Melting glaciers 'alarming'

2005-12-08 11:18

San Francisco - Two of Greenland's largest glaciers are retreating at an alarming pace, most likely because of climate warming, scientists said on Wednesday.

But researchers at the annual meeting of the American Geophysical Union also presented studies of the retreat of Alaska's Columbia Glacier that suggest more complexity in the processes of glacial melt.

One of the Greenland glaciers, Kangerdlugssuaq, is currently moving at about 15km a year compared to 5km a year in 2001, said Gordon Hamilton of the University of Maine's Climate Change Institute.

The other glacier, Helheim, is speeding at about 11km a year - up from 6.5km a year during the same period.

"It's quite a staggering rate of increase," Hamilton said during the AGU meeting.

Glaciers worldwide play a major role in discharging flowing water into oceans.

Sea levels have swelled globally an estimated 10cm to 20cm over the past century due to melting glaciers and polar ice - enough to cause some low-lying places to be awash at high tide or during severe storms.

Glaciers melting fast

Melting of Greenland ice and calving of icebergs from glaciers is responsible for about 7% of the annual rise in global sea level.

Global warming is frequently blamed for retreating glaciers around the world. The rapid retreat of Greenland glaciers suggest that climate change is a factor, Hamilton said.

Meanwhile, one of the fastest melting glaciers in North America has reached the halfway point of disintegration and will continue retreat for another two decades.

Alaska's Columbia Glacier - about the size of Los Angeles - has shrunk 15km since the 1980s. It is expected to lose an additional 15km in the next 15 to 20 years before the bed of the glacier rises above sea level.

The glacier, which moves about 24m a day, currently releases about 8.3 cubic kilometres of ice every year into the Prince William Sound on the south coast of Alaska.

Understanding what happens during Alaskan glacier retreat could help explain the phenomenon in Greenland, said Tad Pfeffer, associate director of the University of Colorado's Institute of Arctic and Alpine.

Slow warming trend

Pfeffer said climate change warming trends do not directly explain the shrinking Columbia Glacier and other tidewater glaciers. Instead, scientists think the retreat is triggered by a slow warming trend that began five centuries ago.

Significant thinning of the Columbia Glacier is thought to be caused by huge chunks of iceberg that break off into the sound as a result of seawater pressure rather than climate change, Pfeffer said.

The glacier, which is up to 915m thick, has thinned up to 390m in some places over the last two decades.

Since the 1970s, scientists have monitored the Columbia Glacier with satellites, lasers and aerial photography and found that the increase of its so-called calving rate might be dangerous to shipping lanes in the sound.

- AP