Drastic climate change near end of last ice age
Posted on Thursday, June 19, 2008 @ 23:23:36 UTC by vlad
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Greenland ice core analysis shows drastic climate change near end of last ice age
Caption: The North Greenland Ice Core Project camp. Credit: NGRIP
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
Via: http://www.physorg.com/news133107932.html
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