Millar et al: The Sierra Nevada MWP

Otto-Bliesner asked me how I would do a reconstruction. As I’ve said on other occasions, I said that I didn’t know. I’m really reluctant to just apple-pick some series but it’s prbably worthwhile showing that you can pick apples as well as cherries. More constructively, I think that there are some approaches that look better than others. I don’t think that Mannian data mining or forms of cherry picking are very promising. There are many problems with tree ring "site chronologies", but that doesn’t mean that Moberg’s little collection of 11 series is any magic bullet. Out of the various individual proxy studies that I’ve read, I think that two of the most interesting are Naurzbaev et al [2004], about which I reported here and a new one, Millar et al [2006], online here (I’d previously commented on a poster on the same topic here) . The topic has particular resonance for readers of this site as Millar et al. have done a detailed analysis of high-altitude (3000+ m) in the Sierra Nevadas, near the foxtails and bristlecones. Here is an excerpt from the Abstract:

Deadwood tree stems scattered above treeline on tephra-covered slopes of Whitewing Mtn (3051 m) and San Joaquin Ridge (3122 m) show evidence of being killed in an eruption from adjacent Glass Creek Vent, Inyo Craters. Using tree-ring methods, we dated deadwood to 815-1350 CE, and infer from death dates that the eruption occurred in late summer 1350 CE….Using contemporary distributions of the species, we modeled paleoclimate during the time of sympatry [the MWP] to be significantly warmer (+3.2 deg C annual minimum temperature) and slightly drier (-24 mm annual precipitation) than present,

The value of 3.2 deg C is a big and almost inconceivable number. But compare this to the following comment in Naurzabaev et al [2004] about Siberia, which I’d referred to previously, where a similar number is implied:

Trees that lived at the upper (elevational) tree limit during the so-called Medieval Warm Epoch (from A.D. 900 to 1200) show annual and summer temperature warmer by 1.5 and 2.3 deg C, respectively, approximately one standard deviation of modern temperature. Note that these trees grew 150-200 m higher (1-1.28C cooler) than those at low elevation but the same latitude, implying that this may be an underestimate of the actual temperature difference.

In my post about Naurzbaev et al., I pointed out that, when the two effects were added together, the annual and summer differences were even larger – and, as it turns out, remarkably similar to that reported by Millar et al [2006] in California.

surely it’s more reasonable to allow for the altitude effect: this would yield an estimate that the MWP annual temperature was 2.58-2.86 deg C warmer than at present and the summer MWP temperature was 3.38-3.66 deg C warmer than at present.

Millar et al [2006] applied ecological niche modeling to subfossil medieval trees located at high altitudes; ecological niche modelling is David Stockwell’s specialty so it will be interesting to see what he thinks. The locations – Whitewing Mtn and San Joaquin Ridge – are both in Mono County CA, very close to the bristlecones and foxtails. Other comments from the running text of Millar et al [2006] and I recommend reading it all:

Late Holocene climates have been described from diverse records in the Sierra Nevada and Great Basin (Woolfenden, 1996; Stine 1994). The last millennium began with a 450-year phase that corresponds to the widespread Medieval Climate Anomaly (MCA), and extended from ca. 900-1350 CE in the Sierra Nevada. Proxy records indicate this to have been a dry and warm period, where lake and river levels declined (Yuan et al., 2004; Meko et al., 2001; Stine, 1990, 1994), treelines increased (Graumlich, 1993; Graumlich and Lloyd, 1996), and glaciers retreated (Konrad and Clark, 1998). The MCA was followed by a cool phase coinciding with the northern hemispheric Little Ice Age (LIA), which extended in the Sierra Nevada from 1400-1900 CE (Clark and Gillespie, 1997). Closed lake levels remained moderately low, suggesting decreases in effective precipitation and/or runoff relative to present (Stine, 1990). Treeline elevations declined (Graumlich and Lloyd, 1996; Lloyd and Graumlich, 1997) and the largest glacial advances since the Pleistocene are recorded (Clark and Gillespie, 1997). The LIA ended ~1900 CE; early 20th century proxies record rising temperatures, precipitation increases (Graumlich, 1993) and increasing lake and river levels (Stine, 1990, 1994).

We modeled paleoclimates based on ecological niche theory. The six species that we identified from Whitewing Mtn do not occur together at present. We reasoned that during the period of sympatry on Whitewing Mtn, the climate must have been compatible for all the species, i.e., fundamental niche spaces overlapped (Jackson and Overpeck, 2000). Thus, conditions represented by the intersection of individual climate spaces of the deadwood species would estimate a potential climate of Whitewing Mtn during the time of the summit assemblage. A similar rationale was used by Arundel (2005).Extensive drought during the Medieval period has been further interpreted from lake sediments (Yuan et al., 2004; Benson et al., 2002; Li et al., 2000; Kleepe, in press), tree-ring reconstructions (Meko, et al., 2001), and glacial records (Konrad and Clark, 1998). Tree-ring reconstructions indicate increased temperature relative to present (Graumlich, 1993; Scuderi, 1993) and higher treelines (Graumlich and Lloyd, 1996; Lloyd and Graumlich, 1997), and pollen reconstructions show greater abundance of fir in high-elevation communities than at present (Anderson, 1990)…

The ecologic patterns and climatic estimates at Whitewing and San Joaquin Ridge corroborate studies showing significant Medieval warmth in the California region but provide evidence for differences between high and low elevations in moisture availability. Whereas mid-low elevations in the Sierra Nevada experienced extreme Medieval drought, precipitation at Whitewing appears to have been adequate to support mesic-adapted species. A projection of warm Medieval temperatures with only small decreases in precipitation at high elevations is not inconsistent with extreme drought at lower elevations indicated by other studies.

So the "regional" MWP phenomenon supposedly localized to northern Europe, is observable in Siberia and California.Readers of this site are familiar with the "site chronologies" for bristlecones and foxtails which have hockey stick shapes, which are "active ingredients" of the MBH hockey stick and other multiproxy studies.

The advantage of the approaches taken by Naurzbaev and Millar is that they are not based on correlations or on picking, but on ecological niches. While there may some hair on this concept when examined closely, intuitively it has far more appeal than (say) Thompson’s attempt to defy the “amount effect” through weak correlation arguments. The Naurzbaev and Millar studies are also very hard to reconcile with a view that certain key Hockey Team series are accurately reflecting local climate. The bristlecone and foxtail "site chronologies" used by the Hockey Team (not just in MBH but serially) show a "cold" MWP. How can these "site chronologies" be reconciled with the detailed findings of Millar et al [2006]? This is distinct from issues of CO2 fertilization. Similarly, how can the findings of Naurzbaev et al [2004] be reconciled with the Yamal site chronology which likewise argues for a "cold" MWP in this region relative to modern times (in this case, not even being consistent with the updated Polar Urals chronology.)

Moberg attempted to get away from tree ring site chronologies, but simply picked an odd selection of sediments, with his results dominated by a few questionable series. I don’t think that Moberg’s a magic bullet.

Before there was a Hockey Team, paleoclimatologists on a millennial scale studied "low frequency" vegetation changes. Millar et al [2006] is a sophisticated effort in the spirit of the paleoclimatologists before the Hockey Team. My guess is that this is the way forward – abandon Mannian attempts to extract "signals" from cherry-picked and noisy proxy series and try to develop some really good information, one site at a time.

Sierra Nevada Research Center website
Constance Millar website
Millar, C.I., J.C. King, R.D. Westfall, H.A. Alden, and D.L. Delany. 2006. Late Holocene forest dynamics, volcanism, and climate change at Whitewing Mountain and San Joaquin Ridge, Mono County, Sierra Nevada, CA, USA. Quaternary Research. In Press. (Article in PDF Format; Figures in PDF Format)


  1. Mike Rankin
    Posted Mar 14, 2006 at 11:51 AM | Permalink

    Seems like a strong signal for at least regional warmth in the MWP. Surprising the magnitude. In viewing the related threads, saw a reference to a paper by Samuli Helama. I recently found his account on Finland treering analysis. Didn’t publish data or specific code though. Also noted activity of TCO in the old thread. Haven’t “seen” him in a long time.

  2. Steve McIntyre
    Posted Mar 14, 2006 at 12:08 PM | Permalink

    There is similar changes of treeline in the Kola peninsula. So the “regions” would include the Sierra Nevadas, Siberia, northern Europe and Greenland. In the older literature, there is considerable interest in treelines and vegetation, but it seems to have been swept away recently by Hockey Team methods.

  3. Armand MacMurray
    Posted Mar 14, 2006 at 1:26 PM | Permalink

    In the first blockquoted section above, they report an increase of +3.2 °C in the “annual minimum temperature.” To what extent is this temp measure comparable with what Naurzbaev and the hockey team report? At first blush, it sounds like it could be oranges vs grapefuits (related, but not directly comparable). I’m sorry if this is covered elsewhere in the Millar paper, as I haven’t read it yet.

  4. Posted Mar 14, 2006 at 3:27 PM | Permalink

    While the local warmth seems very likely, it would be more interesting to have similar data from many other places. Additional 3 degrees seem like a lot but my guess is that in 10 years, people will work with even greater elevations of temperature in the past.

  5. muirgeo
    Posted Mar 14, 2006 at 4:37 PM | Permalink

    So multi-proxy studies are not reliable and many of the proxy sources are suspect. But these Sierra proxy sources seem to both be of interest and coincidently to you liking. Not cherry picking are we.

    What about the soon to be gone 7,000 year old snow cap on Mt Kilimanjaro. I wonder why its melting now but did not melt with the extreme climate change found in the MWP Sierra. Likewise how do we explain the recession of the Quelccaya glacier in Peru revealing previously buried 5,000 year old forbs.

    Like I always say..there exist in the scientific peer reviewed literature NO studies that significantly deviate from the results of MBH.

  6. Hans Erren
    Posted Mar 14, 2006 at 5:01 PM | Permalink

    glaciers george?

  7. Posted Mar 16, 2006 at 12:26 AM | Permalink

    So muirgeo, you have two choices:

    * Millar et al [2006] is not a study in the scientific peer-reviewed literature.
    * Millar et al [2006] does not significantly deviate from the results of MBH.

    Which is it?

  8. Paul Gosling
    Posted Mar 16, 2006 at 3:21 AM | Permalink

    Archaeological evidence eg Mesa Verde in Colorado, also indicates prolonged drought at least at the end of the 13th century. This would seem to suggest that if GW results in a circa 2 degree increase in temperature much of N. America may become quite dry, so much for the corn belt.

  9. Steve McIntyre
    Posted Mar 16, 2006 at 6:39 AM | Permalink

    #8. I’m not fully conversant with the archaeological evidence, but my impression was that the Mesa Verde culture flourished in the MWP – the end of the 13th century is after the medieval period, which had more rather than less settlement. I’ve also seen some specialists distinguish between warm-wet, warm-dry, cold-wet and cold-dry scenarios. Woodhouse has written about the “20th century pluvial” in the American Southwest. Intuitively it seems to me that societies built at desert margins will be relatively vulnerable to climate change.

  10. JerryB
    Posted Mar 16, 2006 at 11:46 AM | Permalink

    Re #3,


    The Millar et al paper does not mention a mean annual mean temperature difference; it does mention the following:

    “Medieval mean annual minimum temperature was warmer than current by 3.2 C, with large differences in winter (+3.5 C, January) and summer (+4.0 C, July). Mean annual maximum temperature was also greater in the Medieval period (+2.3 C), with greater differences in winter (+3.2 C, January) than summer (+2.6 C, July).”

    Depending on how the “mean annual (minimum/maximum)” were calculated, it may, or may not, be plausible to infer a mean annual mean difference of about 2.75 C.

  11. Hans Erren
    Posted Mar 16, 2006 at 2:32 PM | Permalink

    Ancestral Puebloans lived on Mesa verde between 550 and 1300.

    Most of the cliff dwellings were built from the late 1190’s to the late 1270’s.

    Below is a photograph of the drought (drouth) record (1276-1299) on display in the mesa verde museum, I was there last september.

    By 1300 Mesa Verde was deserted, the Ancestral Puebloans “moved on” south into New Mexico and Arizona.

  12. jae
    Posted Mar 17, 2006 at 3:45 PM | Permalink

    Below is a photograph of the drought (drouth) record (1276-1299) on display in the mesa verde museum, I was there last september.

    By 1300 Mesa Verde was deserted, the Ancestral Puebloans “moved on” south into New Mexico and Arizona.

    Now THERE is a good use for tree ring measurements. I still can’t figure out how climatologists can tell the difference between drought and temperature by “reading the tree rings,” unless the trees grew in an area where drought is very unlikely (a rain forest?)

  13. Steve Sadlov
    Posted Mar 29, 2006 at 1:48 PM | Permalink

    RE: 12. And the converse, Swamp Cypress, which are thought to be excellent moisture proxies. Now here’s an idea. Examine Bristlecones solely for possible correlation to other indicators of paleo moisture and see what you get. Hmmmmmm ….

  14. Steve Rodriguez
    Posted Apr 11, 2006 at 5:44 PM | Permalink

    stumbled onto this blog looking for record of past climate flux may provide clues on how global change may manifest in CA and PNW. Something that bothers me about the models predicting sea level rise and catastrophic melt scenarios, which is related to the lack of data points at a regional scale, is how the DISTRIBUTION

  15. Steve Rodriguez
    Posted Apr 11, 2006 at 5:56 PM | Permalink

    WHOOPS- continue that thought- How the distribution of precipitation regionally and independent of seasonal temperature cycles may affect montane glaciaers and ecosystem characteristics. for instance, consider what would be the net effect of no net increase in precip or temperature but rather an increase of precipitation in the months of April and May that was accompanied by a slight decline in temperature in those months. Extend the scenario by considering the persistent albedo and atmospheric cooling effects due to the lingering snow pack at high elevation. Such seasonal distribution hypotheses are almost never mentioned-only the periodic(in discreet annual units) net changes in temp and precip. The inter-annual interaction of temperature and precipitation, especially in higher elevations, is dynamic and likely has produced some of teh anomalous ecosystem responses mentioned in the studies and above comments. Any thoughts? hope I am not too late to get a response.

  16. Steve Sadlov
    Posted Apr 11, 2006 at 6:03 PM | Permalink

    Steve, sounds like you are fairly familiar with the Sierra Nevada! Interesting that the exact scenario you’ve described seems to be happening right now. We’ve had this persistent Siberia Express in place in California and certain, the snow pack is amazing. I checked a location at the Sierra crest on Sunday and one of the basalt fortress formations I am familiar with, which normally juts at least 10 – 15 feet out of the snow at this time of year, was nearly buried.

  17. Steve Rodriguez
    Posted Apr 11, 2006 at 6:23 PM | Permalink

    RE 16: Well yes, I have been paying attention to the amazing weather here in CA this year. But I also know that if you check the recent record you will find that the trend in late season precip (Apr and May)here has been steadily positive over the last 35 years or so. An interesting change with a relatively observation period.

3 Trackbacks

  1. By Medieval Treeline in Finland « Climate Audit on Oct 28, 2010 at 11:41 AM

    […] results from treelines are not limited to the north Atlantic and Greenland, but extend to the Sierra Nevadas (117 W), Sweden, Finland, Polar Urals (65 E) and a Siberian transect (90-100E). I’ll add a […]

  2. […] discussed here and here. Post-medieval lakes have even submerged medieval trees. Miller (2006) discussed here and here estimated great warmth in alpine California as […]

  3. […] This failure to cite and reconcile opposite results is another instance of both shoddy practice by the scientists and all too typical indolent reviewing by senior journals. How could a competent reviewer of this article either be unaware of Ababneh’s contrary results or not require a reconciliation? Another frustrating aspect of this study is its failure to discuss seemingly discordant findings from Millar et al (2006) – findings which were noted in the NAS panel report (though IPCC refused to mention them.) Millar et al had observed subfossil stumps well above present treelines and reported: […]

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