Definition of hockey stick

This refers to the shape of a graph where one variable rises steadily over a period of time and then dramatically increases towards the end of the period.  The shape resembles an ice hockey stick blade. [1]

A “hockey stick” graph showing much higher global temperatures in the last few decades, than over the previous millennium, was used as a key piece of evidence in climate change science to represent the recent rise in global temperatures.

The Intergovernmental Panel on Climate Change nicknamed the graph “hockey stick”, which shows a spike in temperatures in the past century. The graph was slammed as “exaggerated” by one of the UK’s leading statistician, Professor David Hand, in a vindication of claims that global warming sceptics have been making for years.

Prof Hand from the Royal Statistical Society, said that the graph has had been compiled using “inappropriate” methods.

The graph was a key part of the "climategate" email scandal.  E-mails were hacked in the autumn of 2009 from the Climatic Research Unit at the University of East Anglia (UEA). They caused a storm, as they appeared to show scientists manipulating and concealing data.

In the e-mails, UEA’s Professor Phil Jones referred to a “trick” to “hide the decline” in temperatures suggested by certain sources of data. A similar trick was alleged by climate sceptics to have been used in the hockey stick graph.

The UEA scientists said that “trick” merely referred to a scientific technique.

Prof Hand said his criticisms should not be seen as invalidating climate science. He pointed out that although the hockey stick graph – which dates from a study led by US climate scientist Michael Mann in 1998 – exaggerates some effects, the underlying data show a clear warming signal.

A report commissioned by UEA with advice from the Royal Society, the UK’s prestigious national science academy – exonerated UEA’s unit’s scientists, it criticised climate experts for failures in handling statistics.

“It is very surprising that research in an area that depends so heavily on statistical methods has not been carried out in close collaboration with professional statisticians,” the report concluded. [2]

Global warming graph attacked by study

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