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Record ice core gives fair forecast

As long as humans do not mess it up, the Earth's climate is set at fair for the next 15,000 years. That is according to information extracted from the oldest ice core ever drilled.

The Antarctic core is the first to reach as far back as a warm period with characteristics similar to our own interglacial. So it should help make more accurate predictions about when to expect the next deep freeze.

The ice core, drilled from a feature in central Antarctica called Dome C, is around 3 kilometres long and 10 centimetres wide. Changes in the relative proportions of hydrogen isotopes in the ice layers allow scientists to compile a complete record of Antarctic temperatures going back 740,000 years.

The core shows the waxing and waning of eight ice ages. Most critically for making predictions about our climate, it is the first core to record a period known as Termination V, around 430,000 years ago.

Warming pattern

At this point, the world moved from a glacial period into a long, warm interglacial, similar to this era. The previous longest ice-core record, drilled by the Soviet Union at Vostok in Antarctica between 1980 and 1988, went back only 420,000 years.

"All interglacials are slightly different, but we believe Termination V is the most similar to our own," says chief author of the new study, Eric Wolff, at the British Antarctic Survey in Cambridge, UK. It mirrors the pattern of solar warming between seasons and at different latitudes that are caused by fluctuations in the Earth's orbit known as the Milankovitch cycles.

It shows that the Termination V interglacial was unusually long, lasting 28,000 years. The current interglacial is now 12,000 years old, and some scientists feared that we might be heading for an ice age soon since at least one post-Termination V interglacial lasted just 10,000 years.

But the new findings suggest that even without the human hand in global warming, a new ice age would be unlikely for perhaps another 15,000 years, Wolff says.

Ice blanket

The core also sheds light on how ice ages have changed over the past million years. Since Termination V, ice ages have been very intense, with periods of cold weather that blanketed much of the northern hemisphere in ice for 80,000 years punctuated by short interglacials lasting typically 20,000 years.

But the new core shows that, prior to Termination V, the cold and warm periods of the glacial cycle each lasted around 50,000 years but were much less intense.

"Marine deposits suggested some of this, but it stands out much more clearly in the ice record," Wolff says.

Meanwhile, European and US scientists are discussing plans to survey for a site in Antarctica that will extend the record still further. "We want to go back at least 1.2 million years next time," Wolff says. "But we have to find somewhere that we can do it."

Journal reference: Nature (vol 429, p 623)



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