More on the Gridded MXD Data

We’ve noted that Briffa’s gridded MXD has high correlations to temperature, much higher than run-of-mill proxies. We’ve also noted that Mann (like Briffa) truncated this data at 1960 because of divergence. At the time that Mann et al 2008, the gridded MXD data was not available anywhere – Mann cited a webpage as follows:

The gridded maximum density dataset was developed differently by Osborn et al. (http://www.cru.uea.ac.uk/~timo/datapages/mxdtrw.htm) [as used by Rutherford et al. (2)] with the specific goal of capturing century to multicentury variability.

While Briffa has published many articles on his MXD data, the only article providing even a cursory description of the gridded version was Rutherford (Mann) et al 2005, which stated:

The version of the MXD dataset used here was compiled using a combination of grid-box estimates based on traditionally standardized MXD records (with limited low frequency information) and regional estimates developed to retain low-frequency information (OSB; the data in the MXD network are available online at http://fox.rwu.edu/~rutherfo/supplements/jclim2003a). The latter were developed using the age-band decomposition (ABD) method of standardization, wherein density data from trees of similar ages are averaged to create long chronologies with minimal effect of tree age and size (Briffa et al. 2001).

Unfortunately, the information that the data was available at http://fox.rwu.edu/~rutherfo/supplements/jclim2003a was untrue. Previous attempts to get this data had failed. In September, as noted previously, I sent an FOI request to CRU in England for any gridded data that they had sent to Mann. (Note that requesting in terms of documents is more effective). This led to a new tranche of data and file information at Osborn’s webpage, and, of course, the usual puzzles.

The creation of the gridded series (by coauthors Osborn, Briffa and Jones) is described in Rutherford et al 2005 as follows:

OSB therefore worked first with the traditionally standardized data at the individual chronology scale and gridded them to provide values in 115 5° by 5° grid boxes (26 available back to A.D. 1400) in the extratropical NH (Fig. 1b). They then developed temperature reconstructions by the local calibration of the MXD grid-box data against the corresponding instrumental grid-box temperatures. The “missing” low-frequency temperature variability was then identified as the difference between the 30-yr smoothed regional reconstructions of Briffa et al. (2001) and the corresponding 30-yr smoothed regional averages of the gridded reconstructions. OSB add this missing low-frequency variability to each grid box in a region. After roughly 1960, the trends in the MXD data deviate from those of the collocated instrumental grid-box SAT data for reasons that are not yet understood (Briffa et al. 1998b, 2003; Vaganov et al. 1999). To circumvent this complication, we use only the pre-1960 instrumental record for calibration/cross validation of this dataset in the CFR experiments.

You have to watch a bit carefully here – you expect “OSB” to be an acronym for a peer reviewed publication describing the gridding process, but OSB (which confusingly is Briffa, Osborn and Schweingruber GPC 2004, as noted by PAt Frank below) contains no description of the gridding method. I was wrongfooted a bit by this and tried to find additional descriptions elsewhere in the Briffa opus, before deciding that this was the description of the gridding operation.

To understand what happened in the gridding process, I picked a cell with only one site (72N, 132E), but there are many others and plotted the underlying chronology of the one site, together with three versions of the gridded data: the Osborn version, the “Mann original” version and the Mann infilled version. The 4 plots are shown below and give a variety of puzzles.

The earliest value of the underlying site chronology (omoloya) is in 1496 (end-1991). The gridded version is almost identical in the period 1496-1991 (correlation of about 0.99), but it begins in 1400. Where did the first 96 years come from? Is there another tranche of unarchived data? Or was there some “infilling” of the early data? Rutherford et al 2005 is silent on this.

In any event, we know that Mann truncated post-1960 values and used “infilled” data for 1960-1995 instead of real data. However the effect in this particular series is a little unexpected: the infilled data doesn’t go up as much as one would have expected given the trouble that they’ve gone to replacing real data with imaginary data. It “diverges” from temperature as well. In fact, for this gridcell, the “original” original data has a higher correlation to temperature than the replacement data.

Update – Osborn’s webpage (and I think that this info was provided in Sept 2008 in response to my FOI request) mentions that the 341 sites used in Rutherford et al 2005 were selected as follows:

the MXD data from the 341 sites determined by Briffa et al. (2002a) to exhibit correlations with nearby gridded April-September temperature of at least +0.22 were used in this study. See Briffa et al. (2002a) and the data description above for further details

This is helpful, as Rutherford et al do not mention 341 sites, instead saying:

it [ABD] has been applied only at a regional scale for the MXD network used here, rather than at the level of the 387 original site chronologies.

13 Comments

  1. Jeff Alberts
    Posted Oct 31, 2008 at 1:48 PM | Permalink

    Looks like the post got truncated…

    Steve: Not truncated – I had a trailing sentence that I didn’t notice when I went out.

  2. Paul29
    Posted Oct 31, 2008 at 1:59 PM | Permalink

    A real cliffhanger ….
    .
    .
    ….

  3. MarkB
    Posted Oct 31, 2008 at 2:06 PM | Permalink

    Come back next week and see the thrilling conclusion of….

  4. Mark T.
    Posted Oct 31, 2008 at 2:13 PM | Permalink

    Cue Soap music…

    Mark

  5. Posted Oct 31, 2008 at 3:44 PM | Permalink

    Next week: who shot SM?

  6. Jeff Alberts
    Posted Oct 31, 2008 at 6:14 PM | Permalink

    For some reason I’m wanting to sing the Banana Splits song…

  7. Pat Frank
    Posted Oct 31, 2008 at 6:54 PM | Permalink

    Page 2309 of Rutherford, 2005 says, “Osborn et al. 2004, manuscript submitted to Global Planet. Change, hereafter OSB.” Reading your quote, I figured OSB meant Osborn, though a more common way of indicating one author would be TJO, in Osborn’s case.

    I separately searched “Briffa” and “Osborn” in “Global and Planetary Change,” and only one paper turned up: K. R. Briffa, T. J. Osborn, and F. H. Schweingruber (2004) “Large-scale temperature inferences from tree rings: a review” Global and Planetary Change 40(1-2), 11-26, now BOS04. The 2004 date is reasonable for a “submitted” comment in Rutherford, 2005, because R05 was itself submitted only in September 2003. BOS04 is thus likely to be “OSB.”

    BOS04 (OSB) is a review article with no Methods Section, no equations or mathematical descriptions of any kind, and no supplemental information. That is, it is not the sort of article where one expects to find a complete, or even a useful, methodological description.

    The only relevant passage I found in BOS04 regarding grid-box calibration was in the legend to Figure 8: “Average temperature over land areas north of 20°N, as observed (black) and reconstructed by a simple linear regression recalibration of published series by [Jones et al., 1998] in red; [Mann et al., 1999] in purple; [Briffa and Osborn, 1999] in green; [Briffa et al., 2001] in blue; and [Esper et al., 2002] in pink. The series used from [Mann et al., 1999. M.E. Mann, R.S. Bradley and M.K. Hughes, Northern Hemisphere temperatures during the past millennium: inferences, uncertainties and limitations. Geophysical Research Letters 26 (1999), pp. 759–762. Mann et al., 1999] was an average of land grid boxes north of 20°N from their spatially resolved reconstructions. Each series was recalibrated over 1881–1960 against, (a) annual-mean temperature and (b) April–September mean temperature. Note the effect on the temperature magnitudes in the two sets of series caused by calibrating the same data against these alternative predictands.

    This isn’t a particularly detailed description of what was done.

    Also, in Figure 6: “Fig. 6. (a) Instrumental temperatures (red) and tree-ring density reconstructions of temperature (black) averaged over all land grid boxes north of 50°N, smoothed with a 5-year low-pass filter.

    I found nothing in BOS04 that described any infilling of missing data. Yet another small mystery, given the statement in R05 that, “OSB add this missing low-frequency variability to each grid box in a region.

    Steve: Thanks for this. I missed that definition – I’d read the article and, as you say, it doesn’t describe the method. I’ve edited the text to clarify this.

  8. Jeff Id
    Posted Oct 31, 2008 at 7:03 PM | Permalink

    The infilled data average has the upslope shape, in the same way the Luterbacher individual series had odd shapes but the average was a perfect match. If you average the (briffa) infilled data the net is an uptrend link below in my old post.

    http://noconsensus.wordpress.com/2008/10/05/mxd-tree-removal-service-choppin-wood-off-a-hockey-stick/

  9. icman
    Posted Oct 31, 2008 at 10:07 PM | Permalink

    John A

    Classic

  10. Bob North
    Posted Nov 1, 2008 at 12:02 AM | Permalink

    It’s like trying to get a detailed picture looking through one of those glass block walls.

  11. tty
    Posted Nov 1, 2008 at 9:54 AM | Permalink

    If you look in the Wayback machine (http://web.archive.org/web/20080123183704/http://fox.rwu.edu/~rutherfo/supplements/jclim2003a/) it seems that fox.rwu.edu/~rutherfo/supplements/jclim2003a/ was actually online for a short period in late 2007 and early 2008. The main page was archived, but unfortunately none of the linked data files. Either they never existed or they were blocked from archiving by using robots.txt, a precaution that seems to be fairly common in the climate science community.

    Steve: It’s not that the archive was empty. What I said was that it didn’t contain the MXD data. This directory contained a placeholder saying to contact Tim Osborn, which I did, but he refused to provide the data. As I mentioned above, I tried again recently using UK FOI legislation and had some success.

  12. Posted Nov 23, 2009 at 2:02 AM | Permalink

    I’m a regular reader of your blog but am sometimes puzzled by acronyms (MXD in tihs case). Can I ask that you define them each post (after all recent events are likely to lead to a lot of new readers.)

    • Raven
      Posted Nov 23, 2009 at 3:11 AM | Permalink

      Re: Ron Manley (#13),
      Your best bet it to use google.

      “MXD Climate” brings up:

      http://www.climateaudit.org/?p=150

      Figure 1 below shows the following Tornetrask maximum density (MXD) chronologies

      Searching on “maximum density (MXD) chronologies” will bring up numerous references on the topic.

2 Trackbacks

  1. [...] View original here: More on the Gridded MXD Data « Climate Audit [...]

  2. By The FOI Myth #2 « Climate Audit on Dec 29, 2009 at 8:37 PM

    [...] Whereas previous attempts to obtain this data directly or through the journal (edited by Andrew Weaver) had been unsuccessful, this request through FOI was resolved promptly and expeditiously by CRU placing the requested information on a webpage (see CA discussions here here [...]

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