Earth’s atmosphere, giving scientists a record of greenhouse gases that stretches back more than 650,000 years, and the chemical make-up of the ice provides clues to the average global temperature. From these and other records, scientists have built a record of Earth’s past climates, or “paleoclimates.” Paleoclimatology allowed scientists to show that climate changes in the past have been triggered by variations in Earth’s orbit, solar variation, volcanic eruptions, and greenhouse gases.