Climate researchers need records from far back in Earth's history to understand how the climate works and predict how it might change in the future. Systematic weather records using instruments such as thermometers and rain gauges didn't begin until the mid-19th century. Prehistoric ice is one of the few places scientists can find clues to climate changes over a much longer span of time.

Ice cores are samples drilled from glaciers with augers-- hollow shaft drills. The auger drills through the ice all the way to the bottom of the glacier. The ice is removed as cylinders -- or cores -- and is sent to laboratories to be stored in freezers and studied.

On the cores the ice nearest the surface shows visible layers that can be counted like tree rings. Ice from further down is compressed by the tremendous pressure and does not have visible layers. Trapped within the ice are bubbles of air -- samples of the atmosphere when the ice was formed. Scientists melt ice from different depths of a glacier to determine how the atmosphere has changed over time. They have learned how to estimate the temperature of the Earth's surface when ice was formed. Precipitation can be determined by measuring the thickness of layers, and drought by looking at how much dust is in the ice. Volcanic ash gives hints to past volcanic activity.

Two deep cores were drilled in Greenland in the early 90s. Evidence from these cores suggests that Earth sometimes undergoes dramatic climate swings of 10 or more degrees Fahrenheit in a period of just several years, possibly in a single year.

	Copenhagen Ice Core Lab One major ice core research facility is located in Copenhagen. Take a tour through the freezers of these labs to see how miles of ice core samples are stored.