This column is provided as a public service by the Geophysical Institute, University of Alaska Fairbanks, in cooperation with the UAF research community. Ned Rozell is a science writer at the institute.

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At the top of Alaska’s panhandle, Malaspina Glacier spills from a funnel of rock in the St. Elias Mountains and spreads to form a huge pancake between the mountains and the sea. That pancake is as large as Rhode Island, but Malaspina is thinning fast.

Since the early 1970s, Malaspina and its main source of ice, Seward Glacier, have lost the snow and ice equivalent of about 15 cubic miles of water. To put that number in perspective, Craig Lingle of the Geophysical Institute says that’s roughly the amount of water Canada’s Mackenzie River pumps into the ocean during a month of spring breakup. The Mackenzie, Canada’s largest river system, drains an area almost the size of Mexico.

Lingle, a glaciologist, tallied up Malaspina and Seward glaciers’ ice loss by finding glacier heights on a USGS digital elevation model made from 1972, 1973, and 1976 air photos. He compared those with a 1995 satellite radar image and laser height measurements taken by Keith Echelmeyer, a glaciologist and pilot from the Geophysical Institute. Lingle found that in just over 20 years, melting has reduced the average thickness of Malaspina and Seward glaciers by about 60 feet.

Each time scientists measure Alaska’s large icefields, they find that glaciers are adding large amounts of fresh water to the ocean. In a UAF study, Gudfinna Adalgeirsdottir earned her master’s degree by determining that during the past 40 years, the Harding Icefield on the Kenai Peninsula has lost up to 85 feet of ice, the height of a five-story building.

All that melted ice drains into the sea, where it seems Alaska is doing more than its share of raising the level of the world’s oceans. The Intergovernmental Panel on Climate Change estimated that the meltwater from glaciers and small ice caps might account for one-fifth of the sea-level rise during the last century. Mark Meier, a glaciologist at the University of Colorado’s Institute of Arctic and Alpine Research, estimates that the largest portion of that may have come from mountain glaciers bordering the Gulf of Alaska.

Lingle said the ice lost by the Malaspina-Seward glacier system accounts for almost one half of one percent of global sea level rise during the past 20 years. That number seems small, but it’s impressive considering that Malaspina and Seward are just two of thousands of glaciers in Alaska.

Scientists haven’t yet tallied the volume loss of even bigger expanses of Alaska and Canada ice, such as the Bagley Icefield and Bering Glacier. When they do, Lingle suspects they’ll find more compelling evidence of global warming’s effect on Alaska glaciers.

Photo of Malaspina Glacier from the space shuttle:
http://zebu.uoregon.edu/earth/glacier.gif

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