ICE SHELF:
Section of an ice sheet that extends into the sea a
considerable distance and that may be partially afloat.
PERMAFROST:
Perennially frozen ground that occurs wherever the
temperature remains below 32°F (0°C) for several years.
THERMOHALINE CIRCULATION:
Large-scale circulation of the
world ocean that exchanges warm, low-density surface waters with
cooler, higher-density deep waters. Driven by differences in temperature
and saltiness (halinity) as well as, to a lesser degree, winds and tides.
Also termed meridional overturning circulation.
Global warming has had particularly strong effects on the polar regions,
warming the northern polar region (
the Arctic
) at about twice the rate of
the rest of the world. The situation in the south polar region (the
Antarctic) is more complex, with the West
Antarctic Peninsula
seeing as
much warming as
the Arctic
but the bulk of the continent seeing no
warming. Warming is already having dramatic impacts in the Arctic,
melting permafrost, shrinking summer sea-ice coverage to levels never
recorded before, changing the lifestyles of Arctic peoples, threatening
polar-bear populations, and accelerating the melting of the Greenland ice
sheet. The latter has possible effects on ocean circulation patterns that
shape climate worldwide, but especially in the Northern Hemisphere.
Historical Background and Scientific Foundations
The north polar region, the Arctic, has no clear geographic boundary but
is usually defined as the surface on the globe from the
North Pole
southward to the
Arctic Circle
, that is, the line of 66° 33' north latitude,
which slices through Alaska, Scandinavia, and the southern tip of
Greenland as it circles the world. The central Arctic is overlain by the
Arctic Ocean
, which is covered by a relatively thin layer of floating sea
ice, and surrounded by the northern coasts of Asia, Europe,
North
America
, and Greenland. The only large, open connection that the
Arctic
Ocean
has with the other oceans of the world is between Greenland and
Europe in the North Atlantic, making that region a key link in the global
system of ocean circulations. The largest mass of ice in the Arctic is the
Greenland ice cap, which is 1 mi (1.6 km) thick on average and contains
954,000 cubic mi (3.9 million cubic km) of ice, about 10% of the ice on
Earth— enough, were it all to melt, to raise
sea level
by at least 21 ft
(6.5 m).
The south polar region, the Antarctic, is geographically quite different,
with the continent of Antarctica centered on the pole and completely
surrounded by the Antarctic ocean. All of Antarctica but the tip of its
tail-like Western Peninsula is south of the
Antarctic Circle
, 66° 33' south
latitude. Antarctica is 98% covered by an ice sheet that is 2.5 mi (4 km)
thick on average and contains 7 million cubic mi (29 million cubic km)
of ice, 90% of the ice on Earth (and 70% of its freshwater)— enough,
were it all to melt, to raise
sea level
by about 200 ft (60 m).
Indigenous peoples
such as the Eskimos have lived in lower-latitude
Arctic areas for thousands of years, but never had any motive to
undertake the arduous journey to the Pole itself or to explore the interior
of the Greenland ice cap. No human beings visited Antarctica until the
mid-nineteenth century, and there has never been an indigenous
population on that continent. (Today, several hundred people occupy a
number of scientific research stations on the continent, none
permanently.)
In the twentieth and twenty-first centuries, the Greenland and Antarctic
ice caps have played a central role in climate science, since their layered
ice sheets— formed from hundreds of thousands of years of annual
snowfalls, compressed into ice and buried under later years' snows—
preserve samples of ancient air and, in the varying atomic weights of
their oxygen atoms, a record of air temperatures at the times their water
fell from the sky. Climate records for the Southern Hemisphere have
been pushed back 800,000 years from the present by deep ice cores from
Antarctica, with researchers hoping, as of early 2008, to obtain cores
going back 1.5 million years. In Greenland, climate records from ice
cores go back over 110,000 years.
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