A new
ice age? Not soon, a 2-mile deep snow shows
By ANDREW C. REVKIN, NY Times News Service
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 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 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 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 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.” 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 megatelescope,” 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.”
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