Paleoclimatology

Paleoclimatology is a branch of science that deals with the study of climate change taken on the scale of the entire history of Earth. It uses records from following sources to determine the past state of the climate system on Earth.
Tree Rings
Glacial Ice Cores
Ocean Sediments – The ratio of oxygen 16 to oxygen 18 preserved in the steady rain of dead organisms.
Radiocarbon dates of organic material
Pollen samples found in packrat middens and lake bed samples.
Variations in desert varnish coatings found on rocks in the arid southwest
Variations found in peatbog deposits
Sedimentary rock records.