Evolution of the "SPPI global temperature index"

I document the changes that the index has undergone in the last one and a half years.

In January 2009 the SPPI started publishing its “SPPI Monthly CO2 Report” (since March/April 2010 they seem to be published as double issues). The editor of the reports is Christopher Monckton. In these reports information can be gleaned about the “SPPI global temperature index”, that seems to be the basis for Monckton’s own charts, where he compares “IPCC projections” to “global temperature”. It turns out, that this “temperature index” is simply the mean of a varying pool of temperature anomalies (both terrestrial and satellite, namely HadCRUt3, NCDC, RSS, and UAH) and zeroed to the minimum value over the time period of the plot it is used in. Its pool has varied considerably since January 2009 and its offset depends on the time period of the graph it is used in.

The varying pool of anomalies

All reports include a graph about the 29-year global warming trend. The caption of this graph spells out, which anomaly datasets were used in the “SPPI global temperature index”. Here is a compilation of evolution of the data source attribution of the graph over time.

January through June 2009:

“Data source: SPPI index, compiled from HadCRUt3, NCDC, RSS, and UAH.”

July through October 2009 (NCDC is dropped from the index, no explanation given):

“Data source: SPPI index, compiled from HadCRUt3, RSS, and UAH.”

November 2009 through March 2010:

“Data source: SPPI index, compiled from RSS, and UAH. SPPI no longer uses any terrestrial-temperature datasets, because they have become near-universally discredited as unreliable.”

April and June 2010:

“Data source: SPPI index, compiled from RSS Inc. UAH has not reported data for two months and has been excluded from this graph, but will be relied upon again when data become available. SPPI no longer uses any terrestrial-temperature datasets, because they have become discredited as unreliable.”

How the index is calculated

The first mention of how the index is calculated can be found in a figure caption in the February 2009 issue:

“Using the SPPI global temperature index, which is the mean of two terrestrial and two satellite global mean temperature anomaly datasets,”

Starting in the June 2009 issue the calculation of the index is explained in detail. In the following compilation the changes to previous versions are highlighted.

Our global-temperature graphs show changes in real-world temperature at or near the Earth’s surface. Each temperature graph represents the mean of two surface and two satellite datasets: the monthly surface temperature anomalies from the Hadley Center in the UK and the National Climatic Data Center in the US, and the lower-troposphere anomalies from the satellites of Remote Sensing Systems, Inc., and of the University of Alabama at Huntsville.

On each graph, the anomalies are zeroed to the least element in the dataset. For clarity, the IPCC’s range of predictions is zeroed to the start-point of the least-squares linear-regression trend on the real-world data. Since late 2001, global temperature has been falling fast.

From the July 2009 to October 2009 issue:

Our global-temperature graphs show changes in real-world temperature at or near the Earth’s surface. Each temperature graph represents the mean of one surface and two satellite datasets: the monthly surface temperature anomalies from the Hadley Center in the UK and the National Climatic Data Center in the US, and the lower-troposphere anomalies from the satellites of Remote Sensing Systems, Inc., and of the University of Alabama at Huntsville. We do not use the NCDC/GISS datasets.

On each graph, the anomalies are zeroed to the least element in the dataset. For clarity, the IPCC’s range of predictions is zeroed to the start-point of the least-squares linear-regression trend on the realworld data. Since late 2001, global temperature has been falling fast.

From November 2009 to April 2010 issue:

Our global-temperature graphs show changes in real-world temperature at or near the Earth’s surface. Each temperature graph represents the mean of one surface and two satellite datasets: the monthly surface temperature anomalies from the Hadley Center in the UK, and the lower-troposphere anomalies from the satellites of Remote Sensing Systems, Inc., and of the University of Alabama at Huntsville. We do not use the Hadley/CRU or NCDC/GISS datasets: the Climate-gate scandal has shown these to be mere science fiction.

On each graph, the anomalies are zeroed to the least element in the dataset. For clarity, the IPCC’s range of predictions is zeroed to the start-point of the least-squares linear-regression trend on the real-world data. Since late 2001, global temperature has been falling fast.

June 2010:

Our global-temperature graphs show changes in real-world temperature at or near the Earth’s surface. Each temperature graph represents the mean of two satellite datasets: the monthly lower-troposphere anomalies from the satellites of Remote Sensing Systems, Inc., and of the University of Alabama at Huntsville. We do not use the Hadley/CRU or NCDC/GISS datasets: the Climate-gate scandal has shown these to be unreliable.

On each graph, the anomalies are zeroed to the least element in the dataset. For clarity, the IPCC’s range of predictions is zeroed to the start-point of the least-squares linear-regression trend on the real-world data. Since late 2001, global temperature has been falling fast.

Note that the figure caption as of April 2010 claims that UAH was temporarily dropped from the index, so the index should simply be a shifted version of RSS.

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