A THREE-KILOMETRE column of ice has been drilled from Antarctica by European scientists, shedding important new light on both the past and the future of the world’s climate.

The deepest ice core ever sunk, it would stretch from Nelson’s Column to Harrods if laid on end in Central London. The core has provided researchers with the oldest and most detailed record of climate change ever obtained, stretching back 740,000 years.

Analysis of the core has already suggested that the next ice age lies 15,000 years in the future. But the prospect of a stable climate has been thrown into doubt by human activity causing global warming. The ice also shows that today’s greenhouse gas concentrations in the atmosphere are by far the highest for at least 440,000 years.

Every time much smaller increases in greenhouse gas levels are recorded in the ice, a significant rise in global temperatures has followed. The findings offer further support for the scientific consensus that the Earth is facing potentially catastrophic global warming.

“The rate of increase (in greenhouse gases) is more than 100 times faster than any rate we can detect from the ice cores we have seen so far,” said Professor Thomas Stocker, of the University of Berne in Switzerland, a member of the European Project for Ice Coring in Antarctica.

Eric Wolff, of the British Antarctic Survey in Cambridge, another leader of the project, said: “We’re doing an experiment for which there is no analogue in hundreds of thousands of years of history. It’s a bit of a rollercoaster ride.”

Ice cores are among the most valuable sources of data on the world’s past climate as they record both variations in temperature and in concentrations of gases such as carbon dioxide and methane that contribute to the greenhouse effect. This is critical to establishing the cause of past warming and cooling trends, and to predicting the effects of rising greenhouse gas levels.

Cores from Greenland reach back more than 100,000 years through the last Ice Age, and a core from Lake Vostok in Antarctica dates back about 400,000 years. The new core drilled in Eastern Antarctica, however, will double this record when it is completed next year.

Some 740,000 years of data, from a core measuring 3.19km, are already available, and the results of the first analysis are published today in the journal Nature.

The new core confirms evidence from ocean sediments that the Earth has endured eight ice ages during this time, each separated by a warmer period known as an interglacial. While ice ages typically last about 100,000 years, the interglacials are much shorter at an average of 10,000 years.

But though the last Ice Age ended 12,000 years ago, scientists do not believe another is on the way. The interglacial most similar to our own, which began about 430,000 years ago, lasted for 28,000 years, suggesting that the current benign conditions will extend long into the future.

Dr Wolff said that the results dismissed arguments that global warming could benefit humanity by heading off a looming ice age. “If people say to you that increasing greenhouse gases is a good thing, because otherwise we’d go into an ice age, you can say categorically that we wouldn’t,” he said. “Left to nature’s own devices, we’d have another 15,000 years at least. Another ice age is not imminent.”

So far bubbles of air in the ice core have been examined for greenhouse gas concentrations for its first 440,000 years. These show levels of carbon dioxide hovering between 200 parts per million (ppm) during ice ages and 280ppm during interglacials. These small rises seem to be linked with the rising temperatures of the warmer periods.

Since the industrial revolution, however, carbon dioxide concentrations have risen to about 375ppm — a level that alarms scientists.

“In everything we have got up to now, temperature and greenhouse gases are absolutely in step with each other,” Dr Wolff said. “I don’t see any particular reason this shouldn’t continue into the future. It is worrying.”

The temperature data also show that interglacial periods before about 430,000 years ago did not get as warm as those that came later, though the scientists do not yet understand why. “There will be an explanation, but we don’t know what it is yet,” Professor Stocker said.

The ice core has taken eight years to drill, as average temperatures of -55C in the polar desert mean that work can take place only in the high Antarctic summer months of December and January.

The drilling is expected to strike bedrock next year. The project team is also drilling a core at Dronning Maud Land on the Atlantic side of Antarctica. Started in 2002, the second core should reach bedrock 2.76km deep in 2006.

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