One of the pillars on which the alarmist case for doing something about global warming rests is the contention that the 20th century was the warmest in the last thousand years. This proposition is most dramatically expressed in the "hockey stick" graph contained in the Intergovernmental Panel on Climate Change's third assessment report. The graph shows temperatures mostly flat for the last 1,000 years, before a sudden, sharp rise in the 20th century that, on a graph, looks like the blade of a hockey stick. The graph is very persuasive — it caused Sen. John McCain (R., Ariz.) to express...