Robustness

[Climate Audit was started on Jan 31, 2005. Prior to its startup I had some notes at a prior website http://www.climate2003.com, which John A transferred to the CA blog at its start-up.]

If 2 PCs are used in the AD1400 North American network along with conventional (centered) PC calculations, we argued in our Nature submissions that MM-type results are obtained. This is now effectively acknowledged by MBH. To try to salvage MBH98, they now argue that they should be entitled to increase the number of PCs in the AD1400 North American network from 2 to 5 and that our not doing so is “incorrect”. They point out that, using centered PC methods, the PC4 (instead of the PC1) has a hockey stick shape (from the bristlecone pines) and, as long as they can use the PC4, the PC4 now drives world climate history. Doesn’t this just seem silly? Now we’re not dealing with a “dominant” pattern of world climate, but a PC4. ROTFLOL.

Secondly, I defy anyone to show me how the actual retention of PC series in MBH98 can be derived from the Preisendorfer criteria now said to be used in MBH98 for tree ring networks (although MBH98 itself only talked about spatial distributions for tree ring PC retention). Below are two plots made on the same basis as the plot shown at Mann’s blog for the AD1400 North American network – only here for the AD1600 Vaganov and AD Stahle/SWM networks. In the first case, MBH98 retained 2 PCS and in the second case, MBH98 retained 9 PC series. I do not believe that there is any rational policy here. I sure can’t see how the actual retention can be linked to Preisendorfer. It would be helpful to see some source code here. Maybe there’s something weird and inconceivable like their centering method.

Thirdly, what does this do to their claims of robustness? A robust reconstruction obviously should not stand or fall on whether 2 or 5 PCs are used in the AD1400 North American network – but this is exactly what Mann et al. are saying. Remember all the grandiose claims about MBH98 being robust to the presence or absence of dendroclimatic indicators altogether (see both MBH98 and Mann et al.[2000]). Now it seems that MBH98 is not even robust to the presence or absence of a PC4. Also remember that Mann et al. have known about the lack of robustness to the bristlecones for a long time – look at the PC1 in the BACKTO_1400-CENSORED directory. It’s almost exactly the same as ours. Maybe someone can explain to me how you can claim robustness after doing the CENSORED calculations.

Vagonov
Stahle

In the figures above, lines are from Preisendorfer-type simulations using AR1 coefficients. Red is using centered calculations; black is MBH98 method, showing both the archived value and our emulation. (I did these calculations a few months ago; I haven’t reconciled why the emulation differs from the archived value in the Vaganov AD1600 network, but the discrepancy is not large and is non-existent in the Stahle/SWM network. Again riddle me this: why does the AD1600 Vaganov network have 2 PCs and the AD1700 Stahle/SWM network have 9 PCs?

8 Comments

  1. TCO
    Posted Sep 10, 2005 at 6:04 PM | Permalink

    I guess I don’t really understand PC’s. What is a PC? Is it like a fourier transform where one adds terms and gets closer to description of the original curve? Are the PCs additive? Does looking at a PC4 in isolation mean anything? Isn’t it sorta like a factor in a multiple regression (and 4th least important one)? Do they plot the PC? Or the average temperature? And why even do all this PC stuff, vice just plotting the average results (maybe smooth a little)?

  2. JerryB
    Posted Sep 10, 2005 at 7:10 PM | Permalink

    Oh, for Pete’s sake. (I do not know why the expresion commonly refers to Pete’s sake, instead of Tom’s, or Martha’s, sake).

    In any case, that expression came to mind upon reading comment 1 in this thread.

    Another expression that came to mind is “get a grip”.

    TCO,

    You might try googling “principle component analysis”, and then reading the various tutorials, and other introductory pages, to which google presents links, instead of suggesting that Steve provide what amounts to tutoring on a non-trivial subject.

  3. TCO
    Posted Sep 10, 2005 at 7:15 PM | Permalink

    I like pestering him.

  4. TCO
    Posted Sep 10, 2005 at 7:16 PM | Permalink

    But there actually is some serious point in here that if a PC is just a part of an overall summation that when one graphs it one is not really graphing temperature.

  5. TCO
    Posted Sep 10, 2005 at 7:17 PM | Permalink

    And if the PC4 has a hockey stick shape is irrelevant no? Only the summation is relevant, no?

  6. JerryB
    Posted Sep 10, 2005 at 7:39 PM | Permalink

    TCO,

    If you like pestering people, permit me to suggest that you pester someone who has lots of spare time, and who welcomes the attention of of prolific pesterers.

  7. TCO
    Posted Sep 10, 2005 at 7:41 PM | Permalink

    You feeling lucky? -Dirty Harry

  8. DaleC
    Posted Aug 21, 2008 at 8:06 AM | Permalink

    The graphics in the head post have disappeared?

    This is the most relevant post I could find for a question about the series vag26.

    In the \MBH98\Nature_Corr\PROXY\dataall.txt at row 170 column 2084 (this is the column for vag26) the data is 1.5700000e+03.

    In context from row 163, the beginning of the series, the preceding points are

    9.1000000e+01
    1.5100000e+02
    1.1100000e+02
    1.5800000e+02
    1.8500000e+02
    7.4000000e+01
    1.8900000e+02
    1.5700000e+03

    The last point, 1570, is ten times bigger than the prior points. On a plot of all vag01 to vag61 excluding the phantom vag55 the 1570 stands out as ten times higher than all the other points which clump at the bottom. The 1570 looks ridiculously wrong.

    The equivalent data in ordinary notation is at /www.climateaudit.org/data/mbh98/UVA/VAGANOV.dat. If you load this file into Excel, the above data starts at cell AA:239.

    91
    151
    111
    158
    185
    74
    189
    1570
    142
    88

    This file has more data points than dataall.txt. Looking now from cell AA:660, which is year 1983, the data is

    91
    151
    111
    158
    185
    74
    189
    1570
    142
    88

    that is, exactly the same as the first ten data points, from year 1562.

    I have hunted around, but cannot find anything on this. Is there an explanation?

Follow

Get every new post delivered to your Inbox.

Join 3,317 other followers

%d bloggers like this: