NAS 1995

Jean S has written me suggesting that I review the NAS panel claim that Mann was the “first systematic, statistically based synthesis of multiple climate proxies”. This claim is true only in the sense that Al Gore invented the Internet and I will discuss this in the next few days.

While I was reviewing the earlier literature, I stumbled across a previous NAS report, which dealt with some of the topics of the present study: Natural Climate Variability on Decade-to-Century Time Scales (1995) available here and here. It reports on a 1992 workshop involving many leading figures with two interesting essays on proxies – one by Jones and Briffa and one by Bradley and Diaz. NAS panelists Gerald North, John Wallace and Robert Dickinson are mentioned as participants.

There are many interesting perspectives on pre-MBH views of what you could do with proxies.

I couldn’t help but notice the following recommendation:

Climate data must be made freely available to researchers worldwide; data from many sources contribute to the solution of research problems.

It’s nice to know that the present NAS panel also more or less endorses this position. It is disquieting that problems still persist and the matter needs to be dealt with over and over again, seemingly with minimal impact on the Hockey Team.

The Diaz and Bradley essay is entitled “Documenting Natural Climatic Variations: How Different is the Climate of the Twentieth Century from That of Previous Centuries?” and well worth a read. The list of sites here includes many familiar names (most of which recur in MBH98) – a point which I will return to on another occasion. Diaz and Bradley state:

With the exception of the data from tropical ice cores, the proxies indicate that the recent decades were not very unusual, either in regard to the mean or in terms of increased variability. While seasonal and annual temperature changes in the last two decades have been rather large in most areas of the Northern Hemisphere, the available paleoclimate evidence suggests that in many areas there have been decadal periods during the past several centuries in which reconstructed temperatures were comparable to those of the 1970s and 1980s, with climatic variability as large as any recorded in recent decades. …

Figures 6 through 8 show decadal-mean values of various tree-ring reconstructions, generally representing summer (or growing-season) mean temperature. For the most part, these tree-ring reconstructions do not sample the 1980s; nevertheless, it is clear from the degree of interdecadal variability that it would be hard to point to any particular recent period as being unique or exceptional.


From NAS 1995.

With the exception of the tropical ice cores, the recent decades were not generally unique, in terms of either the average values or increased variability….

We can only say that, for most areas of the coterminous United States, the climate of the most recent decades cannot be considered unique, even in the context of the last century.

The Jones and Briffa essay here has some interesting nuggets. They say:

We fail to see any consistent trends in interdecadal variability associated with these tree-ring temperature reconstructions (see indices 5-9, 12-13, and 16-18 in Table 2). Interdecadal variability is typically about half the interannual values. This implies that substantial low-frequency variance is present in the paleotemperature record, so that recent high values of reconstructed decadal-mean summer temperature may yet represent an oscillation within the range of natural variability….

In only one (the Northern Urals, Briffa et al., 1995) of the thousand-year dendroclimatic reconstructions is the twentieth century clearly the warmest century. [SM note: this is the problematic Polar Urals reconstruction of Briffa et al 1995, that I've written many posts on. The updated version has a very elevated MWP] In all of the other reconstructions, however, this century is one of the warmest. Warmer (summer) conditions occurred in previous centuries, but never at the same time at all locations. Clearly, a greater geographical spread of long paleoclimatic reconstructions is required; types of proxy evidence that cover seasons other than summer must be employed before the apparently unprecedented warmth shown in instrumental records of the twentieth century can be placed in a longer-term context. …

In the discussion afterwards, Thomas Karl observed:

Dr. Jones also showed that there is little coherence among the several 1000-year tree-ring time series that have been assembled. That is very interesting; if it is true, putting together a global-scale multi-century time history of temperature change will be very challenging indeed!

Here’s another interesting question and answer:

MYSAK: What’s the state of the art in extracting, say, precipitation or runoff from tree-ring data?

JONES: Most of the tree-ring work we’ve dealt with is from Scandinavia, where the response is clearly to temperature. In southern Europe or the southern part of the United States you can get a good reconstruction of river flow or precipitation from trees, because there the trees are responding to moisture. In between, as in England or northern Germany, the trees are responding to a mix of the two, and it’s hard to unravel the climate signal.

So Bradley and the older members of the Hockey Team seem to have got stuck trying to extract the desired signal from the dog’s breakfast of proxies. This is the milieu leading up to MBH98. It’s not that Mann was the “first” to do a multiproxy study. Even Mann didn’t claim that. It’s not even that Mann had new proxies to work with that were unavailable to Bradley and Jones in 1993. I’ll analyse proxy usage in another post, as the selection differences between MBH98 and Bradley and Jones 1993 (or the list in NAS 1995) are illuminating.

What they perceived theie originality (and this was the contemporary view) was that they used a “new statistical approach”, because “conventional” methods had proved “relatively ineffective”. Bradley said last year that the disctinctive contribution was that Mann had “originated new mathematical approaches that were crucial to identifying strong trends” [Goldscheider, 2005]. NAS 1995 is interesting because it shows the pre-MBH mentality quite clearly. In case you’re wondering, it isn’t mentioned in the NAS bibliography.


16 Comments

  1. Larry Huldén
    Posted Jun 28, 2006 at 2:52 PM | Permalink | Reply

    I think that you (Steve McIntyre and nobody else Steve) has reached the essential point of climate science in producing a synthesis of the relevant data !

  2. Jean S
    Posted Jun 28, 2006 at 3:37 PM | Permalink | Reply

    It is interesting what you find nowadays when you start googling around, you found an old NAS report, I found out that there was an interesting conference (including honored Michael E. Mann and Raymond Bradley as key-note speakers) in London two weeks ago: HOLIVAR2006. I wonder if any of the readers took part?

    Anyhow, check the abstracts (available on-line, some even have the posters there), there are very interesting ones (see, e.g., posters by Sidorava et al and Liderholm et al)!! BTW, judging from the abstracts, I think despite the rumours to the contrary, LIA and MWP are alive and well ;)

    Few other abstracts caught my eye: I was not aware of the pollen-based temperature reconstructions. Some googling revealed that actually in Moberg (2005) such proxy construction was used. Further googling led me to the following low-frequency temperature reconstruction data:
    http://www.helsinki.fi/science/palaeoclim/datadown.htm

    Rather interesting when plotted ;)

  3. jae
    Posted Jun 28, 2006 at 4:01 PM | Permalink | Reply

    We fail to see any consistent trends in interdecadal variability associated with these tree-ring temperature reconstructions (see indices 5-9, 12-13, and 16-18 in Table 2). Interdecadal variability is typically about half the interannual values. This implies that substantial low-frequency variance is present in the paleotemperature record, so that recent high values of reconstructed decadal-mean summer temperature may yet represent an oscillation within the range of natural variability….

    This is almost certainly the “bottom line” for tree ring studies. And those guys should have known it all along. Didn’t they review the literature?

  4. Jean S
    Posted Jun 28, 2006 at 4:22 PM | Permalink | Reply

    Damn, Casper Ammann and Gavin Schmidt also had posters in HOLIVAR06. Wish I’d been in London two weeks ago ;) Well, I can’t wait someone over RC to rebut Sidorova et al conclusions anytime soon :)

  5. TCO
    Posted Jun 28, 2006 at 5:39 PM | Permalink | Reply

    This panel looks rather skewed to the actitivist: http://www.holivar2006.org/panel.php

  6. TCO
    Posted Jun 28, 2006 at 6:00 PM | Permalink | Reply

    This is an interesting one as well. There are some nice motherhood statements at the beginning (although poster detail really pertains to standardization of tree rings). Our friend Torn is there though.

    http://www.holivar2006.org/abstracts/pdf/T3-001.pdf

  7. BAD
    Posted Jun 28, 2006 at 9:35 PM | Permalink | Reply

    Just for clarity, Al Gore never claimed to “invent” the internet. The actual quote was “During my service in the United States Congress, I took the initiative in creating the Internet.”

    This would imply that he might not have came up with the idea of the internet, but he basically made it. Still false, still helps make your point.

  8. ET SidViscous
    Posted Jun 28, 2006 at 9:46 PM | Permalink | Reply

    #7 I think that was presactly Steve’s point.

  9. TCO
    Posted Jun 29, 2006 at 4:48 AM | Permalink | Reply

    I think Gore’s point is that he was country when country wasn’t cool. If ya know what I mean.

  10. Geoff
    Posted Jun 29, 2006 at 8:17 AM | Permalink | Reply

    #2, Jean S. – You may want to have a look at a recent analysis on pollen data here with the full article for free and another recent review in a statistics (!) journal here (abstract only).

    Refs:
    1) 2006, Delauney, Analysis of cedar pollen time series: no evidence of low-dimensional chaotic behavior, International Journal of Biometeorology , Vol. 50, Number 3, January 2006, pps. 154 – 158

    2) 2006, Haslett, Bayesian palaeoclimate reconstruction, Journal of the Royal Statistical Society: Series A; Volume 169 Page 395 – July 2006

  11. Geoff
    Posted Jun 29, 2006 at 8:23 AM | Permalink | Reply

    ok, one more time, here and here.

  12. Geoff
    Posted Jun 29, 2006 at 8:28 AM | Permalink | Reply

    Last try tonight, here and here.

  13. bender
    Posted Aug 7, 2006 at 8:29 AM | Permalink | Reply

    Re #2
    Sidorova’s poster IS interesting. Look at the inferred trend leading up to AD 1000. It is both steep and prolonged. Much like the steep and prolonged trend from AD 910-990 in the NH reconstruction of Cook et al. (1999), who show temperatures over that interval may have increased monotically by 2.2°C. See the value of including confidence envelopes on reconstructions? 2.2°C in 80 years. That helps to put the current NH warming trend in some perspective.

  14. bender
    Posted Aug 7, 2006 at 8:30 AM | Permalink | Reply

    Re #2
    Sidorova’s poster IS interesting. Look at the inferred trend leading up to AD 1000. It is both steep and prolonged. Much like the steep and prolonged trend from AD 910-990 in the NH reconstruction of Cook et al. (2004), who show temperatures over that interval may have increased monotically by 2.2°C. See the value of including confidence envelopes on reconstructions? 2.2°C in 80 years. That helps to put the current NH warming trend in some perspective.

  15. bender
    Posted Aug 7, 2006 at 8:32 AM | Permalink | Reply

    John A:
    Can you delete #13 (and this one)? I got the year wrong and ‘submit’ too quickly.

  16. Posted Nov 26, 2008 at 10:11 AM | Permalink | Reply

    In accordance with the data provided on NG site the rate of warming is increasing. The 20th century’s last two decades were the hottest in 400 years and possibly the warmest for several millennia, according to a number of climate studies. And the United Nations’ Intergovernmental Panel on Climate Change (IPCC) reports that 11 of the past 12 years are among the dozen warmest since 1850.

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