cc: <tom@ocean.tamu.edu>, <td@gfdl.gov>, Malcolm Hughes <mhughes@ltrr.arizona.edu>, <mann@virginia.edu>, <rbradley@geo.umass.edu>, Phil Jones <p.jones@uea.ac.uk>, <k.briffa@uea.ac.uk>
date: Wed, 28 Feb 2001 13:22:39 -0500 (EST)
from: "Henry N. Pollack" <hpollack@geo.lsa.umich.edu>
subject: Re: letter to Science
to: "Michael E. Mann" <mann@multiproxy.evsc.virginia.edu>

Hello everyone!

On Wed, 28 Feb 2001, Michael E. Mann wrote:

> ........................................... Although one analysis of
> heat flow measurements suggests warmer temperatures than the surface
> proxies during the Middle Ages (Huang and Pollack, GRL. 1997), the
> considerable sensitivity of the resulting trends to a priori statistical
> assumptions has lead borehole researchers to restrict their attention to
> the more reliably interpretable temperature fluctuations during the past
> five centuries (Huang and Pollack, Nature). .........................

Henry Pollack comments on the above statement:

 Linking the two geothermal studies (1997, 2000) is not quite kosher. We
did not later "restrict our attention" to the last five centuries because
of the considerable sensitivity to the a priori assumptions in the 1997
GRL paper. Throughout the range of the a priori assumptions there is an
indication of warmth in the middle ages. But as I mentioned in my comments
to Tom Crowley yesterday, whether that warmth exceeded the end-of-20th
century temperatures is perhaps debatable. I said to Tom that the hockey
stick will not rise or fall on the basis of the 1997 GRL paper that
analyzed heat flow variations with depth.


Our later emphasis on the past five centuries was intended to bring into
sharper focus the late pre-industrial and industrial eras. The five
century study reported in Nature used much higher quality data, actual
temperature vs. depth data rather than inferred heat flow vs. depth data.
It is no secret that the results of this five century study show some
disagreement with the hockey stick also, in the magnitude and timing of
the LIA minimum. That is another issue, not one directly addressing Wally
Broecker's discussion of the MWP.

Cheers,
Henry

p.s. I will be traveling as of this afternoon (2/28), returning on 3/5. I
would be grateful to receive a final copy of what you submit, but
respectfully decline to sign on as a co-author.

