Fwd: Glaciers and Sea Ice Endangered by Rising Temperatures
- --- In Paleontology_and_Climate@yahoogroups.com, "Patrick Neuman"
January 22, 2004-1
2004 Earth Policy Institute
Glaciers and Sea Ice Endangered by Rising Temperatures
By 2020, the snows of Kilimanjaro may exist only in old photographs.
The glaciers in Montana's Glacier National Park could disappear by
2030. And by mid-century, the Arctic Sea may be completely ice-free
during summertime. As the earth's temperature has risen in recent
decades, the earth's ice cover has begun to melt. And that melting is
In both 2002 and 2003, the Northern Hemisphere registered record-low
sea ice cover. New satellite data show the Arctic region warming more
during the 1990s than during the 1980s, with Arctic Sea ice now
melting by up to 15 percent per decade. The long-sought Northwest
Passage, a dream of early explorers, could become our nightmare. The
loss of Arctic Sea ice could alter ocean circulation patterns and
trigger changes in global climate patterns.
On the opposite end of the globe, Southern Ocean sea ice floating
near Antarctica has shrunk by some 20 percent since 1950. This
unprecedented melting of sea ice corroborates records showing that
the regional air temperature has increased by 2.5 degrees Celsius
(4.5 degrees Fahrenheit) since 1950.
Antarctic ice shelves that existed for thousands of years are
crumbling. One of the world's largest icebergs, named B-15, that
measured near 10,000 square kilometers (4,000 square miles) or half
the size of New Jersey, calved off the Ross Ice Shelf in March 2000.
In May 2002, the shelf lost another section measuring 31 kilometers
(19 miles) wide and 200 kilometers (124 miles) long.
Elsewhere on Antarctica, the Larsen Ice Shelf has largely
disintegrated within the last decade, shrinking to 40 percent of its
previously stable size. Following the break-off of the Larsen A
section in 1995 and the collapse of Larsen B in early 2002, melting
of the nearby land-based glaciers that the ice shelves once supported
has more than doubled.
Unlike the melting of sea ice or the floating ice shelves along
coasts, the melting of ice on land raises sea level. Recent studies
showing the worldwide acceleration of glacier melting indicate that
the Intergovernmental Panel on Climate Change's estimate for sea
level rise this centuryranging from 0.1 meters to 0.9 meterswill
need to be revised upwards. (See table of selected examples of ice
melt from around the world.)
On Greenland, an ice-covered island three times the size of Texas,
once-stable glaciers are now melting at a quickening rate. The
Jakobshavn Glacier on the island's southwest coast, which is one of
the major drainage outlets from the interior ice sheet, is now
thinning four times faster than during most of the twentieth century.
Each year Greenland loses some 51 cubic kilometers of ice, enough to
annually raise sea level 0.13 millimeters. Were Greenland's entire
ice sheet to melt, global sea level could rise by a startling 7
meters (23 feet), inundating most of the world's coastal cities.
The Himalayas contain the world's third largest ice mass after
Antarctica and Greenland. Most Himalayan glaciers have been thinning
and retreating over the past 30 years, with losses accelerating to
alarming levels in the past decade. On Mount Everest, the glacier
that ended at the historic base camp of Edmund Hillary and Tenzing
Norgay, the first humans to reach the summit, has retreated 5
kilometers (3 miles) since their 1953 ascent. Glaciers in Bhutan are
retreating at an average rate of 3040 meters a year. A similar
situation is found in Nepal.
As the glaciers melt they are rapidly filling glacial lakes, creating
a flood risk. An international team of scientists has warned that
with current melt rates, at least 44 glacial lakes in the Himalayas
could burst their banks in as little as five years.
Glaciers themselves store vast quantities of water. More than half of
the world's population relies on water that originates in mountains,
coming from rainfall runoff or ice melt. In some areas glaciers help
sustain a constant water supply; in others, meltwater from glaciers
is a primary water source during the dry season. In the short term,
accelerated melting means that more water feeds rivers. Yet as
glaciers disappear, dry season river flow declines.
The Himalayan glaciers feed the seven major rivers of Asiathe
Ganges, Indus, Brahmaputra, Salween, Mekong, Yangtze, and Huang He
(Yellow)and thus contribute to the year-round water supply of a vast
population. In India alone, some 500 million people, including those
in New Delhi and Calcutta, depend on glacier meltwater that feeds
into the Ganges River system. Glaciers in Central Asia's Tien Shan
Mountains have shrunk by nearly 30 percent between 1955 and 1990. In
arid western China, shrinking glaciers account for at least 10
percent of freshwater supplies.
The largest aggregation of tropical glaciers is in the northern
Andes. The retreat of the Qori Kalis Glacier on the west side of the
Quelccaya Ice Cap that stretches across Peru has accelerated to 155
meters a year between 1998 and 2000three times faster than during
the previous three-year period. The entire ice cap could vanish over
the next two decades.
The Antizana Glacier, which provides Quito, Ecuador, with almost half
its water, has retreated more than 90 meters over the last eight
years. The Chacaltaya Glacier near La Paz, Bolivia, melted to 7
percent of its 1940s volume by 1998. It could disappear entirely by
the end of this decade, depriving the 1.5 million people in La Paz
and the nearby city of Alto of an important source of water and
Africa's glaciers are also disappearing. Across the continent,
mountain glaciers have shrunk to one third their size over the
twentieth century. On Tanzania's Kilimanjaro, ice cover has shrunk by
more than 33 percent since 1989. By 2020 it could be completely gone.
In Western Europe, glacial area has shrunk by up to 40 percent and
glacial volume by more than half since 1850. If temperatures continue
to rise at recent rates, major sections of glaciers covering the Alps
and the French and Spanish Pyrenees could be gone in the next few
decades. During the record-high temperature summer of 2003, some
Swiss glaciers retreated by an unprecedented 150 meters. The United
Nations Environment Programme is warning that for this region long
associated with ice and snow, warming temperatures signify the demise
of a popular ski industry, not to mention a cultural identity.
Boundaries around Banff, Yoho, and Jasper National Parks in the
Canadian Rockies cannot stop the melting of the glaciers there.
Glacier National Park in Montana has lost over two thirds of its
glaciers since 1850. If temperatures continue to rise, it may lose
the remainder by 2030.
In just the past 30 years, the average temperature in Alaska climbed
more than 3 degrees Celsius (5 degrees Fahrenheit)easily four times
the global increase. Glaciers in all of Alaska's 11 glaciated
mountain ranges are shrinking. Since the mid-1990s, Alaskan glaciers
have been thinning by 1.8 meters a year, more than three times as
fast as during the preceding 40 years.
The global average temperature has climbed by 0.6 degrees Celsius (1
degree Fahrenheit) in the past 25 years. Over this time period,
melting of sea ice and mountain glaciers has increased dramatically.
During this century, global temperature may rise between 1.4 and 5.8
degrees Celsius, and melting will accelerate further. Just how much
will depend in part on the energy policy choices made today.
Copyright © 2004 Earth Policy Institute
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