A quest to drill the oldest ice core in Antarctica is beginning

THE MID-PLEISTOCENE transition was a significant event in the history of Earth’s climate. It marks the point, between 1.2m and 900,000 years ago, when the ice-age cycle of freezing glacial periods alternating with warm interglacial ones (which began about 2.6m years before the present day) flipped from being 40,000 years long to 100,000 years. Climatologists would like to know why.The answer is important because, on past performance, the cycle should be about to turn cold again. Studies of post-transition cycles, though, suggest that one important regulator of what is happening is carbon dioxide, a greenhouse gas that people have been pumping into the atmosphere in unnatural quantities for a century or more. Understanding CO’s influence on climates gone by may help predict the details of its role in the future. Teams from Australia, China and Europe are therefore engaged in a friendly competition to gather samples of air that are as much as 1.5m years old. These they hope to find trapped in the lower layers of what will be the deepest ice cores drilled from the continent of Antarctica.