# Talk:Climate commitment

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## [Untitled]

(William M. Connolley 23:41, 21 Mar 2005 (UTC)) I've substantially revised SEW's text. I'm not at all sure that "these models don't include small ice caps" is right: the IPCC projections certainly do, and since ~2.5 oC -> 0.5 m/c, 0.5 oC -> 0.1 m/c would be consistent with the small ice caps being included.

Umm.. that was your text. [1] (SEWilco 09:34, 22 Mar 2005 (UTC))
(William M. Connolley 09:53, 22 Mar 2005 (UTC)) Oops! I pasted that in from Nature without reading it carefully, then forgot. Well, I suppose it must be true then.

## Why "At the time of the TAR there were not yet studies of the levels of unrealized climate commitment that might remain in the current climate"?

(William M. Connolley 11:45, 12 Apr 2005 (UTC)) I don't understand why you (Silverback) insist on putting this in. There is a perfectly good link right there to a GRL pub at the time of the TAR considering just this point. What you have added is wrong, as demonstrated by that link (have you looked at the publication?). The only reason I can see for you putting this is is because you want this to be a new idea, and the only reason I can see for you wanting this is some kind of anti-IPCC bias.

I did look at the link, and I believe even thanked you for it (on my talk page?) That article was from 2001, the same as the TAR, but, I believe it wasn't in time to make the TAR, because I didn't see it discussed in the TAR. Is it listed in the references?--Silverback 14:02, Apr 12, 2005 (UTC)
I just did another check of the TAR and did not find the paper in any of the references. It appears, as I suspected, that the paper was after the TAR was published, or at least after it had taken shape.--Silverback 14:18, Apr 12, 2005 (UTC)

(William M. Connolley 19:46, 1 May 2005 (UTC)) I've just removed: <!-- not sure how useful this sentence is - please reword to clarify if you find it's worth it: I'm not sure which sentence you are referring to. The second pretty much balances the first. The one after this arrow --> At the time of the TAR there were not yet studies of the levels of unrealized climate commitment that might remain in the current climate. <!-- upon rereading, i think i know what you meant: The TAR was the first such study - right? No, the TAR did not study climate commitment, it did briefly discuss one study, and that study was of the commitment that would result from projected future levels, not of the commitment already in the current climate.-->.

I'm not sure whose edit comments these are. So... climate commitment is basically obvious. The idea has been around since at least the SAR. I can't see any reason to believe that At the time of the TAR there were not yet studies of the levels of unrealized climate commitment that might remain in the current climate. is true. Its certainly not true as phrased, as the paper I provided shows ("time of the TAR" is 2001, in conventional reckoning. "time the tar was being prepared" might be true, but again I see no particular reason to believe it. Shouldn't there be some kind of evidence for it?

## based on

I don't get it. How does "doubling or quadrupling" fit to "assuming no further increase"? Sebastian (talk) 09:52, 2005 Apr 27 (UTC)

(William M. Connolley 17:49, 27 Apr 2005 (UTC)) Assuming no further increase *past* the doub ling or quadrupling....
I'm sorry, i still don't find it clear. As a layperson, i first assumed that "given level" refers to the latest level we measured. I gather that's not what you mean. Do you just simply mean: "assuming an arbitrary constant level"? Why not write this instead? This seems much clearer than "assuming no increase above the given level", which leads to misunderstandings. The fact that the level is often 1, 2 or 4, and never 3 or 5 times the currently measured level seems, at least as it stands here, not very relevant to a general definition of such studies. Moreover, the assumption that there is a sudden jump from 1 to 4 right now seems very counterintuitive. — Sebastian (T) 06:17, 2005 Apr 28 (UTC)
(William M. Connolley 14:33, 28 Apr 2005 (UTC)) Yes, " a given level" means an arbitrarily chosen level, not current levels. Errr... would it be better if you re-wrote it, because clearly my words aren't making sense to the educated layperson. If you re-write it I'll check it.
I'm not secure enough to write it in the article, but here's what I would write:

Climate commitment describes the fact that climate reacts with a delay to influencing factors ("climate forcings") such as the presence of green house gases. Climate commitment studies assess the amount of future warming that is "committed" under the assumption of constant forcings. For this so-called "given level" they may assume the present level or some other arbitrary value.

I have two problems with this, though:
• why does it make sense to admit any arbitrary value?
• how does the study treat the past, where we know that the value was not 4 times the present value? Or do these studies start at some time in the future? What sense does this make, given that we want to deal with delays? — Sebastian (talk) 07:23, 2005 Apr 30 (UTC)

(William M. Connolley 19:48, 1 May 2005 (UTC)) I'll try to edit based on what you've written. For the past: I don't understand. I don't think these studies do treat the past. Why any arbitrary value? Well, the interest in this is that if we stop emitting CO2, climate change doesn't stop. So *if* you want to limit cl ch to some value, you need to know the committed change, at whatever value you might have stopped at (of course, in reality, the "given level" would be perhaps where the inc flattened out rather than stopped dead).

(Sebastian 07:33, 2005 May 2 (UTC):) I'm sorry that i still didn't get my point across. I thought i could avoid learning latex, but a formula says more than a thousand words.

OC the studies don't try to yield results for the past, but the past needs to be taken into consideration because of the delayed response. Allow me to extremely oversimplify. Assume your response y follows the forcing x according to the simple equation

${\displaystyle {\dot {y}}=x-ay}$

If you choose ${\displaystyle x=constant}$ then you can solve this easily analytically. Let's assume we're now at ${\displaystyle t=0}$ and so far we constantly measured

${\displaystyle x(t\leq 0)=X}$

To obtain values for ${\displaystyle y(t>0)}$ we need to know ${\displaystyle x(t=0)}$. Even if you don't use it explicitly, it must be implicit in your assumptions. (For complicated systems, ${\displaystyle x(t=0)}$ may not be enough so that we need ${\displaystyle x(t)}$ at least for some ${\displaystyle t<0}$, which is what i meant by "how does the study treat the past". This simple example (and maybe even your full model) may not need ${\displaystyle x(t<0)}$, but we know these values, so i feel the model should at least steadily fit to them – natura non facit saltum).

Here is my problem: The way i understand you, you seem to be using something like the following instead:

${\displaystyle x(t)={\begin{cases}X,&t\leq 0\\4X,&t>0\end{cases}}}$

Or what function would best represent the sort of assumptions you describe in my example? — Thanks

(William M. Connolley 20:06, 2 May 2005 (UTC)) Err, not sure I got all that, but to put it my way: most commitment studies are for 2x CO2 or 4x CO2. In that case, you con't need to worry about the past, because you know you have a steadily increasing history of forcing. So thats easy. The case of stabalising at current CO2 is a bit harder, but only a bit, because again a history of inc GHG's is the major forcing. And if you're running a GCM (which has reproduced the T history) then you've included the past forcing history anyway. Did that help?

## "one of the most important papers in the field"

Where does that assessment come from? Citation count, what? William M. Connolley 12:19:11, 2005-08-24 (UTC).