cc: Edward Cook date: Wed, 1 Oct 2008 09:48:31 -0400 from: Edward Cook subject: Re: recognize this?! to: Keith Briffa , Tim Osborn Hi Keith and Tim, I have quickly read through the Esper paper and have the following comments to make. First, I hadn't seen it before, so it is all new to me. It is certainly true that Jan did not do a proper job citing Briffa et al. (1992). That was a clear mistake, especially given that Douglass (1929) was cited for crossdating. I also note that Jan did not cite Osborn et al. (1997) on adjusting the variance in series for sample size changes. That too was an clear oversight given that Frank et al. (2007) was cited. Hopefully, neither was done intentionally. I tend to give people the benefit of a doubt on that unless it is a chronic problem in their publications. The latter issue of variance adjustment is also relevant to the discussion concerning spatial homogeneity or lack thereof. Am I correct in assuming that some form of variance adjustment was made to the series used in the AR4 report? I haven't read the report closely enough to recall if that was done. If it was done, that would tend to force the data towards an appearance of greater homogeneity, I would guess, hence the relative stability of the bootstrap intervals, etc.. In any case, I do tend to agree with Jan that nothing very definitive can be said about the spatial homogeneity of the putative MWP until we get more records to look at that truly express temperature and not something else. The whole issue of whether or not the MWP was more spatially heterogeneous or not is a huge "red herring" in my opinion anyway. A growing body of evidence clearly shows that hydroclimatic variability during the putative MWP (more appropriately and inclusively called the "Medieval Climate Anomaly" or MCA period) was more regionally extreme (mainly in terms of the frequency and duration of megadroughts) than anything we have seen in the 20th century, except perhaps for the Sahel. So in certain ways the MCA period may have been more climatically extreme than in modern times. The problem is that we have been too fixated on temperature, especially hemispheric and global average temperature, and IPCC is enormously guilty of that. So the fact that evidence for "warming" in tree-ring records during the putative MWP is not as strong and spatially homogeneous as one would like might simply be due to the fact that it was bloody dry too in certain regions, with more spatial variability imposed on growth due to regional drought variability even if it were truly as warm as today. The Calvin cycle and evapotranspiration demand surely prevail here: warm-dry means less tree growth and a reduced expression of what the true warmth was during the MWP. That is my take on the Esper and Frank paper, with obvious editorial comments included as well. Cheers, Ed ================================== Dr. Edward R. Cook Doherty Senior Scholar and Director, Tree-Ring Laboratory Lamont-Doherty Earth Observatory Palisades, New York 10964 USA Email: [1]drdendro@ldeo.columbia.edu Phone: 845-365-8618 Fax: 845-365-8152 ================================== On Sep 29, 2008, at 11:06 AM, Keith Briffa wrote: X-Mailer: QUALCOMM Windows Eudora Version 7.1.0.9 Date: Mon, 29 Sep 2008 09:50:59 +0100 To: Keith Briffa <[2]k.briffa@uea.ac.uk> From: Tim Osborn <[3]t.osborn@uea.ac.uk> Subject: recognize this?! Dr Timothy J Osborn, Academic Fellow Climatic Research Unit School of Environmental Sciences University of East Anglia Norwich NR4 7TJ, UK e-mail: [4]t.osborn@uea.ac.uk phone: +44 1603 592089 fax: +44 1603 507784 web: [5]http://www.cru.uea.ac.uk/~timo/ sunclock: [6]http://www.cru.uea.ac.uk/~timo/sunclock.htm -- Professor Keith Briffa, Climatic Research Unit University of East Anglia Norwich, NR4 7TJ, U.K. Phone: +44-1603-593909 Fax: +44-1603-507784 [7]http://www.cru.uea.ac.uk/cru/people/briffa/