Geophys. Res. Lett. http://doi.org/jw9 (2012)

Credit: © ISTOCKPHOTO/THINKSTOCK

The global surface temperature timeseries — which is thermometer based — provides key evidence for global warming. However, uncertainties associated with this record are large, and it also suffers from limitations in temporal and spatial coverage.

A new Paleo Index has been compiled by David Morrill Anderson, of the National Ocean and Atmospheric Administration's National Climate Data Center, USA, and colleagues. The index was derived from 173 temperature-sensitive proxy timeseries including: corals, ice cores, speleothems (mineral deposits in caves), lake and ocean sediments and historical documents. It extends back to 1730, with a global distribution. The Index shows a significant upward trend for 1880–1995, as well as accelerated warming after 1980.

Comparing the Paleo Index with global surface temperature shows similar small-scale trends, providing independent evidence of the warming observed. These findings support the thermometer data, increasing confidence in the accuracy of the global surface temperature timeseries.