climate-debate

Sheenjek, Alaska: A Jacoby-MBH Series

by S. McIntyre, Dec13, 2023 in ClimateAudit

MBH98 used three Jacoby tree ring chronologies from Alaska: Four Twelve (ak031) – discussed here, Arrigetch (ak032) and Sheenjek (ak033). Sheenjek will be discussed in this article.

In our compilation of MBH98 in 2003, we observed that the Sheenjek chronology archived at NOAA Paleo was not the same as the “grey” version used in MBH98.   While we used the MBH98 version to benchmark our emulation of the MBH98 algorithm, we used the version archived at NOAA in our sensitivity analysis, both in our 2003 article and in our early 2004 submission to Nature.  In his reply to our submission, Mann vehemently protested that the “introduc[tion of] an extended version of another Northern Treeline series not available prior to AD 1500 at the time of MBH98” “introduce[d] problems into the important Northern Treeline dataset used by MBH98”:

Finally, MM04 introduce problems into the important Northern Treeline dataset used by MBH98. Aside from incorrectly substituting shorter versions of the “Kuujuag” and TTHH Northern Treeline series for those used by MBH98, and introducing an extended version of another Northern Treeline series not available prior to AD 1500 at the time of MBH98, they censored from the analysis the only Northern Treeline series in the MBH98 network available over the AD 1400-1500 interval, on the technicality that it begins only in AD 1404 (MBH98 accommodated this detail by setting the values for AD 1400-1404 equal)

The other “Northern Treeline series” referred to here was Sheenjek chronology ak033.crn.  I checked Mann’s assertion alleging that the data was “not available prior to AD1500 at the time of MBH98”. This was contradicted by NOAA, who confirmed that the chronology that we had used had been available since the early 1990s.

In the figure below, I’ve compared three Sheenjek chronology versions:

  • the MBH98 version from 1580-1979 (plus 1980 infill);
  • the ModNegExp chronology (dplR) calculated from measurement data (ak033.rwl), which, in this case, has been available since the 1990s. It covers period 1296-1979.
  • the archived chronology at NOAA (ak033.crn). Also covering the period 1296-1979.

The issues relating to Sheenjek are different than observed at Four Twelve.

  • The MBH98 and the chronology (rwl) freshly calculated from measurement data using ModNegExp option (emulating contemporary Jacoby technique) are very, very similar for their period of overlap (1580-1979).  Neither show elevated 20th century values or a closing uptick. If anything, a modest decline in late 20th century.
  • however, the MBH98 version excludes all values prior to AD1580.  There is no good reason for this exclusion. There are 28 cores in the ak033.rwl in 1579, far above usual minimums.  In the 15th century, there are more cores for Sheenjek than for the Gaspe series which was used by MBH98 in its AD1400 network, even when it only had one core. (And even no cores for the first five years.)
  • the Sheenjek chronology archived at NOAA (ak033.crn) was clearly derived from the ak033.rwl dataset, as the series in middle and bottom panels are highly correlated. However, from its appearance, it looks like the archived Sheenjek chronology was calculated with very flexible splines (rather than “stiff” ModNegExp) and that this has attenuated the “low frequency” variability observed in the middle panel using ModNegExp option.
  • We used the ak031.crn version in our sensitivity study. If the same exercise was repeated using the middle panel version, it would yield relatively high early 15th century results.

It is not presently known who chopped off Sheenjek values prior to AD1580 in the MBH98 version. Or why.

All cores in the Sheenjek dataset were included in D’Arrigo et al 2006 NWNA Composite.

Also here