Overview of Paleoclimatology

Paleoclimatology is the study of how climate has changed during the entire history of the Earth.
In the past 150 years, humans started keeping records of weather changes using:

For millions of years, the Earth has been keeping its own records in the form of...
...tree rings
...ice layers
...sediment varves

By combining all this climate data, paleoclimatology can be used to understand how and why our climate changes and to predict future climate change.