July, 1998
In June analysts at the National Snow and Ice Data Center (NSIDC) in Boulder reported the abrupt disappearance of a 200 km2 section of ice sheet in Antarctica. The lost ice, part of the Larsen ice sheet on the Antarctic Peninsula, is a small portion of the West Antarctic Ice Sheet. But the loss could trigger the rapid break-up of larger ice sheets.
The ice chunk, about 20 km long and 5 km wide, disappeared during the
interval between two satellite images of
the area taken on February 26 and March 23 of 1998, in the relatively warm
late Antarctic summer. In the past several decades five large sections
of ice have disappeared abruptly, and analysts believe this recent event
will trigger a similar large ice disintegration during the coming Antarctic
warm season. Warming temperatures are widely blamed for recent and anticipated
reductions in the extent of ice around the continent.
The missing ice sheet lay between two land extensions on the edge of the Larsen B ice shelf (see satellite image above). Normally extensive ice floes surrounding the ice edge protect the shelf from ocean swells, whose motion can quickly break up ice--especially when melting has weakened the sheet. In recent decades floes of floating ice been absent more frequently and for longer periods than in the past. This exposure, together with warmer temperatures, may have caused the disintegration on the edge of the ice. This activity on the Larsen B ice shelf parallels events on the adjacent Larsen A ice shelf, which disintegrated in just a few weeks three years ago. A July report in the journal Nature indicates that the Larsen B sheet could disappear just as abruptly within the next couple of years.
Reasons for concern over the ice loss are three-fold. First the rapid
change suggests Antarctic ice may be less 
stable
and persistent than traditionally thought, and more vulnerable to rapid
change. Second, this event calls attention to recent scenarios for the
depletion of the much larger West Antarctic Ice Sheet. With edge ice depleted
there would be no obstacles blocking the outflow of the massive rivers
of ice that make up the continental ice sheet. The glaciers could flow
more quickly into the ocean, where they would melt. Although disintegration
of the entire West Antarctic Ice Sheet should take two hundred years or
more, it would raise global sea levels by as much as six meters (about
20 feet). Such a rise would flood many populated areas. Finally, glaciologists
note that the recent ice losses, and the possibility of more activity in
the coming Antarctic summer, reflect warming global temperatures. Further
ice disintegration in the next few years could be warnings of larger changes
in progress.
To read more, see
Environmental Science, A Global Concern,
Cunningham and Saigo, 5th ed.
Climate change and global warming: pages 375-80
Environmental Science, Enger and Smith,
6th ed.
Global warming: pages 360-64
For further information, see these related web sites:
News
reports from the National Snow and Ice Data Center
News
on global warming from the EPA
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