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

One of the glaciers, Kangerdlugssuaq, is currently moving about 9 miles a year compared to 3 miles a year in 2001, said Gordon Hamilton of the University of Maine's Climate Change Institute.

The other glacier, Helheim, is retreating at about 7 miles a year — up from 4 miles a year during the same period.

"It's quite a staggering rate of increase," Hamilton said at the American Geophysical Union annual meeting.

Glaciers play a major role in discharging water into oceans. Sea levels have swelled globally an estimated 4 inches to 8 inches during the past century due to melting glaciers and polar ice — enough to cause some places to be awash at high tide or during severe storms.

Melting of Greenland ice and calving of icebergs from glaciers is responsible for about 7 percent 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 9 miles since the 1980s. It is expected to lose an additional 9 miles in the next 15 to 20 years before the bed of the glacier rises above sea level.

The glacier, which moves about 80 feet a day, currently releases about 2 cubic miles 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.

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 3,000 feet thick, has thinned up to 1,300 feet in some places in the last two decades.