Geology Reference
In-Depth Information
1
Introduction
1.1. Background
Other methods such as ice core analysis of ice caps and
ice shelves are also used. After all, snow is the messenger
of the sky and the environment.
Sea ice covers most of the oceanic surface of the pri-
mary cryospheric area of the global surface. The world of
sea ice encompasses the polar region, particularly the
Arctic basin and a belt around the continent of Antarctica.
Out of the 71% of Earth's surface that is covered by
ocean about 7%-15% is covered by sea ice at certain times
(more in the winter and less in the summer). That is
equivalent to 5%-10% of Earth's surface. Sea ice area in
the Arctic varies between a minimum of about 4 million
km 2 in September to a maximum of about 15 million km 2
in March. The corresponding figures for the Antarctic
are 3 million and 18 million km 2 in February and
September, respectively. Sea ice can develop very smooth
or very rough surfaces. It can be soft or hard, a bare sur-
face or snow covered, stagnant (fastened to the shoreline)
or mobile pack ice, and stiff and silent or crushing with
loud noise. It exhibits seasonal variations to which life in
the polar regions is closely adapted. In the Arctic region,
sea ice starts its growth in September/October and reaches
its maximum in March when it covers the entire Arctic
basin. This trend is reversed during the summer, and the
ice extent reaches its minimum in September. In the
Antarctic the annual fluctuations range between a mini-
mum in February to a maximum in September when ice
extends to latitudes between 55° and 65°S.
For a limited time during the summer months, certain
areas of the polar waters in the Arctic zone are used
extensively by ships (ice strengthened or escorted by ice-
breakers) where the floating bodies of new and old sea ice
and icebergs can prove hazardous. The expected reduc-
tion of sea ice extent, the reduction of the navigationally
hazardous old ice, and the increase in the duration of
summer melting season will certainly increase marine
Our world is divided into five regions according to the
position of the Sun throughout the year: a tropical region
around the equator, two temperate regions and two polar
regions. On two equinoxes, March 21 and September 23,
the Sun is directly overhead the equator and the Sun's
rays reach both the North and the South Poles. On June
21 (the summer solstice), the Sun is directly overhead the
Tropic of Cancer (about 23.5°N) in the northern temper-
ate region, and on December 22 (the winter solstice) it is
positioned directly overhead the Tropic of Capricorn
(about 23.5°S) in the southern temperate region. In the
two polar regions, mostly relevant to the material in this
topic, the Sun never sets in their summer and never rises
in their winter. The Arctic region (or zone) containing
the north polar region with latitudes greater than “about”
66.6°N and the Antarctic region (or zone) containing the
south polar region having latitudes greater than “about”
66.6°S are the primary cryospheric regions of the world.
Although the latitudes of the Arctic and the Antarctic
circles depend on Earth's axial tilt, which fluctuates
slightly with time (about 2° over a 40,000 year period),
the variations in the boundaries of the polar region are
very small and negligible. The secondary cryospheric
regions are the Alps, Andes, Himalaya, Rockies, etc.
Among the secondary cryospheric regions, the Himalayan
belt covers and affects the largest effective area of human
habitation.
Climate change has been affecting all the cryospheric
regions of the world, and the effects can be directly
observed and quantified using air‐ and space‐borne
remote sensing as well as land‐based instruments.
Remotely sensed images of the land‐ and ocean‐based
snow and ice information are paramount in understand-
ing the state of health of Earth for sustainability of life.
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