Brandon Shollenberger writes in with this little gem:
I thought you might be interested in a couple posts I wrote discussing some odd problems with the BEST temperature record. You can find them here:
But I’ll give an overview. BEST calculated its uncertainty levels by removing 1/8th of its data and rerunning its averaging calculations (then examining the variance in the results). I’ve highlighted two problems I haven’t seen people discuss before. If you’re familiar with the Marcott et al reconstruction’s inappropriate confidence intervals, some of this may sound familiar.
First, BEST only reruns its averaging calculations to determine its uncertainty. It does not rerun its breakpoint calculations. As you may know, BEST breaks data from temperature stations into segments when it finds what it believes to be a “breakpoint.” The primary way it looks for these breakpoints is by comparing stations to other stations located nearby. If a station seems too different from its neighbors, it will be broken into segments which can then be realigned. This is a form of homogenization, a process whereby stations in the dataset are made to be more similar to one another.
This process is not repeated when BEST does its uncertainty calculations. The full data set is homogenized, and subsets of that homogenized data set are compared to determine how much variance there is. This is inappropriate. The amount of variance BEST finds within a homogenized data set does not tell us how much variance there is in BEST’s data. It only tells us how much variance there is once BEST is finished homogenizing the data.
Second, to determine how much variance there is in its (homogenized) data set, BEST reruns its calculations with 1/8th the data removed, eight times. This produces eight different series. When comparing these different series, BEST realigns them so they all share the same baseline. The baseline period BEST uses for its alignment is 1960-2010.
This is a problem. By aligning the eight series on the 1960-2010 period, BEST artificially deflates the variance between those series in the 1960-2010 period (and artificially inflates the variance elsewhere). That makes it appear there is more certainty in the recent portion of the BEST record than there actually is. The result is there is an artificial step change in BEST uncertainty levels at ~1960. This is the same problem demonstrated for the Marcott et al temperature record (see here).
All told, BEST’s uncertainty levels are a complete mess. They are impossible to interpret in any meaningful way, and they certainly cannot be used to try to determine which years may or may not have been the hottest.