A New Ice Age? None Soon, Snow 2 Miles Deep Implies

June 10, 2004


Despite the recent trend toward 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 modern civilizations 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 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 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, with a duration of 28,000 years, that reached its peak 430,000 years ago.

The findings are described today in the journal Nature by the European Project for Ice Coring in Antarctica.

The evidence comes from a shaft of ice extracted over five grueling years from Antarctica's deep-frozen innards, composed of thousands of ice layers that were formed as each year's snowfall was compressed over time.

The deepest ice retrieved so far comes from layers 10,000 feet 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 various glaciers and ice sheets around the world, but until now none have 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 W. Wolff, an author of the paper who is an ice core expert with the British Antarctic Survey.

Several independent researchers familiar with the project said the case that the current warm period would be prolonged was now strong. Yet even with this new evidence, they said, it is based on a sketchy view of the climatic past.

One expert, Dr. Gerard C. Bond of the Lamont-Doherty Earth Observatory of Columbia University, said that even though earth's orbital characteristics were similar to those of 400,000 years ago, and even though sea and ice records showed similar temperatures, one match did not necessarily make a pattern.

Still, Dr. Jerry F. McManus of the the Woods Hole Oceanographic Institution, an expert on oceans and past climates, wrote a commentary for Nature in which he described the new ice core record as "spectacular."

Dr. McManus said it was particularly important because it gave the first full view of conditions during a past warm interval that, in terms of both the planet's orbit and its atmospheric conditions, was most like the current one.

He and the paper's authors also noted that there was a wild card now that could cause the current era to stray from past patterns: the intensification of earth's natural 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, because the researchers had only just begun to analyze air bubbles trapped when the various layers formed. The bubbles are an archive of past atmospheric conditions that can show how greenhouse gases and temperatures varied long before humans were an influence.

Dr. Richard B. Alley, an ice core expert at Pennsylvania State University not affiliated with the project, called it "a triumph of brilliant persistence" in the face of broken drills and temperatures of 60 below zero at the drilling site, which is hundreds of miles from the nearest permanent research hub.

"The current publication is something akin to the first run on a new accelerator or the first look at a galaxy through the latest mega-telescope," Dr. Alley wrote in an e-mail message. "The results are clearly of value in and of themselves, but are even more exciting for what they promise in the future."