On June 29, after 5 years of drilling through the Greenland ice sheet, National Science Foundation-sponsored researchers extracted the world's deepest ice core, reaching 3052 feet, and they are about to hit rock bottom. The 5.2-inch-diameter core through the summit of the ice sheet, along with a European core completed last year 30 km away, is furnishing the longest, most detailed record available of the Northern Hemisphere's climate, reaching back about 250,000 years. Together, the cores are altering ideas about the very nature of the Earth's climate system.
The cores reveal a climate whose dynamism has startled researchers. “The biggest surprise so far is that climate changes much more rapidly and frequently than we ever believed before,” said Paul Mayewski, chief scientist for NSF's Greenland Ice Sheet Project. Patterns of climate stored in the ice show that climate changed substantially every few thousand years, until the end of the last ice age.