Shades of upside down Tiljander. McIntyre is delving further into the Marcott proxy issue and it looks almost certain now there’s a statistical processing error (selection bias).
Steve McIntyre writes:
In the graphic below, I’ve plotted Marcott’s NHX reconstruction against an emulation (weighting by latitude and gridcell as described in script) using proxies with published dates rather than Marcott dates. (I am using this version because it illustrates the uptick using Marcott methodology. Marcott re-dating is an important issue that I will return to.) The uptick in the emulation occurs in 2000 rather than 1940; the slight offset makes it discernible for sharp eyes below.
uptricksupticks arise because of proxy inconsistency: one (or two) proxies have different signs or quantities than the larger population, but continue one step longer. This is also the reason why the effect is mitigated in the infilled variation. In principle, downticks can also occur – a matter that will be covered in my next post which will probably be on the relationship between Marcottian re-dating and upticks.
Read his full post here: How Marcottian Upticks Arise
Maybe we need an Uptick Rule for paleoclimatology