Abuse of non-linear

358610673_817599326392037_7869233237770661970_n People are prone to saying things like "But impacts of climate change are different — they are non-linear" by which they mean scary, dangerous, worrying, problem-causing. But this is an abuse of terminology. A damage function that is, say, zero up to 2 oC and zillions above that is non linear; a damage function that is lots below 2 oC and zero above is also non-linear. But we only care about the first sort.

In the real world, pretty well everything is non-linear. So saying that the impacts of GW are non-linear is trivial and uninteresting, in and of itself. People segue far too casually from "non-linear" (trivial) to "thresholds exist" (largely undemonstrated) to "we're passing those thresholds and terrible things are happening" (using insurance in the US as an example is a terrible idea because the markey is so heavily distorted by regulation and govt intervention that market prices often don't apply).

Thresholds are lovely things in simple theoretical models but I think less applicable to the real world. Everything is fuzzy, distributed: there are rarely absolute thresholds.

Other confusions

Is GW accelerating? Just recently Hansen asserts "We did not say that the global temperature record to date shows an acceleration of the global warming rate". And yet Hansen-2020 says "Record global temperature in 2020, despite a strong La NiƱa in recent months, reaffirms a global warming acceleration that is too large to be unforced noise". Perhaps the addition data after 2020 to 2023 shows a slow-down?


* Are the impacts of climate change non-linear?

DICE damage functions.

Neoclassical tipping points of no return.

Economists greatly underestimate the price tag on harsher weather and higher seas. Why is that?

* ATTP's Abandoning the idea of an “optimal pathway” for climate policy makes me think of On getting out more. This is Jonathan Koomey's stuff; it is all so badly broken that it is hard to know where to start; see my comments chez ATTP.

* American universities have an incentive to seem extortionate. They are much cheaper than the “crisis of college affordability” suggests.

* Tipping points: AH likes good ones but doesn't like bad ones. Arf.



Anonymous said...

I looked at acceleration in global temperature and concluded "needs more data" at least for a standard frequentist approach.

The CERES fluxes really look convincingly like heating rates have accelerated. So has sea level rise.

But I suppose most people think of global (near) surface temperature.

...and Then There's Physics said...

I don't really get your apparent objection to pointing out things that are trivial and uninteresting. There are plenty of trivial and uninteresting things that people dispute (you've engaged in the climate debate yourself). Also, I don't really know what it would take to demonstrate to you that there are thresholds, but it seems clear that there are plenty of situations where there are thresholds. Infrastructure is typically designed to cope with events up to some magnitude. If an event exceeds that threshold, then typically things happen that the infrastructure is designed to prevent (flooding being a classic example, but there are others). I do agree that the real world is more complicated than some of these simplistic scenarios imply, but the general idea seems reasonable (if extreme events get more frequent and/or intense then there is greater chance of these events exceeding thresholds where our societies are able to easily cope with the impacts).

Again, we may well continue to upgrade, or implement, infrastructure that will mean that the actual impacts don't get more severe, but I still don't see much of an issue with highlighting these potential risks (you can, of course, disagree, but if it's just a disagreement about framing, then that's just trivial and uninteresting :-) ).

William M. Connolley said...

Anon: thanks; I shall attempt to read it. But: you've outed yourself:-)

ATTP: I think you're being disingenuous. You don't write posts about things you think are T+I.

...and Then There's Physics said...

I wasn't really commenting on my posts being trivial & uninteresting (which may, or may notm, be the case), just on your apparent objection to people pointing out such things. Anyway, I'll leave it at that.

Anonymous said...

Very odd post.

Yes, one could interpret the words used in Dessler's blog post differently without context, but given that he literally draws a picture of how it is to be interpretted, it seems very unfair to use that as an example.

Perhaps the concept does not generalize well beyond flooding, but flooding is approximately binary at the threshold.

Nathan said...

What would be fascinating is knowing the terminology you would prefer...

pray tell, if non-linear is and abuse of terminology, what term would you use?

Tom said...

How about uncertain but potentially problematic? Too many syllables?

I don't think it's the concept of thresholds that is so bad. It's the instant leap from the possibility of a threshold to a non-scientific warning of it approaching like a freight train.

But maybe that's just me.

Mark B said...

Having first hand experience with a river breeching a levee a couple hundred meters from my home, I can assure you that Dessler's example is not a hypothetical. It's precisely how river flooding works.

The water either does or does not come over the levee (It did) and then it does or does not continue to do so for a rate and period long enough to trash your property (It didn't, but other neighborhoods were not so fortunate).

William M. Connolley said...

> what term would you use?

I'm largely with Tom here. But I'll also repeat what I said earlier: the issue is using vague and generally applicable words ("non-linear") to mean a thing they don't ("intrinsically dangerous"). So the solution is less to use better words than to stop sliding muddily between concepts.

> a river breeching a levee

That is indeed a good "threshold" example; but it's a long way from that to "and such examples are common".

Nathan said...

"That is indeed a good "threshold" example; but it's a long way from that to "and such examples are common"."

He provides more in the video.

" So the solution is less to use better words than to stop sliding muddily between concepts."
so a trivial and uninteresting finding?

Nathan said...

I don't agree with your characterisation here
"So the solution is less to use better words than to stop sliding muddily between concepts."

I don't think many people thought this was 'sliding muddily between concepts'.
I think most people understood what was being said, in terms of the intent.
To characterise Dessler's claims as being unclear or muddied or whatever you're doing is just strange.