Kinnard et al 2011 report a highly hockey-stick shaped reconstruction of sea ice. (For a different perspective based on Holocene ocean sediments under the Ellesmere Island ice shelf, see the recent Antoniades et al (PNAS 2011).
Kinnard et al use a regression-based statistical methodology that looks at first blush to be a sort of inverse regression: i.e. of sea ice against a large number of proxies and “proxies”. In any such procedure, there is a serious risk of spurious fits. (After all, you can reconstruct a trend with a sufficient number of white noise series simply by brute force.) Kinnard et al attempt to guard against this by considering the RE statistic. Here they head straight into the home territory of Mannian statistics.
This does not mean that their methodology is wrong, let alone “WRONG”. (I haven’t examined it yet, let alone parsed it.) But it is worrying.
My own preferred technique for examining “multiproxy” data is to first divide the data into subsets of like proxies. The largest subset of Kinnard et al is the 22 O18 series (out of 69 proxies.) This turned out to be a remarkable subset in several ways and I spent much longer examining this data than I had expected or planned. Here is a graphic showing the ten long O18 series in Kinnard et al, arranged from west (Mt Logan, Alaska) to east. The left column shows Mt Logan plus four series in the Canadian archipelago.
The take-home points are that Kinnard et al have provided a huge/unprecedented increase in the number of archived Arctic O18 series – especially long high-resolution series. Whereas Mann et al 2008 had only two Arctic O18 series beginning prior to AD900, Kinnard et al have ten. Most of the ten aren’t new, but, to my knowledge, for the most part, they haven’t been available. And second, that the long Arctic O18 do not give the pronounced HS result of the final Kinnard diagram. Its provenance therefore lies elsewhere: either in other proxies or by sign-flipping and weighting in the regression methodology, resolution of which will require more analysis.
In the meantime, documentation of the new treasure trove of Arctic O18 seems worthwhile in itself.
I’ll look at the proxies from west to east, starting in Alaska.
Mt Logan: In the half-hemisphere from 100E to 80W (going east), Kinnard has only one O18 series – a long series from Mt Logan, Alaska published in 2006 by coauthor David Fisher. This series was discussed a number of years ago at CA: it had an unexpected decrease in O18 values in the modern period, attributed by the authors to changes in regional circulation. To my knowledge, this is the first use of this series in a multiproxy study. (It was not used in Mann et al 2008 or the Ljungqvist articles.
Bona-Churchill: Bona-Churchill is another long O18 series in this hemisphere, but is not used even though Lonnie Thompson is a coauthor. Some years ago, I commented on publication delay of this series (drilled in 2002), speculating that it would have been published in time for AR4 if it had gone the “right” way. Five years later, it remains unpublished and looks like it will remain unpublished through AR5. It is near Mt Logan and I speculated that it would, like Mt Logan, go the “wrong” way in the 20th century. A few years ago, I noticed a graph in an online workshop showing that this was the case. In any event, it wasn’t contributed to Kinnard et al (even though they show a series from Prince of Wales, Ellesmere Island of similar vintage.)
Eastern Canadian Archipelago
There are four long O18 series from the eastern Canadian archipelago, all more or less 80W. From north to south, Agassiz, Ellesmere Island (81N), the new Prince of Wales, Ellesmere Island (78N), Devon Island (75N) and Penny, Baffin Island (69N).
Agassiz: Mann (2008), Ljungqvist (2009) and Vinther (2010) use data ultimately deriving from a core drilled in the 1970s. Mann used the version that was on Fisher’s CD in the early 1990s (now also at NCDC) and “infilled” subsequent data (infill not shown here). Its first value was only 1340. Vinther 2010 re-dated Fisher’s Agassiz cores and combined the short series with less-resolved earlier data. It is negatively correlated to the earlier version, at some points being almost opposite. Kinnard uses a later series with values up to 1987. This is referenced to Fisher’s 1996 contribution to the NATO workshop. To my knowledge, this is the first digital appearance of this data. Christiansen and Ljungqvist 2011 say that they use the Vinther version rather than the very smooth series of L2009 but their data as used isn’t available.
The 1987 Fisher series shows an increase in the 20th century but only after a long secular decline, the increase merely returning to “precedented” values.
Prince of Wales, Ellesmere Island (78N): This is a previously unpublished series drilled in 2002. Values are shown only until 1995. Again, it shows a 20th century increase but only after a long secular decline, and once again the increase is to precedented values:
Devon (75N): Kinnard have archived a long O18 from Devon Island up to 1994. Again, to my knowledge, this is the first digital appearance of this series. It was not used in Mann et al 2008, which doesn’t appear to have used a Devon O18 series, but used a melt and one other series from this site. Ljungqvist 2009 archived the Fisher series from the 1973 drilling program. Like the nearby Ellesmere Island O18 series, there is a long term secular decline, with an increase in mid-20th century to precedented values (though a decline in the closing values.)
Penny, Baffin Island (69N): Yet another “new” long series. Mann et al 2008 used a short version of this series based on a co.e from the 1970s (1761-1970). The “new” Kinnard version goes from 727 to 1992. Again it shows a sort of increase through the 20th century, but again only to precedented values. The secular decline observable in the more northerly cores is not observable
North of 75N: Kinnard has five O18 series from north Greenland (here north of 75N): two long series (NGRIP and B18) and three shorter series (Camp Century, B26 and B21 starting in 1242-1502). Mann et al 2008 used one short series from this area- Fisher’s composite of Camp Century, North Central and North Site (traceable to DELNORT3.STK) which goes only from 1761 to 1972. Ljungqvist (2009) appears to be a smoothed version of NGRIP.
Central Greenland 70-75N: Central Greenland between 70 and 75N has been a staple in multiproxy reconstructions. Kinnard has four cores from this area – two long cores (Crete ending 1974 and GISP2 ending 1987) plus two short cores (B16, Site A). Mann et al 2008 used the same version of GISP2 as Kinnard; they used a slightly different Crete version: Fisher’s combination of Crete with some nearby sites, extending it from 1974 to 1982. Ljungqvist has a GISP-related series that is smoother. Ljungqvist’s series from Alley combines borehole information with O18 information and needs to be construed as a borehole series rather than a O18 series simpliciter.
Greenland S of 70N: Kinnard has 3 Greenland sites south of 70N – one long series (Dye-3) and two short series (Dye-2 and 20D). Mann et al 2008 used a short series from Dye-2 (identical to the Kinnard version of Dye-2 which is not shown here). Ljungqvist 2009 used a smoothed version of Dye-3 ending in 1960. The Kinnard version of Dye-3 is identical to the Vinther 2010 version.
Other Grenland: The Renland series is somewhat east (71N, 27W) of the “Central Greenland” group shown here and starts in the medieval period. Mann et al 2008 also used a Vinther composite of Greenland sites from different regions ( Crete, Milcent and GRIP from the “central” group, Dye-3 from the “southern” group and Renland from the east.
Kinnard archived 4 O18 series from “eastern islands” – two from Svalbard (17-24E), one from Franz Josef Land (64E) and one from Severnaya Zemlya (95E) -none of which have appeared in previous studies. These series do not shed direct light on the MWP=modern comparison as none have values in the MWP. (I don’t know whether this is due to glacier flow – as a result of which many temperate glaciers e.g. Chile have only quite recent values – or due to reformation of the glacier in the LIA or both.) All are more recent than 1995 (but values are archived only to 1995).
Comparison to Kinnard Hockey Stick
If, as a first rough check, one compares a simple average of the long O18 series to the Kinnard reconstruction (inverted so that “warm” is up), one gets the graphic below – both shown in SD units for simplicity. There is nothing in the long O18 series that yields the pronounced Kinnard hockey-stick.
As noted in the preview, this means that the derivation of the Kinnard hockey stick must come from elsewhere: either from the other ice core proxies (Na+, melt, MSA), from the D’Arrigo tree rings or from the other proxies (a few sediments and documentary series) or from regression procedures. If so, one needs to check out which series have been heavily weighted and whether series have been flipped through the regression methods. Splicing is also something that needs to be looked at: for example, while the O18 series from the Eastern Islands don’t permit a direct medieval-modern comparison, has their stepwise introduction introduced a medieval-modern differential that does not exist in the long series?
Whatever the results of this analysis may be, Kinnard et al deserve credit for ensuring this remarkable expansion of the public archive of Arctic O18 series.