Replicating the “Trick” Diagram
Michael Mann, Dec 2004
No researchers in this field have ever, to our knowledge, “grafted the thermometer record onto” any reconstruction. It is somewhat disappointing to find this specious claim (which we usually find originating from industry-funded climate disinformation websites) appearing in this forum [realclimate].
Phil Jones, Nov 1999
I’ve just completed Mike’s Nature trick of adding in the real temps to each series for the last 20 years (ie from 1981 onwards) and from 1961 for Keith’s to hide the decline.
Gavin Schmidt, Nov 2009
Scientists often use the term “trick” to refer to a “a good way to deal with a problem”, rather than something that is “secret”, and so there is nothing problematic in this at all.
I’ve been able to make a very close emulation of Jones’ 1999 WMO diagram. Jean S at Climate Audit reported on the key features of Mike’s Nature trick as used by Jones first. I’ve confirmed his results and identified digital versions of all the relevant series. A turnkey script generating the diagram is in the first comment below. A few observations on issues that required parsing. There seem to be two NCDC versions of the Jones reconstruction; the WMO diagram uses (or appears to use) a version archived in connection with Jones et al 2001. The NCDC archive for MBH is reference 1902-1980 while the diagram is reference 1961-1990; the difference in CRU references is applied to the MBH reconstruction to recenter it. (The value ties in with a comment in the Climategate Letters.) I used an old CRU version (archived with the truncated Briffa reconstruction) otherwise the delta was larger. In order to get the endpoint of the graph to look right, I needed to have both 1998 and 1999 values of the instrumental series.
A reader below (sensibly) proposed the following additional explanation. The green line is tree-ring data on the left. On the right it has been smoothly merged into temperature data. This is “Mike’s Nature trick”, that Mann falsely claimed was never done. The replacement of actual data with spliced temperature data “hide the decline” in the green tree-ring data curve in the late 20th century, making the reconstruction seem able to model recent temperatures, when it didn’t.