers?

You start with an erroneous assumption as to how the feedback should look,

Why would that be erroneous? What is the problem?

and then when it doesn't meet your false assumption you declare it evidence that AGW is a hoax.

All it shows is that the process in the ice core is not showing positive feedback behavior.

By your own words it is based on analyzing the reasoning of a person or persons you do not even know. Not very scientific. I think the term you would use for that is "ad hominem".

Now I'm completely lost. Reasoning has nothing to do with ad hominems. Ad hominems are red herrings about non relevant information pertaining a person, intended to degrade the credibility. I've looked twice, there is no irrelevant information about persons in this thread, although the quoted post here appears to be very revealing about it's author.

I think it would be required to substantiate your claims with objective reasoning or be exposed for what these claims really signify.

you accuse the scientific community and the worlds governments of a grand conspiracy to plunge the world into a totalitarian state. And yet, when someone questions your questionable sources, you accuse them of fallacy.

Please show me where I do that. I'm no aware of ever accusing governments of conspiracy, victim of a positive feedback lfear mongering loop yes, but not conspiracy. So the allegation is another strawman.

You show me a peer reviewed study that explains the warming and cooling trends contained in the data without CO₂ and then we have something to talk about. You cannot do this because there is no way to explain past and present climate without CO₂!

That's the fallacy of the restricted choice or the ignorance fallacy, either A or B or C and the ignorance fallacy: it can't be A or B therefore it must be C. I don't know of anything else.

But again, debunking theories is not about offering competing ideas, it's about showing that the idea is false, which is still standing here, without substantiated claims showing otherwise

Anyway: peer reviewed, no CO2:
https://www.physicsforums.com/showthread.php?t=108165

I have seen experiments go badly wrong with disastrous effects. We only have one planet. I suggest we stop this experiment now. The projected results are not looking favorable for the subject.

The hyperbole. There is no such thing as an experiment. The variation in CO2 is nowhere near the maximums of the paleo climate of the past, even when there were ice ages in the distant past, CO2 has been higher.

 

[Skyhunter]

Let us begin here the study I believe you are looking for in the OP.

http://icebubbles.ucsd.edu/Publications/CaillonTermIII.pdf

Nothing you have provided me here has convinced me that their conclusions are in error.

 

[Andre]

Nothing in the world will ever convince you, not even a new ice age, that's for sure. However, you just show the first of a series of white swans, which lead to the all-swans-are-white hypothesis which I killed with a black swan.

I asked you to substantiate your claims and demonstrate why I did not kill the positive feedback hypothesis, not to produce white swans. Have a look at the 4AR WG1 chap 6, lots of white swans. I know them. In fact Caillon et al is my first reference in demonstrating how the positive feedback hypothesis was develloped.

 

[Skyhunter]

Nothing in the world will ever convince you, not even a new ice age, that's for sure. However, you just show the first of a series of white swans, which lead to the all-swans-are-white hypothesis which I killed with a black swan.

I asked you to substantiate your claims and demonstrate why I did not kill the positive feedback hypothesis, not to produce white swans. Have a look at the 4AR WG1 chap 6, lots of white swans. I know them. In fact Caillon et al is my first reference in demonstrating how the positive feedback hypothesis was develloped.

Your interpretation of what the data should look like is not a black swan, disproving the white swan theory. Actually I found your use of the white swan theory as an analogy to be a stretch.

You are choosing an area where their is still a lot of unknowns and attempting to twist the unknowns it into a proof of the falsification of a widely accepted theory.

I see that no engineers commented on your positive feedback model.

I don't know much about it but from a layman's perspective you are saying that the feedback response is polarized + -, 0 1, on off, etc. Why should I assume that feedback is as you say it should be?

Why should I assume that because you can demonstrate exceptions that the rule is invalid?

Is there more going on than we know? Absolutely. But as far as the CO₂ amplifying and enhancing the warming during the interglacials, it is the only explanation, at present that explains it. The science behind the theory is sound. If your little positive feedback model were the black swan that debunked the IPCC, I think it would get more attention than a thread on the Earth Forum on PF.

 

[Andre]

Your interpretation of what the data should look like is not a black swan, disproving the white swan theory. Actually I found your use of the white swan theory as an analogy to be a stretch.

You are choosing an area where their is still a lot of unknowns and attempting to twist the unknowns it into a proof of the falsification of a widely accepted theory.

.

No there is a claim that temperature differences between interglacials and ice ages are boosted by CO2 positive feedback. It's repeated about seven times in the last chapter 6 of WG1 part of the 4AR. That claim proofs to be false by the lack of persistance typical for positive feedback, especially with such a lag.

I see that no engineers commented on your positive feedback model.

Curiously indeed. What can you make of that? There are a few engineers around here renowned for never missing an opportunity for beating up crackpots. Hmmm, why didn't that happen?

I don't know much about it but from a layman's perspective...

Now is this from the same person who said:

...I found your analysis of the date to be amateurish and biased...

So my guess is that the post where that came from, is a copy-paste of a reply on a email requesting to crunch this attack. The offensive maverick style is typically Gavin. Could also be Mike.

you are saying that the feedback response is polarized + -, 0 1, on off, etc. Why should I assume that feedback is as you say it should be?

I think I tried to explain that feedback is either positive, negative or zero with large differences in system response. By the way, I should explain that over three decades ago on the Mil Acadamy my second study choice was system response and feedback, signal processing. Level about equivalent to Bsc, but that's a long time ago. Halfway that period I needed some refreshment for a test pilot course. I admit to be rusty on the calculus but I have some proficiency in building simulation models (not prediction models). That's actually surprisingly easy considering the head acheing complex math.

Why should I assume that because you can demonstrate exceptions that the rule is invalid?

The essential part is that it demonstrates that the rising CO2 did not provide warming feedback. Now, skip the last unneccesary word: It demonstrates that the rising CO2 did not provide warming. Actually more precise: It demonstrates that increasing CO2 values had no effects on the Antarctic isotopes.

If it didn't do it then, why should it do it now. If water didn't boil at 200F in the ice ages, why would it do so now? Physical rules have no exceptions otherwise it wouldn't be a physical rule.

Is there more going on than we know? Absolutely. But as far as the CO₂ amplifying and enhancing the warming during the interglacials, it is the only explanation, at present that explains it.

No it does not explain anything, as soon as you bring the different specialities together, what you get is a mess.

The science behind the theory is sound. If your little positive feedback model were the black swan that debunked the IPCC, I think it would get more attention than a thread on the Earth Forum on PF.

if you study Thomas Kuhn you would understand why that is not so:

http://www.des.emory.edu/mfp/Kuhn.html

 

[mheslep]

I see that no engineers commented on your positive feedback model.

Curiously indeed. What can you make of that? There are a few engineers around here renowned for never missing an opportunity for beating up crackpots. Hmmm, why didn't that happen?

I'm an engineer, electrical. I'm not sure I follow the definitions of the system or the forcing function you are guys are trying to model. I'll just state that to the degree that pieces of the system can be described as linear and time-invariant then in that region any introduction of positive feedback will introduce an exponential term something like
$$e^{at}, a>0$$
or
$$sin(\omega t) e^{at}$$
into the system output depending on the damping and bandwidth of the original system and the positive feedback (sub) system. If the system is non-linear, well, most anything can happen in non-linear as long as energy is conserved but as an engineer Id just keep looking for some trick that would allow me to approximate the system as linear.

 

[Skyhunter]

I found your interpretation biased because you are using your own models reaction to bias your conclusion. I find it amateurish because you are basing your conclusion on a small sample of data. CO₂ and ¹⁸O, relating one to the other as if they existed in a vacuum and not as part of a complex climate environment.

14,000 years ago when we see a spike in CO₂ and a drop in ¹⁸O.

What else was happening 14,000 years ago that might have had an impact on climate aside from CO₂?

http://www.newsandevents.utoronto.ca/bin4/030313a.asp

Sea level changes recorded in corals and organic material from places like Barbados and Vietnam indicated that roughly 14,000 years ago, the world's sea level rose by an average of 20 metres over the course of about 200 years - roughly 100 times faster than today's rate of sea level rise.

The 2002 article countered the long-standing belief that the melting ice came from North America. Instead, said Mitrovica, it mostly came from the Antarctic. The profound climate repercussions of this event, known as meltwater pulse 1A (mwp-1A), are described in the latest paper, which is co-authored with Clark, principal investigator Professor Andrew Weaver and post-doctoral fellow Oleg Saenko of the University of Victoria.

The team created a computer model to simulate the effect of mwp-1A. They found that if a massive influx of freshwater were suddenly deposited in the southern oceans, it intensifies a massive river of warm water called thermohaline circulation.

Whether or not the mwp was triggered by Antarctica or Greenland the effects of such events are important factors when deciphering and interpreting the paleo record. Not only does all the fresh water in the oceans change circulation, but it also alters the isotopic ratio of the oceans.

Your interpretation does not consider these factors.

Your simple model does not contain a carbon cycle.

Climate models used by climate scientists that do not contain a carbon cycle treat CO₂ as a forcing, and not a feedback.

The fact that the real world does not match the expectations of your model, IMO is more a statement about your model than the positive feedback of CO₂.

The scientists on the NERC thread seemed to have trouble understanding your question about CO₂. My take was they couldn't believe you would be questioning something so fundamentally well understood and universally accepted. Without CO₂ the Earth is a snowball. The effect is well and thoroughly understood, measured, and quantified.

If you want to be have your ideas considered seriously you need to explain the warming without CO₂. Telling scientists that they are making fundamental mistakes without a plausible counter explanation for what is observed is not going to convince anyone.

My take is you just want to become famous by exposing a false scientific assumption. I am just speculating here based on the subjects of most of your threads. You have threads and posts about a conspiracy to supress CO₂ measurements, accusing scientists of not knowing BC from BP, challenging the interpretation isotope proxies, 10,000 year old cities buried under glaciers, to challenging the basic science underlying the greenhouse effect.

Good luck on your search for your black swan. but I don't think you have found one here.

 

[mheslep]

My take was they couldn't believe you would be questioning something so fundamentally well understood and universally accepted. Without CO₂ the Earth is a snowball. The effect is well and thoroughly understood, measured, and quantified.

If you want to be have your ideas considered seriously you need to explain the warming without CO₂.

Eh? I thought it was well known that most of the delta between a pure black body Earth and current temps was due to water vapor? Is it all CO₂?

 

[Andre]

I found your interpretation biased because you are using your own models reaction to bias your conclusion. I find it amateurish because you are basing your conclusion on a small sample of data. CO₂ and ¹⁸O, relating one to the other as if they existed in a vacuum and not as part of a complex climate environment.

...
Good luck on your search for your black swan. but I don't think you have found one here.

You have very peculiar ideas. There is something as curiousity.

About the feedback model. You must realize that it's merely a simulation of a standard positive feedback process, any process. regardless if it is nature, electricity, mechanical, the same principles apply. once more: One of the principles of a strong positive feedback mechanism, as required here is the bi-stability in the extreme values, either high or low, on or off. Nothin in between. Once the system departs from one stable extreme, the positive feedback becomes increasingly the overwhelming primary steering factor, regardless if it is mechanical, electric or natural. This means that halfway the system is highly insensitive to natural inputs. So, whatever happens halfway should be irrelevant, the system should barely react to that. But yet it does. it reverses trend for some reason, despite the overwhelming primary controlling positive CO2 feedback. Which reason is irrelevant, whatever happens.

The point is that this reason must be strong, much much stronger than the positive feedback, successfully shutting down the feedback effects for some 800 years. That doesn't really make sense. Alternately, it is simply showing that there is no strong positive feedback. That's it, regardless what the complexity of the systems.

I'll get back to meltwater pulse 1A which you describe in the other thread

 

[kamerling]

In the other thread we / errm I discussed that theories cannot be proven but they can be falsified.

Actually, without positive feedback, more CO2 is merely a mild friendly climate alleviator at the most

So the issue here is the positive feedback factor of CO2 on the termination of ice ages. It is exhaustively discussed that in the ice cores we see the oxygen isotope (d18O) spikes rise before the CO2 does (d18O is assumed to be temperatures). As the CO2 is lagging 600+/- 400 years, normally this would refute the idea that CO2 causes temperature rise, instead temperature rise seems to rise the CO2.

But there is always a remedy, positive feedback. So some trigger (earth -milankovitch wobbles are assumed to trigger a first faint warming, which induces CO2 increase with some delay, probably because of warming oceans and as soon as CO2 rises, positive feedback kicks in, increasing the warming, which increases the CO2 etc etc a strong positive feedback loop. Case solved.

However, if that is a hypothesis, where are the studies that test it? I haven't seen one. Why are the warmers not pointing at any scientific substantiation when talking about positive feedback?

because it's not true?

I think the main reason this is believed, is that the temperature difference between glacial minima and maxima can't be explained with just the effects of milankovich cycles+ice albedo+increased water vapour.

To make this calculation you would take data from periods where the temperature was stable and not from periods with rapid warming where production of meltwater, ice albedo changes, changes in sea currents etc. could easily produce variations in the temperature that have nothing to do with co2

 

[kamerling]

You have very peculiar ideas. There is something as curiousity.

About the feedback model. You must realize that it's merely a simulation of a standard positive feedback process, any process. regardless if it is nature, electricity, mechanical, the same principles apply. once more: One of the principles of a strong positive feedback mechanism, as required here is the bi-stability in the extreme values, either high or low, on or off. Nothin in between.

This is simply not true. If the positive feedback is small enough it will result in amplification of the forcing.

 

[vanesch]

This is simply not true. If the positive feedback is small enough it will result in amplification of the forcing.

This is correct. Positive feedback can do anything.

If you have a system with an "open loop" amplification A, which means that

(out) = A (in-raw)

then positive feedback means that one adds part of (out) to the input:

(in-raw) = (in) + b x (out)

where b gives you the strength of the feedback.

(out) = A ( (in) + b x (out) )

You can solve this for the output:

(out) = A / (1 - A x b) (in)

So it seems that the system WITH feedback has an overall amplification of:

A_overall = A / (1 - A x b)

For negative feedback, the sign of b is reversed, and we see that for NEGATIVE feedback, we have that the overall amplification is a fraction of the "open loop" amplification. In fact, if the open loop amplification A is big enough, then A_overall ~ -1/b and our amplifier is now purely determined by the negative feedback, something which electronicians like a lot.

For positive feedback, it depends on whether A x b is bigger than 1 or not. If A x b is smaller than 1, then we've just INCREASED the overall amplification. The thing acts as a stronger amplifier than in "open loop". If A x b comes close to 1, we get HUGE amplifications, and when it crosses 1, we get an instable behaviour.

 

[Andre]

Note that I said:

You have very peculiar ideas. There is something as curiousity.

About the feedback model. You must realize that it's merely a simulation of a standard positive feedback process, any process. regardless if it is nature, electricity, mechanical, the same principles apply. once more: One of the principles of a STRONG positive feedback mechanism, as required here is the bi-stability in the extreme values, either high or low, on or off. Nothin in between. ....

For a bi-stable flip flop mechanism all you need is the total gain (both process and feedback) in the closed loop to be >1.

 

[vanesch]

For a bi-stable flip flop mechanism all you need is the total gain (both process and feedback) in the closed loop to be >1.

Yes, that's correct. But the loop gain (my b x A) might be smaller than 1 ; in that case you simply get amplification. And if you allow for a frequency-dependent loop gain, then you can do whatever you want.

But even in the static case, say, if the "amplifier" open loop has a gain of say, 1 degree for 1000 ppm (just an example), then for an increase by 300 ppm you'd have an increase of 0.3 degree in open loop. Now, imagine that there is a feedback mechanism that gives you a b-factor of, say, 900 ppm per degree. Well, then the loop gain is b x A = 900 x 1/1000 = 0.9, and our closed loop amplification now becomes:

(1/1000 degree per ppm) / (1 - 0.9) = 1/100 degree per ppm.

So now an initial increase of 300 ppm will give you an output of 3 degrees, 10 times more.

But there is no bistability in this model.

I'm not saying that this is so, but I'm saying that it is not mathematically impossible.

My personal objection would be that it needs "fine tuning": the feedback mechanism (the b) must be such that it is just a little bit below the inverse of the amplification, and if these are two totally distinct phenomena, there is a priori no reason why these numbers should be close. It doesn't exclude the possibility, but it would be strange.

It would be strange that some atmospheric transmission gives us 1/1000 degree per ppm, and that a totally different process, oceans or I don't know what, give us 900 ppm / degree.

Because this is CLOSE to instability, and on the other hand if it were only, say, 90 ppm/degree, the effect would not be noticable (a change by a factor of 1.1 instead of a change by a factor of 10).

 

[Andre]

Note that for the http://www.biocrawler.com/encyclopedia/Global_climate_change bi-stability is required for the swaps from the glacials to the interglacials. It is believed that when small Earth orbital variations (Milankovitch cycles) amplify each other, they would trigger the swap to the other stable condition only, CO2 being the driving force in combination with ocean temperatures to maintain that condition for a prolongued time. (warm oceans means less capacity for gas absorbtion, means more CO2 in the atmosphere means higher temperatures for interglacials and vice versa for glacial periods).

This bi-stability was also the conclusion from the enigmatic Dansgaard Oeschger events as can be seen here:

http://www.ncdc.noaa.gov/paleo/abrupt/images/cariaco.jpg

Both the Cariaco basin (Caraibic sea and the Greenland Ice cores) display behavior what could be explained as a bi stable positive feedback system. Hence my initial introduction that going in and out ice ages is assumed to be a oversteered process, ocasionally swapping from low to high system limits, and that is what is refuted by the Antarctic cold reversal of ~14 K years ago.

There are more problems with that feedback idea though, not only the one that this thread was about. See also here.

 

[vanesch]

I have been thinking a bit about this, and I see a problem, as a matter of principle.

First of all, "strong positive feedback" by itself doesn't give rise to bi-stability. It only gives rise to exponential divergence, one way or another. To obtain bi-stability, one needs a non-linear system, of which the "feedback" is only a local linearisation. In fact, to obtain bi-stability, you need a system which has an instable region (with strong positive feedback, in the local linear approximation) AND you need two regions with stability (hence, BI-stability!). In these regions of stability, you CANNOT have strong positive feedback - rather negative feedback.

So demonstrating that one has bi-stability would NOT be a proof of positive feedback OUTSIDE of the region in between the two former regions of stability.

So if you have a positive feedback (instability) in between one stable situation (glacial period) and another stable situation (interglacial), which makes one "flip" quickly from one to the other once the external perturbation is large enough to leave the "islands of stability", then this is in no way a proof that one has the same instability on the OUTSIDE of this interval. Even more so: if we are now in an interglacial period, we should rather be stabilized against further heating, because otherwise there is no reason to expect that the heating that occurred between the glacial and the interglacial would STOP at the interglacial: if we are truly in a system with general positive feedback, it would continue to diverge.

That said, it is also possible that ABOVE the interglacial island of stability, there is a NEW region of instability, but this then has nothing to do with the instability in between glacial and interglacial periods, as it is necessarily separated from it by an island of stability.

To take your electronic flip-flop analogy: between 0.5V and 4.5V (TTL), yes, there's an instability given by the positive feedback. But when reaching 0.5 or 4.5 V, the diminishing gains of the transistors (because they are squeezed off) bring this instability to an end, and even reach a stable operation. If you now artificially bring the output to 4.7V, it will not diverge again, to say, 10V or so, but will return to 4.5V after taking away the stimulus.

 

[Andre]

So if I understand the reasoning we still have the problem of the reversal halfway, not opposed by the alleged positive feedback of the rising CO2.

See also the uploaded graph in the OP.

Another problem, proposed by some, is that positive feedback with a total gain >1 would violate the energy conservation law, apparently it would create energy, if I'm understanding correctly.

Apart from that there are several other issues with regarding the ice ages as a bi-stable feedback process, as I have shown in several older threads. But I'm happy to repost that if there is some interest in it.

 

[vanesch]

Another problem, proposed by some, is that positive feedback with a total gain >1 would violate the energy conservation law, apparently it would create energy, if I'm understanding correctly.

This is probably not true: in a flip-flop, you do have such feedback. The energy comes from the power supply. Here, it comes from the sun. When I was a student, I had courses by an assistant who was a PhD student, and his PhD was about bi-stability, and positive feedback, in optical non-linear systems. It went as follows:
he had a material (a kind of semiconductor, I don't remember exactly what it was), which had more or less optical absorption (actually, in the IR, he used a CO2 laser) as a function of its temperature - I think the idea was that at higher temperature, more electrons got into the conduction band, and as such, absorbed more light etc...

Well, he was able to construct a bi-stable system, by having a (big) laser beam shooting at his piece of material (which was also connected to a cooling system with waterflow). When the material was cold enough, it was transparent to the laser beam, and remained cold and transparent. But if he applied a "glitch" of heat (heating the cooling water temporarily), the thing got a bit less transparent, absorbed more laser light, which heated the thing even more etc... and he flipped into the "dark" state, which was stable in itself.
He could make it flip back in the transparent state by stopping the laser beam for a small moment (it cooled then and became transparent again).

His hope was to make a kind of optical transistor out of this, but I think it stopped there.

But this shows that such kind of systems is conceivable.

 

[Andre]

This is probably not true: in a flip-flop, you do have such feedback. The energy comes from the power supply. Here, it comes from the sun.

The source of that statement was subject in this thread:

https://www.physicsforums.com/showthread.php?t=220771

with the http://met.hu/doc/idojaras/vol111001_01.pdf stating:

Runaway greenhouse theories contradict to the energy balance equations and therefore, can not work.

Interpreting "runaway" as total gain >1

 

[vanesch]

Interpreting "runaway" as total gain >1

But what about the thing this PhD student made in the lab then ? It had a "hot" and a "cold" state, there was incoming radiation (from the laser), and there was a heat sink (the cooling system).

 

[Andre]

Maybe the analogy is not perfect. I'm sure that there are plenty of positive feedback systems not cheating with the energy bill, but I'm not sure about climate and atmosphere. I will have to study that paper to understand his reasoning.

But apart from that I have some doubts with the MODTRAN method. Of course it nicely illustrates that doubling greenhouse gasses gives a near constant delta in the IR radiation; but, the idea with MODTRAN is to restore the original IR radiation by adjusting the "Ground T offset, C". The question is if this is legal. All you have is the additional delta in radiation but the way to change that into temperature finds Stefan-Boltzmann's law on its path with the quadruple root. Hence the radiation energy required to increase temperature rises much quicker than the supply of radiation energy. This seems pretty effective against runaway tendencies. So putting in a number in the Ground T-offset cell may be disdaining some physical laws and create energy.

Apart from that, there is also the main water feedback mechanism which assumes constant relative humidity, which in turn is exponentially related to the temperature (Clausius Clappeyron). So boosting the water cycle for more relative humidity needs exponentially more energy, which also may act as a fairly effective brake on the runaway condition.

 

[vanesch]

This is slightly related, but I read the fourth assesment report summary of the IPCC, and something struck me. They say on p38 of http://www.ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr.pdf

Direct emission of water vapour (a greenhouse gas) by human
activities makes a negligible contribution to radiative forcing. However,
as global average temperature increases, tropospheric water
vapour concentrations increase and this represents a key positive
feedback but not a forcing of climate change. Water vapour changes
represent the largest feedback affecting equilibrium climate sensitivity
and are now better understood than in the TAR. Cloud feedbacks
remain the largest source of uncertainty.

So the hypothesis is that water vapor, for which there is a cycle with a large reservoir (oceans,...) will not be a "directly modifiable variable", but will be given by an equilibrium value of the system, even if humans would put a lot of water vapor in the atmosphere. I can understand that. But the question is: why isn't the same valid for the CO2 ? After all, it is also part of a cycle, there are big reservoirs (oceans, vegetation) of it, so why do we assume that we CAN change the CO2 concentration in the atmosphere by just "adding a bit to it" ? Why doesn't CO2 in the atmosphere settle to an equilibrium value, just as water vapor does ?

Now I know the argument of the isotope ratios but that is not convincing that the AMOUNT of CO2 is due to fossil fuel burning by itself. Imagine the following situation: you're at the shore, it is low tide, and now you're going to pour tons and tons of water in the sea. That water contains a chemical or isotopic marker - say, a higher deuterium content. You see that the water level is rising. When you analyse the water at the shore, you see that it has a higher deuterium content. Conclusion: you have been rising the level of the sea !

No, of course not: the tide is rising. But because you've been poring high-deuterium content water in the sea, near to where you are going to analyze the water, you will find a higher fraction of it in your samples. But that's no proof that the SEA LEVEL increase is due to you poring water in the sea. The sea level will settle to an equilibrium value determined by the tidal system, and will not care about the few tons of water you pored into it.

Now, imagine that the CO2 is part of a big carbon cycle, which will determine the equilibrium value of CO2 in the atmosphere (analogy: the tides of the sea). Now, if, at some place along this cycle, you inject marked CO2 (with different C-12/C-13 ratio), let us say, at the "atmosphere" side (the poring in of a few tons of water in the sea), then of course you will find a trace of this injection in the samples. But that doesn't prove that the VALUE of the CO2 level (the height of the tide) is rising because of your injection!

So what deductive argument can make us conclude that the RISE of the CO2 in the atmosphere is due to the amount we inject in the carbon cycle ? And why doesn't this value settle to an equilibrium value in its cycle, just as water vapor does ?

Are there arguments, such as the slowness of the carbon cycle (does it take hundreds of years for instance) so that we haven't yet reached equilibrium ? Or are the amounts injected significant with respect to the entire quantity of carbon in the cycle ? (that would be, in our analogy, that we've injected an amount of water which is not negligible compared to the total contents of the sea).

The point is: if the CO2 concentration in the atmosphere is part of a dynamics, then it is this dynamics which is going to determine the CO2 level at equilibrium, and extra injections will not change this equilibrium value by much more than the amount injected over the total amount in the cycle - except of course temporarily, if the kinetics of the cycle is slow.
So if one wanted to change the CO2 concentration in the atmosphere, then the most intelligent thing would not to just inject CO2 in the atmosphere (and "fight" against the dynamics of the carbon cycle), but rather to change the parameters of the cycle so that the equilibrium value in the atmosphere would change.

 

[Andre]

Exactly.

I'm getting average 5-6 e-mail a day (the max was 50) from several e-mail circles discussing these dynamics. A few topics: estimates about the half value time of CO2 towards a new static balance point range from four, five years to several hundreds. The isotope ratio (d13C) of CO2 is decreasing, which is consistent with fossil fuel consumption but it's also consistent with possible increased ocean over turning, as deep ocean carbonates/CO2 are also depleted with 13C and radioactive 14C. But this discusion is less relevant if it is evident that the impact of increased levels of CO2 on global climate is rather overrated, especially the role of water vapor feedback as in the IPCC quote.

 

[siphon]

One idea that needs to be looked at is the affect of atmospheric water on CO2. If we react water with CO2 we get carbonic acid, which is not a gas a room temperature. As the CO2 heats the earth, more water goes into the atmosphere. The net affect is water regulating CO2 by reacting with it to form something that rains.

There is also another affect, connected to the greenhouse heat storing affect of CO2. A CO2 molecule can store energy as bond bending, vibration, rotation and translation. If we add H20 to the blend, because of carbonic acid H2CO3, any sticky collision with water will bleed energy out of CO2 even if H2CO3 forms and reverses. The reason this is so, is if H2O and CO2 combine for a second, this will lower the degrees of freedom for CO2. In H2CO3, the CO2 goes from linear to triangle. This messes the vibrations and bond bending it once had, since it gets stuck bent. The two molecules now have to rotate and translate together, but being one bigger thing, the CO2 has slowed down. When the CO2 breaks free it has lower energy, and has to build this up again. The net affect is lowering CO2 greenhouse efficiency with more water collisions.

The latter is a theory based on chemistry logic.

 

[Bystander]

(snip) Why doesn't CO2 in the atmosphere settle to an equilibrium value, just as water vapor does ?

(snip)So what deductive argument can make us conclude that the RISE of the CO2 in the atmosphere is due to the amount we inject in the carbon cycle ? And why doesn't this value settle to an equilibrium value in its cycle, just as water vapor does ?

Are there arguments, such as the slowness of the carbon cycle (does it take hundreds of years for instance) so that we haven't yet reached equilibrium ? (snip)The point is: if the CO2 concentration in the atmosphere is part of a dynamics, then it is this dynamics which is going to determine the CO2 level at equilibrium, and extra injections will not change this equilibrium value by much more than the amount injected over the total amount in the cycle - except of course temporarily, if the kinetics of the cycle is slow.
So if one wanted to change the CO2 concentration in the atmosphere, then the most intelligent thing would not to just inject CO2 in the atmosphere (and "fight" against the dynamics of the carbon cycle), but rather to change the parameters of the cycle so that the equilibrium value in the atmosphere would change.

The mass of the atmospheric CO₂ "reservoir" is ~ 3x10¹⁵ kg; the exchange rate with the biological "reservoir" is 3-6x10¹⁴kg/a; atmospheric "residence time" is then 5-10 a. Water mass is ~ 10¹⁶ kg, and residence time is weeks to months (depending on sources you choose for water mass and annual precipitation rates).

"Equilibrium" is not the word you want to use, "dynamic steady state" concentrations of various substances within various reservoirs as functions of various processes transporting those substances among those multiple reservoirs is about as close as you're going to get. "Mixing rates" for reservoirs? Weeks for hemispheric circulation; 1-2 a for mixing between northern and southern hemisphere atmospheres; millennia for marine "overturn" and exchange of gases with the atmosphere.

Isotope ratios? Fossil fuels are indistinguishable from biological carbon (light); lime burning is heavy; "whitings" are heavy; molluscs and corals are ____ (you really got to know, I'll dig it up); carbon-14 formation takes place only in the atmosphere, and uptake ceases at death for living organisms, or when atmospheric mixing ceases (abyssal waters in the Atlantic conveyor).

You want a "complete" list of carbon reservoirs? And exchange rates? And reservoir mixing rates? We can work on it; it's going to be a major project.

 

[vanesch]

"Equilibrium" is not the word you want to use, "dynamic steady state" concentrations of various substances within various reservoirs as functions of various processes transporting those substances among those multiple reservoirs is about as close as you're going to get.

Granted.

You want a "complete" list of carbon reservoirs? And exchange rates? And reservoir mixing rates? We can work on it; it's going to be a major project.

I was more thinking about the argument - if I understood it correctly - that the CO2 rise in the atmosphere is "for 60% due to fossil fuel burning", and that the proof that it is *this* CO2 is the isotopic ratio which has a "fossil signature". Now, maybe this is just a summary of a much more complex argument - that's actually my question.

But if the argument stops there, then this is only at most *suggestive*, and no *proof*: you cannot logically derive the necessity of the CO2 rise by just observing this isotopic marking.

Now, if it is part of a more complicated model, then the argument depends on the reliability of the model.

In other words, there is no direct link between the amount of CO2 in the atmosphere, the isotopic ratios and an eventual causality of the CO2 from fossil burning onto the rising of the CO2 level. But the way things are formulated often, is that this relation is evident, and that finding a correlation between the isotopic markings and the CO2 level indicates a causal link.

Or otherwise, I didn't understand the argument.

Of course, that's no proof either that this is NOT the case. It is even such, that without isotopic marking, the CO2 level rise could even be due to fossil fuel burning, if the cycle is fast enough. This indicates even more the looseness of the connection between isotopic ratios and the causality of the fossil fuel burning in the rise of the CO2 level.

See, for instance, this is pure speculation on my side of course, but it might be that the reason for the increasing CO2 levels in the atmosphere are due mainly to deforestation - I'm not going to develop that here, as I said, it is just a guess on my part. Deforestation might change the parameters of the carbon cycle, and as such, make the atmosphere settle to another steady-state value, with or without burning of fossil fuels. The observational results would be quite similar if the numbers come out right. Again, I'm just making this up here, I'm not advancing it as a "theory", but just to indicate that *suggestive* evidence (the isotope ratio) is not air-tight proof. Then again, I might misunderstand the whole argument, but that's what I make of it.