date: Fri, 27 Apr 2001 14:45:07 -0700
from: Chick Keller <ckelleratXYZxyzp.ucsd.edu>
subject: Low Frequency signals in Proxy temperatures:
to: "Malcolm K. Hughes" <mhughesatXYZxyzr.arizona.edu>, ckelleratXYZxyzp.ucsd.edu
Well said indeed! This helps me to slowly understand what's being
done and why.
My nagging problem remains however, and that's that there seem to be
too many paleo records published that show much larger amplitude
variations. Now many can be explained, but some look more robust.
For example I think most people are wondering about the total
disagreement between isotope temperatures from GISP II and borehole
temperatures from GRIP and Dye 3. Here the usual land use caution
doesn't apply since I don't think the ice above the boreholes has
And if I understand Tom Crowley's note to me, his reconstruction
averaged normalized records, thus missing large amplitude variations
such as the Keigwin Sargasso one, which he used, but which shows a
large amplitude signal tantalizingly similar to the GRIP/Dye 3
records. (Tom used GISP II which essentially has no low frequency
So I read all the papers, and am impressed by the painstakingly
careful work, but still wonder about a world in which the
hemispherical low frequency temperature amplitude could be (see Jones
et al Science this week) only about 0.4�C between 1000 and about
1950, while parts of the world could have seen amplitudes of up to
2�C in the same period. I suppose you could say that, given natural
forcing only, there can be much larger variance from the mean
(spatially and temporally) than in the past hundred and fifty years
when GHG forcing is forcing more uniformity, but does this make sense?
This is why I keep asking questions about the ability of various
proxies to return low frequency information.
Anything you could say about this would be greatly appreciated.
Finally consider this. I read recently (don't know the pedigree of
this number but it WAS published!!) that Milankovitch cooling at this
point in the Holocene should be about 0.4�C/millenium (other plots
I've seen would suggest about 2.3 to 1/2 of that). If that's true,
then all the cooling since the year 1000 is Milankovitch and there's
no room for variations in solar activity and multiple volcanic
eruptions. Now I'm not saying this is the best way to think about
such things, but it does remind us that much of the cooling seems to
have been due to Milankovitch, and, given the small amplitude of the
proxy records, that is a bit worrisome. What do people think about
Well said Malcolm...
p.s. Chick: You might want to check out the review article by Jones
et al in the latest Science...
At 01:16 PM 4/26/01 -0700, Malcolm K. Hughes wrote:
>Dear Chick - some thoughts on a couple of the points you raised,
>1. There is no reference to the ABD in MBH 98 and 99 because
>was not available at that time - see the dates on Keith's publications that
>2. There are significant regions where the ABD method is not needed,
>because the trees live much longer than those in the Schweingruber
>Keith has been using, and grow under conditions that make only very
>standardization necessary. There is a growing body of evidence that these
>tree-ring records can capture century-to-millennial change accurately (Hughes
>and Graumlich, 1996 and Hughes and Funkhouser 1998, for example). In fact, the
>MBH reconstruction before AD 1400 was largely based on these.
>3. Keith has pooled information from extremely large regions
>get large enough samples), whereas we (MBH) have been particularly
>spatial variability, ruling out the use of ABD.
>4. The ABD method is new, needs testing, and, I predict, will be modified
>as it is tested.
>5. The benefit of annual resolution is that direct calibration and
>cross-validation against instrumental records is possible with a
>high degree of
>rigor. We are relaxing this condition somewhat in our ongoing analyses, and it
>will be interesting to see how the uncertainties increase as one includes
>records with poorer temporal resolution. This is an issue that the
>such records do not address, so far as I can see.
>Professor Malcolm K. Hughes
>Laboratory of Tree-Ring Research
>University of Arizona
>Tucson, AZ 85721
Professor Michael E. Mann
Department of Environmental Sciences, Clark Hall
University of Virginia
Charlottesville, VA 22903
e-mail: mannatXYZxyzginia.edu Phone: (804) 924-7770 FAX: (804) 982-2137
Charles. "Chick" F. Keller,
IGPP.SIO.UCSD - Attn: Chick Keller
9500 Gilman Drive
La Jolla, CA 92093-0225
(858) 822-1510 office
(858) 534-2902 FAX
(858) 456-9002 home
Is the noticeable increase in surfers off Scripps Beach a possible
indication of global warming?