Proxy Data.

Developing an accurate temperature history before proper records were kept requires the use of various types of proxy data. Many records indicate that there has been more than one period in the past that was warmer than the current warm period.  Grafting proxy data onto the more accurate and recent instrumental record data is a contentious business. A survey below found 79 studies in which proxy data from various locations “show periods of at least 50 years during the past 1000 years which were warmer than any 50 years period of the 20th century.”

See Sallie Baliunas and Willie Soon, Lessons & Limits of Climate History: Was the 20th Century Unusual? George C. Marshall Institute, 2003, p. 13,

In the Third Assessment Report (2001), the Intergovernmental Panel on Climate Change (IPCC) presented what has become known as the hockey stick graph and gave much prominence to it. The graph was the basis for the IPCC’s statement that “the 1990s (likely) have been the warmest decade and 1998 the warmest year of the millennium.” [Note that 1998 was an El Nino year.  An El Nino is a huge weather system that occurs regularly and creates a warming trend for its duration.  La Nina is a huge weather system that creates a cooling trend for its duration and again occurs regularly.  2007/2008 is a La Nina period which is why it is expected that 2008 will be cooler than usual.]

A Canadian mathematician, Stephen McIntyre and a Canadian Economist, Ross McKitrick, have published three critiques of the hockey stick, two in Energy & Environment in 2003 and a third in Geophysical Research Letters in 2005.  The U.S. House Energy and Commerce Committee requested a study be undertaken to evaluate these criticisms and the subcommittee’s conclusions supported them.

See Implications for Climate Change Assessments,” House Energy and Commerce Subcommittee on Oversight and Investigations, July 20, 2006. http://energycommerce.house.gov/

See Testimony of Edward J. Wegman, “Questions Surrounding the ‘Hockey Stick’ Temperature Reconstruction: Implications for Climate Change Assessments,” House Energy and Commerce Subcommittee on Oversight and Investigations, July 20, 2006. http://energycommerce.house.gov/108/Hearings/07192006hearing1987/Wegman3108.htm.

Gore suggests that despite these criticisms it doesn’t matter because other scientists have confirmed their results. However as McIntyre and McKitrick have pointed out, and as the subcommittee report confirmed, those other scientists often work with the original authors, and tend to use the same datasets. Because of these connections and shared proxies, the other studies might not be as independent as they appear to be.

A detailed technical explanation and the criticisms of the hockey stick data can be found at Stephen McIntyre’s Web site, http://www.climateaudit.org

For a non-technical discussion, see Ross McKitrick, “What Is the Hockey Stick Debate About?” Paper presented to the Australian APEC Study Group, April 4, 2005.

In addition The National Research Council, after examining the hockey stick data and concluding that there were methodological errors in the "hockey stick" graph recommended that proxies sensitive to precipitation, such as the hockey stick ones, be avoided in temperature reconstructions. However, none of the reconstructions for the past millennium in the 4th Assessment report, of February 2nd 2007, observe the National Research Council recommendations.

See the Fraser Institute report: "Independent Summary for Policymakers. IPCC Fourth Assessment Report. Recent refutations of hockey stick millennial paleoclimatic methods and conclusions." p.36

That the hockey stick curve has been trashed raises some serious concerns about the integrity of the IPCC process since this was their prime evidence for human induced global warming. It is clear that the IPCC had time to address this issue in the 4th Assessment report and chose not to.