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To: DavesM who wrote (19722)	5/26/2006 10:49:45 PM
From: Wharf Rat	Respond to of 541877

Message 22490203

To: DavesM who wrote (19722)	5/27/2006 12:44:26 AM
From: Wharf Rat	Respond to of 541877

Response: One record does not a global Medieval warm period make. 'Global' is the key word there. It turns out that many of the so-called 'MWP's seen in seperate records actually occur at different times, and so would not show up in the global mean. I recommend reading the Bradley et al (2003) Science Perspective dealing with this matter. - gavin See also our discussion of "Hockey Stick myth #2", and the section "Was there a "Little Ice Age" and a "Medieval Warm Period" in chapter 2 of the 2001 IPCC report which specifically discussed the Keigwin (1996) record you mention and its likely reflection, at least in part, of changes in the North Atlantic Oscillation in past centuries. Changes in the NAO appear to play a prominent role in the spatial pattern of climate change in past centuries (see e.g. the review paper: Schmidt, G.A., D.T. Shindell, R.L. Miller, M.E. Mann, and D. Rind 2004. General circulation modelling of Holocene climate variability. Quaternary Sci. Rev., 23, 2167-2181, doi:10.1016. ). Regional influences due to changes in the NAO and the El Nino/Southern Oscillation in past centuries complicate the relationship between regional and truly hemispheric or global temperature estimates. For precisely this reason, the numerous proxy and model-based estimates of the variations in the average temperature of the Northern Hemisphere (not just just the Mann et al reconstruction, as implied by your comment) show far more modest temperature changes than those typically interpreted from specific proxy records from any one region. -mike (Mann) realclimate.org ========================== Probably more than you want to know realclimate.org