The hockey stick: The original and later versions. Temperature reconstructions of the past 1000 years

If the beleaguered climate scientists of the University of East Anglia have a weakness, it is in their statistics – yet their conclusions that the planet is warming stands on solid ground.

That’s the conclusion of the third independent inquiry into “climategate” – the fallout from last November’s release of hundreds of emails from the Climatic Research Unit (CRU) at the university, which is located in Norwich, UK.

Crucially for the scientists who work at the CRU, the inquiry – led by Ron Oxburgh, a former chair of the UK House of Lords science and technology select committee – cleared them of any professional misconduct.

“We found absolutely no evidence of any impropriety whatsoever,” said Oxburgh at a press briefing in London today.


“We are absolutely satisfied that these people were doing their job fairly. I don’t think they even minded what the outcome [of their research] was, as long as it was as close to truth as possible,” he continued.

Career decision

That will have been a comfort for the CRU team. As Oxburgh put it, they were “unlikely to have worked as scientists again” had the inquiry panel found them guilty of professional misconduct.

The panel found that the statistical tools that CRU scientists employed were not always the most cutting-edge, or most appropriate. “We cannot help remarking that 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,” reads the inquiry’s conclusions.

However, “it is not clear that better methods would have produced significantly different results,” the panel adds.

Messy data

Oxburgh was commissioned by the university to review the professional conduct of the CRU scientists. The UK Royal Society recommended his appointment and that of the panel of scientists which assisted him.

David Hand, president of the UK Royal Statistical Society and a member of Oxburgh’s panel, said the work of climate scientists is a “particularly challenging statistics exercise because the data are incredibly messy”.

Climate scientists must gather temperature data from disparate sources. Over the course of decades, temperature probes may have to be moved – because of the growth of cities, for example – and temperatures are not always measured in the same way at different stations around the globe.

Hockey stick

He said the strongest example he had found of imperfect statistics in the work of the CRU and collaborators elsewhere was the iconic “hockey stick” graph, produced by Michael Mann of Pennsylvania State University in University Park.

The graph shows how temperatures have changed over the past 1000 years (see graphic, right).

Hand pointed out that the statistical tool Mann used to integrate temperature data from a number of difference sources – including tree-ring data and actual thermometer readings – produced an “exaggerated” rise in temperatures over the 20th century, relative to pre-industrial temperatures.

That point was initially made by climate sceptic and independent mathematician Stephen McIntyre. The upwards incline on later versions of the graph has been corrected to be shorter and less exaggerated (for the full story of the hockey stick controversy, see Climate: The great hockey stick debate, and Climate myths: The ‘hockey stick’ graph has been proven wrong).

Hand said he was “impressed” by McIntyre’s statistical work. But whereas McIntyre claims that Mann’s methods have “created” the hockey stick from data that does not contain it, Hand agrees with Mann: he too says that the hockey stick – showing an above-average rise in temperatures during the 20th century – is there. The upward incline is just shorter than Mann’s original graphic suggests. “More like a field-hockey stick than an ice-hockey stick,” he told New Scientist.

Two other inquiries, by British members of parliament and Pennsylvania State University, have also cleared the scientists of misconduct. Two further inquiries, one led by former British civil servant Muir Russell and the other conducted by British police, are still under way.