April 8, 2009

Global-Warming Fears Abound As Large Ice Shelf Breaks Loose

According to the UN Environmental Program, an enormous breakaway piece of Antarctica's ice shelf could amplify the already significant effects of global warming in the region.

The 40-kilometer (25-mile) ice bridge "“ which was the Wilkins Ice Shelf's last bridge to the coast "“ has now completely broken off and can be seen in satellite images as a free-floating island of ice roughly the size of Jamaica.

Before it starting melting in the early 1990's, Wilkins Ice Shelf had an area of roughly 16,000 square kilometers or 6,000 square miles.  As early as last summer, the ice bridge was its last link to the Charcot and Latady islands.

UNEP officials speculate that the ice bridge may have been protecting the shelf and that the break-off of the ice bridge "may now allow ocean currents to wash away far more of the shelf."

One of the important functions of the ice shelf has been to deflect sunlight rather than absorb it, thus helping to moderate global temperatures.  UNEP officer Christian Lambrechts expressed fears that the broken ice shelf may end-up "contributing to continued and accelerated (global) warming" as more area of the ocean's surface are exposed to absorb sunlight.

The Antarctic Peninsula has been impacted by increasing global temperatures more intensely than almost anywhere else on the planet.

Global temperatures of have increased by 2.5 Celsius (4.5 Fahrenheit) in the last half century.  This represents a six-fold increase over historical global averages for the same length of time.

An ice shelve is a large sheet of ice that floats on the ocean's surface but remains connected to land on at least one side.

Ice shelves do not raise sea levels, since they displace their own volume's worth of water as they float on top of the ocean.  Researchers fear, however, that the glaciers that caused the shelf to form may now leak directly into the ocean without forming a new shelf.

"Although the Wilkins ice bridge collapse will have no direct consequence on sea level rise, it might have an indirect impact, as the decay of the ice shelf will reduce the stability of the glaciers that are feeding it," worried Lambrecht.

Since scientists have begun monitoring the effects of global warming, they have observed the loss of 7 major Antarctic ice shelves in just the past 20 years.

Breakaway ice shelves do not usually happen all at once.  It is a gradual process where small pieces break-off over time, slowly weakening the remaining shelf until the main shelf itself comes loose from land.  The giant pieces of ice then break into continually smaller pieces and eventually melt as they float northwards into warmer waters.

Image Courtesy British Antarctic Survey


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