date: Mon, 18 Aug 2008 12:58:09 -0400 from: Michael Mann subject: Re: Revised version the Wengen paper to: Phil Jones , Gavin Schmidt Phil (and Gavin), there is one more big problem in the current draft. the borehole section is hugely unbalanced. it is truly awful, and this was never dealt w/ in the previous revisions. I can't sign my name to a paper that has such a whitewash treatment of borehole data (this section looks like it was written by Pollack and Gonzalez-Rouco, w/out any of acknowledgment of the many problematic issues that have been raised by others). At a very minimum , for my name to remain on this paper, the following changes need to be made. Please let me know if you have any questions or comments about the changes. I feel I must state this as being mandatory for inclusion of my name in the paper. I can't sign my name to a grossly misbalanced discussion of borehole data. I hope you understand this, mike 1. 2nd paragraph, page 44, first sentence: Borehole reconstructions have particular value because they do not have to be calibrated against the instrumental record and because temperature itself is measured directly. should be changed to: Borehole reconstructions have an advantage in that they arguably needn't be calibrated against the instrumental record because they measure temperature itself is measured directly. However, a disadvantage is that, as discussed above, they measure GST rather than the desired quantity (SAT), and under certain conditions there may be substantial differences between the two (see below). 2. last paragraph of section, last two sentences (bottom of page 44/top of page 55) Mann and Schmidt (2003), suggested that GST reconstructions may be biased by seasonal influences and snow cover variability, an interpretation contested by Chapman et al. (2004). Thousand-year simulations by González-Rouco et al. (2003, 2006) using the ECHO-G model suggests that seasonal differences in coupling are of little significance over long time scales. this is not correct. Mann and Schmidt (2003) show that there is a potentially very large seasonal bias in estimating winter SAT from winter GST, and any time that winter and summer trends are not similar (which they *happen* to be in some fairly unrealistic simulations such as Gonzalez-Rouco et al) this might not appear to be a problem. But in general, it is a huge problem!. Confidentially, we have a paper we will be submitting soon that provides an example (simulated early through mid holocene changes) where the impact of the snowcover GST bias on annual mean GST is huge, and leads to a highly biased assessment of past SAT changes from GST trends. More on that soon. But in the near term, it suffices to acknowledge the problem first hinted at by Mann and Schmidt, by revising the paragraph above to: Mann and Schmidt (2003) show that GST estimates during the winter season are biased by seasonal influences related to changing snow cover, and that less that 50% of the total spatiotemporal variance in GST is explained by SAT variations during the cold half of the year. Chapman et al. (2004) contest the implications this has for recent temperature trends [contested in turn by Schmidt and Mann (2004)], and some long-term simulations [e.g. by González-Rouco et al. (2003, 2006) using the ECHO-G model] suggests the possibility that seasonal differences in coupling might be of little significance over long time scales as long as temperature trends are similar in different seasons. However, in cases where there are large seasonal differences in climate trends (a possibility that remains for the past few centuries--see Mann et al, 2003) such seasonal bias issues could lead to misleading inferences regarding long-term SAT trends from indicators of past GST change. References: Mann, M.E., Rutherford, S., Bradley, R.S., Hughes, M.K., Keimig, F.T., [1]Optimal Surface Temperature Reconstructions using Terrestrial Borehole Data, Journal of Geophysical Research, 108 (D7), 4203, doi: 10.1029/2002JD002532, 2003. Schmidt, G.A., Mann, M.E., [2]Reply to comment on ``Ground vs. surface air temperature trends: Implications for borehole surface temperature reconstructions'' by D. Chapman et al., Geophysical Research Letters, 31, L07206, doi: 10.1029/2003GL0119144, 2004. Phil Jones wrote: Dear All, Here's the revised version of the paper, together with the responses to the reviewers. We have told John Matthews, that we will get this back to him by the beginning of next week. To us in the UK this means Aug 26/27 as next Monday is a national holiday. So, to those not away at the moment, can you look through your parts and get any comments back to us by the end of this week or over the weekend? Can you also look at the references - those in yellow and let me know of any that have come out, or are able to correct those that I think just look wrong? I hope you'll think of this as an improvement. Cheers Phil Prof. Phil Jones Climatic Research Unit Telephone +44 (0) 1603 592090 School of Environmental Sciences Fax +44 (0) 1603 507784 University of East Anglia Norwich Email [3]p.jones@uea.ac.uk NR4 7TJ UK ---------------------------------------------------------------------------- -- Michael E. Mann Associate Professor Director, Earth System Science Center (ESSC) Department of Meteorology Phone: (814) 863-4075 503 Walker Building FAX: (814) 865-3663 The Pennsylvania State University email: [4]mann@psu.edu University Park, PA 16802-5013 website: [5]http://www.met.psu.edu/dept/faculty/mann.htm "Dire Predictions" book site: [6]http://www.pearsonhighered.com/academic/product/0,3110,0136044352,0 0.html