POLAR THAW: Global Warming in the Arctic and Antarctic (continued)
In the Arctic, even warmer.
Scientists have been estimating past temperatures from
cores in the Greenland ice cap, pollen layers in ancient lakes, and tree
ring coring. These records indicate that the current temperature is the
highest it has been in 400 years. As in Antarctica, the greatest temperature
changes occur during the winter months, which are as much as 6° C
warmer than they were 30 years ago.
Relying in part on recently declassified nuclear submarine
sonar measurements of the Arctic Ocean permanent sea ice, scientists believe
that since 1974 it has thinned from 9 feet to 6 feet and shrunk in area
by 14 percent. Overflight radar and laser measurements by NASA also found
that many of Greenland's outlet glaciers are thinning and discharging
into the Atlantic Ocean more rapidly. These changes may influence annual
weather cycles and an interconnected set of deep ocean "conveyors"
that drive the Gulf Stream and other currents.
A rise in Arctic temperatures may sound like good news
for some farmers and residents of northern latitudes, but overall its
effects are ominous. Forest fires and insect attacks are plaguing the
boreal forests that ring the Arctic, cover 11 percent of the planet's
surface and comprise one third of the world's forests. At the same time,
the boreal forest and its associated shrub population are starting to
migrate north, overtaking the native tundra. Glaciers in Alaska and elsewhere
are shrinking, and at the same time snowfall over much of the Arctic is
increasing. Permafrost is freezing less often in winter and thus thawing
more deeply in summer, damaging forests and manmade structures and allowing
rivers to erode vast areas along the Arctic Ocean shore.
These drastic changes are affecting native
species - and the people who call the Arctic their home. Polar bears
cannot reach their denning spots or their prey. Caribou's habitual feeding
locations are changing. Researchers can now measure changed and earlier
growth of tundra plants. Native Alaskans have reported adverse shifts
in ice and in the permafrost underlying their communities. Perhaps most
threatening, dying forests and thawing permafrost are beginning to pump
a huge flux of carbon dioxide into the atmosphere in a region that once
served as a carbon absorber. This feedback loop could combine with increased
open Arctic Ocean waters to escalate the rate of change.
Article © 2001 Gary Braasch (based in part on an
information sheet by Gary Braasch and Dr. Daniel Lashof of NRDC. Dr. Lashof
bears no responsibility for errors in this version.)
For sources of information for this article, please see
the References for World View of Global
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