Changes

==The Hockey Stick Temperature Reconstruction==

==The Hockey Stick Temperature Reconstruction==

[[Image:Hockey stick chart ipcc.jpg|right|thumb|300px|The flawed Hockey Stick graph in a 2001 IPCC report shows blue proxy values along the "shaft" with red instrumental values superimposed as the "blade".]]

[[Image:Hockey stick chart ipcc.jpg|right|thumb|300px|The flawed Hockey Stick graph in a 2001 IPCC report shows blue proxy values along the "shaft" with red instrumental values superimposed as the "blade".]]

One of the main pieces of evidence for anthropogenic global warming presented during the 3rd IPCC report was a temperature reconstruction done by climatologist [[Michael Mann]]. The resulting graph of the Northern Hemisphere temperature is shaped like a hockey stick, and it is used as evidence for the unusualness of the earth's temperature in the past few decades.  While dramatic, the graph encountered serious questions from the beginning.  It failed to reproduce two Northern Hemisphere climate episodes that were well documented in the literature, the Medieval Warm Period and The Little Ice Age.  Concerned about these discrepancies, [[Stephen McIntyre]] and [[Canada|Canadian]] economist Ross McKitrick attempted to reproduce the result and discovered a serious flaw in the statistical methods used to construct the hockey stick graph.  Because of this, the 4th Assessment Report of the IPCC included several different temperature reconstruction methods instead of favoring just one hypothesis.

One of the main pieces of evidence for anthropogenic global warming presented during the 3rd IPCC report was a temperature reconstruction done by climatologist [[Michael Mann]]. The resulting graph of the Northern Hemisphere temperature is shaped like a hockey stick, and it is used as evidence for the unusualness of the earth's temperature in the past few decades.   

 

While dramatic, the graph encountered serious questions from the beginning.  It failed to reproduce two Northern Hemisphere climate episodes that were well documented in the literature, the Medieval Warm Period and The Little Ice Age.  Concerned about these discrepancies, [[Stephen McIntyre]] and [[Canada|Canadian]] economist Ross McKitrick attempted to reproduce the result and discovered a serious flaw in the statistical methods used to construct the hockey stick graph.  Because of this, the 4th Assessment Report of the IPCC included several different temperature reconstruction methods instead of favoring just one hypothesis.

==Natural variability of the climate system==

==Natural variability of the climate system==