Melting of Earth's Ice Cover Reaches New High
by Lisa Mastny
Worldwatch News Brief 00-02

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 (see data table below) 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.

The Earth's ice cover acts as a protective mirror, reflecting a large share of the sun's heat back into space and keeping the planet cool. Loss of the ice would not only affect the global climate, but would also raise sea levels and spark regional flooding, damaging property and endangering lives. Large-scale melting would also threaten key water supplies as well as alter the habitats of many of the world's plant and animal species.

Some of the most dramatic reports come from the polar regions, which are warming faster than the planet as a whole and 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.

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. Within the past decade, three ice shelves have fully disintegrated: the Wordie, the Larsen A, and the Prince Gustav. Two more, the Larsen B and the Wilkins, are in full retreat and are expected to break up soon, having lost more than one-seventh of their combined 21,000 square kilometers since late 1998-a loss the size of Rhode Island. Icebergs as big as Delaware have also broken off Antarctica in recent years, posing threats to open-water shipping.

Antarctica's vast land ice is also melting, although there is disagreement over how quickly. One study estimates that the Western Antarctic Ice Sheet (WAIS), the smaller of the continent's two ice sheets, has retreated at an average rate of 122 meters a year for the past 7,500 years-and is in no imminent danger of collapse. But other studies suggest that the sheet may break more abruptly if melting accelerates. They point to signs of past collapse, as well as to fast-moving ice streams within the sheet that could speed ice melt, as evidence of potential instability.

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 United States, as the influx of fresh water into the North Atlantic may disrupt ocean circulation patterns that enable the warm Gulf Stream to flow north.

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 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 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 collapse of the WAIS, an ice mass the size of Mexico, would raise sea levels by an estimated 6 meters-while melting of both Antarctic ice sheets would raise them nearly 70 meters. (Loss of the Arctic sea ice or of the floating Antarctic ice shelves would have no effect on sea level because these already displace water.)

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 the 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.

TABLE 1: SELECTED EXAMPLES OF ICE MELT AROUND THE WORLD

Arctic Sea Ice
Arctic Ocean
Has shrunk by 6 percent since 1978, with a 14 percent loss of thicker, year-round ice. Has thinned by 40 percent in less than 30 years.

Greenland Ice Sheet
Greenland
Has thinned by more than a meter a year on its southern and eastern edges since
1993.

Columbia Glacier
Alaska, United States
Has retreated nearly 13 kilometers since 1982. In 1999, retreat rate increased from 25 meters per day to 35 meters per day.

Glacier National Park
Rocky Mtns., United States
Since 1850, the number of glaciers has dropped from 150 to fewer than 50. Remaining glaciers could disappear completely in 30 years.

Antarctic Sea Ice
Southern Ocean
Ice to the west of the Antarctic Peninsula decreased by some 20 percent between 1973 and 1993, and continues to decline.

Pine Island Glacier
West Antarctica
Grounding line (where glacier hits ocean and floats) retreated 1.2 kilometers a year between 1992 and 1996. Ice thinned at a rate of 3.5 meters per year.

Larsen B Ice Shelf
Antarctic Peninsula
Calved a 200 km2 iceberg in early 1998. Lost an additional 1,714 km2 during the 1998-1999 season, and 300 km2 so far during the 1999-2000 season.

Tasman Glacier
New Zealand
Terminus has retreated 3 kilometers since 1971, and main front has retreated 1.5 kilometers since 1982. Has thinned by up to 200 meters on average since the 1971-82 period. Icebergs began to break off in 1991, accelerating the collapse.

Meren, Carstenz, and Northwall Firn Glaciers
Irian Jaya, Indonesia
Rate of retreat increased to 45 meters a year in 1995, up from only 30 meters a year in 1936. Glacial area shrank by some 84 percent between 1936 and 1995. Meren Glacier is now close to disappearing altogether.

Dokriani Bamak Glacier
Himalayas, India
Retreated by 20 meters in 1998, compared with an average retreat of 16.5 meters over the previous 5 years. Has retreated a total of 805 meters since 1990.

Duosuogang Peak
Ulan Ula Mtns., China
Glaciers have shrunk by some 60 percent since the early 1970s.

Tien Shan Mountains
Central Asia
Twenty-two percent of glacial ice volume has disappeared in the past 40 years.

Caucasus Mountains
Russia
Glacial volume has declined by 50 percent in the past century.

Alps
Western Europe
Glacial area 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.

Mt. Kenya
Kenya
Largest glacier has lost 92 percent of its mass since the late 1800s.

Speka Glacier
Uganda
Retreated by more than 150 meters between 1977 and 1990, compared with only 35-45 meters between 1958 and 1977.

Upsala Glacier
Argentina
Has retreated 60 meters a year on average over the last 60 years, and rate is accelerating.

Quelccaya Glacier
Andes, Peru
Rate of retreat increased to 30 meters a year in the 1990s, up from only 3 meters a year between the 1970s and 1990.

Sources available upon request. For additional examples go to
http://www.worldwatch.org/alerts/000306t.html

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