Scientists Link Melting Sea Ice and Ice Shelf Calving to Climate Change

Plus Zebra Mussels, Women Cyclists, Bird Conservation, the Greater Sage-Grouse, the Middle Huron River, ESA Listings, Colorado Fracking, and Clearcutting Near Yellowstone

This week we turn our attention to the poles and some of the new scientific findings at the ends of the earth.

Hurricanes and cyclones are associated with subtropical regions of the world, whipping against Florida or crashing through the South China Sea. Cyclones form in polar regions as well, and scientists have noted that they have increased in frequency over the last 50 years. This increase in the number of polar cyclones has been predicted by scientists, with ramifications for the Arctic, Antarctic, and the rest of the world as well.

Due to global warming, polar sea ice has retreated over the last 50 years, which has accelerated in the last decade. The common assumption has been that warmer air over the sea and ice melts the ice, but some recent research finds other factors are at play.

Polar cyclones reduce sea ice

In August of 2016, a South Korean icebreaker got caught in an Arctic cyclone. Though the experience must have been nerve-wracking, scientists on the ship took the unique opportunity to gather data from inside the storm.

A team of researchers examined the data and found that sea ice receded 5.7 times faster than normal during the storm. The team published their findings in Geophysical Research Letters, a peer-reviewed journal of the American Geophysical Union.

Warm air was less a factor in the sea ice melt than the strong winds that pushed water away from the cyclone, causing upwelling of warmer water from below. The cyclone also mixed the warmer and colder water. The mixing and upwelling warmed the entire upper level of ocean water, thus melting the sea ice.

The melting sets up a feedback loop. The cyclones clear large areas of water from around the ice. The water has a higher albedo than the sea ice, which means that it absorbs more solar radiation and warms more than the ice. And that warmer water melts even more sea ice. More warming = more cyclones = more open water free of sea ice = more absorbed solar radiation = more warming, etc.


Ice shelf calving linked to global warming

In 2019, a very large section of the Amery Ice Shelf calved, the largest calving since 1963, when an even larger iceberg broke away from the shelf. Though calving of polar ice shelves is a natural occurrence and happens all the time, this calving surprised scientists, who did not expect this portion of ice to break off from the shelf for another ten years.

Several Antarctic ice shelves have collapsed in recent years, leading scientists to take an increased interest in them. A scientific team whose academic affiliations spread across the world, from the United Arab Emirates, the Netherlands, the U.S., and Australia, has linked the 2019 calving event with global warming.

In this case, a series of powerful twin polar cyclones over seas adjacent to the Amery Ice Shelf created tides and upwelling of water levels, which led to the weakening of a pre-existing rift and the subsequent calving. As mentioned above, the increasing number of these cyclones has been linked to climate change, and still more of these intense storms are expected.

Ice shelves develop when polar glaciers meet the sea. Glaciers push the ice out into the sea, where it floats on the water. Ice shelves are usually from 300 to 3000 feet thick and are only found in Antarctica, Greenland, Canada, and northern Russia.

The Amery Ice Shelf is the third largest in Antarctica. Although it takes up a small portion of the Antarctic coastline, the Amery drains about 16 percent of the East Antarctic Ice Sheet. The calved section of the shelf was 632 square miles, about half the size of Long Island.

Ice shelves are constantly accumulating mass as the glaciers push their ice seaward. The accumulation is balanced by calving, when large chunks of the shelf break off and drift into the sea. Many ice shelves may be shrinking due to increased calving caused by global warming.

Because sea ice floats, increased calving, in and of itself, will not lead to sea level rise. But just as a clog in a garden hose decreases the flow of water from the nozzle, ice shelves slow the flow of glaciers to the sea. Shrinking ice shelves mean more glacial ice moves from land to ocean, thus raising sea levels.

Explosive cyclones are more intense and last longer than ordinary cyclones. They are more prevalent in the Southern Hemisphere than in the Northern Hemisphere. A study of these more powerful cyclones found that they increased in both hemispheres from 1979 through 1999. Another study, over a longer period of time, found similar results. Additionally, these cyclones are shifting poleward, resulting in an increase in the number and intensity of explosive cyclones around the Antarctic.

An extreme situation is the formation of twin cyclones, which feed off each other, making each one twice as strong. The scientists note that explosive twin cyclones have only been observed in the tropics, mid-latitudes, and Arctic. The scientists believe that the two twin cyclones described in their study may be the first to be studied in the Antarctic.

In this case, the first explosive cyclone developed on September 18, 2019, and further developed into two stationary twin polar cyclones that sat to the west of the Amery Ice Shelf on September 19-22. On September 23, the second explosive cyclone developed, turning into twin polar cyclones on September 24-25. These cyclones were positioned to the east of the ice shelf.

Both of the events brought in warm moist air from the north, as well as storm surges and other ocean and weather conditions that put a strain on the ice shelf, which led to the calving. More explosive cyclones and the formation of twin cyclones may be expected to lead to additional large calving of the Antarctic ice shelves.

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