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Topics - Peter Ellis

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Arctic sea ice / What is a model?
« on: April 15, 2017, 08:45:00 PM »
For Andrew B.

Quite so.  An exponential trend is a simplistic, naive mathematical model with no direct connection to the many many years of accumulated scientific knowledge of Earth's climate system.  Which is why I'm so baffled that you prefer it.

Again distorting what I wrote...

1) Trendline fitting is a mathematical/statistical tool. As the name implies, it extracts a trend from noisy data. No, it's not a climate model, and the exponential function is not a climate model either.

I never said it was a climate model, I said it was a mathematical model. In extrapolating an exponential trend, you are using a mathematical formula to model what you think will happen to the climate.  It is therefore a model. Maths is modelling.  I can't put it more plainly.

A sine wave is a model of the behaviour of a pendulum.  Linear acceleration is a model of how an apple falls under gravity - a model which breaks down when air resistance is significant, or when the distances involved are large enough that the gravitational field varies. Newtonian gravitation is a better model, but one which also breaks down when considering air resistance.

Both models also break down when you extrapolate inappropriately: for example in the real world the acceleration will stop when the apple hits the ground. Extrapolation from simplistic models will always be wrong, the only question is how wrong.  The more factors you leave out of your model, the more likely you are to be wrong.

Your exponential trend-fitting leaves out... pretty much everything.

To put it another way: what do you think will happen when the ice reaches zero?  Will it continue to decline at an exponential rate and go into negative territory?  Rhetorical question: of course it won't.  So you implicitly must acknowledge that the exponential trend model will break down at some point.  Why do you think that is necessarily at the point when ice is zero, and not before?

2) A climate model: see the Wikipedia definition which, while not perfect, is good enough. Let's stick to it and not try to redefine the meaning of the term.
We can both play the definition game:

model  (mŏd'l)   
A systematic description of an object or phenomenon that shares important characteristics with the object or phenomenon. Scientific models can be material, visual, mathematical, or computational and are often used in the construction of scientific theories. See also hypothesis, theory.

The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.

You could also look at the Wikipedia page about scientific modelling.

One form of scientific modelling - the type you are using - is when you attempt to describe aspects of a given phenomenon via a system of equations.  That is what you are doing with your exponential extrapolation. It remains a model even if you are incapable of grasping the fact that it's a model.

3) "Which is why I'm so baffled that you prefer it." I have no idea whatsoever what you could mean by that. But if you want to further explain your point of view, may I suggest you start a new thread?
You are asserting that PIOMAS modelling is materially wrong and that an exponential progression of melt is more likely.  i.e. that the future evolution of Arctic sea ice is better MODELLED by an exponential trend than by the more complex outputs of PIOMAS. You have produced no evidence or reasoned argumentation to support your view other than some hand-waving "feels like this" mumbo-jumbo. I am baffled why you are doing this.

Arctic sea ice / What's wrong with HYCOM?
« on: July 15, 2015, 02:39:47 PM »
Plinius first mentioned it here about a week ago:
If you look at this again:

There is a perfect, circled boundary in the salinity near the end of the simulation. No way that this is caused by some natural current [...]

It's still there, it's now in the nowcasts as well as the forecasts, and it affects both versions of the Navy's models, see here:

Does anyone have any contacts with the people running these models so we can ask what's going on?  As it stands, I don't think either of the versions of the model can be remotely trusted since they are both giving grossly unphysical outputs.

Permafrost / Toward Improved Discussions of Methane & Climate
« on: August 01, 2013, 10:46:24 PM »
An article from Skeptical Science that seems to me to be pretty fair and balanced.

The clincher for me is the palaeoclimate argument: given that orbital forcings meant the Arctic was warmer (and quite possibly seasonally ice-free) several thousand years ago, with no runaway methane release, means the same likely applies to current warming.

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