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Ancient
ice drilled from deep inside a glacier shows that the
past century has been the hottest period in 1,000 years
in the high Himalayan Mountains.
Researchers
said the new finding is yet another indication the Earth
is warming and supports other studies that show a rapid
melting of mountain ice fields is under way on three continents.
"We
think this is alarming," says Ellen Mosley-Thompson
of Ohio State University, the co-author of a study appearing
Friday in the journal Science.
Mosley-Thompson
is a member of a team, led by Lonnie G. Thompson of Ohio
State, that has analyzed ice cores from some of the most
remote mountains in the world. The new cores, cylindrical
specimens of ice, came from a glacier more than 20,000
feet high in the Himalayas.
"This
is the highest climate record ever retrieved," Thompson
said in a statement. "It clearly shows a serious
warming during the late 20th century, one that was caused,
at least in part, by human activity."
Herman
Zimmerman, director of the National Science Foundation's
earth sciences division, said the new studies "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," Zimmerman said. The
NSF sponsored the 1997 expedition that extracted the Himalayan
ice cores.
Mosley-Thompson
said the team has the ice cores record chemical clues
of the climatic conditions that existed when the ice was
deposited.
The
most recent core, from the Dasuopu Glacier on the flank
of the 26,293-foot Mt. Xixabangma, included ice that was
laid down more than 12,000 years ago.
An
analysis of the Dasuopu ice deposited during the last
1,000 years shows a dramatic trend of warming, Mosley-Thompson
said.
"The
last century has been warmer than the previous nine centuries,"
Mosley-Thompson said, while the last decade has been the
warmest period of all.
Other
studies, based largely on surface temperature readings,
have found a global average warming of almost one degree
over the last century, but the effect may be even more
dramatic in the world's mountains, she said.
"These
high elevation ice fields seem to be warming more strongly
than what you could call the global average," Mosley-Thompson
said.
She
said there has been a significant shrinkage of permanent
ice fields in Asia, South America and Africa that provide
a significant part of the flow in major rivers. Many such
rivers are in areas with monsoon weather patterns, where
there usually is little rain for six months of the year.
Ice melt from the rivers has become an increasingly important
source of water for cities and farms, Mosley-Thompson
said.
"For
these rivers to continue to flow year-round, they have
to be fed by ice in the high mountains," Mosley-Thompson
said. If the ice fields continue to shrink, she said,
"the question then is where will the river flow come
from during the dry season."
Mosley-Thompson
said the mountain warming effect seems to be worldwide.
"Everywhere we go, we get the same picture"
of shrinking ice fields and increasing high altitude warming,
she said.
In
northern Peru, there is a marked shrinkage of ice fields
in the Andes and a dry season reduction in flow of up
to 70 percent in the Rimac River which supplies water
to Lima, Mosley-Thompson said. In Africa, aerial photos
taken of Mt. Kilimanjaro and checked against 1912 maps
found a 75 percent loss of ice mass, she said.
There
are no records to give a historic comparison for the Mt.
Xixabangma ice fields, but she said that Indian scientists
have found rapid shrinkage of ice fields around nearby
Mt. Everest and tentative findings of a reduced dry season
flow in rivers draining the Tibetan plateau.
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