Temperature proxy data from the past 1000 years was needed to construct the 'hockeystick" curve. Actual temperature measurements could not be made during much of this time simply because the thermometer wasn't invented until 1709. Such thermometers were not widely used for decades and the concept of heat was unknown (Fourier provided the Laws of Heat Transfer much later) so that actual climate temperature data did not systematically begin for another 200 years. Thus proxies such as core samples and tree rings were used.

     What McKitrick and McIntyre have found in their hockeystick analysis is shattering and profound. It destroys the credibility and integrity of the IPCC, the editors of Nature magazine, and the 2500 hundred or so members of a so-called consensus of climate experts. M&M have once again shown that consensus is not science.