Perhaps the greatest single difference between being a “real climate scientist” and policies recommended here is that “real climate scientists” do not hesitate in excluding data ex post because it goes the “wrong” way, a practice that is unequivocally condemned at Climate Audit and other critical blogs which take the position that criteria have to be established ex ante: if you believe that treeline spruce ring widths or Arctic d18O ice core data is a climate proxy, then you can’t exclude (or downweight) data because it goes the “wrong” way.
This seems trivially obvious to anyone approaching this field for the first time and has been frequently commented on at critical blogs. However it is a real blind spot for real climate scientists and Tingley and Huybers are no exception.
Fisher’s Mount Logan ice core d18O series is a longstanding litmus test. It goes down in the latter part of the data and is not popular among multiproxy jockeys. Tingley and Huybers excluded Mt Logan from their data set, purporting to justify its exclusion as follows:
We exclude the Mount Logan series that is included in  because the original reference  indicates it is a proxy for precipitation source region and is out of phase with paleotemperature series.
In the figure below, I show two Arctic d18O series – on the top is Windy Dome, a Thompson series from Franz Josef Land used by Tingley and Huybers and on the bottom is the Mt Logan series that they excluded.
Windy Dome d18O goes up in the 19th and 20th century. The possibility that some portion of the increase might be attributable to change in source region doesn’t cross Tingley and Huybers’ mind. On the other hand, Mt Logan goes down and the authors unhesitatingly attribute this to change in source precipitation and exclude it from their network (post hoc.)
However, they don’t consider the bias inherent in this sort of ex post exclusion. Attributing the decrease at Mt Logan to changes in precipitation source is very plausible. But it’s equally plausible and even probable that changes in precipitation sources could also work in the opposite direction, exacerbating any increase due to temperature. Perhaps there was a change in source region for Windy Dome that contributed to its recent increase in d18O values. Exclusion of Mt Logan, without a compensating exclusion of an accentuated upward series, will impart a bias to any composite.
If scientists believe that Arctic d18O is a proxy for temperature, then they cannot exclude data after the fact because it goes the “wrong” way, as Tingley and Huybers have done here. Particularly if they have no compunction about using contaminated data that goes the “right” way.
If authors take longer to report data that goes the “wrong way”, this will also bias composites at any given time. For example, Lonnie Thompson’s Bona-Churchill series, which is near Mt Logan, also goes the wrong way. Has this contributed to the delay (now exceeding 10 years) in reporting these results?