http://www.ngdc.noaa.gov/paleo/

Paleoclimatology Branch page. Paleoclimatology is the study of past climate, for times prior to instrumental weather measurements. Paleoclimatologists use clues from natural "proxy" sources such as tree rings, ice cores, corals, and ocean and lake sediments to understand natural climate variability. NOAA Paleoclimatology operates the World Data Center for Paleoclimatology and the Applied Research Center for Paleoclimatology, with the goal to provide data and information scientists need to understand natural climate variability as well as future climate change.