Glaciers and sea ice speed the big melt

Posted: 2 February 2004

Author: Janet Larsen

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 accelerating.

During the last decade, the Arctic Ocean has seen more than a 40 per cent thinning of sea ice over a large area between Fram Strait and the North Pole. Scientists believe the thinning is a result of two causes. Rising air temperatures, possibly the consequence of global warming, are melting the ice from above. And warmer water is also rising from the depths to attack the ice from below.

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 per cent 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 unprecedentedmelting of sea ice corroborates records showing that the regional air temperature has increased by 2.5 degrees Celsius (4.5 degrees Fahrenheit) since 1950.

Greenland threat

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 kilometres (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 kilometres (19 miles) wide and 200 kilometres (124 miles) long.

Fractures in the Larsen B ice shelf©  P. Skvarca, Instituto Antártico Argentino and S. Tojeiro, Fuerza Aérea Argentina
Fractures in the Larsen B ice shelf© P. Skvarca, Instituto Antártico Argentino and S. Tojeiro, Fuerza Aérea Argentina
Fractures in the Larsen B ice shelf© P. Skvarca, Instituto Antártico Argentino and S. Tojeiro, Fuerza Aérea Argentina

Elsewhere on Antarctica, the Larsen Ice Shelf has largely disintegrated within the last decade, shrinking to 40 per cent of its previously stable size. Following the break-off of the Larsen A ection in 1995 and the collapse of Larsen B in early 2002, melting of the nearby land-based laciers 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 theworldwide acceleration of glacier melting indicate that the Intergovernmental Panel on Climate Change's estimate for sea level rise thiscentury - ranging from 0.1 metres to 0.9 metres - will need to be revised upwards. (See Earth Policy Update for 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 JakobshavnGlacier 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 kilometres of ice, enough to annually raise sea level 0.13 millimetres. Were Greenland's entire ice sheet to melt, global sea level could rise by a startling 7 metres (23 feet), inundating most of the world's coastal cities.

Glacial lakes

Glacier, Himalayas© DEP Kumar/UNEP/Topham
Glacier, Himalayas© DEP Kumar/UNEP/Topham
Glaciers are melting in the Himalayas© DEP Kumar/UNEP/Topham

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 thepast decade. On Mount Everest, the glacier that ended at the historic base camp of Edmund Hillary and Tenzing Norgay, the first humans to reach thesummit, has retreated 5 kilometers (3 miles) since their 1953 ascent.

Glaciers in Bhutan are retreating at an average rate of 30-40 metres 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.

Asian rivers

The Himalayan glaciers feed the seven major rivers of Asia--the 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 per cent between 1955 and 1990. In arid western China, shrinking glaciers account for at least 10 per cent 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 2000-three 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 metres over the last eight years. The Chacaltaya Glacier near La Paz, Bolivia, melted to 7 percent of its 1940svolume 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 animportant source of water and power.

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 per cent since 1989. By 2020 it could be completely gone.

Ski industry

Skiing on the Toggenburg pistes, Switzerland. Photo: Switzerland Tourism
Skiing on the Toggenburg pistes, Switzerland. Photo: Switzerland Tourism
Fun on the Toggenburg pistes, Eastern Switzerland/Liechtenstein. Global warming is threatening this celebrated winter sport, as snow fall decreases and glaciers melt.© Switzerland Tourism

In Western Europe, glacial area has shrunk by up to 40 per cent 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 metres. 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 rtemperature 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 areshrinking. Since the mid-1990s, Alaskan glaciers have been thinning by 1.8 metres 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.

Janet Larsen is a Research Associate at the Earth Policy Institute in Washington DC. Related links:Greenland's ice cap under threat (report by Dr David Whitehouse, BBC News Online science editor, 7th April 2004) Earth Policy InstituteThe earth in peril, scientists warn