Earth's climate has undergone dramatic changes over the geologic timescale. At one extreme, Earth has been glaciated from the poles to the equator for periods that may have lasted millions of years. At another, temperatures were once so warm that the Canadian Arctic was heavily forested and large dinosaurs lived on Antarctica. Paleoclimatology is the study of such changes and their causes. At Princeton, we study Earth's long-term climate history, discovering vital clues about anthropogenic global warming and how climate is affected by human endeavor.