Saturday, June 2, 2012

4814.txt

date: Tue Mar 14 15:03:01 2006
from: Keith Briffa <k.briffaatXYZxyz.ac.uk>
subject: Re: NRC Committee on Surface Temperature Reconstructions
to: edwardcook <drdendroatXYZxyzo.columbia.edu>

Ed
agree with your remarks here - was not suggesting you integrated my comments - just forward
my message to North . However , if standardisation issue too hand-wavy now , just forget
it and send yours . Agree particularly with your remarks re Alley.
Very frustrating but am now having to catch up loads of stuff left when working on IPCC so
teaching etc must take precedence over trying to fashion careful statements
Keith
At 13:36 14/03/2006, you wrote:

Hi Keith,
Given the rather different ways we have expressed ourselves, I thing
it is best if we organize it as an Ed Cook followed by Keith Briffa
thing or vice versa. That way we can each say exactly what we want
and it relieves the burden of integrating it all into something that
sounds like a formal paper. We don't have time for that now. A formal
paper can come later. I also want to be sure that relevant points are
referenced. I am not sure it helps our case if we just throw out the
issue of standardization without any clear demonstration why it
matters with respect to divergence. It opens up a huge quagmire that
really requires explicit tests and demonstrations to make the point.
Otherwise, the committee may think we are simply in reaction mode
trying to salvage a bad situation by throwing out anything we can to
save the day. What I wrote was "fine as far as it goes", but it was
explicitly intended to target one obvious weakness in the pro- divergence school, e.g.
that they have absolutely no evidence that it
ever happened in the past. Rather the only available published
evidence points in exactly the opposite direction. For all the august
scientists on the committee and those invited speakers, I am shocked
and dismayed that they would so uncritically accept divergence as an
argument for throwing tree rings out the window. It is incredibly
unscientific, if not anti-scientific, in the way they have reacted. I
will certainly be happy to tell them that if it is necessary. Guys
like Richard Alley may sound like they are trying to be fair, but the
truth is they are not because they refuse to acknowledge their
ignorance of the subject and are too uncritical in their
extrapolations of facile information into the past. It is so patently
absurd. I also question what Gerry North was thinking when he gave
McIntyre an extra 30 minutes of time to rabbit on about how everyone
else is dishonest and wrong. That was shameful. So I have no
confidence that this NRC committee will ever give tree rings a fair
shake.
Ed
On Mar 14, 2006, at 7:51 PM, Keith Briffa wrote:

Fine as far as it goes - the additional issue , of the wide
uncertainty associated with medieval period warmth estimates is
also relevant , as are the points I made re many series not
exhibiting this problem , and those that do , potentially effected
by standardisation issues. I would simply ask that my previous
message be include with yours when you send this Ed
Keith
At 10:13 14/03/2006, edwardcook wrote:

Hi everyone,
Here is a draft of what I want to quickly send to
Ian Kraucunas, Ph.D.
Board on Atmospheric Sciences and Climate
National Research Council of The National Academies
500 Fifth Street NW, Keck 705
Washington, DC 20001
Email: ikraucunasatXYZxyz.edu
Phone: (202) 334-2546
Fax: (202) 334-3825
He originally invited me to talk before the NRC. I do not have any
other information on who to send it too. Please let me know what you
think, but don't be too pedantic or critical at this stage. I get the
feeling we have very little time to make an impact on the NRC
committee and its report. I personally think that I am correct as far
as I can take the argument. Let me know if I should send this on to
Richard as well.
Ed
Dear Ian,
I have heard via emails and telephone conversations about some rather
serious developments that could have an unfairly negative impact on
the use of tree rings for reconstructing past climate and the
upcoming IPCC assessment, especially that related to surface
temperatures. Apparently as part of her talk Rosanne D'Arrigo
mentioned the phenomenon of "divergence" between instrumental
temperatures and tree growth in the latter few decades of the 20th
century. The large-scale nature of this phenomenon was first
described in Nature by Keith Briffa back in 1998 (Briffa et al.,
1998) and to this day its cause is not well understood at all. A
number of hypotheses have been mentioned, which range from natural
(climatic change) to anthropogenic (i.e. pollution related), but the
actual cause is still unknown.
Somewhat alarmingly, it is my impression now the the NRC committee
members and other influential participants of the meeting have come
to the conclusion that the observed 20th century "divergence" calls
into serious question the value of the tree-ring reconstructions of
temperatures over the past millennium. The implicit assumption being
made is that the "divergence" is being caused by climatic change
related to 20th century warming, conditions that could have also
prevailed back during the Medieval Warm Period (MWP) some 800-1000
years in the past. If this were the case, then the concerns of the
committee would be justified. However, the available evidence does
not support such a conclusion. In a paper I published in Quaternary
Science Reviews in 2004 (Cook et al., 2004), I reviewed the
properties and interpretation of the tree-ring data used in the Esper
et al. (2002) paper published in Science. The reasonably well
distributed set of tree-ring data in both boreal and more temperate
latititude sites around the Northern Hemisphere allowed me to split
up the data into sub-regional ensembles, including 8 sites in the
55-70° north band and 6 sites in the 30-55° south band. The purpose
was to show the overall robustness of the multi-centennial
temperature signal in the tree-ring data. This plot from the QSR
paper is attached below as is the paper itself.
In his 1998 paper, Briffa showed that the divergence was largely
restricted to the region covered by the north band described in Cook
et al. (2004). Consistent with that finding, the north ensemble mean
shown below reveals a serious downturn in growth after about 1950.
This is an expression of the "divergence" that has been described
first by Briffa and also by D'Arrigo in her NRC talk. In contrast,
the south ensemble mean shows the opposite, i.e. a substantial growth
increase which is much more consistent with 20th century warming. If
one than follows the plots back in time, all of the sub-region
ensemble means track each other remarkably well at multi-centennial
time scales even when they enter the putative MWP 800-1000 years ago.
In fact, at no time prior to the 20th century is there separation
between north and south that is remotely comparable to that found
after ca. 1950. This result suggests that no large-scale "divergence"
of the order found during the 20th century occurred during the MWP
even though that period is suggested to have been somewhat warmer
than average overall. This result clearly refutes the argument that
"divergence" of the kind noted in the 20th century happened in the
past. It also suggests a unique anthropogenic cause to the 20th
century divergence.
I am not aware of ANY evidence that demonstrates the occurrence of
large-scale "divergence" in the past. It is therefore unjustified to
call into question the use of tree rings for reconstructing
temperatures over the past millennium based on a naive extrapolation
of growth "divergence" into the past when it appears to be unique to
the 20th century. The NRC committee members must be made aware of
this if their report is to have the necessary scientific credibility
that is expected of it.
Sincerely,
Edward R. Cook
References
Briffa, K.R., Schweingruber, F.H., Jones, P.D., Osborn, T.J.,
Shiyatov, S.G., Vaganov, E.A. 1998. Reduced sensitivity of recent
tree-growth to temperature at high northern latitudes. Nature 391:
678-682.
Esper, J., Cook, E.R., Schweingruber, F.H. 2002. Low-frequency
signals in long tree-ring chronologies for reconstructing past
temperature variability. Science 295: 2250-2253.
Cook, E.R., Esper, J., D'Arrigo, R.D. 2004. Extra-tropical Northern
Hemisphere land temperature variability over the past 1000 years.
Quaternary Science Reviews 23(20-22): 2063-2074.


Hi everyone,
Here is a draft of what I want to quickly send to
Ian Kraucunas, Ph.D.
Board on Atmospheric Sciences and Climate
National Research Council of The National Academies
500 Fifth Street NW, Keck 705
Washington, DC 20001
Email: <[1]mailto:ikraucunas@nas.edu>ikraucunas@nas.edu
Phone: (202) 334-2546
Fax: (202) 334-3825
He originally invited me to talk before the NRC. I do not have any
other information on who to send it too. Please let me know what
you think, but don't be too pedantic or critical at this stage. I
get the feeling we have very little time to make an impact on the
NRC committee and its report. I personally think that I am correct
as far as I can take the argument. Let me know if I should send
this on to Richard as well.
Ed
Dear Ian,
I have heard via emails and telephone conversations about some
rather serious developments that could have an unfairly negative
impact on the use of tree rings for reconstructing past climate
and the upcoming IPCC assessment, especially that related to
surface temperatures. Apparently as part of her talk Rosanne
D'Arrigo mentioned the phenomenon of "divergence" between
instrumental temperatures and tree growth in the latter few
decades of the 20th century. The large-scale nature of this
phenomenon was first described in Nature by Keith Briffa back in
1998 (Briffa et al., 1998) and to this day its cause is not well
understood at all. A number of hypotheses have been mentioned,
which range from natural (climatic change) to anthropogenic (i.e.
pollution related), but the actual cause is still unknown.
Somewhat alarmingly, it is my impression now the the NRC committee
members and other influential participants of the meeting have
come to the conclusion that the observed 20th century "divergence"
calls into serious question the value of the tree-ring
reconstructions of temperatures over the past millennium. The
implicit assumption being made is that the "divergence" is being
caused by climatic change related to 20th century warming,
conditions that could have also prevailed back during the Medieval
Warm Period (MWP) some 800-1000 years in the past. If this were
the case, then the concerns of the committee would be justified.
However, the available evidence does not support such a
conclusion. In a paper I published in Quaternary Science Reviews
in 2004 (Cook et al., 2004), I reviewed the properties and
interpretation of the tree-ring data used in the Esper et al.
(2002) paper published in Science. The reasonably well distributed
set of tree-ring data in both boreal and more temperate latititude
sites around the Northern Hemisphere allowed me to split up the
data into sub-regional ensembles, including 8 sites in the 55-70�
north band and 6 sites in the 30-55� south band. The purpose was
to show the overall robustness of the multi-centennial temperature
signal in the tree-ring data. This plot from the QSR paper is
attached below as is the paper itself.
In his 1998 paper, Briffa showed that the divergence was largely
restricted to the region covered by the north band described in
Cook et al. (2004). Consistent with that finding, the north
ensemble mean shown below reveals a serious downturn in growth
after about 1950. This is an expression of the "divergence" that
has been described first by Briffa and also by D'Arrigo in her NRC
talk. In contrast, the south ensemble mean shows the opposite,
i.e. a substantial growth increase which is much more consistent
with 20th century warming. If one than follows the plots back in
time, all of the sub-region ensemble means track each other
remarkably well at multi-centennial time scales even when they
enter the putative MWP 800-1000 years ago. In fact, at no time
prior to the 20th century is there separation between north and
south that is remotely comparable to that found after ca. 1950.
This result suggests that no large-scale "divergence" of the order
found during the 20th century occurred during the MWP even though
that period is suggested to have been somewhat warmer than average
overall. This result clearly refutes the argument that
"divergence" of the kind noted in the 20th century happened in the
past. It also suggests a unique anthropogenic cause to the 20th
century divergence.
I am not aware of ANY evidence that demonstrates the occurrence of
large-scale "divergence" in the past. It is therefore unjustified
to call into question the use of tree rings for reconstructing
temperatures over the past millennium based on a naive
extrapolation of growth "divergence" into the past when it appears
to be unique to the 20th century. The NRC committee members must
be made aware of this if their report is to have the necessary
scientific credibility that is expected of it.
Sincerely,
Edward R. Cook
References
Briffa, K.R., Schweingruber, F.H., Jones, P.D., Osborn, T.J.,
Shiyatov, S.G., Vaganov, E.A. 1998. Reduced sensitivity of recent
tree-growth to temperature at high northern latitudes. Nature 391:
678-682.
Esper, J., Cook, E.R., Schweingruber, F.H. 2002. Low-frequency
signals in long tree-ring chronologies for reconstructing past
temperature variability. Science 295: 2250-2253.
Cook, E.R., Esper, J., D'Arrigo, R.D. 2004. Extra-tropical
Northern Hemisphere land temperature variability over the past
1000 years. Quaternary Science Reviews 23(20-22): 2063-2074.

--
Professor Keith Briffa,
Climatic Research Unit
University of East Anglia
Norwich, NR4 7TJ, U.K.
Phone: +44-1603-593909
Fax: +44-1603-507784
[2]http://www.cru.uea.ac.uk/cru/people/briffa/

--
Professor Keith Briffa,
Climatic Research Unit
University of East Anglia
Norwich, NR4 7TJ, U.K.

Phone: +44-1603-593909
Fax: +44-1603-507784
[3]http://www.cru.uea.ac.uk/cru/people/briffa/

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