One of the world's largest icebergs broke off from Antarctica's Larsen C ice shelf and attracted global attention this week, but the Larsen shelf's deterioration has been in progress for more than two decades. Its dramatic decline is documented in successive images from National Geographic Atlases of the World.
Large chunks of the ice shelf can be seen disappearing in successive maps from the 1990, 2005, and 2015 editions of the atlas.
A 1990 National Geographic image shows the ice shelf largely intact.
The decline continued Wednesday when a colossal iceberg the size of Delaware splintered from the Larsen C ice shelf. Measuring about 5,600 square km, it is among the largest icebergs in history to break off from the continent.
The next edition of the National Geographic Atlas of the World is expected to publish in 2019 and will be updated to show the fractured Larsen C ice shelf.
Ice shelves are thick floating platforms of ice that are connected to land masses, and they surround about 75 percent of Antarctica’s coastline. The Larsen Ice Shelf, named after Norwegian explorer Carl Anton Larsen, is on the northeast coast of the Antarctic Peninsula along the Weddell Sea.
While there is no definitive proof climate change is the reason for the latest Larsen C event, warmer ocean temperatures are making ice shelves increasingly susceptible to breaks and collapses.
When NASA first photographed the Larsen Ice Shelf in the 1960s, the fatal rift that separated this iceberg from Larsen C was already visible.
Ice shelves naturally undergo a process called calving, or shedding large pieces of ice, but the iceberg from Larsen C is the third large iceberg to break from the ice shelf since 1995—a pace that has some researchers concerned. (Read: Antarctica's Sea Ice Shrinks to New Record Low)
By 2005, large segments of the Larsen Ice Shelf are gone.
In January 1995, Larsen A, the northernmost area of the Larsen Ice Shelf, lost about 1,990 square km of ice in a storm as a large iceberg broke off farther south. In 1999, the National Geographic Atlas of the World added a note about the ice shelf, mentioning the accelerated disintegration for the first time.
Then in 2002, the majority of Larsen B—which is located south of Larsen A—broke off and collapsed just over a month-long period, further reducing the shelf by 3,200 square km.
Scientists attributed the splintering of both icebergs to a series of unusually warm summers, and an especially warm summer in 2002. Researchers observed substantial melting during this time, noting that melted areas acted like wedges and pushed already-present cracks even deeper. (Read: Antarctica Is Covered With More Meltwater Than Thought)
In 2005, the National Geographic Atlas of the World was updated to reflect the break of Larsen B.
The remains of the Larsen B ice shelf, which is thought to be at least 10,000 years old, is disintegrating quickly and is likely to be completely gone by the end of the decade.
Meanwhile, the new Larsen C iceberg—which weighs a trillion tons—will likely break into smaller pieces. Some could remain in the Weddell Sea for decades, while other parts could find themselves swept up in the Weddell Sea Gyre, which is a circuit of ocean flow.
This would push the ice fragments north toward South America, past the west of South Georgia and the South Sandwich Islands, Helen Amanda Fricker, an Antarctic expert at the Scripps Institution of Oceanography, told the Washington Post.
SEE THE GIANT CRACK IN THE LARSEN ICE SHELF THAT YIELDED ANTARCTICA ICEBERG
RE-WRITING THE MAPS
In the most recent edition of the National Geographic Atlas of the World in 2015, the note about the Larsen Ice Shelf was expanded to include information about Larsen B, and credited its collapse to exceptionally warm summers.
"Capturing these changes is challenging," says Ted Sickley, National Geographic's director of cartographic databases. "The pace of environmental change appears to be increasing, but at the same time we benefit from improved satellite imagery and other technology that help us identify and add these changes to our maps."
Because so much of the Larsen Ice Shelf has splintered off, scientists now worry that it could be less stable, which could mean more disintegration. The remaining ice sheets are also thinning at a rate of between 1.8 and 2.7m each year.
If the new Larsen C iceberg were to completely melt, sea levels would rise by 0.1 millimeters, NASA climate scientist Gavin Schmidt told Climate Central.