At
RealClimate.org, Stefan Rahmstorf has written "
2000 Years of Sea Level" about a study published on June 20, 2011 in PNAS. Andrew Kemp and co-authors BP Horton, JP Donnelly, ME Mann, M Vermeer, and S Rahmstorf reconstruct sea levels from 500 AD to the present, and relate these levels to the temperatures of the past, using a multi-proxy reconstruction that was first presented in Mann et al. (PNAS, 2008). (The Kemp11 PDF can be downloaded at the RC post.)
It turns out that the chosen temperature recon is heavily dependent on the
four three uncalibratable Tiljander data series. This reliance grows stronger as one goes back in time, and shorter (younger) records "drop out."
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)".
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?
