Glacier melt rate a surprise

Ice in Southeast vanishing twice as fast as expected

//www.juneauempire.com/stories/080206/loc_20060802017.shtml

The glaciers of Southeast Alaska are shrinking twice as quickly as scientists had previously estimated, according to a new study.

The findings from Fairbanks and Juneau glaciologists are slated for publication in a leading scientific journal.

During a 52-year period, the Panhandle lost ice in 95 percent of its glacier-covered areas, said Roman Motyka, of Juneau, one of the study's co-authors.

The scientists participating in the study pinpointed the amount of ice loss by analyzing changes in the elevation of Southeast Alaska's glaciers between 1948 and 2000.

Their measurements show Southeast Alaska lost an average of roughly 14.6 cubic kilometers of ice per year during that time period.

A cubic kilometer roughly equates to 264 billion gallons of water - about a quarter more than Los Angeles consumes in one year, according to estimates by NASA.

"It's a pretty substantial loss of ice," Motyka said, noting the melting of Panhandle glaciers raised global sea levels by roughly 0.4 millimeters per year. In all of the years combined, Panhandle ice loss caused the world's oceans to rise roughly 2.4 millimeters, according to the study.

Scientists involved in the study said this week the Panhandle's ice reservoirs have retreated more drastically during the past couple of years.

The study's lead author, Chris Larsen, also of the Geophysical Institute, plans further measurements this month at Panhandle glaciers, ranging from Petersburg's Stikine Icefield to the St. Elias Mountain Range.

Scientists aren't the only ones noticing the wastage of most of the Panhandle's glaciers.

Juneau residents and tourists visit the retreating Mendenhall Glacier daily. Some of the most dramatic ice losses in the Panhandle are underway at lake-terminating glaciers, such as the Mendenhall, fed by the Juneau Icefield, according to the study.

"I just few over the Juneau Icefield three days ago. I was absolutely shocked by how dry and shrunken it looked," said Nick Jans, a Juneau author, on Tuesday.

Further to the south, the amount of ice loss at Tracy Arm's South Sawyer Glacier is "not even conceivable," said Juneau photographer Mark Kelley.

Kelley has photographed the glacier for the past 25 years and recently collaborated with Jans on a 40-page book about Tracy Arm's glaciers. In
2004, the South Sawyer Glacier retreated approximately one-half mile, clogging the water with icebergs.

"Just think about that volume. The glacier was 1,100 feet thick and a mile across," Kelley said.

Motyka is concerned a runaway process - initially triggered by climate warming but now controlled by glacial calving dynamics - may already be underway in Southeast Alaska.

More of the same could be in store for world's other coastal glaciers, he said.

"We have a lot of ice (in Southeast Alaska), but Greenland has more," Motyka said.

In Greenland, Motyka and other Geophysical Institute scientists are attempting to learn how dramatic loss of ice at the base of a large tidewater glacier, the Jakobshavn, is affecting the ice sheet at the top.

"I worry that these (tidewater) glaciers will bring down the ice sheet, no matter what happens with climate," Motyka said.

"If Greenland goes unstable, a lot more water will be going into the ocean. This could cause problems with ocean currents," Motyka explained.

The Panhandle study - now under review by third-party scientists - is the first to measure ice loss at all major Panhandle glaciers.

The study measured changes in glacial elevation at 74 individual glaciers. "It's total coverage," Larsen said.

A previous study, published in 2002, profiled ice loss at 12 glaciers in Southeast Alaska. When those results were extrapolated to the rest of the Panhandle, the result was a significant underestimate of regional ice loss, Motyka said.

The new study was enabled by a 2000 NASA Endeavour space shuttle project called the Shuttle Radar Topographic Mission. Among other duties, the shuttle mission produced a new three-dimensional radar map of Southeast Alaska.

Motyka and his colleagues collected the NASA maps and compared them to topographical maps and high-resolution photographs of Southeast Alaska dating back to 1948.

After final revision, a paper describing the Panhandle study will be published in the Journal of Geophysical Research.

Elizabeth Bluemink can be reached at elizabeth.bluemink@juneauempire.com

[foto] Brian Wallace / Juneau Empire A landmark in retreat: Tourists, above, look Tuesday at the Mendenhall Glacier, which has retreated about three quarters of a mile since the summer of 1982, shown below. The glacier partially covered Nugget Falls 24 years ago. A new study shows glaciers in Southeast Alaska are shrinking twice as fast as previously estimated.


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