Comments on: More on Mongolia

By: ylf

ylf — Thu, 05 Mar 2009 02:52:25 +0000

But how to make a reconstruction from tree rings when both observed climate data and tree ring series contain linear trends? Some guy suggests whitening both series and then correlate.

By: Warwick Hughes

Warwick Hughes — Fri, 23 Jun 2006 23:50:04 +0000

Thanks Steve for recalling my USSR gridcell pages re Irkutsk. My Figure 3 that you show is only there to demonstrate the seven widely varying GHCN data versions available for Irkutsk. The GHCN preferences are indicated by the last digit in their series names, hence 0 is their first choice, 1 their second choice etc.
Readers might like to ponder why the GHCN tean would have opted for the strongest warming version post 1880 as their first choice when they must know Irkutsk is a fair sized city.
But back to my subject.
I hope readers found my link “Lake Baikal Region” to the page below presenting station trends for the Irkutsk gridcell and the neighbour to the east containing the significant sized city of Ulan Ude.
http://www.warwickhughes.com/climate/baikal.htm
So few stations that the full horror of the Jones et al cosmic mistake is clearly visible.
So, do I take it that tree ring trends from nearby Mongolia are being generated that agree with the urban warming trends in these gridcells ? What a hoot.
I wonder if there are trees in downtown Irkutsk that are old enough to study ?

By: TAC

TAC — Mon, 12 Jun 2006 23:05:16 +0000

#16 I may have been a bit hasty with my thanks [;-)]. Huybers’s manuscript reports some interesting findings, but I’m not sure I learned that much about his methods. In particular, it would not be easy to reproduce his results from the manuscript. For example, the reference to multitaper methods [Percival and Walden, 1993 -- incidentally, it is missing in the bibliography, though it is well known] does not adequately explain the estimation of “coherence” (my memory is that there are questions about how you define the taper, though I haven’t looked at this in a while). Presumably there are background documents that lay out the mathematics, but they aren’t cited. While I don’t have reason to think anything was done wrong, when you have complicated variability (in this case due to both process and measurement error) in both the response and predictor variables, things get tricky (generally speaking, linear models are not appropriate in such cases without simplifying assumptions). PCA in theory can avoid some of these problems, and it may be an appropriate tool in this situation, though I don’t know for sure. I’d like to see the arguments laid out formally.

Here is the sort of thing I have in mind: Assume — because of process physics — that the ring width or density at site i is functionally related to temperature, T, at the site. However, we cannot employ T or W because we don’t know them. Instead, we invert the function and insert our “best” estimates:

latex \hat{T}_{i}(t) = T_{i}(t) + \epsilon_{\hat{T}}(t) [\tex]

latex T_{i}(t) = f_{T,\Theta_{T}}(t) + \epsilon_{T}(t) [\tex]

latex \epsilon[\tex]s? How do these errors propagate through the model? If we assume they’re all negligible and iid, well, that’s fine, but I’d like to see it up front. [I understand that GRL's page limits make this suggestion impractical].

In any case, it is an interesting manuscript presenting interesting results on an interesting topic.

By: TCO

TCO — Sun, 11 Jun 2006 13:11:48 +0000

I don’t think people should write letters so much. They should write papers. Letters should be restricted to very small points and breaking news. Everything else should be a paper.

By: TAC

TAC — Sun, 11 Jun 2006 10:33:31 +0000

#12 Thanks for the Huybers preprint. I will read it, but, based on the number of equations (0; that’s about average given GRL’s 4-page limit), that I likely won’t understand it until I’ve also read the background articles.

By: TCO

TCO — Sun, 11 Jun 2006 05:30:04 +0000

Pretty interesting article. Haven’t put it under the TCO microsceop yet, but looks decent.

By: TCO

TCO — Sun, 11 Jun 2006 04:29:46 +0000

I’m reading the Huybers article now. Interesting seeing him making some points about skill versus significance and degrees of freedom wrt low frequency calibration. Glad to see someone is publishing…;)

By: TCO

TCO — Sat, 10 Jun 2006 22:13:40 +0000

Steve, the terms “woop” and “rat” were meant affectionately. Take a look at his bio on that site and you’ll understand. Or he will anyhow. And yes, it is a bit funandgamesy but I got that big book on Hotelling from the library and sitting next to me, so let me have a little sugar with the medecine. (I’m still trying to figure out the right way to mix in snark about a certain December football game into the mix…)

By: Steve McIntyre

Steve McIntyre — Sat, 10 Jun 2006 19:29:06 +0000

#9. Take a look at Peter Huybers’ new article at his website looking at variability across a continuum of scales. Huybers is thoughtful and bright. Some time I’ll try to post a teaser on the article.

By: TCO

TCO — Sat, 10 Jun 2006 17:00:48 +0000

No that’s TJ. Could it be Cubasch? No…he’s Ulrich. Oh well…