[tt] PhysOrg: Greenland ice core analysis shows drastic climate change near end of last ice age

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Greenland ice core analysis shows drastic climate change near end of last 
ice age
http://www.physorg.com/printnews.php?newsid=133107932

Temperatures spiked 22 degrees F in just 50 years, researchers say
Information gleaned from a Greenland ice core by an international
science team shows that two huge Northern Hemisphere temperature
spikes prior to the close of the last ice age some 11,500 years ago
were tied to fundamental shifts in atmospheric circulation.
The ice core showed the Northern Hemisphere briefly emerged from the
last ice age some 14,700 years ago with a 22-degree-Fahrenheit spike
in just 50 years, then plunged back into icy conditions before
abruptly warming again about 11,700 years ago. Startlingly, the
Greenland ice core evidence showed that a massive "reorganization"
of atmospheric circulation in the Northern Hemisphere coincided with
each temperature spurt, with each reorganization taking just one or
two years, said the study authors.
The new findings are expected to help scientists improve existing
computer models for predicting future climate change as increasing
anthropogenic greenhouse gases in the atmosphere drive up Earth's
temperatures globally.
The team used changes in dust levels and stable water isotopes in
the annual ice layers of the two-mile-long Greenland ice core, which
was hauled from the massive ice sheet between 1998 to 2004, to chart
past temperature and precipitation swings. Their paper was published
in the June 19 issue of Science Express, the online version of Science.
The ice cores -- analyzed with powerful microscopes -- were drilled
as part of the North Greenland Ice Core Project led by project
leader Dorthe Dahl-Jensen of the Centre for Ice and Climate at the
Neils Bohr Institute of the University of Copenhagen. The study
included 17 co-investigators from Europe, one from Japan and two
from the United States -- Jim White and Trevor Popp from the
University of Colorado at Boulder.
"We have analyzed the transition from the last glacial period until
our present warm interglacial period, and the climate shifts are
happening suddenly, as if someone had pushed a button," said
Dahl-Jenson.
According to the researchers, the first abrupt warming period
beginning at 14,700 years ago lasted until about 12,900 years ago,
when deep-freeze conditions returned for about 1,200 years before
the onset of the second sharp warming event. The two events indicate
a speed in the natural climate change process never before seen in
ice cores, said White, director of CU-Boulder's Institute for Arctic
and Alpine Research.
"We are beginning to tease apart the sequence of abrupt climate
change," said White, whose work was funded by the National Science
Foundation's Office of Polar Programs. "Since such rapid climate
change would challenge even the most modern societies to
successfully adapt, knowing how these massive events start and
evolve is one of the most pressing climate questions we need to
answer."
Both dramatic warming events were preceded by decreasing Greenland
dust deposition, indicating higher tropical temperatures and
significantly more rain falling on the deserts of Asia at the time,
said White. The team believes the ancient tropical warming caused
large, rapid atmospheric changes at the equator, the intensification
of the Pacific monsoon, sea-ice loss in the north Atlantic Ocean and
more atmospheric heat and moisture over Greenland and much of the
rest of the Northern Hemisphere.
"Here we propose a series of events beginning in the lower latitudes
and leading to changes in the ocean and atmosphere that reveal for
the first time the anatomy of abrupt climate change," the authors
wrote. White likened the abrupt shift in the Northern Hemisphere
circulation pattern to shifts in the North American jet stream as it
steers storms around the continent.
"We know such events are in Earth's future, but we don't know when,"
said White. "One question is whether we can see the symptoms before
big problems occur. Until we answer these questions, we are speeding
blindly down a narrow road, hoping there are no curves ahead."
Each yearly record of ice can reveal past temperatures and
precipitation levels, the content of ancient atmospheres and even
evidence for the timing and magnitude of distant storms, fires and
volcanic eruptions, said White. The cores from the site -- located
roughly in the middle of Greenland at an elevation of about 9,850
feet -- are four-inch-diameter cylinders brought to the surface in
11.5-foot lengths, said White.

Source: University of Colorado at Boulder