cc: , , Malcolm Hughes , , , Phil Jones , date: Wed, 28 Feb 2001 13:22:39 -0500 (EST) from: "Henry N. Pollack" subject: Re: letter to Science to: "Michael E. Mann" 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.