From January 31 to March, 2002, scientists in airplanes, on research ships, and in front of NASA satellite imaging screens watched in amazement as the Antarctic Larsen B Ice Shelf, a 1,255 square mile mass of ice larger than the state of Rhode Island, collapsed completely in a period of just 35 days.
Ice shelves are large sheets of floating ice that form where continental glaciers slowly drain into the ocean. Research published in the journal Nature shows the Larsen B Ice Shelf has been stable for at least 10,000 years, with chunks breaking off at roughly the same rate they were replenished by the draining of the contributing glaciers. (For reference, the earliest human civilizations – Mesopotamia and so on – appeared about 6,000 years ago.) This balance of ice loss and replenishment, which had persisted for at least about twice the entire duration of human civilization, ended abruptly in 2002.
A 2014 paper published in the journal Science reported studies of the Larsen B grounding zone (the zone where the floating ice shelf had been connected to the coastal bedrock) showing it had been stable before the collapse. This indicates the collapse was driven by unusually high surface temperatures, exceeding the highest surface temperatures that have occurred for at least the past 10,000 years. Ponds of melt water formed on the surface of the ice shelf (you can see them in the first satellite image above). Those filled small cracks on the surface of the ice, and the weight of the water then drove the cracks through the full thickness of the shelf. Read more here.
Like the Arctic in the Northern Hemisphere, Antarctica has undergone a surface temperature rise faster than the global average, about 0.5 degrees Celsius per decade, since at least the late 1940’s. The 2002 event was a dramatic illustration that large, previously stable ice shelves can be highly sensitive to surface temperature changes.
Since ice shelves are already floating on the ocean, the collapse of one does not itself contribute very significantly to sea level rise. However, ice shelves slow down the flow of continental glaciers into the sea, and that ice contributes directly to sea level rise. In fact, a detailed 2004 study of five glaciers previously buttressed by the Larsen B Ice Shelf showed they had sped up by factors between 2 and 8 by the end of 2003, contributing an additional 6.5 cubic miles per year of water to the oceans. Potential sea level rise from a complete melting of this region of Antarctica, the Antarctic Peninsula, is estimated at 0.46 meters. Potential sea level rise from a combined melting of the Greenland and Western Antarctic ice sheets similar to melting that occurred in the distant past would cause a sea level rise of 10 meters, flooding about 25% of the current U.S. population. To read more, see this U.S. Geological Survey fact sheet.
As for the Larsen B Ice Shelf, a 2015 NASA study indicates the surviving portion will disintegrate within a few years (see video below).
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