cc: p.jones@uea.ac.uk, k.briffa@uea.ac.uk, mhughes@ltrr.arizona.edu, tom@ocean.tamu.edu date: Tue, 27 Feb 2001 14:49:21 -0500 from: "Raymond S. Bradley" subject: my thoughts on broecker's article to: mann@multiproxy.evsc.virginia.edu 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 present." 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 beats me] 5. One (of two) boreholes in Antarctica show warmer temperatures ~1000 years ago 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 Tel: 413-545-2120 Fax: 413-545-1200 Climate System Research Center: 413-545-0659 Climate System Research Center Web Page: Paleoclimatology Book Web Site (1999): http://www.geo.umass.edu/climate/paleo/html