The
Earth’s ice cover is melting in more places and at higher rates
than at any time since record-keeping began. Reports from around the
world compiled by the Worldwatch Institute show that global ice-melting
accelerated during the 1990s—which was also the warmest decade
on record.
Scientists suspect that the enhanced melting is among the first observable
signs of human-induced global warming, caused by the unprecedented release
of carbon dioxide and other greenhouse gases over the past century.
Glaciers and other ice features are particularly sensitive to temperature
shifts.
Some of the most dramatic reports come from the polar regions, which
are warming faster than the planet as a whole and which have lost large
amounts of ice in recent decades. The Arctic sea ice, covering an area
roughly the size of the United States, shrunk by an estimated 6 percent
between 1978 and 1996, losing an average of 34,300 square kilometers—an
area larger than the Netherlands—each year.
Thinning Ice
The Arctic sea ice has also thinned dramatically since the 1960s
and 70s. Between this period and the mid-1990s, the average thickness
dropped from 3.1 meters to 1.8 meters—a decline of nearly 40 percent
in less than 30 years. The Arctic’s Greenland Ice Sheet—the
largest mass of land-based ice outside of Antarctica, with 8 percent
of the world’s ice—has thinned more than a meter per year
on average since 1993 along parts of its southern and eastern edges.
The massive Antarctic ice cover, which averages 2.3 kilometers in thickness
and represents some 91 percent of Earth’s ice, is also melting.
So far, most of the loss has occurred along the edges of the Antarctic
Peninsula, on the ice shelves that form when the land-based ice sheets
flow into the ocean and begin to float. Icebergs as big as Delaware
have also broken off Antarctica in recent years, posing threats to
open-water
shipping.
Outside the poles, most ice melt has occurred in mountain and subpolar
glaciers, which have responded much more rapidly to temperature changes.
As a whole, the world’s glaciers are now shrinking faster than
they are growing, and losses in 1997-98 were "extreme," according
to the World Glacier Monitoring Service. Scientists predict that up
to a quarter of global mountain glacier mass could disappear by 2050,
and up to one-half by 2100, leaving large patches only in Alaska, Patagonia
and the Himalayas. Within the next 35 years, the Himalayan glacial
area
alone is expected to shrink by one-fifth, to 100,000 square kilometers.
The disappearance of Earth’s ice cover would significantly alter
the global climate—though the net effects remain unknown. Ice,
particularly polar ice, reflects large amounts of solar energy back
into space, and helps keep the planet cool. When ice melts, however,
this exposes land and water surfaces that retain heat, leading to even
more melt and creating a feedback loop that accelerates the overall
warming process. But excessive ice melt in the Arctic could also have
a cooling effect in parts of Europe and the eastern U.S., as the influx
of fresh water into the North Atlantic may disrupt ocean circulation
patterns that enable the warm Gulf Stream to flow north.
Water Shortages and Massive Floods
As mountain glaciers shrink, large regions that rely on glacial
runoff for water supply could experience severe shortages. The Quelccaya
Ice Cap, the traditional water source for Lima, Peru, is now retreating
by some 30 meters a year—up from only 3 meters a year before 1990—posing
a threat of water shortage to the city’s 10 million residents.
And in northern India, a region already facing severe water scarcity,
an estimated 500 million people depend on the tributaries of the glacier-fed
Indus and Ganges rivers for irrigation and drinking water. But as the
Himalayas melt, these rivers are expected to initially swell and then
fall to dangerously low levels, particularly in summer. In 1999, the
Indus reached record high levels because of glacial melt.
Rapid glacial melting can also cause serious flood damage, particularly
in heavily populated regions such as the Himalayas. In Nepal, a glacial
lake burst in 1985, sending a 15-meter wall of water rushing 90 kilometers
down the mountains, drowning people and destroying houses. A second
lake near the country’s Imja Glacier has now grown to 50 hectares,
and is predicted to burst within the next five years, with similar
consequences.
Large-scale ice melt would also raise sea levels and flood coastal
areas, currently home to about half the world’s people. Over the past
century, melting in ice caps and mountain glaciers has contributed on
average about one-fifth of the estimated 10-25 centimeter (4-10 inch)
global sea level rise—with the rest caused by thermal expansion
of the ocean as the Earth has warmed. But ice melt’s share in sea
level rise is increasing, and will accelerate if the larger ice sheets
crumble. Antarctica alone is home to 70 percent of the planet’s
fresh water, and the collapse of the Western Antarctic Ice Sheet—an
ice mass the size of Mexico—would raise sea levels by an estimated
six meters, while the melting of both Antarctic ice sheets would raise
levels nearly 70 meters.
Wildlife is already suffering as a result of global ice melt, particularly
at the poles, where marine mammals, seabirds and other creatures depend
on food found at the ice edge. In northern Canada, reports of hunger
and weight loss among polar bears have been correlated with changes
in the ice cover. And in Antarctica, loss of sea ice together with rising
air temperatures and increased precipitation, is altering the habitats
as well as feeding and breeding patterns of penguins and seals.
Lisa Mastny is a researcher at the Worldwatch Institute, where
she writes about a wide range of environmental issues. Visit www.worldwatch.org
or call (202) 452-1999 for more information. This article is reprinted
with the kind permission of the author and the Worldwatch Institute.
Some Ice-cold Facts
*
Since 1850, the number of glaciers in the Glacier National Park in America’s
Rocky Mountains has dropped from 150 to fewer than 50. Those remaining
could disappear completely in the next 30 years.
* In India, the Dokriani Bamark Glacier in the Himalayas retreated 20
meters in 1998, and has retreated a total of 805 meters since 1990.
* The glacial area of the Alps in Western Europe has shrunk by 35 to
40 percent and volume has declined by more than 50 percent since 1850.
Glaciers could be reduced to only a small fraction of their present
mass within decades.
* At Mount Kenya in Africa, the largest glacier has lost 92 percent
of its mass since the late 1800s.
* The Columbia Glacier in Alaska has retreated nearly 13 kilometers
since 1982. Last year, the retreat rate increased from 25 to 35 meters
per day.
* In China, glaciers on the Duosuogang Peak in the Ulan Ula Mountains
have shrunk by some 60 percent since the early 1970s.
