CRU explains ‘trick’ and ‘hide the decline’

The University of East Anglia on Thursday night published its 3,500-word submission to the UK’s Parliamentary Select Committee on Science and Technology, on the climate change furore which erupted late last year when emails were stolen from its servers.

The paper goes into all the accusations arising from the emails, and is worth reading (the submission and appendix have been published in Word format).

Here’s an excerpt from the part dealing with perhaps the most-cited accusations, about the words “trick” and “hide the decline”:

3.5.2 “Trick” and “hide the decline”.

These accusations relate to the portrayal of the 1000-year Northern Hemisphere temperature record in one diagram in a publication for the WMO in 1999.  The diagram integrated temperature records based on thermometer observations (which started in the 1850s) with “proxy” data (from ice cores, tree-rings, written and other sources), extending much further into the past than the instrumental record.

3.5.3 One of the three proxy-temperature reconstructions was based entirely on a particular set of tree-ring data which exhibited strong correlation with thermometer measured temperature from the 19th century to the mid-20th century. But after 1960 it did not show a realistic trend of temperature by comparison with these thermometer measurements.

3.5.4 This observation (that some otherwise temperature-sensitive tree-ring chronologies do not track the observed rise in recent temperatures) is well known.  It is referred to in the literature as the “decline” or “divergence” phenomenon. The use of the term “hiding the decline” referred to the method of combining the tree-ring evidence and instrumental temperatures, removing the post-1960 tree-ring data to avoid giving a false impression of declining temperatures.  What it did not refer to was any decline in the actual thermometer evidence of recent warming.

3.5.5 CRU never sought to disguise this specific type of tree-ring “decline or divergence”.  On the contrary, CRU has published a number of pioneering articles that illustrate, suggest reasons for, and discuss the implications of this interesting phenomenon (e.g. Briffa et al., 1998 a, b; Briffa, 2000 listed in the legend of the WMO figure).

3.5.6 As for the (now notorious) word “trick”, so deeply appealing to the media, this has been richly misinterpreted and quoted out of context.  It was used in an informal email, discussing the difficulties of statistical presentation.  It does not mean a “ruse” or method of deception.  In context it is obvious that it is used in the informal sense of “the best way of doing something”.  In this case it was “the trick or knack” of constructing a statistical illustration which would combine the most reliable proxy and instrumental evidence of temperature trends.

It is a detailed defence, but whether it’s enough to undo the doubt sown in many minds about climate science – and science more generally – remains to be seen. CRU director Phil Jones will be appearing before the committee on Monday.

Related links:

The real problems with climate science (FT Energy Source)
Wiki-fied science and other ideas for the IPCC (FT Energy Source)
Antarctic ice melting supports global warming (FT Energy Source)

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