The glacier, one of the state's top tourist destinations, is one of the most obvious casualties of a trend confirmed by scientists at the University of Alaska Fairbanks last week.

They found that melting glaciers are responsible for at least 9 percent of the global sea-level rise over the past century.

Portage Glacier has been in gradual retreat since the early 1800s. But the U.S. Geological Survey, which studied the site in the early 1970s, could not forecast how quickly that retreat would occur.

"They made a really wild assessment that it would take until 2020 to recede out of sight," said Dave Blanchet, a Forest Service hydrologist.

In fact Portage Glacier disappeared from view of the visitors center in 1993, Blanchet said.

Now the glacier has retreated so far that only a small portion of it is in the lake, and there are far fewer icebergs calving into the water, he said. Erosion from the water is likely what sped up the glacier's shrinking, he added.

Mona Spargo, a Forest Service spokeswoman and lifelong Alaskan, said Portage Glacier's diminishment is obvious to residents such as herself.

"It's disappointing when you go there and you say, 'Oh man, remember what it used to be like?'"

Portage Glacier is not the only victim. The University of Alaska Fairbanks team flew over 67 glaciers and compared their readings to measurements taken by the U.S. Geological Survey in the 1950s.

Writing in the journal Science, they said the glaciers had lost, on average, more than half a meter a year in height, or more than a foot and a half.

The most dramatic change the team found was at Columbia Glacier in Prince William Sound, said Anthony Arendt, a graduate student who worked on the study. That glacier has been shrinking about 23 feet (7 metres) a year, he said.

Stan Stephens, a retired cruise ship captain from Valdez, said he has seen what the melting is doing to Columbia Glacier - putting huge chunks of glacial ice in the bay, many of them drifting into the area used by oil tankers.