cc: firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, tomatXYZxyzan.tamu.edu
date: Tue, 27 Feb 2001 14:49:21 -0500
from: "Raymond S. Bradley" <rbradleyatXYZxyz.umass.edu>
subject: my thoughts on broecker's article
I just re-read Broecker 2001 Perspective.
He does, in fact state: "The case for a global Medieval Warm Period
admittedly remains inconclusive". This is true. He got something right.
But he makes a mess of supporting evidence....
He cites Steig et al (ref 13) re the Greenland borehole temperature
change. There is nothing in Steig et al about this --he should have cited
Dahl-Jenssen et al.
He cites Clow:
"Clow has carried out a deconvolution of the temperature record at the
Antarctic Taylor Dome site (19). His reconstruction shows that the air
temperature was 3�C colder during the time of the Medieval Warm Period
than during that of the Little Ice Age. This record suggests that
conditions in Antarctica underwent an antiphased oscillation during the
Medieval Warm Period-Little Ice Age period."
At Broecker's own LIA shindig at Lamont, Clow clearly stated that while the
Taylor Dome borehole showed warmer conditions in "Medieval times" another
Antarctic site (I forget where) did not. Nothing on this has been
published, but Wally chose to ignore the info. Clow provided, which would
otherwise eliminate one of his few lines of argument.
He then says:
"Evidence for the Medieval Warm Period from other parts of the world exists
but is spotty and/or circumstantial. From an analysis of 6000 continental
borehole thermal records from around the world (14), Huang et al. conclude
that 500 to 1000 years ago, temperatures were warmer than today, but that
about 200 years ago, they cooled to a minimum some 0.2� to 0.7�C below
Huang et al did not examine 6000 boreholes--they looked at 616 records of
which 479 showed a net warming, and there is NOTHING in that article about
the Medieval period. It is all about the last 500 years.
Broecker's argument thus boils down to this:
1. Trees can't reproduce log-term climate change because I know they can't
2. We know it was warmer because Vikings went to Greenland
3. One borehole in Greenland shows warmer temperatures ~1000 years ago
4. Swiss glaciers (well some of them) were less extensive (than what?)
around AD 1200 and 1500 BP. [What this says about the magnitude of warming
5. One (of two) boreholes in Antarctica show warmer temperatures ~1000
6. The Bond cycle explains everything because I say it does.
I think any response should just point out these errors (perhaps more
diplomatically) and conclude that while there is no evidence at present for
a global MWP it deserves further study. This is, in fact, what I said in
my Perspectives article last year...
Raymond S. Bradley
Professor and Head of Department
Department of Geosciences
University of Massachusetts
Amherst, MA 01003-5820
Climate System Research Center: 413-545-0659
Climate System Research Center Web Page:
Paleoclimatology Book Web Site (1999):