Our conclusion, after detailed study of the Mann et. al. data base, is that the “hockey stick” graph is an artefact of poor data handling, selective use of sources, reliance on obsolete versions of source data and erroneous statistical calculations. Correcting the copying errors and updating the source data yields the following revision to the original graph:

The top diagram is from the Mann et. al. study (with the error bars removed). The vertical axis measures “anomalies” or departures from a notional hemispheric “average temperature” in tenths of a degree C. The bottom diagram is based on the corrected data. Applying the Mann et. al “multiproxy” procedure on their own data, when updated and correctly collated, contradicts the claim that the late 20

The above shows the same comparison using 20-year moving averages.

You can get the spreadsheet that produced these pictures here.

Here is the same figure in b&w.

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