Evidence from the oldest layers of Antarctic ice ever collected suggests that the earth is not even halfway through the current warm era
NEW YORK – Despite the recent trend towards global warming, scientists have long wondered whether the earth is nearing another Ice Age, an end to the 12,000-year temperate spell in which civilisations arose.
Some have said such a transition is overdue, given that each of the three temperate intervals that immediately preceded the current one lasted only about 10,000 years.
But now, in an eagerly awaited study, a group of climate and ice experts say they have new evidence that the earth is not even halfway through the current warm era. The evidence comes from the oldest layers of Antarctic ice ever sampled.
Some scientists earlier proposed similar hypotheses, basing them on the current configuration of the earth’s orbit, which seems to set the metronome that ice ages dance to. Temperature patterns deciphered in sea-bottom sediments in recent years supported the theory.
But experts say the new ice data are by far the strongest corroborating evidence, revealing many similarities between today’s atmospheric and temperature patterns and those of a prolonged warm interval lasting 28,000 years, that reached its peak 430,000 years ago.
The findings were described yesterday in the journal, Nature, by the European Project for Ice Coring in Antarctica. The evidence comes from a shaft of ice extracted over five years from Antarctica’s deep-frozen innards.
The deepest ice retrieved so far comes from layers 3,040m deep and dates back 740,000 years. The relative abundance of certain forms of hydrogen in the ice reflects past air temperatures.
Many ice cores have been cut from glaciers and ice sheets around the world, but until now, none has reached back beyond 420,000 years, making this core the first to capture fully the conditions during that long-lasting warm period, called Termination V.
‘It’s very exciting to see ice that fell as snow three-quarters of a million years ago,’ said Dr Eric Wolff, an author of the paper and an ice core expert with the British Antarctic Survey.
Several independent researchers said the case that the current warm period would be prolonged was now strong, but pointed out that it was still based on a sketchy view of the climatic past.
Dr Gerard Bond, of the Lamont-Doherty Earth Observatory at Columbia University, said although the earth’s orbital characteristics were similar to those of 400,000 years ago, one match did not necessarily make a pattern.
Still, ocean and climate expert Jerry McManus, of the the Woods Hole Oceanographic Institution, wrote in Nature that the new ice core record was ‘spectacular’. It gave the first full view of conditions during a past warm interval that, in terms of the planet’s orbit and its atmospheric conditions, were most like the current one, he said.
He and the paper’s authors also noted that there was now a wild card that could cause the current era to stray from past patterns: the intensification of the earth’s insulating ‘greenhouse effect’ by smokestack and tailpipe emissions of carbon dioxide and other gases.
Many experts said the most important data from the new ice core were yet to come, as researchers had only just begun to analyse air bubbles trapped in the layers.
In the next six to 12 months, the European team is to decipher changes in the atmosphere over the full 740,000-year span. And more ice is still being extracted, which could take the record back an extra 100,000 years or more. \– The New York Times