The Dictionary of the Climate Debate (DCD)

Hockey Stick Controversy

IPCC head John Houghton announcing the 2001 report — note the background image.
IPCC head John Houghton announcing the 2001
report — note the background image.

A political controversy that began in 2003 when Steve McIntyre and Ross McKitrick challenged the MBH98 reconstruction of Northern mean temperature changes over the past millennium — known as the Hockey Stick — done by Michael E. Mann, Raymond Bradley and Malcolm Hughes.

This reconstruction was controversial because it eliminated the Medieval Warm Period, which made recent temperature increases seem much more pronounced (thus the blade on the stick). It became significant because it was highlighted in the 2001 IPCC Third Assessment Report as strong evidence for anthropogenic global warming and, for this reason, was widely published in the media.

Michael Mann on the "central icon of the climate debate"

Mann defend himself on the BBC

Click here to hear a 2005 BBC interview where Michael Mann defends his methodology.

1. Click here to read the Mann, Bradley, and Hughes paper that first presented the reconstruction.

2. Click here to read the McIntyre and McKitrick paper that challenged their work.

3. Click here to read the Real Climate blog post where Mann defends his methodology.

4. Click here to read Steve McIntyre's full version of his side of the story.

5. By 2010 the professional statisticians joined the climate skeptics in attacking the hockey stick. For example, McShane and Wyner's paper A Statistical Analysis of Multiple Temperature Proxies: Are Reconstructions of Surface Temperatures Over the Last 1000 Years Reliable? Basically, they re-affirm McIntyre's damning critique. Here's a quote:

"In this paper, we assess the reliability of such reconstructions and their statistical significance against various null models. We find that the proxies do not predict temperature significantly better than random series generated independently of temperature.… Finally, the proxies seem unable to forecast the high levels of and sharp run-up in temperature in the 1990s either in-sample or from contiguous holdout blocks, thus casting doubt on their ability to predict such phenomena if in fact they occurred several hundred years ago."

Click here to read skeptic statistician William Briggs' review of it. To read the full paper, click here.

Click here to read Real Climate's first response to the paper (Note: They ARE in fact the AGW first responders). Make sure you read the comments.

6. Climategate emails have revealed that even Mann's collegue's in the climate political battle had strong doubts about his work.

For example: Tom Wigley: "I have just read the M&M stuff critcizing MBH. A lot of it seems valid to me. At the very least MBH is a very sloppy piece of work -- an opinion I have held for some time." (East Anglia Confirmed Emails from the Climate Research Unit - 1098472400)

Click here for a more complete compilation of criticisms.

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