Monday, February 6, 2017

Goodbye Larsen C

Meanwhile, at the southern tip of the earth, where the sun is heating up the Antarctic summer as it shines for 24 hours a day, a great big thing is happening. Sometime within the next few minutes to the next few weeks the Larsen C ice shelf will calve an iceberg (assuming it does not shatter) that is about 10% the total size of the current Larsen C ice shelf. This will be one of the largest calving events ever witnessed by humans.

The iceberg is expected to be approximately 5,000 square kilometers in size. This is big. The state of Delaware is only 6,452 square kilometers in size.

Larsen C is the last remaining Larsen ice shelf. It is stuck to the giant finger of Antarctica that points out from the South Pole towards Tierra del Fuego. Larsen A spectacularly disintegrated in January of 1995. Seven years later Larsen B began collapsing, and by March of 2002 big chunks had broken off. By 2005 most of Larsen B was gone.
Location of the Larsen C ice shelf


Larsen B was estimated to be around 12,000 years old. Larsen C is much older.

Cracks have been observed in Larsen C for some time. Over last summer one of the cracks shot out across the face of the ice shelf, and this summer it has extended to within a few kilometers of creating a giant calving event. The crack grew by over 10 kilometers in just the first three weeks of January 2017, and is now about 180 kilometers long. The crack is estimated to be half a kilometer deep in some places.
NASA picture of the big Larsen C crack
 

“If Larsen C were to collapse at some point in the next 100 years, you’d expect within the few decades after that collapse, a much faster rate of sea level rise than if it hadn’t collapsed.” -- Paul Holland of the British Antarctic Survey


Because these ice shelves mostly float on water there should not be much, if any, sea level rise immediately associated with this amazing calving event. Geologists estimate, however, that the loss of the ice shelf will hasten the rush to the sea of glaciers behind it. The loss of Larsen C might –eventually- raise the level of oceans by 10 centimeters.

There are larger ice shelves in Antarctica; shelves closer to the pole. Larsen C is only the fourth largest of the Antarctic ice shelves. If the bigger ice shelves “go” the accelerated melting of the glaciers they hold back could raise the level of the oceans by tens of meters; in other words a hundred times as much as the eventual impact of the collapse of Larsen C. By all indication the big ice shelves, like the Ross Ice Shelf, are stable. When Larsen A collapsed in 1995 reports indicated that Larsen C was stable.

There is a critical need to better understand what is happening in the Antarctic. The impact of meters of sea level rise, even if it occurred over several decades, could significantly change the nature of civilization. This is not an exaggeration.









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