Antarctica And Rising Sea Level

by Daniel Brouse and Sidd Mukherjee

The U.N. weather agency said the Antarctic peninsula has set a heat record of 63.5° Fahrenheit (17.5 degrees Celsius) on March 24, 2015. In March of 2017, there is about 10% less sea ice in Antarctica than the previous record minimum. “One would probably say that the old record was obliterated,” said Jan Lieser, a sea ice scientist at the Hobart-based Antarctic Climate and Ecosystems Co-operative Research Centre.

Antarctica contains 90% of the world’s fresh water as ice. If all the ice melts, sea levels will rise by 60 meters (200 feet). The sea ice melting doesn’t raise the sea level as the ice is already floating. The ice that is above land is a different story.

The problem with the ice in Antarctica is that much of the ice is on land. As the land ice melts or falls into the ocean the sea level rises. Compounding the problem is the elevation of the land. Over the centuries the weight of the ice has caused the land to sink. As the ocean temperature warms, water is starting to seep in under the ice. The warm water under the ice sheet is accelerating the destabilization of the sheet.

“There was a physicist called John Mercer at the Byrd polar research center here at Ohio State, who was warning of WAIS collapse as early as 1968,” said Sidd Mukherjee research physicist at Ohio State University.

Then in 1978 Mercer wrote:
“One warning sign that a dangerous warming is beginning in Antarctica, will be a breakup of ice shelves in the Antarctic Peninsula just south of the recent January 0C isotherm; the ice shelf in the Prince Gustav Channel on the east side of the peninsula, and the Wordie Ice Shelf; the ice shelf in George VI Sound, and the ice shelf in Wilkins Sound on the west side. ”

Each of these shelves is in retreat or gone. Mercer was more correct than he knew. Recent work by Bassis et al. shows that ice shelves collapse shortly after the temperature of the top surface exceeds the 0C melting point through a process called hydrofracture, where water filled crevasses penetrate all the way to the bottom of the shelf. Bassis et al. also pointed out that a cliff of ice higher than 100m (300 ft) is unstable against collapse. These cliff heights are attained where the bedrock is more than 1Km below sea level, as in large parts of WAIS. When the shelves melt leaving cliffs behind which directly face the ocean they will collapse along large sections of WAIS. The more frightening estimates for WAIS deglaciation are on the order of centuries, rather than millennia, indeed decadal time scales cannot be entirely ruled out. We know from past records that sea level can rise as fast as a foot a decade and maintain that rate for five hundred years. Such rates of sea level rise will destroy most coastal cities of the world, since coastal infrastructure cannot be moved inland or protected by seawalls quickly enough.

Antarctica Larsen C Ice Crack

Antarctica Larsen C Ice Crack

In January of 2017, a UK research team discovered a huge increase in a massive 90-mile crack running through the Larsen C shelf (pictured to the right). The crack might soon split off a chunk of ice the size of Delaware. Larson C is part of Eastern Antarctic. Larson A and Larson B have already collapsed.

The Western Antarctic Ice Sheet (WAIS) is the segment of the continental ice sheet that covers West Antarctica. The melting of the West Antarctic ice sheet alone would raise global sea levels by more than 20 feet, according to researchers from the British Antarctic Survey. Over the last several years, WAIS has become unstable. A 2016 study by Khazendar, Rignot, and others adds to the mounting evidence that the threshold for an irreversible disintegration has begun.

“It’s generally accepted that it’s no longer a question of whether the West Antarctic Ice Sheet will melt, it’s a question of when,” said leader Ian Howat, associate professor of earth sciences at Ohio State in a 2016 study published in the journal Geophysical Research Letters. “This kind of rifting behavior provides another mechanism for rapid retreat of these glaciers, adding to the probability that we may see significant collapse of West Antarctica in our lifetimes.”

Ice calving is the breaking of ice chunks from the edge of a glacier. Calving causes mini-tsunamis daily in Antarctica.

The Thwaites Glacier is of great concern. Thwaites Glacier is an unusually broad and fast Antarctic glacier flowing into Pine Island Bay. As the warming temperature of sea water melts the bottom of the glacier, it allows water to enter underneath the ice. A University of Washington study determined that the Thwaites Glacier will gradually melt, leading to an irreversible collapse over the next 200 to 1000 years.

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