date: Tue Mar 14 15:03:01 2006
from: Keith Briffa <k.briffa@uea.ac.uk>
subject: Re: NRC Committee on Surface Temperature Reconstructions
to: edwardcook <drdendro@ldeo.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: 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.
     ￼
     ￼
     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/

