cc: Chris Miller <Chris.Miller@noaa.gov>, mhughes@ltrr.arizona.edu,  dverardo@nsf.gov, broecker@ldeo.columbia.edu, rfweiss@ucsd.edu,  k.briffa@uea.ac.uk, drdendro@ldeo.columbia.edu
date: Mon, 03 Feb 2003 14:16:20 -0500
from: "Michael E. Mann" <mann@multiproxy.evsc.virginia.edu>
subject: Re: [Fwd: tree rings and late 20th century warming]
to: Jeff Severinghaus <jseveringhaus@ucsd.edu>,  Phil Jones <p.jones@uea.ac.uk>, Thomas R Karl <Thomas.R.Karl@noaa.gov>,  Ray Bradley <rbradley@geo.umass.edu>

   Jeff,
   Choice of aligning has no influence on the slope of the curve, it simply changes the mean
   baseline for comparison. The Mann et al reconstruction has the same amplitude increase as
   the full Northern Hemisphere annual mean instrumental record over the calibration interval
   (1900-1980). On this simple point, there is no debate. And this seems to be the origin of
   your misunderstanding of the issues involved.
   Briffa & Osborn use a slightly different convention from that used elsewhere (e.g. IPCC and
   in the attached Science piece which I've re-sent for the benefit of your expanded recipient
   list), and by their convention the instrumental record is observed to lie ever-so-slightly
   above the MBH reconstruction over the entire interval available for comparison (mid 19th
   century-> 1980). This difference is actually quite small, so I'm not sure why we're even
   discussing it in the first place. It, however, does not in any case impact a comparison of
   the trends in the two series, which match remarkably well over that same interval.  This is
   despite the fact that the MBH reconstruction represents the entire Northern Hemisphere
   (which gets half of its contribution from the tropics i.e., latitudes < 30N) while the
   instrumental series shown by Briffa & Osborn is only the extratropics north of 20N.
   This is old stuff, and I would guess that the others cc'd in on this message  (Ray,
   Malcolm, Keith, Phil) are not interested in re-hashing these old discussions.  The state of
   the the science here has moved well beyond these semantic and/or conventional arguments,
   focusing instead on detailed intercomparisons of methods and data (employing rigorous
   diagnostics of reconstructive fidelity (collaborative between
   Bradley/Briffa/Hughes/Jones/Mann/Osborn/Rutherford). There is little disagreement between
   us on the broad trends when seasonal and spatial sampling issues, and differing conventions
   for e.g. defining reference periods, have been taken appropriately into account.
   I hope you find that the above information clarifying Jeff. Due to other demands on my
   time, I have to sign out now on this series of exchanges.
   best regards,
   Mike Mann
   At 09:55 AM 2/3/03 -0800, Jeff Severinghaus wrote:

     Gentlemen:
     Please accept my apologies if I have gotten the story wrong.  I am not a specialist in
     the tree-ring field, and was simply reporting what I saw in the Briffa and Osborne
     paper, several other papers, and what several tree-ring people have told me in
     conversations.  I agree, we need to keep the level of misinformation out there down to a
     minimum! I regret adding to it.
     I am still confused, however, about Mike's explanation for the Briffa and Osborne
     paper's curve appearing flat after 1950 AD.  Can you try explaining this again, Mike,
     please?  I don't understand how aligning could change the slope of a curve.  The curves
     appear to continue to 1990 AD or so, and the Esper et al. curve continues to 1993.  So
     the explanation that the records only go up to 1980 doesn't seem to hold in this case.
     The dashed black line is the instrumental record for warm-season >20 N latitudes and it
     does indeed diverge from the tree-ring records in the 1980s.  Can you help me out here?
     Sincerely,
     Jeff
     At 4:36 PM +0000 2/3/03, Phil Jones wrote:

     Tom,
          Mike's answer is a fair response. Jeff has mixed some facts up and this is maybe
     because we've never explained them clearly enough. There are two facts:
     1.  There are few tree-core series that extend beyond the early 1980s. This is because
     many of the sites we're using were cored before the early 1980s. So most tree-ring
     records
     just don't exist post 1980.
     2. The majority of the recent warming is post-1980, so no proxy would pick this up.
     This warming has been large and it would be good to go back and see if the trees have
     picked it up.  It would give more faith in tree-ring reconstructions, but any
     reconstruction
     method is being pushed to the limit by the rate of temperature rise over the late 20th
     century. Applies to other proxies but you have to note the following:
         It is important to remember that locally few regions exhibit statistically
     significant
     warming. Highly significant at the hemispheric level, but not great at the local level
     due to high level's of variability. The spatial scales are important and this is
     difficult to
     get across.
     Cheers
     Phil
     At 09:15 03/02/03 -0500, Michael E. Mann wrote:

     Dear Tom,
     Have no fear, Jeff has still got his facts wrong, even after going back and checking
     once...
     First off, I never made any such comment to Jeff--he clearly misunderstood comments that
     I made at EGS a year ago in response to a question he asked. Of course, it is well know
     that there are a number of competing explanations [this is what I said--to quote this as
     offering "no explanation" is a bit unfair Jeff, don't you think? As I recall, I even
     invited Tim Osborn in the audience to add his own comments--but he had little to say]
     for the fact that *high latitude*, primarily *summer responsive*, tree-ring *density*
     data have exhibited a noteable decline in the past few decades in the amplitude of their
     response to temperature variability. We have discussed this issue time and again in our
     own work, and  Keith Briffa, Malcolm Hughes, and many others have published on this, w/
     competing possible explanations (stratospheric ozone changes, incidentally, is the least
     plausible to me of multiple competing, more plausible explanations that have been
     published). See e.g.:
     Vaganov, E.A., M.K. Hughes, A.V. Kirdyanov, F.H. Schweingruber, and P.P. Silkin,
     Influence of Snowfall and Melt Timing on Tree Growth in Subarctic Eurasia, Nature, 400
     (July 8), 149-151, 1999.
     It should *also* be noted that we used essentially none of these data in the multiproxy
     Mann/Bradley/Hughes (MBH) reconstruction, and that the MBH reconstruction tracks the
     instrumental record quite well through the very end of our calibration interval
     (1980--it stops then because there are far fewer paleo records available after 1980).
     This was shown in our 1998 Nature article quite clearly, and of course remains true
     today. Jeff made the mistake of only looking at the Briffa & Osborn paper, which doesn't
     properly align the 20th century means of the various reconstructions and  instrumental
     record.
     An appropriate alignment of all the records is provided in IPCC, and in the attached
     Science perspective from last year. This shows how well the Mann et al reconstruction
     (and several model-based estimates) track the entire instrumental record. There are some
     good reasons that some of the other purely tree-ring based reconstructions differ in
     their details, in addition to the greater influence of the recent high-latitude density
     decline issue, and these are discussed in IPCC and the Science piece. Of course, we have
     in, our own work provided detailed calibration and verification statistics that
     establish the skill in our reconsruction in capturing the details of  both the modern
     instrumental record, and independent, withheld earlier instrumental  data (19th century
     and, more sparsely, 18th century), and we publish uncertainties that are based on
     rigorous analysis of the calibration and cross-validation residuals. I  know that Jeff
     has seen me talk on this many times, and probably has read our work (I would hope), so
     I'm frankly a bit disappointed at the comments. I would have liked to think that he
     would have approached us first, before broadcasting a message full of factual errors.
     Please let me, or any of the others know, if we can provide any further information that
     would help to clarify (rather than obscure!) the facts,
     cheers,
     mike
     At 07:49 AM 2/3/2003 -0500, Thomas R Karl wrote:

     Colleagues,
     Correct me if I am wrong, but I always thought the failure was a lack of tree cores
     subsequent to the 1980s.  Please correct me if I am wrong, and if Jeff is correct, then
     indeed we have a significant implication.
     Tom
     -------- Original Message --------
     Subject: tree rings and late 20th century warming
     Date: Sun, 2 Feb 2003 16:15:04 -0800
     From: Jeff Severinghaus <[1]mailto:jseveringhaus@ucsd.edu><jseveringhaus@ucsd.edu>
     To: <[2]mailto:Thomas.R.Karl@noaa.gov>Thomas.R.Karl@noaa.gov
     Dear Dr. Karl,
     I enjoyed your presentation yesterday at the MIT Global Change forum. You
     may recall that I asked about the failure of tree rings to record the 20th
     century warming.  Now that I look at my records, I realize that I
     remembered this wrongly: it is the LATE 20th century warming that the tree
     rings fail to record, and indeed, they do record the early 20th century
     warming.
     If you look at the figure in the attached article in Science by Briffa and
     Osborn, you will note that tree-ring temperature reconstructions are flat
     from 1950 onward.   I asked Mike Mann about this discrepancy at a meeting
     recently, and he said he didn't have an explanation.  It sounded like it is
     an embarrassment to the tree ring community that their indicator does not
     seem to be responding to the pronounced warming of the past 50 years. Ed
     Cook of the Lamont Tree-Ring Lab tells me that there is some speculation
     that stratospheric ozone depletion may have affected the trees, in which
     case the pre-1950 record is OK.  But alternatively, he says it is possible
     that the trees have exceeded the linear part of their temperature-sensitive
     range, and they no longer are stimulated by temperature.  In this case
     there is trouble for the paleo record.  Kieth Briffa first documented this
     late 20th century loss of response.
     Personally, I think that the tree ring records should be able to reproduce
     the instrumental record, as a first test of the validity of this proxy.  To
     me it casts doubt on the integrity of this proxy that it fails this test.
     Sincerely,
     Jeff
     copies to Ray Weiss, Wally Broecker
     Jeff Severinghaus
     Associate Professor of Geosciences
     Scripps Institution of Oceanography
     University of California, San Diego 92093-0244
     (858) 822-2483 voice
     (858) 822-3310 fax
     Address for Fedex deliveries:
     Rm 211 Vaughan Hall
     8675 Discovery Way
     La Jolla, CA 92037

     ______________________________________________________________
                         Professor Michael E. Mann
                Department of Environmental Sciences, Clark Hall
                           University of Virginia
                          Charlottesville, VA 22903
     _______________________________________________________________________
     e-mail: mann@virginia.edu   Phone: (434) 924-7770   FAX: (434) 982-2137

     <[3]http://www.evsc.virginia.edu/faculty/people/mann.shtml>[4]http://www.evsc.virginia.e
     du/faculty/people/mann.shtml

     Prof. Phil Jones
     Climatic Research Unit        Telephone +44 (0) 1603 592090
     School of Environmental Sciences    Fax +44 (0) 1603 507784
     University of East Anglia
     Norwich                          Email    p.jones@uea.ac.uk
     NR4 7TJ
     UK
     ----------------------------------------------------------------------------


     <br>
     <br>
     Jeff Severinghaus
     Associate Professor of Geosciences
     Scripps Institution of Oceanography
     University of California, San Diego 92093-0244
     (858) 822-2483 voice
     (858) 822-3310 fax
     Address for Fedex deliveries:
     Rm 211 Vaughan Hall
     8675 Discovery Way
     La Jolla, CA 92037
     <br>
     </blockquote></x-html>

   _______________________________________________________________________
                        Professor Michael E. Mann
             Department of Environmental Sciences, Clark Hall
                         University of Virginia
                        Charlottesville, VA 22903
   _______________________________________________________________________
   e-mail: mann@virginia.edu   Phone: (434) 924-7770   FAX: (434) 982-2137
          [5]http://www.evsc.virginia.edu/faculty/people/mann.[6]shtml
   Attachment Converted: "c:\eudora\attach\MannPersp2002.pdf"

