The fluctuations may portend global climate change, which could bear on everything from the level of the sea to the condition of the ski slopes, they said Monday at the annual meeting of the American Geophysical Union in San Francisco.
Until recently, Antarctica was thought to be retaining its icy stature, but new data from microwave satellite instruments sensing levels of snow, ice and frozen ground in the cold, remote region indicate it may not be impervious to global warming, researchers said.
"My study shows that a number of areas previously believed to be gaining mass in the Antarctic are in fact close to being balanced or even losing mass," said Eric Rignot, research scientist at the National Aeronautics and Space Administration's Jet Propulsion Laboratory in Pasadena, Calif.
The trend has been evident elsewhere for some time.
"The average reduction in the area of glaciers has been about 5 percent in the past 40 years," said Richard Armstrong, senior research scientist at the National Snow and Ice Data Center at the University of Colorado in Boulder.
"This amounts to about 90 cubic kilometers of fresh water lost to the oceans, and don't expect to see that again any time soon, at least not in the next 100,000 years or so ... When glaciers are gone, they're gone until the next ice age."
The area of ice covering the Arctic Sea has been decreasing by about 3 percent per decade since 1979, scientists said. Also, the thickness of the ice has been declining rapidly -- an average of 1.5 meters between the mid-1980s and early 1990s, Armstrong said.
"We attribute at least some of the thinning to changes in Arctic atmosphere and ice circulation patterns," Walter Tucker, research geophysicist at the Army Cold Regions Research and Engineering Laboratory in Hanover, N.H., told reporters. "While no similar trend was evident in ice thickness near the North Pole, the data unquestionably indicate a decrease in total ice volume in the western Arctic Ocean."
In 1986-1987, older, thicker ice comprised some 65 percent of the total ice cover; now it makes up less than 40 percent, having been replaced by a newer, thinner variety, he said in an interview.
"At low latitudes, glacial changes are pronounced, uncontested and solid evidence of climate warming," Rignot said. "But what is happening in the polar ice sheets is less clear."
Rapid changes in the little studied region of West Antarctica have been detected where the ice slips off the continent and begins to float and where it thins, speeding its flow, researchers said.
Between 1991 and 2001, the area's massive Pine Island, Thwaites and Smith glaciers thinned by more than 15, 25 and 45 meters, respectively, at points where they leave land for sea. In the process, they lost 157 cubic kilometers of ice to the ocean. If that rate is maintained, the glaciers could sever their land ties and begin to float within 150 years, said Andrew Shepherd, research fellow at The Centre for Polar Observation and Modeling at the University College London.
"We now know that the retreat of the Pine Island, Thwaites and Smith glaciers was due to a widespread thinning of ice that extended from their termini to over 200 kilometers inland," Shepherd told a news conference. "When the region is losing its mass to the ocean, the sea levels are affected. Our studies indicate this may be an accelerating process."
The new data, which will be presented at several sessions Tuesday through Thursday, focus on the shrinking state of the cryosphere, regions where water is found in its solid state, as snow or ice.
"The cryosphere is an integral part of the global climate system with important links and feedbacks generated through its influence on clouds, precipitation, hydrology and circulation of the atmosphere and the oceans," Armstrong said.
Earth's ice and snow exist relatively close to their melting points so with a slight change in temperature, they alter their state, from solid to liquid or back again. The cryosphere, therefore, serves as an important early and visually obvious indicator of global climate change, scientists told United Press International.
"In the world of climate change, trends are most readily observed in the Earth's cold regions, where the sensitivity of ice and snow to temperature changes serves as an early indicator of even relatively small differences," Armstrong said. "Today's receding and thinning sea ice, mountain glacier mass losses, decreasing snow extent, melting permafrost and rising sea level are all consistent with warming."
The international Intergovernmental Panel on Climate Change recently concluded summer temperatures during the past few decades were the warmest in at least 600 years, scientists said.
Earth has warmed by 0.5 degrees Celsius (1 degree Fahrenheit) over the past century, and more than half of that increase has taken place in the past 25 years, Armstrong said.
"As slight as that may seem, it's enough to make a difference."
The consequences could vary from the disappearance of small glaciers -- "imagine Glacier National Park without glaciers" -- to the downfall of the ski industry -- "places like (California ski resorts) Mammoth and Lake Tahoe exist at temperatures a few degree below freezing; a rise of a degree or two may be enough to mean there'll be rain every day instead of snow," Armstrong said in an interview.
Warming can also lead to reduced summer stream flows, accelerated growing seasons, earlier grazing opportunities as well as decreased water supplies, which would be especially critical in such areas as the American Northwest or the alpine countries of Europe, which rely heavily on hydropower, scientists said.
On a global scale, rising sea levels, expected to increase 54-fold over current levels, might go up by a meter in the next 100 years, leaving some South Pacific islands under water, they said.
"And that's under current trends, but our new evidence suggests it may rise even faster," Armstrong said.