RETREAT OF GLACIERS DUE
TO GLOBAL WARMING
Climate change is already affecting ecosystems
in a number of ways:
• Reduction of arctic and antarctic regions
• Changes in rainfall patterns and climates
• Loss of species and habitat.
Retreat of glaciers since 1850
In historic times, glaciers grew during the Little
Ice Age, a cool period from about 1550 to 1850. Subsequently, until
about 1940, glaciers around the world retreated as climate warmed.
Glacier retreat declined and reversed, in many cases, from 1950
to 1980 as a slight global cooling occurred. Since 1980, glacier
retreat has become increasingly rapid and ubiquitous, so much so
that it has threatened the existence of many of the glaciers of
the world. This process has increased markedly since 1995.
STATE OF GLACIERS TODAY DUE TO GLOBAL WARMING
Excepting the ice caps and ice sheets of the Arctic
and Antarctic, the total surface area of glaciers worldwide has
decreased by 50% since the end of the 19th century. Currently glacier
retreat rates and mass balance losses have been increasing in the
Andes, Alps, Himalaya’s, Rocky Mountains and North Cascades. As
of March 2005, the snow cap that has covered the top of Mount Kilimanjaro
for the past 11,000 years since the last ice age has almost disappeared.
PROBLEMS CAUSED BY RETREAT OF GLACIERS
The loss of glaciers not only directly causes
landslides, flash floods and glacial lake overflow, but also increases
annual variation in water flows in rivers. Glacier runoff declines
in the summer as glaciers decrease in size, this decline is already
observable in several regions. Glaciers retain water on mountains
in high precipitation years, since the snow cover accumulating on
glaciers protects the ice from melting. In warmer and drier years,
glaciers offset the lower precipitation amounts with a higher meltwater
input.
Of particular importance are the Hindu Kush and
Himalayan glacial melts that comprise the principal dry-season water
source of many of the major rivers of the South, East and Southeast
Asian mainland. Increased melting would cause greater flow for several
decades, after which “some areas of the most populated regions on
Earth are likely to ‘run out of water’” as source glaciers are depleted.
The recession of mountain glaciers, notably in
Western North America, Franz-Josef Land, Asia, the Alps, Indonesia
and Africa, and tropical and sub-tropical regions of South America,
has been used to provide qualitative support to the rise in global
temperatures since the late 19th century. Many glaciers are being
lost to melting further raising concerns about future local water
resources in these glacierized areas. The Lewis Glacier, North Cascades
after melting away in 1990 is one of the 47 North Cascade glaciers
observed and all are retreating.
Of particular concern is the potential for failure
of the Hindu Kush and Himalayan glacial melts. The melt of these
glaciers is a large and reliable source of water for China, India,
and much of Asia, and these waters form a principal dry-season water
source. Increased melting would cause greater flow for several decades,
after which “some areas of the most populated region on Earth are
likely to literally run out of water.
arctic and antarctic glaciers
Despite their proximity and importance to human
populations, the mountain and valley glaciers of temperate latitudes
amount to a small fraction of glacial ice on the earth. About 99%
is in the great ice sheets of polar and subpolar Antarctica and
Greenland. These continuous continental-scale ice sheets, 3 km (1.8
miles) or more in thickness, cap the polar and subpolar land masses.
Like rivers flowing from an enormous lake, numerous outlet glaciers
transport ice from the margins of the ice sheet to the ocean.
Glacier retreat has been observed in these outlet
glaciers, resulting in an increase of the ice flow rate. In Greenland
the period since the year 2000 has brought retreat to several very
large glaciers that had long been stable. Three glaciers that have
been researched, Helheim, Jakobshavns and Kangerdlugssuaq Glaciers,
jointly drain more than 16% of the Greenland Ice Sheet. Satellite
images and aerial photographs from the 1950s and 1970s show that
the front of the glacier had remained in the same place for decades.
But in 2001 it began retreating rapidly, retreating 7.2 km (4.5
miles) between 2001 and 2005. It has also accelerated from 20 m
(65 ft)/day to 32 m (104 ft)/day.
Jakobshavn Isbræ in west Greenland is generally
considered the fastest moving glacier in the world. It had been
moving continuously at speeds of over 24 m (78 ft)/day with a stable
terminus since at least 1950. In 2002, the 12 km (7.5 mile) long
floating terminus entered a phase of rapid retreat. The ice front
started to break up and the floating terminus disintegrated accelerating
to a retreat rate of over 30 m (98 ft)/day. The acceleration rate
of retreat of Kangerdlugssuaq Glacier is even larger. Portions of
the main trunk that were flowing at 15 m (49 ft)/day in 1988-2001
were flowing at 40 m (131 ft)/day in summer 2005. The front of the
glacier has also retreated and has rapidly thinned by more than
100 m (328 ft).
Glacier retreat and acceleration is also apparent
on two important outlet glaciers of the West Antarctic Ice Sheet.
Pine Island Glacier, which flows into the Amundsen Sea thinned 3.5
± 0.9 m (11.5 ± 3 ft) per year and retreated five kilometers (3.1
miles) in 3.8 years. The terminus of the glacier is a floating ice
shelf and the point at which it is afloat is retreating 1.2 km/year.
This glacier drains a substantial portion of the West Antarctic
Ice Sheet and has been referred to as the weak underbelly of this
ice sheet. This same pattern of thinning is evident on the neighboring
Thwaites Glacier.
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