The PAGES2K Arctic reconstruction uses Gifford Miller’s Hvitavatn (Iceland) data upside down. The error “matters” because this series is one of rather few PAGES2K series that show a Hockey Stick. Such gross errors ought to be corrected before the data is cited for policy purposes or said to confirm previous studies.
PAGES2k, the lead author of which is Darrell Kaufman, a longtime promoter of varvology, expands the Kaufman et al 2009 sediment network to 22 series, adding a number of new series, including Hvitarvatn, Iceland, where Kaufman used the data upside down to the interpretation of Gifford Miller, the original author and a very eminent paleoclimatologist. Miller’s report on Hvitarvatn was previously discussed at CA here.
Here is a plot of the first eight PAGES2K Arctic sediment series (log basis). WIthin these eight series, the series on the right second from the top, Hvitarvatn (Larsen 2011) is the only one showing a dramatic increase in 20th century values relative to medieval values.
Hvitarvatn was also discussed at length in Miller et al 2012, an interesting article previously discussed at CA here. In that blog post, I presented the graphic of Hvitavatn varve thicknesses from Miller et al, as shown below. Miller interpreted the increased varve thicknesses at Hvitavatn after 1275, together with radiocarbon information on kill dates at Baffin Island, as demonstrating the development of LIA cold and the narrow MWP varves as evidence that ice caps were not in close proximity. Miller stated:
Here we present precisely dated records of ice-cap growth from Arctic Canada and Iceland showing that LIA summer cold and ice growth began abruptly between 1275 and 1300 AD, followed by a substantial intensification 1430–1455 AD.
From Miller et al 2012 Figure 2C-D. (c) Ice cap expansion dates based on a composite of 94 Arctic Canada calibrated 14C PDFs. (d) 30-year running mean varve thickness in Hvítárvatn sediment core HVT03-2 [Larsen et al., 2011].
Miller et al discussed varve changes at Hvitavatn at length, including the following:
Thus, supra-decadal changes in Hvítárvatn varve thickness track the intensity of Langjökull erosion, and serve as a proxy for ice-cap size [ Larsen et al., 2011]. The response time of Langjökull outlet glaciers to abrupt summer cooling is approximately a decade and the estimated ice-cap equilibration time is 100 years (H. Björnsson, unpublished data, 1997- 2011).
Consequently, Langjökull outlet glaciers will begin to advance within a decade following abrupt summer cooling, although the ice cap will not attain its new equilibrium dimensions for a century. We therefore expect that times of abrupt snowline lowering derived from the Baffin Island kill dates should correspond with the onset of multidecadal trends of increasing varve thickness in Hvítárvatn. To test this prediction we analyzed replicate varved sediment cores from Hvítárvatn, where the past 1200 years is contained in the upper 8 m of the sediment fill. The varve chronology since 800 AD is constrained by seven historically dated tephras, providing 6 year temporal precision [ Larsen et al. , 2011]. The 30-year running mean varve thickness integrates the interannual to decadal variations in hydrologic efficiency of the delivery systems and tracks the evolution of Langjökull’s growth and decay in response to summer temperature changes over the past 1200 years..
From both the Canadian evidence (many sites became ice-covered in the late 13th Century and remained so until the past decade) and Icelandic evidence (consistently thick varves following the late 13th Century), we can conclude that multidecadal average summer temperatures never returned to those of Medieval times until the 20th Century…
The expansion and subsequent retreat of Langjökull recorded by a peak in varve thickness between 850 and 950 AD also coincides with ice-cap growth in Arctic Canada. This is followed by two centuries of unusually thin varves between 950 and 1170 AD, indicative of reduced glacial erosion in response to increased summer warmth. This suggests that the lack of ice-kill dates on Baffin Island during the same interval is the result of ice-melt rather than extended cold, a finding that could not be determined from the dated vegetation record alone.
Turning now to the PAGES use of this record. The PAGES2K SI says that its proxy records must “exhibit a documented temperature signal” and be “published in peer reviewed literature as a proxy for temperature”:
The proxy records selected by the Arctic2k group for the Arctic continental-scale temperature reconstruction (Fig. S7) meet the following criteria: (1) situated north of 60°N, (2) extend back in time to at least 1500 CE, (3) have an average sample resolution of no coarser than 50 years, (4) include at least one chronological reference point every 500 years, (5) exhibit a documented temperature signal, and (6) are published in peer-reviewed literature as a proxy for temperature, although not necessarily calibrated to temperature (i. e., some records provide only a relative measure of temperature with unknown transformations between the proxy measurement and temperature).
Unfortunately, they did not also require that the use of the record be in the same orientation as the published literature and, in the case of Hvitavatn, the SI states that they used the record in a positive orientation i.e. opposite to the interpretation of Miller et al 2012.
PAGES2K also used a number of Baffin Island varve series. In my previous post on Miller et al 2012, I observed that the varve data on Baffin Island lent itself to the interpretation that Miller had placed on the Hvitavatn, Iceland data – i.e. thick varves indicating glacier proximity, an interpretation of varves that is consistent with interpretations of Ice Age recession.
BTW I strongly commend Kaufman for actually reporting the orientation of each proxy. Previous authors e.g. Neukom et al 2011 have failed to do so, enabling Neukon’s upside down use of Quelccaya data to remain undetected until I noticed it the other day because of PAGES2K disclosure.
Readers should not conclude that Miller has argued that MWP warmth exceeded modern warmth. Miller has argued that recent Arctic glacier melt is exposing sites that were ice covered through the MWP:
The 24 Canadian sites that became ice-covered 800 – 900 AD (Table S4) and did not melt again until the past decade demonstrate that multi-decadal
average summer temperatures in Arctic Canada now exceed those of Medieval times.
This is a line of argument that, in my opinion, might well be used to argue that modern warmth has surpassed MWP warmth. Assembling such facts would be far more persuasive to me than multiproxy varvology with upside down data.