In a recent post commenting on Rich Muller’s lecture of March 19, 2011 (here) – of which the Climategate portion is more or less the same as his Oct 14, 2010 lecture (online here), John Cook observes:
It’s clear that “Mike’s Nature trick” is quite separate to Keith Briffa’s “hide the decline”. Muller has taken different sections of Phil Jone’s emails and morphed them into a single phrase. To understand how this is a misleading characterisation, it’s helpful to examine exactly what “Mike’s Nature trick” and “hide the decline” refer to.
I agree that Mike’s Nature trick is different from what can perhaps call “Keith’s Science trick”. Jones’ WMO diagram is an unholy combination of the two tricks. The taxonomy of the various tricks has been the subject of many CA posts.
1. A digital splice of proxy data up to 1980 with instrumental data to 1995 (MBH98), lengthened to 1998 (MBH99).
2. Smoothing with a Butterworth filter of 50 years in MBH98 (MBH99- 40 years) after padding with the mean instrumental value in the calibration period (0) for 100 years.
3. Discarding all values of the smooth after the end of the proxy period.
The splicing of instrumental data with proxy data prior to smoothing has been established by UC beyond any doubt (as will be reviewed below.)
Nonetheless, both Mann and Gavin Schmidt have vehemently denied such a splice.
Mann and Schmidt have denied the use of the method – see UC’s chronology here.
Some of their vehemence undoubtedly arises from Mann’s original and notorious denial of digital splicing of proxy and instrumental records as follows:
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. Most proxy reconstructions end somewhere around 1980, for the reasons discussed above. Often, as in the comparisons we show on this site, the instrumental record (which extends to present) is shown along with the reconstructions, and clearly distinguished from them (e.g. highlighted in red as here).
In the wake of Climategate, Gavin Schmidt staunchly denied digital splicing e.g. here A reader had written in, accurately observing that Mann had spliced instrumental values prior to smoothing:
I don’t think the Nature trick has been described adequately in your post. It isn’t just graphing the instrument record for comparison, but graphing it to ‘hide the decline.’ They didn’t just cut off the proxy value and add on the instrument record from 1961 on; they used the instrument temperature values to calculate smoothed average value for earlier years as well. That is the ‘trick,’ to let the instrument record replace actual values of the data that are lower than you want.
Gavin responded with the disinformation that has become standard:
[Response: This has nothing to do with Mann's Nature article. The 50-year smooth in figure 5b is only of the reconstruction, not the instrumental data. - gavin]
First, here is the relevant figure from MBH99. Note the closing portion of the smoothed reconstruction with a sort of upside-down S-shape at the end.
Next, on the left is a blowup of the latter part of the above graph.
The overprinted yellow line is a virtually exact emulation of the MBH smooth series: this was obtained by splicing instrumental data from 1981 to 1998 with proxy data up to 1980, followed by truncation after smoothing. (Here to about 1953.) On the right is a graphic also showing the smooth following Mann’s style without splicing instrumental data after 1980.
Left – Excerpt from MBH99 Figure 3 showing emulation of Mannian smooth with spliced instrumental record. Right – also showing (black) the smooth without an instrumental splice.
The trick is clearer in MBH99. The graphic in MBH98 (Nature) is much muddier and doesn’t show the trick as clearly. First, here is the (rather muddy) graphic from MBH98 showing the smooth:
Next, on the left is a blowup of the latter part of the above graph. The overprinted yellow line is an exact emulation of the MBH smooth obtained by splicing instrumental data after 1980 with proxy data up to 1980, followed by truncation after smoothing. (Here to about 1953.) If Mann had not spliced instrumental data after 1980, the smoothed series (following his methodology) would have looked like the version on the right – the orange line showing the result without the instrumental splice.
Although Mann and others have regularly described his “Nature” trick as nothing more than plotting both instrumental and reconstruction data in the same graphic, the “trick” was more than that: it was, as shown above, the splicing of instrumental data with proxy data prior to smoothing. On one occasion however, Mann implictly conceded the Climate Audit exegesis of his Nature trick, stating in an inline comment at realclimate as follows:
In some earlier work though (Mann et al, 1999), the boundary condition for the smoothed curve (at 1980) was determined by padding with the mean of the subsequent data (taken from the instrumental record).
From the precision of the emulation, it appears certain to me that the padding was by the instrumental data (rather than the mean of the subsequent data), but either method involves padding with instrumental data.
Far more serious than “Mike’s Nature trick” is Keith’s Science Trick – the deletion of adverse data (a trick that Mann supported as a Lead Author in IPCC TAR.)
[Note - this section was somewhat rewritten on Sep 5, 2012 adding the figure excerpts in response to a request for clarification of the various tricks.]
Keith’s Science Trick
“Keith’s Science Trick” is first used in May 1999 in Briffa and Osborn (Science 1999) and Jones et al (Rev Geophys 1999). It is nothing more than the deletion of data to hide the decline. The deletion of adverse data to hide the decline was first reported at CA in 2005 here in connection with IPCC TAR spaghetti graph.
In the wake of Climategate, prior incidents of hiding the decline were discussed, including recent analyses of Briffa and Osborn (Science 1999) e.g. here. Following is a graphic showing Keith’s Science Trick – the deletion of adverse data – a practice continued in subsequent spaghetti graphs, including those in IPCC TAR and IPCC AR4.
Figure 2. Annotated version of Briffa and Osborn Science 1999 Figure 1 – see recent posts for derivation.
The Briffa Bodge
The Climategate documents included programs by Tim Osborn and Ian Harris, describing “fudge factors” or “very artificial corrections for decline” e.g. http://di2.nu/foia/harris-tree/briffa_sep98_e.pro. In a submission to the UK Parliamentary Committee, Tim Osborn denied that he had used ‘artificial corrections for [the] decline” in his published articles. While Osborn himself may not have used “artificial corrections”, Osborn carefully did not comment on whether other CRU scientists had used such “artificial corrections”. Briffa’s Tornetrask reconstruction (prominent in several multiproxy reconstructions) had received precisely this sort of adjustment – called the “Briffa bodge”.
In the narrowest sense, Osborn did not use the Briffa bodge (or similar artificial correction) to hide the decline in his articles published after September 1998 (the date of the annotation in the program briffa_sep98_e.pro.) Instead, CRU used Keith’s Science Trick – the deletion of data – to hide the decline.
Phil’s Combo Trick
Phil’s Combo Trick, as others e.g. Hu McCulloch have observed, is a combination of Keith’s Science Trick and Mike’s Nature Trick, leading to a particularly grotesque result.
Values of the Briffa reconstruction were deleted after 1960 (Keith’s Science Trick) and spliced with instrumental data prior to smoothing (Mike’s Nature Trick). But, unlike Mann, Jones didn’t peel the smooth back to the end date of the proxy data.
Cook’s article has a considerable amount of disinformation about proxy reconstructions, not all of which will be canvassed in this note.
There is no “decline” in Mann’s reconstructions. As we shall examine shortly, the source of “the decline” come from temperature reconstructions calculated from tree-ring density at high northern latitudes (Briffa 1998). There are very few of these in Mann’s proxy data and hence his reconstructions never required removal of any declining tree-ring density.
As is well known, the long portion of the MBH98-99 reconstruction is little more than an alter ego for bristlecone chronologies and did not “require” removal of the decline. However, Mann et al 2008 contained many (over 90) Briffa MXD series. They deleted actual data after 1960 and replaced it with RegEM data – with the spliced data being used to supposedly demonstrate the statistical significance of the proxy population.
I disagree with Cook’s assertion that the decline was properly disclosed in spaghetti graphs in either IPCC or academic literature. The decline itself was indeed reported in early Briffa articles – indeed, I used these articles to first detect the deletion of adverse data in IPCC TAR – see here.
However, the adverse data was deleted in all spaghetti graphs comparing reconstructions in academic literature and in IPCC reports to policy-makers and the public. This practice should have been disowned by the climate community long ago.
I agree with Cook’s closing paragraph:
Thus it’s clear that “Mike’s Nature trick” has nothing to do with Briffa’s “decline”. There is no “decline” in Mann et al 1998 and Mann et al 1999. To conflate two separate techniques via the phrase “Mike’s Nature trick to hide the decline” is adding to the glut of ‘Climategate’ misinformation.
Yes, indeed. Mike’s Nature Trick and Keith’s Science Trick are two different tricks. Neither practice should be condoned. If I were judging the two as a sort of reverse beauty contest, I would rank Keith’s Science Trick as the most unacceptable.