Climate Science and Paleoclimatology

Abstract

Although individual instrumental records from various places in North America and Europe are examined to determine trends, including the identification of the warmest and coldest years in the records, the main focus of this chapter is on proxy records. Proxy temperature records are constructed from tree ring, ice core and other paleoclimatic data using statistical methods that link the proxies to observed (instrumental) temperature data. The statistical methods are briefly discussed. Climate scientists use the proxy temperature reconstructions to show that global average temperatures remained constant for upwards of two millennia before rising dramatically beginning in the twentieth century – the temperature reconstructions effectively eliminate the Medieval Warm Period and the Little Ice Age or relegate them to local phenomena. This reconstruction became known as the hockey stick, with the long-run period of constant temperatures constituting the shaft and the recent dramatic upturn the blade of the stick. Along with a similar trend in the concentration of atmospheric carbon dioxide, the hockey stick is the key empirical evidence of global warming used by the IPCC. The criticism and defense of the hockey stick graph are discussed in detail, as are some of the other issues regarding the use of instrumental and proxy temperature reconstructions.