During the same time period, glaciers in Alaska, in Patagonia and Antarctica proceeded steadily at well-established rates. The polar ice cap that lay over most of the Arctic Ocean during winter remained essentially unbroken. Snowcaps atop mountain ranges such as Europe's Alps and even Africa's Mount Kilimanjaro stood solid and predictable.

No more. In all these cases, things have begun changing and scientists are becoming more and more worried.

Global warming, despite mounting evidence, remains a contentious political issue, but this is one warming-related phenomenon that has become incontrovertible.

In some instances, the rate of glacial creep has increased up to eightfold. More worrisome, the change has occurred in a breathtakingly short time - since 2000.

This is phenomenal, said Waleed Abdalati, a senior research at NASA's Goddard Space Flight Center in Greenbelt, Md.

Abdalati and colleagues briefed reporters about their new findings at the American Geophysical Union's annual meeting.

Jakobshavn already was the world's fastest-moving glacier when its pace, during the last half of the 20th century, as about 4 miles (7 kilometers) per year. Now, latest satellite and airborne laser data show its flow has increased - over the last four years - to 10 miles (13 kilometers) per year.

Though less dramatic, similar significant changes have occurred in glaciers all over the world.

The ice-cap situation parallels the changes in the glaciers.

During the late 1990s, for three years in a row the perennial Arctic ice cover dropped to its lowest volumes in recorded history, according to Josefino Comiso, also a senior researcher at Goddard.

The phenomenon is worrisome because it is the type that can fall into a feedback mechanism. As more and more open water appears in the Arctic Ocean, it absorbs more solar heat, which carries over into the winter, leading to an earlier melt the following year and thinner ice during the winter.

In addition, most of the warming is taking place in the western Arctic, Comiso said.

For hundreds of years, explorers and entrepreneurs alike have dreamed about the advantages of a Northwest Passage through the Arctic Ocean that would allow a much-faster passage between Europe and Asia.

Even as recently as the late 1960s, the only possibility of making that passage - even during summer - was by using massive icebreaking ships.

Exxon even experimented with the Manhattan, an icebreaking supertanker that was supposed to carry oil from Alaska's North Slope to U.S. East Coast ports. After one voyage, the company mothballed the idea as uneconomical and potentially too dangerous.

Comiso said the Northwest Passage soon may be a reality during the summer.

The summer of 1998 was almost ice free, he said.

Perhaps the biggest source of worry is the western Antarctic, however.

There, according to Theodore Scambos, with the University of Colorado's National Snow and Ice Data Center in Boulder, a major portion of the western Antarctic ice shelf is showing signs of collapsing.

The shelf is already dumping about 60 cubic miles (250 cubic kilometers) of ice into the ocean each year, with only about 40 percent of that volume replaced by snow. Right now, Scambos said, along the Western Antarctic Peninsula, the glaciers are moving at rates three times to eight times faster than normal.

This acceleration - the phrase creeping at a glacial pace might have to be abandoned - is particularly disturbing.

When Arctic ice melts, it affects sea level only in a limited way because the ice already is floating in the ocean. There is some elevation because warmer temperatures cause the water's volume to expand slightly, but generally sea level remains stable regardless of what happens to Arctic sea ice.

Ice dumped into the oceans from glaciers is another story. In 2001, the Intergovernmental Panel on Climate Change estimated that sea-level rise in this century would average between 0.2 millimeters and 0.4 millimeters per year due to melting.

Over the past four years, however, the glacial acceleration is causing ocean levels to elevate by up to 2 millimeters per year - already several times greater than the IPCC estimate.

Abdalati noted the glaciers have been melting at this relatively furious pace for only a few years, so at this point it is not possible to predict what will happen. He cautioned, however, that where the data on the melting can be compared with long-term climate data, all of these changes seem to be accelerating.

Chief among such correlations, he said, are the links between ice-sheet melting and sea-level rise.

It is happening quicker than we thought - in some cases the responses have been within months, Abdalati said. The data clearly indicate previous estimates (of sea-level rise) are being outpaced.

The aim now, he said, is to increase understanding of the phenomena as quickly as possible and to place a high priority on the research.

Toward that end, he added, we'll hopefully refine (the estimates) in the coming years, but we've got a lot of people working on it.

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