date: Tue Apr  9 11:36:25 2002
from: Keith Briffa <k.briffa@uea.ac.uk>
subject: Fwd: Your review of Asper et al
to: j.burgess@uea.ac.uk

     Date: Mon, 8 Apr 2002 12:31:13 -0600
     To: k.briffa@uea.ac.uk
     From: Chick Keller <cfk@pop.vega.lanl.gov>
     Subject: Your review of Asper et al
     Dear Keith,
     I read the review you and Tim Osborn wrote in Science of the Asper et al paper.
     Your version, plotted in the review "Blowing Hot and Cold", of the Asper et al proxy
     temperatures for the past 1200 years differs from their(figure 3) version, which has
     significantly greater amplitude. You state why you get a smaller  temperature amplitude:
     "For the early 17th century, annual temperature estimates from Esper et al. differ by
     about 0.7C from those of Mann et al. [see figure 3 of (1)].
       However, when we regressed the record of Esper et al. against nonsmoothed data (see
     the figure), this difference was reduced to about 0.4C.
       Recalibrating both curves against year-by-year warm season temperatures (10) reduces
     this difference further to about 0.35C."
     Would Asper et al agree that your version is the more correct for intercomparison with
     other proxy results?  This is important since, as you must know, Asper et al's figure 3
     presents a very different picture of climate variation (and thus climate forcing by the
     sun, etc.) than previously thought, while on the other hand your version of their
     results shows them to essentially agree with the total range of temperature variation
     from other reconstructions (although they still differ on the record from 1100-1400).
     For example your resulting curve for the Asper et al work appears to differ little from
     that in  Crowley and Lowry's Ambio paper in terms of total amplitude, and the two agree
     very well  after 1450 or so. Also, the Asper et al MWP is only about 0.1C higher around
     1000-1100 than that of Crowley and Lowry.
     Finally, it is tempting (but probably dangerous) to compare Esper et al's warming from
     850 to 1000 with a very similar warming (both in rate and amplitude) 1800-1950.  They
     look very similar, but differ dramatically (if you switch to the instrumental record in
     the 20th century) over the next 50 years--cooling after 1000 , but warming even more
     rapidly after 1950.  It is thus tempting to suggest that Asper et al (your version) have
     shown us the maximum warming in the past 1200 years that can occur naturally which is
     significantly less than warming thru the year 2000.
     This probably trying to make too much of a single record, but when added to the other
     records as you did in your review, there seems to be a picture emerging of what
     hemispheric climate variation can be.
     A few other questions--Asper et al used tree rings.  Do you think their different
     results are due to a different method of treating the raw data, or did they simply use
     different tree ring data that gave these differences?
     And--I note (and so does Fred Singer) that all proxy data in your figure does not show
     temperature increases after 1950 in disagreement with the instrumental records.  This
     has been attributed to complications due to increased levels of CO2 in the atmosphere.
     Has there been any other work done recently to understand this better?
     Thank you for putting the Esper et al work into the context of that of yourself and
     others.
     Regards,
     --
     Charles. "Chick" F. Keller,
     Visiting Scientist at
     IGPP, Instititue of Geophysics and Planetary Physics
     MS-C305
     Los Alamos National Laboratory
     Los Alamos, NM 87544
     (505)  667-4820 or  667-0920
     FAX (505) 665-3107

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

   Phone: +44-1603-593909
   Fax: +44-1603-507784
   [1]http://www.cru.uea.ac.uk/cru/people/briffa[2]/

