Van: Michael E. Mann [mann@virginia.edu]
Verzonden: dinsdag 4 januari 2005 17:39
Aan: Marcel Crok; rbradley@geo.umass.edu; mhughes@ltrr.arizona.edu
CC: mann@virginia.edu
Onderwerp: Re: questions regarding MBH98
Bijlagen: Supplementary3.pdf
Dear
Mr. Crok,
Below are some responses to your questions. Unfortunately, I will be
unable to reply in any more detail for more than another week due to surgery I
am having (and post-surgery recovery), so you should direct further inquiries
to my colleagues Bradley and Hughes, as well as the other scientists I mention
below.
I hope you are not fooled by any of the "myths" about the hockey
stick that are perpetuated by contrarians, right-wing think tanks, and fossil
fuel industry disinformation. These myths are each dispelled here.
http://www.realclimate.org/index.php?p=11
Of particular relevant here is "myth #1" (that the "hockey
stick" depends only on Mann et al--more than a dozen other estimates from
proxy data and model simulations get essentially the same result (i.e., the
results agree within the estimated uncertainties). See:
http://www.realclimate.org/index.php?p=7#figures
I must begin by emphasizing that McIntyre and McKitrick are not taken
seriously in the scientific community. Neither are scientists, and one
(McKitrick) is prone to publishing entirely invalid results apparently without
apology (see below). "New Scientist" considered running an article
(by David Paterson) on the MM claims. The editor decided not to run an article,
concluding that their claims were suspicious and spurious after interviews with
numerous experts and after it was revealed that they had suspiciously close
ties with the fossil fuel/energy industry. See e.g.:
http://www.environmentaldefense.org/article.cfm?contentid=3804&CFID=21084385&CFTOKEN=29888831
You can see what USA Today science report Dan Vergano had to say about MM
here:
http://www.usatoday.com/weather/climate/2003-11-18-warming-debate_x.htm
I therefore hope that you will treat their claims with appropriate
suspicion, and I that hope you will solicit comments from paleoclimate experts
such as Phil Jones, Keith Briffa, Jonathan Overpeck, and Tom Crowley, and not
rely upon comments from individuals who have little expertise in this area.
You should also discuss with Caspar Ammann and Gene Wahl of NCAR (ammann@ucar.edu, wahle@alfred.edu). They have independently
discredited (paper in press, I believe) McIntyre and McKitrick. They
independently reproduce the results of MBH98, and reproduce the skill in these
results. They also show that the results of McIntyre and McKitrick can only be
reproduced through a censoring of the dataset.
In summary. please keep in mind that McIntyre and MckItrick (1) never published
their results in a peer-reviewed scientific journal ("Energy and Environment"
is not considered a scientific journal, but a "social science"
journal), (2) The claims, which you repeat below, were REJECTED by Nature
because the reviewers and editors did not believe they had made their case, and
(3) There are now 2 peer-reviewed articles discrediting MM, one that is in
press:
Rutherford, S., Mann, M.E., Osborn, T.J., Bradley, R.S., Briffa, K.R., Hughes,
M.K., Jones, P.D., Proxy-based
Northern Hemisphere Surface Temperature Reconstructions: Sensitivity to
Methodology, Predictor Network, Target Season and Target Domain, Journal
of Climate, in press (2005).
and another by Ammann and Wahl (whom you should contact for more information,
as mentioned above).
Replies to your specific inquiries provided below:
Best regards,
Mike Mann
At 10:22 AM 1/4/2005, Marcel Crok wrote:
Dear
dr Mann, dr Bradley and dr Hughes,
I
am working on a long (10 page) cover story on the Hockey Stick for
Natuurwetenschap & Techniek, a Dutch monthly science magazine which is
comparable with Scientific American.
I
have made a detailed analysis of MBH98 and also of the work of McIntyre &
McKitrick (MM) and Von Storch & Zorita. I also studied your latest comment
on MM04 on the weblog www.realclimate.org
(dd 4 December)
You should be aware that a comment is in press in "Science" casting
significant doubt on the claims of Von Storch and Zorita, and another paper, in
review, suggests that their conclusions are incorrect, . A 3rd paper, by the
Danish Meteorological Institute (DMI) group using the same model as von Storch,
cannot reproduce the von Stroch results (they find much less variability than
von Storch), suggesting that their were some serious problems with the von
Storch simulation as well as with their analysis of the simulation results. I
would suggest that you get in touch with these individuals (e.g. Keith Briffa: k.briffa@uea.ac.uk or Martin Stendel: mas@dmi.dk) for a more balanced view of the Von
Storch claims.
In
my opinion there are some issues still open on which I would like to hear your
comment. This could be done by email, but I would prefer to call one of you and
discuss the topic by phone.
Here
are the issues:
1)
How do you explain the
existence of the directory BACKTO_1400-CENSORED on Mann's ftp-server? MM show
that it contains the results of the calculation of the NOAMER PC's without
using the bristlecone pine series, giving a higher NH temperature in the 15th
century.
It is sad that McIntyre and McKitrick have been reduced to scouring our website
for things like this, to take out of context, and make false and misleading
assertions. We performed a set of sensitivity tests to determine if a skillful
reconstruction was available without correcting certain high-elevation
tree-ring chronologies for sensitivity to possible non-climatic (e.g.
co2-fertilization) effects. These calculations were performed as part of these
analyses, after MBH98. This is all discussed quite clearly in our follow-up
paper to MBH98 published in the journal GRL in 1999:
Mann, M.E., Bradley, R.S. and Hughes, M.K., Northern
Hemisphere Temperatures During the Past Millennium: Inferences, Uncertainties,
and Limitations, Geophysical Research Letters, 26, 759-762, 1999.
This claim by MM is just another in a series of disingenuous (off the
record: plainly dishonest) allegations by them about our work.
2)
Their is a severe debate between you and MM about the skill of the calculation.
You claim a high RE-statistic. MM show that their simulated hockey sticks also
give a high RE-statistic but a very low R^2 statistic.
We showed in our reply to the REJECT MM comment to Nature, that they
incorrectly calculated all of their verification statistics, because they
didn't account for the changing spatial sampling of the Northern Hemisphere
temperature record back in time. See the attached supplementary information
("supplementary3.pdf"--read page 2) that was provided to the
reviewers of the rejected comment by McIntyre and McKitrick. Keep in mind
that the reviewers of their Nature comment, who had the expertise and full
available material to judge whether or not MM's claims were plausible, decided
that they were not.
Our reconstruction passes both RE and R^2 verification statistics if calculated
correctly. Wahl and Ammann (in press) reproduce our RE results (which are twice
as high as those estimated by MM), and cannot reproduce MM's results. There is
little, if anything correct, in what MM have published or claimed. Again, none
of their claims have passed a legitimate scientific peer review process!
See also Rutherford et al (in press--see above) for an extensive discussion of
cross-validation, and the relative merits of different metrics (RE vs CE vs
r2). It is well known to any scientists in meteorology or climatology that RE
is the preferred metric for skill validation because it accounts for changes in
mean and variance prior to the calibration interval (which R^2 does not!). The
preferred use of RE dates back to the famous paper by Lorenz in evaluated skill
in meteorological forecasts.
It must be stated that McKitrick has been shown to be prone to making major
errors in his published work. You should refer to the discussions here:
http://www.realclimate.org/index.php?p=41
and here:
http://cgi.cse.unsw.edu.au/~lambert/cgi-bin/blog/2004/08#mckitrick6
particularly interesting, in the context of this discussion, is his failure in
an independent context (the Michaels and McKitrick paper discussed in the first
link) to understand the issue of cross-validation! That is, in both the
McIntyre and McKitrick '03 paper, and the Michaels and McKitrick '05 paper, the
authors failed to even understand the importance of performing
cross-validation! Such papers could never be published in a respected scientific
journal.
In
MBH98 you didn't calculate the R^2 statistic, but in Mann and Jones (2003) you
did. I asked Eduardo Zorita questions about this and he said he would calculate
both. Why didn't you calculate the R^2 in MBH98?
Repeating what I said above, see Rutherford et al (in press--see above) for an
extensive discussion of cross-validation, and the relative merits of different
metrics (RE vs CE vs R^2). It is well known to any scientists in meteorology or
climatology that RE is the preferred metric for skill validation because it
accounts for changes in mean and variance prior to the calibration interval
(which R^2 does not!). The preferred use of RE dates back to the famous paper
by Lorenz in evaluated skill in meteorological forecasts.
3)
On the weblog www.realclimate.org you
state that MM should use 5 PC's in the NOAMER-network if they use conventional
PCA. Especially the PC4 is important while it accounts for the bristlecone
pine series. This means that the overall result in MBH98 depends on a single
PC4. This is in contrary with the claimed robustness of the MBH98 method. Do
you agree now that the robustness of MBH98 is lower than originally claimed?
Not at all. I think you've misunderstood what is shown on the RealClimate
site. We show that we get essentially the same result, even if you don't use
PCA on the network at all, but use all 95 records available separately. This
is, in our view, the simplest possible demonstration one could imagine that MM's
claims are false. The MBH98 reconstruction doesn't depend on whether PCA is
used or not, let alone the centering convention (which, as noted below, simply
changes the order of the leading patterns). The earliest part of the
reconstruction does depend on certain key chronologists. This was discussed in
some detail in our followup paper (the GRL article referred to earlier) more
than 5 years ago, where we are quite clear about the sensitivity of the
earliest reconstructed values (15th century and earlier) to certain important
North American data. So if one eliminate important data from the dataset, as
McIntyre and McKitrick have done in every case, one will get a different
reconstruction. But such a reconstruction, as it will fail cross-validation,
would never be taken seriously by any legitimate scientist!
I must also refer you to this page here:
http://www.realclimate.org/index.php?p=7
(see also http://www.realclimate.org/index.php?p=11),
where it is made quite clear that numerous reconstructions using entirely
different data, and different methods (or models) come to nearly the same
conclusions (i.e., the reconstructions are consistent within the estimated
uncertainties). It is the fact that numerous groups come up with the same
result that suggests that the "hockey stick" is indeed robust.
I
am looking forward to discuss these issues with one of you. If for time or
other reasons you're not able to respond to this email before friday, January
7, could you please give me a short reply.
Yours
sincerely,
Marcel
Crok
Marcel Crok, editor
Natuurwetenschap & Techniek
Adres:
PO Box 256
1110 AG Diemen
The Netherlands
tel ++31 20 5310 951
gsm ++31 6 16 236 275
email mcrok@natutech.nl
http://www.natutech.nl
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
http://www.evsc.virginia.edu/faculty/people/mann.shtml
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