It turns out that the chosen temperature recon is heavily dependent on the
I tried to leave a remark on this subject at RealClimate.org. Apparently, that site is set to automatically fail any comment tagged with my user name, email, or IP address. Here is the local copy of what I submitted (21 Jun 3:50 PM EDT) --
I was surprised at the provenance of the paleotemperature reconstruction that was used in Kemp et al's Fig. 2A and Fig. 4A. According to Fig. 2A's legend, it is "Composite EIV global land plus ocean global temperature reconstruction, smoothed with a 30-year LOESS low-pass filter". The reference is Mann et al. (2008). In that paper's S.I., the unsmoothed version is in panel F of Fig S6, as the black line labelled "Composite (with uncertainties)".I left a more detailed version at Collide-a-scape as #128 at Climate Critics That Won't Muzzle Themselves (June 21st, 2011 at 1:35 pm; lightly edited) --
This is one of the multiproxy reconstructions that employed the four (actually three) uncalibratable Tiljander lakebed sediment data series.
According to Gavin Schmidt, "...it's worth pointing out that validation for the no-dendro/no-Tilj is quite sensitive to the required significance, for EIV NH Land+Ocean it goes back to 1500 for 95%, but 1300 for 94% and 1100 AD for 90%" (link). Further remarks on this issue as Responses to other RC comments here (see numbers 525, 529, and 531).
The incorrect inclusion of Tiljander could well make this EIV reconstruction progressively worse, as one goes from 1500 AD back to 500 AD. This might explain the increasing divergence between the temperature recon and the sea-level recon, as one travels back from 1100 AD to the beginning of the recons at 500 AD. This pattern is shown in Kemp11's S.I. Figs. S3, S4, and S5.
Did any of the peer reviewers comment on this issue, or request that you use a no-Tiljander temperature reconstruction?
...Yesterday, Kemp et al. 2011 was published in PNAS, relating sea-level variation to climate over the past 1,500 years (UPenn press release). Among the authors is Prof. Mann. Figs. 2A and 4A are "Composite EIV global land plus ocean global temperature reconstruction, smoothed with a 30-year LOESS low-pass filter". This is one of the multiproxy reconstructions in Mann et al. (2008, PNAS). The unsmoothed tracing appears as the black line labelled "Composite (with uncertainties)" in panel F of Fig. S6 of the "Supporting Information" supplement to Mann08 (downloadable from pnas.org).Interestingly, M. Vermeer discussed the Tiljander
This is one of the Mann08 reconstructions that made use of the four (actually three) uncalibratable Tiljander data series.
As scientist/blogger Gavin Schmidt has indicated, the early years of the EIV Global reconstruction rely heavily on Tiljander to pass its "validation" test: "...it's worth pointing out that validation for the no-dendro/no-Tilj is quite sensitive to the required significance, for EIV NH Land+Ocean it goes back to 1500 for 95%, but 1300 for 94% and 1100 AD for 90%" (link). Also see RealClimate here (Gavin's responses to comments 525, 529, and 531).
The dependence of the first two-thirds of the EIV recon on the inclusion of Tiljander's data series isn't mentioned in the text of Kemp11. Nor is it discussed in the SI (link), although it is an obvious and trivial explanation for the pre-1100 divergence noted in the SI's Figures S3, S4, and S5.
Peer review appears to have been missing in action on this glaring shortcoming in Kemp11's methodology.
More than anything, I am surprised by this zombie-like re-appearance of the Tiljander data series -- nearly three years after the eruption of the controversy over their misuse as temperature proxies!