It seems like everyone wants to talk about Tiljander. I don’t, particularly, but you gotta give the customers what they want, so here is a thread to discuss it if you like. The comment policy still applies, but I’ll be laxer. Comments incorrectly paraphrasing others will be harshly dealt with. Vague rantings unsupported by clear evidence or links, ditto. Repeating what everyone else has already said, ditto (this isn’t a vote).
Some useful links you may want:
- Proxy-based reconstructions of hemispheric and global surface temperature variations over the past two millennia (Mea; includes supplementary info)
- McI’s comment on Mea
- Mea reply to McI
- [Update: Supplemental Information for PNAS Article at Mann’s website, plus updates
Hopefully, people have read the Mea supplemental info where they say Potential data quality problems. In addition to checking whether or not potential problems specific to tree-ring data have any significant impact on our reconstructions in earlier centuries (see Fig. S7), we also examined whether or not potential problems noted for several records (see Dataset S1 for details) might compromise the reconstructions. These records include the four Tijander et al. (12) series used (see Fig. S9) for which the original authors note that human effects over the past few centuries unrelated to climate might impact records (the original paper states ”Natural variability in the sediment record was disrupted by increased human impact in the catchment area at A.D. 1720.” and later, ”In the case of Lake Korttajarvi it is a demanding task to calibrate the physical varve data we have collected against meteorological data, because human impacts have distorted the natural signal to varying extents”). These issues are particularly significant because there are few proxy records, particularly in the temperature-screened dataset (see Fig. S9), available back through the 9th century. The Tijander et al. series constitute 4 of the 15 available Northern Hemisphere records before that point.
In addition there are three other records in our database with potential data quality problems, as noted in the database notes: Benson et al. (13) (Mono Lake): ”Data after 1940 no good– water exported to CA;” Isdale (14) (fluorescence): ”anthropogenic influence after 1870;” and McCulloch (15) (Ba/Ca): ”anthropogenic influence after 1870”. We therefore performed additional analyses as in Fig. S7, but instead compaired the reconstructions both with and without the above seven potentially problematic series, as shown in Fig. S8.
So you can look at S8 – I’ve inlined it – to discover that the Tiljander series don’t affect the overall result much.
[Didn't like this post? You want DenialDepot]
[Update: one thing that has puzzled some people is how little effect the Tiljander proxies have on the overall reconstruciton: see S8, which I inlined. But look at S9, and you'll see that the Tiljander proxies are remarkably flat before 1800. This would be consistent, for example, with recent non-climatic artifacts producing more variation than is naturally present. But it also means that the effect of these proxies on the total reconstruction pre-1800 is likely to be extremely slight (which explains fig S8). This is because the scale-this-proxy-to-termperature thingy is done on the overlap with the instrumental period -W]