Paleoclimatology encompasses a wide range of studies that examine earth’s climate in the past. Archaeologists use paleoclimatological data to help reconstruct ancient environments and to study human-environment interactions over long periods of time.
Because primary climatological data—such as temperature and precipitation records—were not accurately recorded until about 1880, researchers must rely on proxy evidence to reconstruct conditions in the distant past. Proxies include dendrochronological (tree-ring), palynological (pollen), and ice core data.
The National Oceanic and Atmospheric Administration website offers an excellent introduction to the science of paleoclimatology, including discussions of proxy records.
Understanding the Past to Predict the Future: NASA explains how reconstructions of past climate can help us understand climate change today.