Professor Michael Mann, the inventor of the Hockeystick temperature graph, had a contentious editorial essay in the January 17th issue of the New York Times. [The Hockeystick graph purports to show that temperatures of the last thousand years declined steadily — until the 20th century, when there was a sudden large rise.]

I am using the word “inventor” on purpose, since the Hockeystick is a manufactured item and does not correspond to well-established historic reality. It does not show the generally beneficial Medieval Warm Period (MWP) at around 1000AD, or the calamitous Little Ice Age (LIA) between about 1400 and 1800. In the absence of any thermometers during most of this period, the Hockeystick is based on an analysis of so-called proxy data, mostly tree rings, from before 1000AD to 1980, at which point the proxy temperature suddenly stops and a rapidly rising thermometer record is joined on.