The thermometer-based global surface temperature time series (GST) commands a prominent role in the evidence for global warming, yet this record has considerable uncertainty. An independent record, longer and with better geographic coverage, would be valuable in understanding recent change in the context of natural variability. We compiled the paleo index from 170 temperature-sensitive proxy time series (corals, ice cores, speleothems, lake and ocean sediments, historical documents). Each series was normalized to produce index values of change relative to a 1901-2000 base period; the index values were then averaged. From 1880 to 1995, the index trends significantly upward, similar to the GST. Smaller-scale aspects of the GST including two warming trends and a warm interval during the 1940s are also observed in the paleo index. The paleo index continuously extends back to 1730 with 66 records. The upward trend appears to begin in the early 19th century but the year-to-year variability is large and the 1730-1929 trend is not significant at the p<0.05 level. In addition to its value in vetting the thermometer-based record, our approach shows the potential of the un-calibrated paleo archive in understanding environmental change; this approach can be applied to aspects of environmental change where the instrumental record is even shorter (ocean pH, sea ice, hydrologic extremes).
The significant positive (warming) trend is widespread, found in Arctic, sub-polar, temperate, and tropical sites....Therefore, the distribution of the paleo sites supports the global extent of warming observed in the instrumental record.
Thus, using only temperature-sensitive paleo proxy records un-calibrated to instrumental data, it is possible to conclude that the warming trend in the GST is supported by independent evidence.
Edited by Br Cornelius, 13 January 2013 - 12:26 AM.