How do ice cores reveal past climates?

Each year, snowfall in places like Antarctica and Greenland compacts into ice, preserving a layered record of the atmosphere. Tiny bubbles trapped in the ice contain ancient air, letting scientists measure past carbon dioxide, methane, and other gases directly. Dust, sea salt, ash, and chemical impurities provide clues about wind, aridity, ocean conditions, and volcanic eruptions. By counting layers and using chemistry, researchers can reconstruct climate changes over hundreds of thousands of years. Antarctic ice cores have provided records extending back roughly 800,000 years.