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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