A little context and a Poll

I’ve been asked to give context to some of the emails.   So far, I have read only a few.   This is one though which should have particular resonance with long time Air Vent or Climate Audit readers.  It was started by a subversive climate denier – Jeff Severinghaus – who happens to have been an Associate professor at the University of California when he asked the exact same questions that we so often ask in “skeptic” blogland.   As you can see, Lord Mann nipped it in the bud as hard as a rabid dog could.

This chain is in reverse order.  I’ve bolded the important bits.  What caught my attention about this email set is that Jeff makes the same arguments that we evil skeptics make about paleo reconstructions.  Non-linearity, loss of sensitivity and the fact that if proxies aren’t tracking temp in the modern era, how can we assume they track historic temps?

All very good quesitons, don’t you think?

What do you think of the answers?

—

cc: Chris Miller <Chris.Miller@noaa.gov>, mhughes@ltrr.arizona.edu, dverardo@nsf.gov, mann@virginia.edu, broecker@ldeo.columbia.edu, rfweiss@ucsd.edu, k.briffa@uea.ac.uk, drdendro@ldeo.columbia.edu
date: Mon, 3 Feb 2003 09:55:14 -0800
from: Jeff Severinghaus
subject: Re: [Fwd: tree rings and late 20th century warming]
to: Phil Jones <p.jones@uea.ac.uk>, “Michael E. Mann” <mann@virginia.edu>, “Thomas R Karl” <Thomas.R.Karl@noaa.gov>, Ray Bradley <rbradley@geo.umass.edu>

<x-rich>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:

<excerpt> 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:

<excerpt>

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
<italic>number</italic> of competing explanations
[<italic>this</italic> 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, <italic>Nature</italic>, <italic>400</italic> (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 <italic>appropriate</italic> alignment of all the records is
provided in IPCC, and in the attached <italic>Science
</italic>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 <italic>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:

<excerpt>

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
<<mailto:jseveringhaus@ucsd.edu><

To: <<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

Professor Michael E. Mann

Department of Environmental Sciences, Clark Hall

University of Virginia

Charlottesville, VA 22903

_______________________________________________________________________

Attachment Converted: “c:\eudora\attach\Briffa&Osborn.pdf”

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