Climate Change Series Mapping climate history and predicting future change means using evidence from a wide range of sources. One of the most important is geology, which can provide data going back hundreds of millions of years – from the “snowball earth” phases when the planet was almost entirely covered with ice, to hot periods when there was no permanent ice at all.
Particularly useful evidence comes from the “ice cores” that are drilled from deep within glaciers and the permanent ice sheets that cover Greenland and the Antarctic. The oldest sample taken so far originated in snow that fell on Antarctica 800,000 years ago. The composition of ice and air bubbles trapped inside reveal much about atmospheric conditions at the time.
