The Value of Multiple Proxies

Direct measurements of climate data such as temperatures are rare before the 20th century. Climate reconstructions for earlier centuries and millenia rely on a range of different climate indicators or proxies. In his Perspective, Mann1 explains how these proxies can be used in multiproxy climate reconstructions to obtaina reliable record of climatic variations over the last millenium. 1: http://www.sciencemag.org/cgi/content/full/297/5586/1481