There has been much discussion on this site regarding the methodology employed by Dr. Hansen’s “Step 1″, also known as the “bias method” in HL87. Readers unfamiliar with the topic may want to read through the material here, here, and here to gain a better understanding of the method and issues raised with employing it.
What was clear since we first unraveled the process was that it was destined to corrupt the combined station data and, as it’s name implies, add a bias to that combined data. What was not clear was what the net effect would be to the regional and worldwide temperature record.
Thanks to Steve’s help, I recently completed an initial look into the effect the bias method has on the temperature record.
On September 18 Steve posted his R implementation of Hansen Step 1, along with Jean S’ Matlab implementation. Although my implementation in Visual Basic was nearly complete, I decided to be pragmatic and abandon my attempt to implement Step 1 and utilize Steve’s R code (R is free, Matlab is not). I stubbornly refused to let go of my familiar VB and Excel and fully embrace R, but fortunately Steve graciously made a few modifications to remove some minor annoyances, and he refined the station ordering when it happened that an MCDW record did not exist.
With code in hand I applied Step 1 against all Russian GHCN stations (Europe and Asia) and collected the bias applied to the individual scribal records in a spreadsheet. I calculated the average bias across all scribal records on a year-by-year basis. What one can see from the following plot is that, for Russian records, the method introduces an artificial cooling to records before 1987.
I have already started work on other regions of the world and want to stress that the results shown may not apply to those regions. All of this is interesting, but preliminary. Keep in mind too that the bias method implemented in Step 1 is but one of many problems, or “algorithms of interest”, already uncovered or waiting to be discovered.