Sea Ice At Lowest Level In 800 Years Near Greenland
ScienceDaily (July 2, 2009) — New research, which reconstructs the extent of ice in the sea between Greenland and Svalbard from the 13th century to the present indicates that there has never been so little sea ice as there is now.
The new study, Macias Fauria et al (Clim Dyn 2009), was coauthored by John Moore and Aslak Grinsted, whom we’ve encountered recently in connection with Rahmstorf smoothing, and Mauri Timonen, with whom we had very cordial correspondence in connection with our profiling of the long Finnish tree ring chronology.
Co-author John Moore had said in commentary here:
I strongly believe in making data available and codes available when the results are published – sometimes we work on data that others control who may not, unfortunately, want it distributed.
I wrote to lead author Macias Fauria requesting the proxy and reconstruction data for Macias Fauria et al 2009 – the sea ice reconstruction used two proxy series, an RCS version of the Finnish tree ring chronology and Svalbard ice core data. Macias Fauria replied that he could not provide the latter data as co-author Isaksson refused to make it public. He did provide me with the tree ring version that they used, the target sea ice series and the reconstruction. Obviously with half the proxy data missing, any statistical analysis of their methodology is thwarted.
The Macias chronology was not the same as the chronologies that Timonen had previously provided to me – Macias used RCS chronology, Timonen didn’t. This was quickly clarified in correspondence with Timonen and Macias Fauria. I did an RCS chronology calculation (using my RCS algorithm – to my knowledge, Briffa and cohorts have maintained secrecy on their code) on the ADV7638 measurement data that Phil Trans B required Briffa to archive last year (after prolonged obstruction by Briffa.)
I got a series that is recognizably related to the Macias chronology, but also critically different.
First, the Macias version has a somewhat different texture. It looks like it’s been somewhat smoothed – perhaps using Rahmstorf smoothing, perhaps not. (Note: A reader notes below that the text says that the smoothing is a 5-year cubic spline.) Secondly, the Macias version has a pronounced trend relative to my emulation from first principles from the 19th through the 20th century. Third, my emulation showed the frequently seen “divergence” between ring widths and temperature, while the Macias verion did not. Macias Fauria explained to Timonen that he modified the Advance10K data set by:
1. Not include the snags.
2. Remove series belonging to the last period in order to have a more evenly distributed sample depth along all the reconstructed period (no age selection was performed), as seen in Fig. 2 of the paper (otherwise most of the data was from the last two centuries).
Perhaps these changes to the data set account for the difference, perhaps it’s a difference in methodology.
Reconciling the difference is impossible right now because the data is incomplete and the originating code is thus far unavailable. I, on the other hand, for a mere blog post have placed the code that generates this graphic in the first comment and it should be turnkey with data and functions that I’ve placed online. Wouldn’t it be nice if the author Moore
strongly believed in making data available and codes available when the results are published.
While the ice core data is not archived, it is represented in small squiggles in dead-tree literature, which give some indication of the shape. It was discussed here where the following image showing very elevated values of the washout proxy discussed in Grinsted et al (JGR 2006) were shown:
These seemingly high 12th century values do not enter into the sea ice reconstruction of Macias Fauria et al 2009, because it begins in 1200. I’m sure that there is an excellent reason for not including 12th century data.