Watt spurious varvology?

The most recent post on Watts Up With That is by Willis Eschenbach, is called Spurious varvology and discusses a recent paper by Martin Tingley and Peter Huybers (Tingley & Huybers, 2013, Nature, 496, 201-205). Their paper uses instrumental data, tree rings and lake sediments to suggest that the “magnitude and frequency of recent warm periods are unprecedented in the last 600 years”. What the post by Willis Eschenbach focuses on is the lake sediment data.

What Willis Eschenbach claims (by simply looking at the plot in the original paper that covers the lake sediment) is that it is obvious that something strange happened in the 20th century. He doesn’t know what, but seems to suggest that the changes are too severe to be due to a “gradual change in temperature”.

Now I don’t know enough to have a sense if this criticism is valid or not, but what struck me is that one of the prime critcisms of the Mann, Bradley & Hughes (1999) hockey stick plot is that they left out some Northern Hemisphere tree-ring data when this data started to diverge from instrumental records in the mid-1900s. This is often referred to as the “hide the decline” controversy. So it seems as though Willis Eschenbach feels capable of looking at some proxy data (lake sediments) and deciding, for some unknown reason, that at some point in time they become unsuitable as a proxy for temperature. He appears to have no evidence for this other than his opinion that the changes seen in the lake sediments are too severe to be a result of gradual changes in temperature. However, when climate scientists decide that a proxy is no longer suitable (with actual evidence that it is diverging from another more accurate record), this is a major controversy and indicates that climate scientists cannot be trusted.

My main issue is one of consistency. You can’t choose to discount some proxy data when it seems wrong to you and then criticise others if they essentially do the same. Furthermore you need more evidence than simply “it doesn’t look right”. At least with the Northern Hemisphere tree-ring data used by Mann, Bradley & Hughes (1999) there is a lot of published work (quite a lot by Keith Briffa I believe) suggesting that it does indeed become an unsuitable proxy in the mid-1900s. I’m not suggesting that this is definitively correct, but it is clearly superior to simply eyeballing a figure from a paper and saying “hmmm, doesn’t look right to me”!

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One Response to Watt spurious varvology?

  1. It seems like one of the main criticisms of this work is that they use sediment data from Korttajärvi Lake despite a paper by Mia Tiljander apparently warning against using the modern portion of this record. I downloaded the paper by Tingley & Huybers and in the Supplementary Information it says “For the Korttajärvi Lake record, we use the organic layer thickness, as the original publication indicates that a thicker organic layer probably indicates a warmer summer and a relatively long growing season” and it cites a paper by Tiljander et al. (2003). I assume that this is the paper mentioned in the criticism, so as I see it they’ve addressed the issue with using the Korttajärvi Lake data. This doesn’t mean that they’ve got it right, but one can’t claim that they’ve blindly used this data set and that they’ve ignored temperature independent changes to the sediment in the 20th century.

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