Audit of the HadCRUT4 Global Temperature Dataset

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A landmark audit of the HadCRUT4 dataset used by the IPCC and others. The audit finds more than 70 areas of concern about data quality and accuracy.


Title: An Audit of the Creation and Content of the HadCRUT4 Temperature Dataset
Author(s): John McLean (PhD)
Pages: 95 plus preamble and appendices (total 135)
Date: October 2018

This report makes more than 70 findings about areas of concern with the HadCRUT4 temperature dataset. These cover the entire process from the measurement of temperatures to the derivation of HadCRUT4 global average temperature anomalies. They relate to the inclusion of data that is obviously in error, inappropriate procedures, poor data processing and significant assumptions about a range of matters including basing conclusions on very little data.

Most of the findings increase the uncertainty in the data and therefore increase the error margin. One however shows that a common but flawed method of data adjustment creates a false warming trend from the adjustments alone. Another finding points out that when stations were closed rather than relocated any distortion in the data remains in the record. Errors are also identified in sea surface temperatures, including some created by a member of the team responsible for that data.

Ultimately it is argued that the flawed data casts doubt on the credibility of IPCC reports that rely on HadCRUT4 data (or earlier versions of the dataset). Due diligence of these matters by governments twenty or more years ago might have avoided poorly-justified policies on climate and energy.


As downloaded from CRU and Hadley Centre on 26 Jan 2018

HadCRUT. ascii


HadSST. of observations



CRUTEM. files

Assorted_global and hemispheric summary files


See appendices in document


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