On top of this and most importantly the Aqua satellite has compromised the IPCC computer models with the negatives cancelling out the positives…as predicted by the “deniers”.
Just how much longer are the media and politicians going to hide the truth from the public?
It is one of the most shameful episodes in the history our our “democracy”.

The problem is there are several definitions of what is meant by ‘positive’ feedback. Amplifying but stable processes may be considered positive under one definition while they are negative under another.

A simple example: we suppose the behaviour is governed by an equation dX/dt = f(X), where X is our variable under study, dX/dt is the rate at which X changes over time, and f(X) is a known function of X that says how the changes in depend on its value. The current value is fed back into the calculation of future values.

You can test to see if the process is stable by looking at df/dX, the rate at which the function changes when you vary X. If df/dX is positive, the process is unstable, and if it is negative, stable. The sign of df/dX is taken to be the sign of the feedback.

But there is another way of looking at it, and I’m sorry to say this this is going to get very mathematical from here on.
This way is to first rewrite the equation as Integral dX = Integral f(X)dt. (If you don’t know calculus, don’t worry about this. I’ve just ’sort of’ multiplied through by the time step dt to get the X step dX that corresponds to it.) The left hand side is X(t2)-X(t1) (I’ve made X a function of time again since X changes with time), the right hand side is some function g(X(t2))-g(X(t1)) representing the cumulative change in feedback. So we can find the value at a future time X(t2) = X(t1) + g(X(t2))-g(X(t1)) which is approximately X(t1) + g’(X(t1))(t2-t1), taking a first order approximation. We can absorb the (x2-x1) into the function and rename it, so we have the form X(t2) = X(t1) + h(X(t1)) where h is some new function of X. This is essentially the form cited by our friend above, where the sound at the next time step is the sound at this time step plus the echo. It is a discrete-time version of the more correct continuous time differential equation.

Now if you consider h(X) to be ‘the feedback’ the condition for stability is somewhat different. If the rate at which it varies as you change X, written dh/dX, is between -1 and 0, then the ‘echo’ cancels part of the signal and it is quieter than it would be without the feedback. If dh/dX is between 0 and 1, then the system is still stable, but the echo reinforces the sound and the eventual level is louder than it would otherwise be. Only if the dh/dX ‘feedback’ equals or exceeds 1 (or falls below -1) does it go unstable.

It is in this second sense that you can get ‘positive’ feedback being stable.

The second approach is used in a branch of mathematics called control theory, and is commonly used for designing electronic circuits. The climatologists have simply borrowed the language.

The two forms of feedback are obviously related, and both are taught in different places as being ‘the feedback’, but they are distinct concepts. So people who remember being taught that positive feedback means instability are not misremembering, nor talking nonsense. But in this case the climatologists’ definition is also correct.

The arguments here consist basically of saying ‘but positive feedback = unstable!” despite it being pointed out time and time again that this is nonsense.

“…despite our experience with other stable systems that says this is unlikely… – nonsense.”

What do you mean by nonsense? Obviously, you think there is positive feedback, but what is your counter evidence? It seems that the arguments posted on climate skeptic are pretty solid regarding positive feedback. Can you post a link to something?

-Rob

PS: Try not to post one of those links for “lazy stupid fools.” Ad hominem away!!! (i.e. Let’s not make personal attacks, it doesn’t progress the debate!)

http://www.nasa.gov/centers/goddard/news/topstory/2004/0315humidity.html

and Roy Spencer points out problems in measuring actual cloud feedback, and overestimating climate sensitivity:

http://climatesci.org/2008/04/22/internal-radiative-forcing-and-the-illusion-of-a-sensitive-climate-system-by-roy-spencer/

- A. McIntire

No, of course not. Only those questions where assorted persons are trying to claim “the debate is over”, “the science is settled”, “there is a scientific consensus”, “we’ve MovedOn from that paper and this time we’ve got all the right answers, honest”, “the conclusive evidence is already out there in the literature, … somewhere”, “we already know all the answers to this stuff, why are you still asking questions?”, “I think you’ll find that if you keep reading long enough you’ll find a rpaper that agrees with me and that’s when you should stop” and similar unscientific nonsense.

You are so transparent. Everybody here can see what you’re doing. Why do you still persist? Do you really think you can still fool anybody?

Yes, Earth Day happens to fall on Lenin’s birthday, but that is happenstance, not a plot by the usual claque of leftists that show up at the GW demonstrations. It is also the birthday of J. Sterling Morton, the originator of Arbor Day, which was proposed by him in 1872, when Vladimir was all of two years old. Earth Day is a lineal descendent of that tradition.

The usual suspects may treat this as serendipity, but lets’s not go along with them.