Beyond the hockey stick

ON APRIL 22 (EARTH DAY) OF 1998, my co-authors and I published the now famous "hockey stick" curve. It was featured on the pages of the New York Times and other leading newspapers, helping it garner worldwide attention.

- MICHAEL E. MANN

Here was a simple graph, derived from sources of "proxy" climate data such as tree rings, ice cores, coral, and lake sediment, depicting the average temperature of the northern hemisphere over the past six centuries. It resembled an upturned hockey stick, with the "handle" corresponding to the relatively constant temperatures over the preindustrial era, and the "blade" corresponding to the dramatic subsequent warming that coincided with the Industrial Revolution. A year later, we extended the graph back 1,000 years, conveying clearly the unprecedented nature of the warming taking place today. That made it a threat to carbon polluters, and it was subject to a crescendo of attacks by fossil-fuel companies and those doing their bidding. The hockey stick has nonetheless stood up to the scrutiny; indeed, other scientists have even extended it back two millennia.