New Light on Old Fudge

One of my first blog postings was on Briffa’s very first fudging (2011 update: the “Briffa bodge”) of a temperature reconstruction – his adjustment of the Tornetrask reconstruction – a reconstruction that is used in virtually every study. This was one of the first encounters with the Divergence Problem. Tornetrask MXD went down in the 20th century. Briffa resolved this by simply “straightening” out the reconstruction (although, unlike in IPCC TAR, at least he reported it in the original article.) At the time, per, an early reader of the blog, remarked that he was “gobsmacked” at this. This has recently come up again in two contexts and this time even I am “gobsmacked”.

If you fell like looking at the earlier post, it will provide some context. In the recent D’Arrigo, Wilson article on the Divergence Problem, they refer to Briffa’s brute force elimination of the downward MXD as an “empirical correction”. (I don’t think that it’s unfair to use the term “fudge factor” for Wilson’s “empirical correction”.)

As a result of the divergence problem, attempts to directly estimate large-scale temperatures for the recent period in dendroclimatic reconstructions have generally not been successful (Briffa et al., 1998a,b; Briffa, 2000; Briffa et al., 2001; Esper et al., 2002; D’Arrigo et al., 2006, see Fig. 3). The inability of many reconstruction models to verify in the recent period has compelled a number of researchers to eliminate recent decades from their calibration modeling, effectively shortening the available periods for direct calibration and verification testing between tree rings and climate (e.g., Briffa et al., 2001; Cook et al., 2004a; Rutherford et al., 2005; D’Arrigo et al., 2006). Another alternative is to use an empirical correction for the divergence effect (e.g., Briffa, 1992; Osborn et al., submitted for publication, Glob. Planet. Change).

I was thinking about posting on this, when I stumbled on Hakan Grudd’s PhD thesis online. Grudd was the first author in Grudd et al 2002, which is cited as authority for the Tornetrask version that Briffa has been using. Grudd has many interesting things to say about the Divergence Problem and has a new reconstruction for Tornetrask. D’Arrigo and Wilson do not mention Grudd’s new work.

Here are some important comments from the introductory part of the thesis:

‘€¢ Over the last two centuries, tree-ring width shows a diverging trend with respect to maximum latewood density and temperature, implying an increasing productivity in response to temperature. If not attended to, this phenomenon introduces a bias in the climatic reconstruction, resulting in depressed temperatures in the pre-instrumental period.

‘€¢ The maximum latewood density data from Torneträsk are continuous from AD 441 to 2004. By including data from young trees in the most recent period, it is demonstrated that the previously reported reduced sensitivity in density to temperature in the late 20th century was an artefact from the age structure in the old data.

‘€¢ A new multi proxy reconstruction for the last 1,500 years, based on maximum latewood density and ring width, shows significantly higher temperatures in the pre-industrial period as compared to previous reconstructions from Torneträsk. Several periods during the past 1,500 years were warmer than the 20th century. The most striking feature is a long and warm medieval period centred on AD 1000. The coldest period occurred around AD 1900 which is consistent with evidence of maximum glacier expansion over this period.

‘€¢ Methodological differences in the development of local dendroclimatological reconstructions sometimes hampers our ability to assess climate variability on a regional scale (Wilson et al., 2005). It is, therefore, imperative to continue to supply open-access databases with raw data, e.g. the International Tree-Ring Data Bank ( and the Dendrochronological Database (, and to develop public tools to extract and standardize the data in a consistent way, e.g. ARSTAN (Cook & Krusic) (

None of Grudd’s new Tornetrask data is archived. I’ve been trying for a couple of years to get the updated Tornetrask data and Briffa has obstructed every attempt. It’s nice that Grudd believes that the data should be archived and I hope that he will do so. I’ve emailed him suggesting that he live up to this.

Paper II (still unpublished) is the salient one. He may not be finding it all that easy to get it published despite Grudd’s competence, since Grudd seems to have left the reservation. Here are some comments:

However, the lack of data after AD 1980 in the Torneträsk records hampers the calibration with instrumental data. This lack of data in the most recent period is a common problem in many tree-ring records throughout the Northern Hemisphere (Briffa et al., 2004). Furthermore, there is increasing evidence for a change in the sensitivity of tree growth to temperature in the most recent period (Jacoby & D’Arrigo, 1995; Briffa et al., 1998b; Briffa et al., 1998c; Briffa et al., 2004; Waterhouse et al., 2004; Wilmking et al., 2004; Driscoll et al., 2005; Wilmking et al., 2005; D’Arrigo et al., 2006). The phenomenon is not fully understood and the evidence is sometimes contradictory (Myneni et al., 1997; Briffa et al., 2004; Waterhouse et al., 2004). A similar change in sensitivity has been reported also for the Torneträsk data (Briffa et al., 1992). Hence, there is an urgent need to update the Torneträsk and other TRW and MXD records and to analyse the data for recent changes in sensitivity to climate.

Our present knowledge about natural climate variability in the last 1,000 years is to a very large extent based on tree-ring proxies. However, many existing tree-ring records have problems with age structure, with changing sample replication, and with a lack of data in the most recent period. Inevitably, sample replication will change through time in long tree-ring records and this will affect the signal-to-noise ratio so that low replication will lead to wide error bars around the reconstructed climate signal. Furthermore, the age of the trees that constitutes a tree-ring chronology will change through time: Some periods in the record will be dominated by relatively young trees while other periods will be dominated by relatively old trees and the climatic growth response may be very different. For example, in nearly all existing records, data for the most recent period is based on tree rings that on average have a high cambial age as compared to the earlier parts of the record. This causes an in-homogeneity in the age structure that may misrepresent the calibrated growth response and lead to spurious reconstruction results. The widely reported change in the sensitivity of recent tree-growth to temperature could, potentially, be explained as an artefact from using inadequate data in the most recent period. Hence, a major task in the near future will be to update and renovate existing tree-ring collections throughout the Northern Hemisphere. The new tree-ring data from Torneträsk isjust one step in this work.

Existing Torneträsk TRW and MXD data are updated to AD 2004 using samples from 35 living trees. The new data are derived from a mixture of young and old trees. This has significantly changed the age structure of the MXD data in the 20th century and the previously reported decline in density after about AD 1950 is no longer present in the data.

The results show that the previously reported loss in sensitivity of MXD to temperature in the late 20th century was an artefact of the age structure in the data. The reconstructed temperatures show higher values in the pre-instrumental period as compared to earlier temperature reconstructions based on Torneträsk TRW and MXD data. The Medieval Warm Period around AD 1000 is notably warmer than temperatures in the 20th century. Other notably warm but shorter periods occur around AD 750, 1400 and 1750. The coldest temperatures occur around AD 1900, which is consistent with the maximum extent of glaciers in Swedish Lapland in the last 1,500 years.

The New Reconstruction

Here’s Grudd’s new reconstruction for Tornetrask, which shows the elevated MWP as advertised:

Original Caption Figure 11. In the lower panel (b), Reconstruction IV is compared with two previously published temperature reconstructions based on tree-ring data from Torneträsk: The thin curve is from Briffa et al. (1992) and based on TRW and MXD. The hatched curve is from Grudd et al. (2002) and based on TRW. All three reconstructions have been smoothed with a 100-year spline filter and have a common base period: AD 1951 — 1970.

Now here’s something funny. Here is my estimate of what Briffa’s original reconstruction would have looked like without his “empirical correction”/fudge (See earlier post) . Look at the bottom row and compare it to the new Grudd version which I’ve shown a second time immediately below for comparison. Although the scales are different, I think the shapes of the two versions are, in the phrase so beloved of the Team, “remarkably similar”. Downstream of the site reconstructions, the scales tend to get standardized, so it’s the shape that matters more than the scale. The interesting thing about this reconstruction is that it has major impact on the Jones et al 1998 reconstruction, which is still a major component of the spaghetti graphs. I’ve asked Grudd for a digital version of his new reconstruction and am looking forward to re-doing Jones et al with the new Grudd version for Tornetrask and the new Esper version for the Polar Urals. Some new light on an old “empirical correction”.



  1. L Nettles
    Posted May 26, 2007 at 5:53 PM | Permalink | Reply


    ‘€¢ adjective Brit. informal utterly astonished.

    Seems about right

  2. Michael Jankowski
    Posted May 26, 2007 at 6:41 PM | Permalink | Reply

    I’ve asked Grudd for a digital version of his new reconstruction and am looking forward to re-doing Jones et al with the new Grudd version for Tornetrask and the new Esper version for the Polar Urals.

    I am looking forward to seeing the “re-doing” getting published…

  3. Paul
    Posted May 26, 2007 at 11:59 PM | Permalink | Reply

    How are these reconstructions scaled against optimal plant growth; which is effected by the trees species responses to carbon, water and light, and not solely temperature?

  4. per
    Posted May 27, 2007 at 4:02 AM | Permalink | Reply

    there must be some interesting subtext here. It’s a swedish PhD, and they only let you get your PhD when you have the requisite number of publications. Given that paper III was in 2000, and the thesis is from 2006, he must have spent at least 6 years on his PhD; which seems a fair time to me.

    Wibjörn Karlén was the supervisor for this thesis, but Per Holmlund and Peter Jansson are cited as co-supervisors.

    It may well be that after 6 years, Hakan developed his own perspective on the science at issue, and is quite clear on his analysis. It will be interesting to see what that is. Paper II looks quite interesting, and it may be that his supervisors have the data.


  5. Peter
    Posted May 27, 2007 at 8:42 AM | Permalink | Reply

    This is truly extraordinary stuff to a layman, but what is even more extraordinary is the refusal to supply data. Would you be able to post a simple list of the data series you have been trying to get without success? Or just a brief note about them if you got a partial? It would be very helpful. The question I am trying to get to is, how much of the data on which AGW is based, whether instrumental or reconstruction, is actually ‘trust me’ with no real verification possible. You have indicated, if I have understood it correctly, that we have very few series, either instrumental or proxy, where it is possible to check the data. Is this right? Is it a majority of the material that is not available? 80%?

    Are there in fact any temperature series or proxy series where the raw data is open to verification and inspection, or is it all on the basis of, I saw this and here is what I concluded, and no you can’t check?

  6. DocMartyn
    Posted May 27, 2007 at 10:13 AM | Permalink | Reply

    I would be interested in the sign-off document that the supervisors have to sign before a candidate gains his Ph.D. If it is like the UK itwill be something along the lines that the supervisors have examined the data collection method and analysis and have found it to be scientifically sound.

  7. Murray Duffin
    Posted May 28, 2007 at 8:45 AM | Permalink | Reply

    This is a most interesting post. Triggered some thoughts. It seems likely that
    northern trees are more likely to be good proxies because they tend to grow in
    country rich in lakes, streams and muskeg, and therefore do not lack for water.
    Also global warming is thought to be more apparent at high latitudes. 1/2 degree
    C average warming might be 1 degree at high latitudes. 1/2 degree in 16 is about 3%.
    1 degree in maybe 7 or 8 is 12 to 15%.
    I think I recall reading some time ago that some Gaspe cedars were dropped from
    the team samples because they grew on the shady side of hills, and showed no
    significant warming signal. Could the trees be reacting more to insolation than
    to warming per se?
    If the sun’s magnetic field is a torus with the poles orthoganal to the solar plane
    then it would seem likely that cosmic rays reaching earth parallel to the solar
    plane would be the most prevalent. These would penetrate a greater thickness of
    atmosphere in high latitudes, giving them more opportunity to become nucleation
    sites. Thus solar modulation of cosmic rays would affect cloud cover more at high
    latitudes, thus causing a greater change in insolation. However trees growing in
    the shade anyway would be less affected, although they should experience a similar
    temperature change to their neighbors on the sunny side of the hill.
    Are high latitude tree rings a proxy for insolation, confirming Svensmarks theory
    of solar modulation of cosmic ray flux?

  8. Lars Berg
    Posted May 31, 2007 at 5:54 AM | Permalink | Reply

    Steve, the law in Sweden says that he HAS TO share his data with any swedish citizen who ask for them. There was a highly publizised case a few years ago where some laymen asked for (de-personalized) data on a study on children with mental disorders. The researcher refused on the grounds that the data would easily identify the individuals and that the data was handed over under confidentiality restrictions. Yet the court ordered the data released. I can see no reason what so ever for this case to be protected. I can ask for the data on your behalf if you want to (as I am a Swedish citizen).

  9. Steve McIntyre
    Posted May 31, 2007 at 6:07 AM | Permalink | Reply

    #8. I haven’t heard back from Grudd. Check in on this in a few weeks.

  10. Steve Sadlov
    Posted May 31, 2007 at 3:00 PM | Permalink | Reply

    There are certainly elements of periodicity in the signal. There is also something I find disturbing. The peaks seem to be less more recently. I must wonder how high the RWP peak was? What does the 10K year scale signal look like? Looking simply at surface morphological features, it would be very naive to imagine we are now somehow free from return of the great ice masses.

  11. per
    Posted Jun 10, 2007 at 7:58 PM | Permalink | Reply

    any update on the data ?

  12. Steve McIntyre
    Posted Jun 10, 2007 at 8:13 PM | Permalink | Reply

    #11. No answer. It’s amazing how much Grudd’s new version is like the plot wihout the Briffa fudge what D’Arrigo and Wilson call an “empirical correction”) , isn’t it?

  13. Peter D. Tillman
    Posted Dec 15, 2007 at 10:08 PM | Permalink | Reply

    Re #12, Bump

    Any further developments with Grudd?

    And thanks for the new Divergence category. Very helpful.

    Cheers — Pete T

  14. Steve McIntyre
    Posted Dec 15, 2007 at 10:16 PM | Permalink | Reply

    No luck – looks like witness protection.

  15. Posted Dec 16, 2007 at 2:31 PM | Permalink | Reply

    Steve Mc: “Witness Protection” is a good metaphor, but, considering this bunch, I think omerta might be even better.

  16. Steve McIntyre
    Posted Feb 5, 2008 at 11:32 PM | Permalink | Reply

    Grudd has now been published. It says inter alia …

    The new tree-ring evidence from Tornetrask suggests that this ‘‘Medieval Warm Period’ in northern Fennoscandia was much warmer than previously recognized….The late-twentieth century is not exceptionally warm in the new Tornetrask record:

    The differences between the new reconstruction and Briffa et al. (1992) are especially significant in the 200-year warm period centred on AD 1000 which coincides with the so called ‘‘Medieval Warm Period’ (Lamb 1966). A warm period around AD 1000 is in line with evidence from other proxy indicators from northern Fennoscandia: Pine tree-limit (Shemesh et al. 2001; Helama et al. 2004b; Kulti et al. 2006), pollen and diatoms (Korhola et al. 2000; Seppa¨ and Birks 2002; Bigler et al. 2006) show indisputable evidence of a ‘‘Medieval Warm Period’ that was warmer than the twentieth century climate. Furthermore, the records of Late Holocene glacier variability in Scandinavia show that glaciers were reduced in size c. AD 900–1000 and that a warm climate prompted the development of soils on the glacier forfields (Karle´n and Denton 1975; Worsley and Alexander 1976; Griffey and Matthews 1978; Matthews 1980; Karle´n 1982; Hormes et al. 2004). The new evidence presented by Tornetra¨sk tree-rings, indicates that the ‘‘Medieval Warm Period’ in northern Fennoscandia may have been considerably warmer than previously recognized

    You can see it for yourself here

  17. Bernie
    Posted Feb 6, 2008 at 6:51 AM | Permalink | Reply

    I scanned this article. It looks intriguing and appears to have fairly dramatic consequences for HS reconstructions. In the acknowledgements it mentions that Briffa has made some helpful comments. It also appears that Grudd’s data is accessible to all – is that correct? Does this provide an opportunity to expand the discussion on data archiving?

  18. Steve McIntyre
    Posted Feb 6, 2008 at 8:31 AM | Permalink | Reply

    It also appears that Grudd’s data is accessible to all

    That’s news to me. I don’t know where it is nor did I see any data bank identified in the article. The new data is not at the WDCp/ITRDB. Perhaps it’s in the password protected top-secret Euro tree ring data base, but Briffa has refused to give me access to this site. I emailed Grudd some time ago asking him for a digitial version of his recon, but got no answer. You may be thinking of the “Open Access” disclaimer on the article – but that’s the article not the data.

    Also many tree ring researchers have very commendable practices about archiving data – the ITRDB data set is very large. The problem is that many key researchers don’t archive data in a timely data, as discussed at length on many threads.

  19. Pat Keating
    Posted Feb 6, 2008 at 8:47 AM | Permalink | Reply

    ‘Gobsmacked’ literally means “punched in the mouth”.

  20. Peter D. Tillman
    Posted Feb 6, 2008 at 2:46 PM | Permalink | Reply


    Thanks for the Grudd article, which is very provocative. Perhaps this would be a good time to renew your request? If he’s unresponsive, Lars Berg at #8 has offered to help obtain same, under Sweden’s “open-access” law.

    Incidentally, in private corresp with a UTor climatologist, he mentioned frustration in trying to get an “equable climate” article published, remarking “equable climate is a dangerous topic!” And he’s a card-carrying AGW guy…. ;-)

    Keep up the good work!

    Cheers — Pete Tillman

  21. Bernie
    Posted Feb 6, 2008 at 3:51 PM | Permalink | Reply

    I misread the following.

    MXD data from Tornetra¨sk were first published by
    Schweingruber et al. (1988). This original data set of 65
    individual tree-series covered the time period AD 441–1980
    and is hereafter denoted SEAL80 [WSL (Dendro Database,
    WSL, Switzerland.
    html). Here, the MXD data is updated to AD 2004 using
    new samples from 35 relatively young trees.
    Thus, the new
    Tornetra¨sk MXD data-base includes samples from a total
    of 100 trees and covers the period AD 441–2004. Dry dead
    wood covers the period AD 441–1789 and living trees cover
    the period AD 1336–2004.

    Re-reading it is clear that the old data set is apparantly available in some form but the new data is not. Is that the issue or is the old data in a processed rather than “raw” format?

  22. SteveSadlov
    Posted Feb 8, 2008 at 6:58 PM | Permalink | Reply

    I wonder what Briffa would think of this?:

    Tornetrask, 1500 year reconstruction.

  23. SteveSadlov
    Posted Feb 8, 2008 at 6:59 PM | Permalink | Reply

    Ah, this is actually the same Grudd study noted above. In any case, it’s now linked from World Climate Report.

  24. bender
    Posted Feb 8, 2008 at 7:02 PM | Permalink | Reply

    #23 Yes. Just took a while to get published.

  25. Posted Feb 15, 2008 at 2:56 PM | Permalink | Reply

    worldclimatereport on Grudd:

One Trackback

  1. [...] Last week, Hakan Grudd sent me a digital version of the MXD series – hooray! Previously I’ve previewed this new version using clips from the articles or thesis e.g here. [...]

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