Guardian: The pioneering ‘hockey stick’ graph collected proxy temperature data from tree rings, lake sediments and ice cores It is a persuasive image. The “hockey stick” graph shows the average global temperature over the past 1,000 years. For the first 900 years there is little variation, like the shaft of an ice-hockey stick. Then, in the 20th century, comes a sharp rise like the stick’s blade. The graph was a pioneering attempt to put together data from hundreds of studies of past …