the positive feedback problem of global warming

[andre]

In the other thread I said

...That's not enough for being catastrophical, is it?

But there are feedbacks, mechanisms that strenghten or weaken the effect. ...Historical data proofs beyond a doubt that a bit of CO2 changes brings about large temperature changes? Hence large domination of positive feedback? Open and shut case?

Now, suppose that that Mammoth wasn't there to spoil the whole global picture and suppose that all the suppositions about temperature were right, it is still essential to proof a large positive feedback factor to explain the these changes with CO2.

So let's have a real close look at the last spike in the Antarctic ice cores some 20,000 years ago.



These are the last data sets from the EPICA dome C (Concordia). Data here:
http://www.ncdc.noaa.gov/paleo/icecore/antarctica/domec/domec_epica_data.html
used these, Monnin et al 2004 for the CO2 and these, Stenni et al 2001 for the isotopes, which is supposed to be a proxy for the temperatures.

Now we see two problems. The first problem has been beaten to death as it seems. CO2 reacts several hunderd years later than the temperature (red arrows following the blue arrows). Yes ...yawn...what else is new, we explained that a hunderd times. First the Milankovitch cycles trigger a bit of warming, that warms the oceans which causes CO2 to release from the oceans, which takes over the warming function to create more warming which releases more CO2 from the ocean. Strong positive feedback. Go and have somebody else bored...yawn.. (sorry imitating the real climate team).

But something is very wrong with that explanation for this given sequence, if you know what positive feedback really does. Anybody want to explain? What is the second problem visible here?

[Jason]

I actually don't see the second problem.  We know that CO2 and temps pretty much mirror one another and that there is often a lag time.  We also know that the ocean absorbs heat, too and delays the effect upon the rest of the earth, also that both the temps of the earth and the oceans have risen by an average of one degree over the last one hundred years.  People who take the skeptic argument often try to limit the number of years they look at and tend to have a bit of a myopic view on thigs, but, in the larger picture, the overall trend towards temperature is, of course, "upwards." ^

[andre]

Thanks for trying, well system feedback is a complicated matter on which 100s of engineers earn their living. Every system had embedded feedbacks, also natural systems with predictable to weird reactions.

Let's go to wikipedia:

The end result of a positive feedback is often amplifying and "explosive." That is, a small perturbation will result in big changes. This feedback, in turn, will drive the system even further away from its own original setpoint, thus amplifying the original perturbation signal, and eventually become explosive because the amplification often grows exponentially (with the first order positive feedback), or even hyperbolically (with the second order positive feedback)

So we see the temps go up first, followed a few hundred years later by the CO2 due to system lag, giving another heating input as positive feedback. That lag is crucial because lag works two ways, it delays going up and going down like inertia. A car needs time to accelerate and time to stop. However this ice core "car" stops instantenously halfway without any delay, while the CO2 is still continuing upwards, pulling the temps up, or not?

Instead the CO2 just follows the temperature with the same delay, a follower is not a feedbacker. On the contrary, the enhanced steering away form the stable centre position makes strong positive feedback systems having a strong affiliation with the system extreem values, either low or high with very low sensitivity for natural disturbances halfway.

That's the ugly fact, which slays a beautiful hypothesis, the great tragedy of science (Thomas Huxley)

No strong enough positive feedback here

[Jason]

Whoa!  It doesn't slay anything.  There are a few conflicts because other factors besides CO2 affect global warming. I have had this discussion with skeptics time and time again, to presume that the climate is only affected by CO2, whether it rises or falls, is a bit too linear in thinking.  On any given year, the temps could go up or down, but the overall trend is still up.  Even your graph proves that, while you are getting hung up on the minutia of the graph, you are ignoring the bigger picture.

[andre]

No Jason, you missed the essense. A positive feedback system in transit from one system limit to the other limit is practicaly insensitive to other factors besides the positive feedback factor itself i.e. CO2. You can't stop it but yet it happens.

Although the math of feedback is rather complicated, it is surprising easy to simulate with a basic model as I did here with an excel spreadsheet:

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

here you can see what the graph should have looked like when the strong positive feedback was to be true:



Note that the red temperature response and the orange CO2 never noticed the reversal of trend in the natural "basic forcing" function. They both just jumped up until they hit the roof.

When you tune down the positive feedback considerably then they start noticing the natural trend reversal:



but we still see a very gradual response to the abrupt trend reversal in the "basic forcing" due to the inertia in the delay, cars don't stop and reverse instantaneously. Yet the ice cores do, proving that even this weak positive feedback is too strong.

Hence the ice core strong response to any forcing half way the transition proofs that there cannot be any significant positive feedback from CO2.