Paleoclimatologists employ a wide variety of techniques to deduce ancient climates.
Mountain glaciers and the polar ice caps/ice sheets provide much data in paleoclimatology.
Older wood not connected to a contemporary record can be dated generally with radiocarbon techniques.
Ice-coring projects in the ice caps of Greenland and Antarctica have yielded data going back several hundred thousand years, over 800,000 years in the case of the EPICA project.
Climatic information can be obtained through an understanding of changes in tree growth.
It uses a variety of proxy methods from the Earth and life sciences to obtain data previously preserved within things such as rocks, sediments, ice sheets, tree rings, corals, shells, and microfossils.
It then uses the records to determine the past states of the Earth's various climate regions and its atmospheric system.