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NSF PR 00-58 - September 14, 2000
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Himalayan Ice Reveals Climate Warming, Catastrophic
Ice cores drilled through a glacier more than four
miles up in the Himalayan Mountains have yielded a
highly detailed record of the last 1,000 years of
earth's climate in the high Tibetan Plateau. Based
on an analysis of the ice, both the last decade and
the last 50 years were the warmest in 1,000 years.
The core also showed a clear record of at least eight
major droughts caused by a failure of the South Asian
Monsoon, the worst of these a catastrophic seven-year-long
dry spell that cost the lives of more than 600,000
The new findings, published in this week's issue of
the journal Science, outline data recovered
from three cores drilled through the Dasuopu Glacier,
a two-kilometer-wide ice field that straddles a flat
area on the flank of Xixabangma, a 26,293-foot (8,014-meter)
peak on the southern rim of the Tibetan Plateau. The
international team, including American,Chinese, Peruvian,
Russian and Nepalese members, retrieved the cores
during a 10-week, 1997 expedition to the region. The
expedition was supported by the National Science Foundation.
"This is the highest climate record ever retrieved,"
explained Lonnie Thompson, professor of geological
sciences at Ohio State University and leader of the
expedition, "and it clearly shows a serious warming
during the late 20th Century, one that was caused,
at least in part, by human activity. This is a very
For the last 25 years, he and his colleagues have drilled
cores from glaciers and ice caps in some of the most
remote parts of the planet in an effort to recover
records of ancient climate. Most current predictions
of global climate change suggest that early signs
of warming will be seen at high elevations where these
ice caps exist. So far, Thompson's work has borne
"This work is a great achievement accomplished under
extremely adverse and hazardous conditions," says
Herman Zimmerman, director of NSF's earth sciences
division. "These investigations of the earth's past
climate leave little doubt that the earth is warming
and that all characteristics of our climate can change
rapidly. This is something that needs to be taken
quite seriously by all the peoples of the world."
Researchers at Ohio State's Byrd Polar Research Center
and the Chinese Lanzhou Institute of Glaciology and
Geocryology divided the three cores and were able
to identify annual layers for the last 557 years.
Samples from these layers were analyzed for dust concentrations,
chemical composition and oxygen- and hydrogen-isotope
The isotope ratios let researchers extrapolate the
air Temperatures present when the ice was formed.
Dust concentrations give an indication of dryness
or wetness in the region, and the analysis of chlorides,
sulfates and nitrates provide clues about volcanic
activity, fossil fuel burning and desertification.
"We now have a record from 23,500 feet in the atmosphere
(about as high as instruments are carried in a weather
balloon), one that has been preserved naturally, that
shows the last 50 years were warmer than any other
equivalent period in the last 1,000 years," Thompson
said.The real surprise came with the monsoon records
the core revealed.
The South Asian Monsoon is a major climate event that
cycles annually across India, Pakistan, the southern
Himalayan region, the Far East and reaches as far
west as Africa. In the summer, when the Eurasian continent
is warmed by solar radiation, prevailing winds flow
offshore, leaving the region moisture-poor so that
drying intensifies. In the winter, when the sun moves
south, the cycle reverses, and the prevailing winds
flow offshore, leaving the region moisture-poor and
during intensifies. Changes in the monsoon cycle can
bring catastrophic flooding or droughts.
The core data showed that in 1790, the cycle changed,
the rains lessened and drought took hold in the region,
a condition that continued for seven years until 1796
when the monsoons returned.
"That event was major," Thompson said. "It killed more
than 600,000 people in one region of India alone.
And that was at a time when global populations were
much less than they are today." (Estimates place the
world population in 1800 at 980 million.) "If a similar
event occurred today, the social and economic disruptions
would be horrendous," he said. Current world population
is just over 6 billion people.
The ice core record showed other serious monsoon failures
and ensuing droughts in 1876-77, and around 1640,
1590, 1530, 1330, 1280 and 1230,though none was as
devastating as the 1790 event. Thompson's paper offered
no indications of what might have triggered the monsoon
The data, however, do seem to point to the impact human
activities have had on changing climate in the region.
Core samples covering the last century reveal a four-fold
increase in dust trapped in the ice and a doubling
of chloride concentrations, suggesting an increase
in both drying and desertification in the region.
"There is no question in my mind," he said, "that the
warming is in part, if not totally, driven by human
activity. I think the evidence for that is so clear
- not only from this site but also from Kilimanjaro
in Africa." Thompson led an expedition to the ice
fields atop the highest mountain in Africa earlier
this year. At least 75 percent of the ice there has
disappeared since 1912, caused in part, he said, by