As noted in the prior post, thanks to the work of Steven McIntyre and others posting at climateaudit.org, the paleoclimate reconstruction of Kaufman et al was shown to have numerous data reconstruction and statistical errors including data flipped upside down for 2 of the proxies. Kaufman's revised spreadsheets with the corrected proxies were posted 10/09 (no longer available on the web) and 12/09. The primary change between the 10/09 and 12/09 spreadsheet is stated as "Record 17 was revised to reflect the interpretation of Geirsdóttir et al. (S29) that temperature is related more strongly to BSi than to the BSi:OM ratio."
Interesting that the one proxy that was changed (between 10/09 & 12/09) was the one showing the greatest warming anomaly 2000 years ago in the original paper. This new interpretation using BSi (biogenic silica) instead of using the ratio of BSi:OM (OM=organic matter=TOC=total organic content) resulted in large changes to the reconstructed temperature anomaly as shown in the prior post, flattening out the anomaly in the earlier portion, resulting the the combined proxies conforming more to a hockey stick shape. How is the science settled if one uses BSi:OM in the original paper and then when the hockey stick doesn't appear, conveniently switches to BSi in the correction?
But lets take a look at the work cited as the reason for this change in interpretation. The graph below from A 2000 year record of climate variations reconstructed from Haukadalsvatn, West Iceland, Geirsdóttir et al , shows (in graph A) that the BSi:TOC was higher than the present 2000 years ago and much higher during the Medieval Warming Period. It also shows that the BSi alone (graph C) shows approximately the same temperature anomaly 2000 years ago as today, and much higher temperatures during the Medieval Warming Period than today. Graph D is the "discredited" Mann/Jones (2003) temperature reconstruction and Graph E is "Moberg et al. (2005) reconstructed Northern Hemisphere temperatures calculated by combining low-resolution proxies with tree-ring data, using a wavelet transform technique to achieve timescale-dependent processing of the data", which also shows the Medieval Warming Period to have higher temperatures than the present. In sum, Geirsdóttir et al and Moberg et al find the Medieval Warming Period hotter than today and do not find a Kaufman/Mann-like hockey stick. Geirsdóttir et al also do not find a hockey stick using either interpretation of the data with BSi or BSi:OM.