The term "hockey stick" was given to this controversy by Jerry Mahlman, a climatologist who described a patter that is relatively flat to 1900 (the shaft) and then a sharp increase after 1900 that corresponds to the blade (see above) (Climate Legacy, 2004). This graph has been the key piece of evidence in views supported by the United Nations and IPCC regarding greenhouse gas emissions and environmental change.
Arguments against using the Hockey Stick as the only answer to climate claim that it is taken out of context when it comes to global climatic time. In addition, graphing the last 150 years causes, what some scientists say, is noisy data in which relatively minor changes appear to be over exaggerated because of the template of the graph. This, called small-amplitude variations, may be true from an empirical sense, but have little meaning statistically when dealing with macro-science like climate (Von Storch, et.al., 2004). In other words, we can change the actual interpretation of the shape of the graph by expanding or contracting the scale to represent either a small portion of a larger even (a), a medium portion of a century like event (B), or a macro, millennium event (C) and the "hockey stick" becomes shaped differently, and therefore interpreted differently as well. For example:
A) Small portion of the graph accentuating the rise in temperature:
B) Median view of graph over centuries:
C) Macro, or millennium view (stretched and exaggerated purposefully):
Thus, if we can imagine stretching this graph back 2-3 millennia, then the past 150 years would not appear as quite an anomaly, but rather likely a regular spike and valley pattern of climate warming and cooling periods.
The actual controversy over global warming and C02 emission impact on the environment is far more pronounced in the popular media, partially thanks to former Vice President Al Gore and his movie an Inconvenient Truth.
No scientific body disagrees that in recent decades temperatures have increased -- this is measurable. Where the disagreement lies, however, is the nature and seriousness of the data. Is this a small or large trend, and how sensitive is climate to human interference. This is no longer a scientific argument, but a geo-political one as well. Too, there will likely not be a definitive answer or proof anytime soon -- the number of complexities and millions upon millions of micro-effects that may influence climate foil even the most advanced computers. Predicting current weather is almost like chaos theory epitomized -- reconstructing past and future weather even more complex.
Figure 3 - Rising Global Temperatures for last 150 years
Figure 2 - C02 Emissions
Figure 4 - Hockey Stick Graph
See: "Al Gore's Climate Change film is propaganda." (September 28, 2007). The Telegraph.
Cited in: http://www.telegraph.co.uk/earth/earthnews/3308582/Al-Gores-climate-change-film-is-propaganda.html; "Al Gore's an Inconvenient Truth Can Be Shown to Schools." (October 2, 2007). The Telegraph. Cited in: http://www.telegraph.co.uk/earth/earthnews/3308930/Al-Gores-an-Inconvenient-Truth-can-be-shown-to-schools.html; Brahic, C. (October 12, 2007). "Al Gore's an Inconvenient Truth: unscientific?" TheNew Scientist. Cited in: http://www.newscientist.com/blog/environment/2007/10/al-gores-inconvenient-truth.html; "Gore Climate Film's Nine 'Errors.' (October 11, 2007). BBC News. Cited in: http://news.bbc.co.uk/2/hi/uk_news/education/7037671.stm