Environmental recorders have been developed to estimate past climate conditions and thus extend our understanding far beyond the 150-year instrumental record of climate change. Annual records of climate have been preserved in tree rings, locked in the skeletons of tropical coral reefs, extracted as ice cores records that have been frozen into glaciers and ice caps, and buried in laminated sediments from lakes and the ocean. Referred to as "proxies," these sources of climate information are calibrated and tested using the 150-year instrumental record of climate change.

What is paleoclimatology?

Paleoclimatology is the study of past climate prior to the existence of instrumental records. NOAA is particularly interested in the climate of the last few thousand years because it helps establish the range of natural climatic variability in a period prior to global-scale human influences on climate. Paleo "proxies" such as tree rings, coral reefs, ice cores, and sediments allow us to reconstruct past climate patterns without thermometers or rain gauges.

What do different paleo proxies tell us about climate variability?

Tree Rings
Trees record information about past environments and climate in their annual growth rings. Dendrochronologists study tree rings to gather records of past temperature and drought.

Corals
Corals build calcium carbonate skeletons over many years and are sensitive to water temperatures and other environmental factors. Their skeletons record annual information on past climate and ocean circulation.

Ice Cores
Scientists travel to the far reaches of the earth to collect data embedded in ice cores. Important ice caps that reveal past climate patterns are found in Greenland, Tibet, the Andes and Antarctica.

Paleoclimatic data sources also include packrat middens, pollen, ocean and lake sediments, speleothems, geomorphic features and historical sources including diaries and journals.