EXAMPLE hockey stick graph
"Hockey stick" is the popular name of the first graph trying to visualize the average temperature of northern hemisphere over the past millennium. The data visualized in the graph are based on numerous indirect indicators of past temperatures such as tree rings, ice cores, sea sediments… The hockey stick provided a compelling visual proof of the exceptional rise of global temperatures in industrial times. The hockey stick graph was first published in a paper by Michael Mann et al (1999), which was an extension of a 1998 study published in Nature. The graph became an important piece of evidence for proving global warming and was highlighted in the second chapter of the 2001 of the IPCC Working Group I.
Sub-controversies
Since its first publication and even more after appearing in the 3rd IPCC assessment report the hockey stick graph has been the object of climateskeptics critiques. Skepticks criticized both the proxies used to infer the data showed in the graph (particularly tree rings) and the statistical methods employed to compute such data. In the 2006 the controversy was closed by the American Academy of Science. Asked by US Congress to assess the validity of the hockey stick (among other climate data), the Academy stated that, although minor errors can be found in Mann methods, his conclusions are scientifically sound and “has subsequently been supported by an array of evidence that includes both additional large-scale surface temperature reconstructions and pronounced changes in a variety of local proxy indicators, such as melting on ice caps and the retreat of glaciers around the world".
Source: http://en.wikipedia.org/wiki/Hockey_stick_controversy
Resources
Document: The original paper by Michael Mann, Raymond Bradley and Malcolm Hughes
Document: Chapter 2: the Scientific Basis, IPCC Third Assessment Report (2001)
