In the mid 1990s scientists realized that the two previous deep ice cores did not contain the record of climate before the beginning of the last ice age. Glacier ice, although it seems very solid, actually flows downhill under the crushing pressure of the upper layers. If a drill site is not chosen properly, the core will contain ice that flowed in from somewhere else, making it impossible to determine the date when the ice was formed. That's what happened with the two prior deep cores, drilled in the 1990s. Researchers now say some quirk of the land below these drill sites must have mixed up the glacier layers at the very bottom.

Lead scientist at the NGRIP station discusses life there and the importance of ice core research.

The perfect spot for an ice core would be above a flat plane or the summit of a broad mountain, as ice in such places flows equally away in all directions, thinning the layers, but not contaminating them with material from elsewhere. The location of the North Greenland Ice Core Project, lead by Danish scientists, was chosen for these characteristics. The goal is to obtain climate records for 20,000 or 30,000 years further back in time than any previous core in the Northern Hemisphere. This period of time includes part of Earth's last warm period (called an interglacial) and the transition from warm period to the most recent ice age (called a glacial).

This transition is of considerable interest because today Earth is poised to enter a glacial period after about 11,000 warm years in an interglacial. From earlier cores, scientists have shown that the transition from glacial to interglacial is a rocky one. The climate seems to "flicker" uncertainly as if it can't decide whether to remain in a glacial or an interglacial state.

Studies of previous ice cores show that during the last such transition, there were instances where the gradually warming climate all of a sudden descended 10 to 15 degrees Fahrenheit back to ice-age conditions in a space of a decade or less. Then the temperature shot back up, in a warming of equal abruptness. Sigfus Johnsen, one of the leaders of the NGRIP project, says it is essential that scientists determine whether Earth does the same thing when going from interglacial to glacial. He says it did in the past, and if it does so again when Earth next descends to glacial conditions, "we're in big trouble."

	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.