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Author Topic: Global Warming : The World Is On Fire  (Read 18316 times)

another_someone

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Re: Global Warming : The World Is On Fire
« Reply #25 on: 31/07/2006 14:11:49 »
quote:
Originally posted by crandles
What makes you so sure of this? Why cannot the appearance of multiple stable states be a result of the forcings applied  eg Milankovitch cycles. To first order, the most important consideration is that the hotter the earth the more heat it ratiates. This creates the stability in the same manner as the leaky bucket analogy. A steady state can be reached. Reduce the size of the hole and the water level starts to rise but it doesn't necessarily overflow the bucket a new equilibrium level is likely to be reached because the flow out of the hole depends on the height of water.

Since there appear to be net positive feedbacks at more than one point in time (eg current, LGM, and other times from which estimates of climate sensititivity have been made), it is possible that at another point in time the net feedbacks could be different but that doesn't mean they are likely to become negative and I suggest that the experts know enough to say they are very unlikely to become negative soon.



A system that has pure positive feedback, and no negative feedback component, will always be in a runaway condition this is not what the Earth has ever done historically.

Even with regard to Venus, which is often cited as a runaway condition that the Earth could fall in to it is not at all in a runaway condition Venus is relatively stable (possibly even more stable than the Earth), but is merely stable at a higher temperature.

Thus, to avoid runaway, you must either have absolutely no feedback, or a substantial component of negative feedback.  Since we know that we do not have a condition on Earth where there is no feedback, thus we may reasonably surmise that there are substantial negative feedback processes in place.



George
 

another_someone

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Re: Global Warming : The World Is On Fire
« Reply #26 on: 31/07/2006 14:32:26 »
quote:
Originally posted by crandles
This is actually funny. [:o)] Who is being selective? Is it the climatologists at realclimate for ignoring the other cause?

or could, just perhaps, it be the case that they are considering both causes of warming (one known to have a positive contribution and the other which is unknown whether it continues or not) and it is you being selective in wanting to consider only one cause of warming and deliberately ignoring the CO2 when that is the cause we know to have a greenhouse effect which will have a positive effect on temperature.

I don't think occam razor suggests ignoring a known cause in favour of an unknown one.



We are not here looking at a known cause versus an unknown cause.

What we are talking about is an observed, but not understood, cause; and a hypothesised but not definitely observed cause.

What I am saying is when one compares hypothesis to observation, observation should always take precident.

We know there is a cause of global warming that does not include CO2, although we have no hypothesis that yet explains what it is.  We know that rises in CO2 seem to follow (not lead) these rises in temperature, and thus may infer (although cannot with certainty know) that CO2 rises are caused by rises in temperature.

We have a hypothesis that suggests that increased levels of CO2 should cause rises in temperature yet we have no quantitative observations of such an effect that could unambiguously show this to happen.

A few things we do know:

  • Temperature rises can occur even in the absence of rising CO2.

  • Temperature falls can happen even after CO2 levels have risen.


We have a hypothesis that suggests that temperatures should rise after an increase in CO2 levels, and that temperatures will continue to remain high as long as CO2 levels remain high.  We know that this hypothesis conflicts with observation.  We can certainly suggest that there are unknown factors that conflict with the hypothetical case, but since we have not explained in any way what these unknown factors are, thus we have no way of knowing whether the hypothetical situation present any significant input into the real and observed results.

I accept that the hypothetical feedback cycle probably has some impact, but what I cannot accept is that it has any impact of significant quantitative levels that they may be observed against all the other (mostly unknown, although clearly present) factors that do affect global temperatures.



George
« Last Edit: 31/07/2006 14:33:04 by another_someone »
 

Offline crandles

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Re: Global Warming : The World Is On Fire
« Reply #27 on: 31/07/2006 14:32:44 »
quote:

Originally posted by another_someone

A system that has pure positive feedback, and no negative feedback component, will always be in a runaway condition this is not what the Earth has ever done historically.




Sorry but that is rubbish. Feedback can be positive but less than a factor of 1 and then you won't get a runaway condition.

Take something really simple like
xi=x(i-1)+forcing+feedback factor * ( x(i-1) - x(i-2) )

try it out with a feedback factor of greater than 1 and you do get a runaway condition. Try it with a feedback factor of between 0 and 1 and you do not get a runaway effect. The eventual change is greater than the forcing so the feedback is positive but there is no runaway effect.

The above alone defeats your "will always be"

With temperature it is much harder to get a runaway effect because of the first order effect that a hotter planet emits more radiation.


Sorry - I think I accidentally edited your post - hopefully back to where it should be.
« Last Edit: 31/07/2006 14:52:41 by another_someone »
 

Offline crandles

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Re: Global Warming : The World Is On Fire
« Reply #28 on: 31/07/2006 14:47:28 »
quote:
We have a hypothesis that suggests that temperatures should rise after an increase in CO2 levels, and that temperatures will continue to remain high as long as CO2 levels remain high. We know that this hypothesis conflicts with observation.


Do you want to try again on that one?

800 years is less than 20% of the 5000 year period. Given that there are lots of these periods and some show those 800 year periods and that the hypothesis is that CO2 (not alone but among other things affects temperature) then that is good observational evidence that CO2 does have the effect expected and that other causes do not dominate over the effect of CO2.
 

another_someone

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Re: Global Warming : The World Is On Fire
« Reply #29 on: 31/07/2006 14:52:04 »
quote:
Originally posted by another_someone
Sorry but that is rubbish. Feedback can be positive but less than a factor of 1 and then you won't get a runaway condition.

Take something really simple like
xi=x(i-1)+forcing+feedback factor * ( x(i-1) - x(i-2) )

try it out with a feedback factor of greater than 1 and you do get a runaway condition. Try it with a feedback factor of between 0 and 1 and you do not get a runaway effect. The eventual change is greater than the forcing so the feedback is positive but there is no runaway effect.

The above alone defeats your "will always be"



Sorry, but how is the above a pure positive feedback mechanism you have a term -x(i-2) by my reckoning that amounts to a negative term, and thus a negative feedback component.


quote:

With temperature it is much harder to get a runaway effect because of the first order effect that a hotter planet emits more radiation.



But that too is a negative feedback, since it is a factor that increases the cooling as an increase in temperature occurs.

Ofcourse, as long as the effect is linear, then the effect will only reduce the rate of runaway, but not be sufficient to stop it.  If you can demonstrate that proportion of temperature radiated increases with increasing temperature, then you would maybe be able to show it was sufficient to stop runaway; but at present, the indications are actually contrary, that as temperature increases, so the amount of ice on our planet reduces, and so the albedo of our planet reduces, and so the negative feedback becomes less effective (i.e. we have a positive feedback cycle that dominates over the negative feedback cycles).  Ofcourse, there may be other planets, with different surface chemistries, that might have a different relationship between albedo and surface temperature.



George
 

Offline crandles

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Re: Global Warming : The World Is On Fire
« Reply #30 on: 31/07/2006 15:14:45 »
quote:
Sorry, but how is the above a pure positive feedback mechanism you have a term -x(i-2) by my reckoning that amounts to a negative term, and thus a negative feedback component.


Sorry not sure how to do subscripts on this forum yet. The i, i-1 and i-2 terms are all supposed to indicate time periods.

So start at a temperature of 10C. Apply a forcing that causes a 1C rise (This could be doubling of CO2 or something else. The temp initially goes to 11C then the feedback starts kicking in. If the feedback factor is 0.5 the temp would go to 11.5 then 11.75 then 11.875 and so on up to 11.999999. That is clearly a positive feedback that does not not lead to a runaway effect.  
« Last Edit: 31/07/2006 15:15:18 by crandles »
 

Offline crandles

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Re: Global Warming : The World Is On Fire
« Reply #31 on: 31/07/2006 15:19:10 »
quote:
Ofcourse, as long as the effect is linear, then the effect will only reduce the rate of runaway, but not be sufficient to stop it. If you can demonstrate that proportion of temperature radiated increases with increasing temperature, then you would maybe be able to show it was sufficient to stop runaway; but at present, the indications are actually contrary, that as temperature increases, so the amount of ice on our planet reduces, and so the albedo of our planet reduces, and so the negative feedback becomes less effective (i.e. we have a positive feedback cycle that dominates over the negative feedback cycles). Ofcourse, there may be other planets, with different surface chemistries, that might have a different relationship between albedo and surface temperature.


No it is basic physics that a hotter body radiates more heat.

(Therefore the effects are much less than linear. This is why climate sensitivity is defined in terms of the effect of doubling CO2 you have to increase CO2 much more than linearly to get a constant response.)

The ice albedo effect is a positive feedback not a negative one. But is is not strong enough to overcome the first order effect that hotter bodies radiate more heat.
« Last Edit: 31/07/2006 15:21:00 by crandles »
 

Offline crandles

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Re: Global Warming : The World Is On Fire
« Reply #32 on: 31/07/2006 15:22:46 »
quote:
Originally posted by another_someone
quote:

With temperature it is much harder to get a runaway effect because of the first order effect that a hotter planet emits more radiation.



But that too is a negative feedback, since it is a factor that increases the cooling as an increase in temperature occurs.




No that is part of the system not a feedback.
 

another_someone

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Re: Global Warming : The World Is On Fire
« Reply #33 on: 31/07/2006 15:59:27 »
quote:
Originally posted by crandles
Do you want to try again on that one?

800 years is less than 20% of the 5000 year period. Given that there are lots of these periods and some show those 800 year periods and that the hypothesis is that CO2 (not alone but among other things affects temperature) then that is good observational evidence that CO2 does have the effect expected and that other causes do not dominate over the effect of CO2.



Sorry, but all that the coincidence between rises in CO2 and increased temperature shows is correlation, not causality.  The fact that increased temperature precedes increases in CO2 is strongly indicative (but does not prove) that CO2 responds to temperature.  Anything else is pure hypothesis.

Ofcourse, so long as there is observable coincidence, it is valid to ask whether there is a two way causality; but there is no necessity to assume this simply to explain the observed evidence.





George
 

another_someone

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Re: Global Warming : The World Is On Fire
« Reply #34 on: 31/07/2006 16:05:49 »
quote:
Originally posted by crandles
Sorry not sure how to do subscripts on this forum yet. The i, i-1 and i-2 terms are all supposed to indicate time periods.



Neither do I, but I did understand what you were saying.

quote:

So start at a temperature of 10C. Apply a forcing that causes a 1C rise (This could be doubling of CO2 or something else. The temp initially goes to 11C then the feedback starts kicking in. If the feedback factor is 0.5 the temp would go to 11.5 then 11.75 then 11.875 and so on up to 11.999999. That is clearly a positive feedback that does not not lead to a runaway effect.  



The system as you described it was :

xi=x(i-1)+forcing+feedback factor * ( x(i-1) - x(i-2) )

this can be expanded to:

xi=x(i-1)+forcing + feedback factor * x(i 1) - feedback factor * x(i 2)

In other words, there is a component of the output (from two time slices earlier) that is subtracted from the input this makes it negative feedback.  There is also a component (from the immediately preceding time slice) where the output is added to the input, and this is a positive feedback.  So your system contains both positive and negative feedback components.



George
« Last Edit: 31/07/2006 16:16:41 by another_someone »
 

another_someone

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Re: Global Warming : The World Is On Fire
« Reply #35 on: 31/07/2006 16:15:29 »
quote:
Originally posted by crandles

quote:
Originally posted by another_someone
quote:

With temperature it is much harder to get a runaway effect because of the first order effect that a hotter planet emits more radiation.



But that too is a negative feedback, since it is a factor that increases the cooling as an increase in temperature occurs.




No that is part of the system not a feedback.



I will probably grant you this (at least insofar as the effect is linear), because it is an effect that is purely dependent upon the inputs to the system, and not dependent upon any function or output of the system itself.

Nonetheless, any non-linearity (such as caused by changes in albedo, or changes in heat retention, must be regarded as feedback effects, since they are caused by changes in state of the system that is itself caused by previous inputs into the system).



George
 

Offline crandles

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Re: Global Warming : The World Is On Fire
« Reply #36 on: 31/07/2006 16:25:22 »
The initial forcing pushes it up from 10 to 11. The new equilibrium level is 12. Therefore the effect of a feedback factor of 0.5 is to increase the movement of the system in the same direction therefore this feedback is positive.

To quote http://en.wikipedia.org/wiki/Positive_feedback

quote:
When a change of variable occurs in a system, the system responds. In the case of positive feedback the response of the system is to change that variable even more in the same direction.


How is what I have shown not a positive feedback?

Artificially spliting my feedback funtion into two simply is not appropriate.

(edit spelling)


« Last Edit: 31/07/2006 16:27:14 by crandles »
 

another_someone

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Re: Global Warming : The World Is On Fire
« Reply #37 on: 31/07/2006 19:38:57 »
quote:
Originally posted by crandles
Artificially spliting my feedback funtion into two simply is not appropriate.



It is not an artificial splitting of your feedback function.

http://en.wikipedia.org/wiki/Feedback
quote:

In cybernetics and control theory, feedback is a process whereby some proportion or in general, function, of the output signal of a system is passed (fed back) to the input. Often this is done intentionally, in order to control the dynamic behavior of the system. Feedback is observed or used in various areas dealing with complex systems, such as engineering, architecture, economics, and biology. Continuous feedback in a system is a feedback loop.



x(i-1) and x(i-2) are two different feedback paths (they must have different paths, because they have different delays), so they must be regarded as separate feedbacks loops.  You bundling them into one feedback path is artificial, because the fact that they have different time delays means they cannot have the same path.



George
 

Offline crandles

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Re: Global Warming : The World Is On Fire
« Reply #38 on: 31/07/2006 20:43:04 »
( x(i-1) - x(i-2) ) could have been written as delta x (ie the change in the x variable) lagged by a timestep.

But suppose I describe another system which initially is in equilibrium at 10 we apply a forcing which moves the system to 11 then a feedback kicks in equal to 3 times the forcing (lagged by 1 timestep so the system moves to 14 and it then stays in equilibrium at 14.

Surely there is no negative feedback in that system and it does not go into a runaway effect.
« Last Edit: 31/07/2006 20:43:33 by crandles »
 

another_someone

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Re: Global Warming : The World Is On Fire
« Reply #39 on: 31/07/2006 23:03:04 »
quote:
Originally posted by crandles
But suppose I describe another system which initially is in equilibrium at 10 we apply a forcing which moves the system to 11 then a feedback kicks in equal to 3 times the forcing (lagged by 1 timestep so the system moves to 14 and it then stays in equilibrium at 14.

Surely there is no negative feedback in that system and it does not go into a runaway effect.



Sorry, I cannot see any description of what might be regarded as a complete system.

A system needs inputs and outputs (the closest to an input would be what you call a 'forcing'), and a complex system will normally have some feedback that moves some of the output back into the input.

You have said the system is initially at equilibrium at 10 you have not told me how this equilibrium is maintained?  One assumes that in order to maintain an equilibrium, there must be negative feedback (one cannot otherwise maintain sustained equilibrium over a range of inputs, since the only way of offsetting changes in input is to feedback some of the output to cancel the input).  What is the nature of this feedback, and how does it alter with further changes in input?

You suggest that with a further increase in input (of some unknown amount), the negative feedback is sufficiently overwhelmed to allow the output to drift to 11 but then there is a step change in the feedback that reduces the negative feedback (or possibly changes it to a net positive feedback) until the output climbs to 14, and then switches back to another negative feedback that holds it steady there.

What you have described is a system with multiple stable regions (an astable system), but you have in no way described mathematically (let alone physically) what the feedback mechanisms are that create this astable system.




George
 

Offline crandles

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Re: Global Warming : The World Is On Fire
« Reply #40 on: 01/08/2006 23:21:26 »
I cannot believe you are not accepting the obvious that a positive feedback does not always cause a runaway effect.

Suppose:
A barrel contains 120 litres of water. The inflow appears fixed at 12 litres a minute. The outflow depends on the height of the water and so is equal to 10% of the volume in the barrel per minute.

This is currently in equilibrium. We now reduce the size of the hole so the the outflow is only .075 times the volume in the barrel (units still litres per minute). Given the current knowledge of the system we would expect a new equilibium to be reached with the barrel containing 160 litres and inflow and outflow equal to 12 litres per minute.

In fact we notice the quantity in the barrel goes above 160 lites so we investigate and discover that the inflow is not fixed at 12 litres a minute but there is a system feedback such that if the outflow in one minute is greater than 9% of the volume in the barrel then the inflow is fixed at 12 litres per minute but if the outflow is less than 9% of the volume then the inflow is set at 15 litres per minute.

This system reaches an equilibrium with 200 litres in the barrel.

This is a positive feedback because the feedback moves the system more in the same direction (increasing volume in the barrel in this example).

The system reaches an equilibrium and does not suffer a runaway effect.

Hopefully that is an adequate description of a system. Now will you accept the obvious?
 

another_someone

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Re: Global Warming : The World Is On Fire
« Reply #41 on: 02/08/2006 14:46:34 »
quote:
Originally posted by crandles
Suppose:
A barrel contains 120 litres of water. The inflow appears fixed at 12 litres a minute. The outflow depends on the height of the water and so is equal to 10% of the volume in the barrel per minute.

This is currently in equilibrium.

 We now reduce the size of the hole so the the outflow is only .075 times the volume in the barrel (units still litres per minute). Given the current knowledge of the system we would expect a new equilibium to be reached with the barrel containing 160 litres and inflow and outflow equal to 12 litres per minute.

In fact we notice the quantity in the barrel goes above 160 lites so we investigate and discover that the inflow is not fixed at 12 litres a minute but there is a system feedback such that if the outflow in one minute is greater than 9% of the volume in the barrel then the inflow is fixed at 12 litres per minute but if the outflow is less than 9% of the volume then the inflow is set at 15 litres per minute.



Sorry, this statement does not make sense.

You cannot 'fix' the input of a system the whole point about an input is that it is not controlled by the system itself.  The external inputs cannot be limited to either 12 or 15 litres/minute they can be absolutely anything, since they cannot be controlled by the system if they are controlled by the system, then they cease to be external inputs and must be regarded as part of the system.

Ofcourse, you can say that there is a negative feedback system that compensates for any external attempt to increase flow above either 12 or 15 litres/minute, and a positive feedback that allows a switch between the two stable states.

If I have a barrel of water, and a tap above that barrel of water the barrel of water cannot control how much I turn on that tap.  Ofcourse, it can have a negative feedback system that causes that if the outflow each minute if less than 9% of the contents, then any water in excess of 15 litres/minute that I allow to flow out of the tap would be deflected so as not to enter the barrel but that requires a negative feedback mechanism.  The barrel cannot cause me to switch off the tap, unless I become a part of the system (e.g. I look into the barrel, and make decisions according to what I see, and thus become a part of the negative feedback mechanism).

The system you describe is a bistable system, which is not at all an uncommon situation, but it requires a mix of positive and negative feedbacks to maintain it a positive feedback to allow it to switch between stable states, and a negative feedback to maintain one or other stable state.

What you are suggesting is a system that creates a nett positive feedback over a very narrow range, and a nett negative feedback outside of that range.



George
 

Offline crandles

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Re: Global Warming : The World Is On Fire
« Reply #42 on: 02/08/2006 18:59:38 »
The above system is an analogy to the climate system. The height of water in the barrel represents temperature. The volume of water is a quantity of heat energy and flows of water are flows of heat energy.

We can change the size of the holes which is analogous to increasing CO2 in the atmosphere to reduce the rate infrared outgoing radiation below what would otherwise be expected for the temperature. This causes temperature and heat in the system to rise. Temperature increasing melts ice causing a positive albedo feedback effect where the system accepts more incoming radiation from the sun rather than it being reflected.

Thus I am not only arguing that positive feedback does not lead to a runaway effect but I am also arguing about the particular case of the climate system and the ice albedo positive feedback is not expected to cause runaway climate change.

It probably wasn't a good system to use for the purpose of showing that positive feedback does not have to lead to a runaway effect because there is negative feedback on the outward energy flow but not on the height/volume of water.

Not really sure why you cannot accept the size of the hole as an input which is under my control. The output I am interested in is the height/volume of water. Nor do I understand you calling it a bistable system as I can change the input, the size of the hole and get equilibriums at an infinite number of different volumes of water in the barrel.

A new system comprises a tower of building blocks plus my neice.

The system is currently in equilibrium at 5 blocks high. I apply a forcing of adding a block. This in the absence of feedback would be expected to move the system to a new equilibrium of 6 blocks high. However there is a feedback in this system, my neice is playing copycat and does whatever I do to the tower. Thus the system actually moves to a new equilibrium level of 7. This is therefore a positive feedback as it moves the system in the same direction. The system does not result in a runaway high tower (or no tower). Therefore not all positive feedbacks lead to a runaway effect.

 

Offline Mjhavok

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Re: Global Warming : The World Is On Fire
« Reply #43 on: 05/08/2006 03:21:23 »
A heat wave in the UK has been happening and I think temperatures have reached 37 degrees celsius.
 

another_someone

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Re: Global Warming : The World Is On Fire
« Reply #44 on: 06/08/2006 00:47:19 »
quote:
Originally posted by Mjhavok

A heat wave in the UK has been happening and I think temperatures have reached 37 degrees celsius.



They did that a week or two back, but they are far more tollerable right now.



George
 

Offline Mjhavok

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Re: Global Warming : The World Is On Fire
« Reply #45 on: 06/08/2006 03:24:48 »
I h8 it lol. Anything that makes me sweat more than normal (apart from the obvious fun thing) means I usually don't like it. I also  skin in the non cancer variety.
 

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Re: Global Warming : The World Is On Fire
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