Mann model

The Mann model is from a climate change model led by Michael E. Mann, a climatologist now at Pennsylvania State University, that shows the link between CO₂ levels and world yearly mean temperatures. It estimates climate trends by stitching together a grab bag of evidence, including variations in ancient tree rings and temperatures measured in deep holes in the earth. It is one of several climate change graphs that has a "hockey stick" profile.

It has a statistical flaw, caused by some flaw with the tree ring cores from which the graph is derived. (Tree rings contain a record of which years were warm and which were cold, as evidenced by the annual growth of the tree, i.e. the thickness of the ring).

On June 22, 2006, the study was endorsed, with a few reservations, by a 12-member panel convened by the National Academies, the U.S.' pre-eminent scientific body.

In a 155-page report, the panel said "an array of evidence" supported the main thrust of the paper. Disputes over details, it said, reflected the normal intellectual clash that takes place as science tests new approaches to old questions.

The panel said that a statistical method used in the 1999 study was not the best and that some uncertainties in the work "have been underestimated," and it particularly challenged the authors' conclusion that the decade of the 1990s was probably the warmest in a millennium.

There are about a dozen other "hockey stick" models that are statistically valid that show essentially the same correlation between CO₂ levels and temperatures. Climate change skeptics have seized on this one flawed graph in an attempt to debunk climate change as a legitimate theory.

Nearly all scientists agree that climate change is real, is caused by human activity, and does have significant consequences, now and in the future.

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