Glaciers are large masses of ice that flow slowly downhill. A glacier grows wherever snow accumulates faster than it melts. It retreats—that is, its terminal edge, the end of the glacial tongue, ends at progressively higher elevations—whenever melting exceeds accumulation. Most of the world’s mountain (alpine) glaciers have been retreating since about 1850. Alpine glaciers have recently accelerated their retreat and large ice-sheet glaciers have been accelerating their flow to the sea along the coasts of Greenland and the West Antarctic Peninsula. Most cases of accelerated glacial retreat are probably a result of human-caused global climate change.
Historical Background and Scientific Foundations
About 75% of the world’s freshwater is in the form of 7.9 million cubic mi (33 million cubic km) of ice. A small fraction of this ice, about 0.55%, exists as alpine valley glaciers, ice fields, and the like. Most is located in the ice sheets of Antarctica (91%) and Greenland (7.9%). Ice sheets are large glaciers that form on the central regions of continent-size landmasses where water is transported by clouds and dropped in the form of snow. Ice sheets eventually get so deep—the average thickness of the Antarctic ice sheet is about 1.3 mi (2.1 km)—that the ice flows slowly under its own weight toward the edges of the landmass. There it feeds riverlike glaciers that slide down valleys to the sea. Hundreds of such glaciers feed water to the ocean around the coasts of Greenland and Antarctica, and account for most glacial flow on the planet.
At their terminal ends, glaciers may either melt directly, as most alpine glaciers do, or break up into icebergs that float off on the ocean. These, too, eventually melt. All glacial water eventually finds its way to the sea. A retreating glacier loses more water than it gains and so causes sea level to rise.
Glaciers have advanced and retreated over large areas of the Northern Hemisphere over geological time, their growth accompanying the cold periods termed glacials (or, more popularly, ice ages). Glacial retreat leaves boulders and masses of scraped-together rocky debris and soil called glacial moraines. Large temporary lakes of glacial meltwater may rupture, causing catastrophic floods and even shifting global climate by dumping freshwater into the oceans and so altering their circulation. Glacial scouring and retreat has produced the tens of thousands of lake basins that dot much of Northern Hemisphere (including those of the Great Lakes); south of the farthest extent of glacial coverage, natural lakes are relatively rare. Ancient sea levels have risen and fallen many yards/meters during glacial and interglacial (warmer) periods as Earth’s water was alternately locked up in glaciers and returned to the sea as meltwater.
The mass of a glacier is the amount of ice it contains; mass is added by accumulating snowfall and lost by evaporation and melting. Together, evaporation and melting are termed ablation. If accumulation is greater than ablation, the glacier advances (lengthens). If ablation is greater than accumulation, the glacier thins and eventually retreats (shortens). Long-term mass balance, the difference between accumulation and ablation, is determined by climate, that is, long-term average weather.
The alpine glaciers of the world have been in retreat since the mid-nineteenth century. Data going back to 1700 show that glacier tongues were stable until about 1850, and then began to shorten steadily in the European Alps, North America, Asia, and the Southern Hemisphere. Exceptionally, some glaciers in New
WORDS TO KNOW
ABLATION (GLACIAL): The erosive reduction of ice or snow from the surface of a mass of ice.
GLACIER: A large mass of ice slowly moving over a landmass, resulting from a multi-year surplus accumulation of snowfall in excess of snowmelt.
ICE SHEET: Glacial ice that covers at least 19,500 square mi (50,000 square km) of land and that flows in all directions, covering and obscuring the landscape below it.
MASS BALANCE (GLACIAL): The difference between the accumulation and ablation (reduction) of ice mass over a period of time.
Zealand and western Scandinavia (a small fraction of the global whole) advanced in the late 1990s.
The processes of accumulation and ablation are complex and differ from glacier to glacier, and between alpine glaciers and the ice sheets of Antarctica and Greenland. In general, accumulation has increased over glaciers and ice sheets worldwide in recent decades, including the interiors of Antarctica and Greenland. This is because global warming allows air to carry higher humidity, resulting in greater winter snowfall. However, ablation—mostly in the form of summer melting—has
grown even more than accumulation. This has resulted in net mass losses for alpine and ice-sheet glaciers.
In March 2008, the World Glacier Monitoring Service of the United Nations announced that the world’s alpine glaciers were melting faster than ever. In particular, the rate of retreat of 30 closely observed “reference glaciers” around the world had doubled from 2004–2005 to 2005–2006. The director of the group, according to a press release from the United Nations Environment Programme (UNEP), said that the latest figures were “part of what appears to be an accelerating trend with no apparent end in sight.” Several glaciers in the Himalayas and elsewhere could disappear completely within a few decades, if current melting trends continue.
Mass loss from Greenland and Antarctica has also accelerated. Sensitive satellite measurements of the altitude and gravitational attraction of the ice dome on Greenland have revealed that some of the largest glaciers funneling ice from the heartland to the sea more than doubled in speed in the early 2000s. These accelerations were partly due to the lubricating effect of water from melting surface ice, but a complete understanding of the acceleration of Greenland’s glaciers was not yet available in 2008. Greenland’s net mass loss doubled from 1996 to 2005, most likely, according to scientists, as a result of human-caused climate change.
Antarctica, too, was melting more rapidly in the early 2000s. In January 2008, a group of NASA and university researchers announced that ice loss from Antarctica had increased by 75% since 1996, from about 112 billion metric tons of ice per year to about 196 bil-
lion, despite increased snow accumulation in the center of the continent. Ice-sheet mass loss does not, as in the case of alpine glaciers, take the form of ice turning to water and flowing to the sea; rather, glaciers at the edge of the sheet speed up, dumping more water into the sea in the form of icebergs. British scientists announced in 2007 that over 300 glaciers on the West Antarctica Peninsula (which, along with the Arctic, has experienced about twice as much warming as the rest of world as a whole) had sped up by 12% from 1993 to 2003.
These observations surprised climatologists, forcing them to revise their earlier view that glaciers as large as the Antarctic and Greenland ice sheets will respond to climate changes only over 1,000 years or more. Rather, the ice sheets seem to be responding in mere decades.
Impacts and Issues
Glacial melting has two main impacts on the environment. First, melting of glacial ice raises sea level by increasing the amount of water in the oceans. Complete melting of the Greenland and West Antarctic ice sheets would raise global sea level between 16 and 33 ft (5 and 10 m), with massive consequences for coastal and island ecosystems and for many human settlements. Although this much melting would probably require several centuries, Greenland and Antarctica melting are each causing sea level to rise about 0.02 in (0.5 mm) per year. Sea level rose at about 0.13 inches (3.3 mm) per year for 1993–2003, partly as the result of increased ocean volume from glacial melting and partly from the expansion of warming seawater. Over 100 million people live no more than 3 ft (1 m) above sea level.
Also, over a billion people depend on meltwater from alpine glaciers for year-round drinking water supplies. Disappearance of many alpine glaciers in the Andes and Himalayas could be disastrous for these persons. Bolivia and Peru may face drinking-water shortages in the near future due to alpine glacial retreat; India and its neighbors, with their much larger populations, face an even larger crisis. Accelerated melting of the glaciers will first afflict downstream populations with increased flooding, then with water shortages as glacier-fed rivers dry up. However, a shortage of data on glacier-fed river flow makes it difficult to predict the timing and magnitude of such events.
Major scientific uncertainties linger about the mechanisms and future progress of glacial melting, especially with regard to the ice sheets of Greenland and Antarctica. In 2008, some research showed that dark soot (carbon) particles from burning fuel may be contributing as much to Himalayan glacial melting as global warming forced by greenhouse gases.
Primary Source Connection
The following article recognizes the concern within environmental and scientific communities for the speed at which the Aletsch Glacier, the largest in the Swiss Alps, is melting. If the fast-paced melting continues, the
IN CONTEXT: MOUNTAIN GLACIERS RETREATING
In early 2008, scientists with the United Nations Environment Programme announced that mountain glaciers were melting faster than ever as a result of global climate change. The rate of melting more than doubled from 2004–2005 to 2005–2006 at 30 closely monitored “reference glaciers” around the world. The melting rate for 2005–2006 was four times greater than that for 1980–1999. Globally, not all glaciers thinned during 2005–2006, but the overall trend was strongly toward accelerated melting. UN scientists warned that people who depend on glacial meltwaters for clean water might be seriously affected by the disappearance of glaciers within a few decades; for example, in India about 750 million people depend on glacial melt from the Himalayas. The report warned that all tropical glaciers, such as those in the Andes Mountains in South America, were likely to disappear in the next 15 years.
glacier could lose about 80% of its surface by 2100. The article acknowledges the consequences of such glaciers melting rapidly if the world’s climate continues to rise.
SWISS GLACIER RETREATS AT A RAPID CLIP
Viewed from atop this lookout in the Riederalp area northeast of Geneva, the Aletsch Glacier curves through a 2,000-meter- (1.2-mile) high valley like a massive freeway of packed ice—23 kilometers (14.2 miles) long, 900 meters deep. The Aletsch is the largest glacier in the Alps. If melted, it would provide a liter of water a day for every inhabitant of Earth for six years.
When Europeans or scientists at the recent global Live Earth program want a quick data point for global warming, the Aletsch provides an example—even if not as dramatic a one as the melt flows in Greenland or Antarctica.
“I call it the retreat of the glacier,” says Laudo Albrecht, a local director of Pronatura, an environmental group with 100,000 members in Switzerland.
The problem is not simply that the Aletsch is melting, scientists say. Glaciers have melted for 2,500 years in Europe; at one ice-age point, the Aletsch nearly covered local mountain peaks. What concerns scientists is the pace of the melt.
“Yes, it should retreat, but not so fast. The glacier is in rapid retreat, which is a fact and a clear sign of climate change,” Mr. Albrecht says.
In the past 30 years, studies show, the Aletsch has been losing 50 meters of length a year and is thinning. Some years show gains in length, others record losses. But the overall figure is one of shrinkage. Last year, it lost 115 meters—though in 2004 and 2005, the glacier gained about 50 meters per year.
“At this rate, by 2100 about 80 percent of the surface of the glacier will be gone,” says Ralph Logon, a Swiss geo-morphologist and expert on glaciers.
Mr. Logon notes that while glacial melting is a long-term concern, it does not receive the same attention in Swiss cantonal politics as immediate problems of floods, avalanches, and other crises.
Yet the implication of glacier and ice cap melts are being seized, dramatically, by federal Europe. On the eve of a European Commission Green Paper released June 26 (“Adapting to Climate Change in Europe—Options for EU Action”) EC President José Manuel Barroso visited the Greenland glacier of Sermeq Kujalleq in Ilulissat.
“Greenland is of major significance to the rest of the world in our struggle to halt climate change,” Mr. Barroso told reporters afterward. “The ice is melting faster than anybody predicted…. 50 kilometers of ice [a year]… three times more than the Alps.” Scientists argue that ocean levels could rise seven meters should Greenland’s ice melt entirely.
The commission’s report argues for dramatic prevention measures to combat the effects of a temperature rise. Within 40 years the effects of climate change could mean a need to “increase the height of dikes, [relocate] ports, industry, and entire cities and villages from low-lying coastal areas….”
Barroso says that the EC will push, at a UN climate summit in Bali this December, for a new treaty to replace the Kyoto Protocol, which ends in 2012.
- Glaciers in the Alps have lost more than 20 percent of their area since the mid-19th century.
- While the thickness changes have fluctuated, losses of more than 1 meter of thickness have occurred in the past 15 to 20 years.
- Glaciers of less than 100 meters are likely to disappear completely within the next 50 to 100 years, at this rate of change.
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