The irreversible retreat of the Antarctic ice shelf

Thanks to Kristy Lewis

The findings, announced in February, used ice velocity data to show that there is a critical tipping point at which the shelves act like a restraining band, holding back the the ice that flows toward the sea. In a dramatic press release, the ESA said that as the ice is lost, it could be “point of no return” for Antarctica’s ice.

Climate: Antarctic ice shelf retreat may be irreversible

Summit County Citizen's Voice,

30 April, 2016

ESA satellites offer clues about climate change consequences

Staff Report

An analysis of data fromEuropean Space Agencysatellites shows that Antarctic ice shelves may be losing their buttressing role as they get thinner and retreat inland.

The findings, announced in February, used ice velocity data to show that there is a critical tipping point at which the shelves act like a restraining band, holding back the the ice that flows toward the sea. In a dramatic press release, the ESA said that, if the ice is lost, it could be “point of no return” for Antarctica’s ice.

The ice shelves are huge and losing them would have serious implications for global climate, speeding the rise of sea level. The Ross Ice Shelf, for example, is the size of Spain and towers hundreds of meters above sea level.

Some of the vulnerable ice shelves have already started to thin and crumble, including the 1995 collapse of the Larsen A ice shelf (about the size of Berlin). 

Seven years later the Larsen B Ice Shelf also collapsed and scientists are currently documenting the disintegration of the Wilkins Ice Shelf.

After the Larsen B Ice Shelf cracked apart, tributary glaciers started flowing eight times faster, increasing the amount of ice discharged to the sea. At least 50 other shelves fringe the continent, some of them much bigger than Larsen B.

The recent analysis of the buttressing role of the shelves was done by scientists with the University of Erlangen-Nuremberg Institute of Geography and with the Laboratoire de Glaciologie et Géophysique de l’Environnement in Grenoble. They used radar data from satellites such as ESA’s ERS and Envisat. Their findings were published today inNature Climate Change.

About 13 percent of the total ice-shelf area consists of a passive part, which simply floats and doesnt’t help hold back the land-based ice. But behind the passively floating zone there is an area of ice the researchers call a ‘safety band’, which is the most critical portion of the ice shelf restraining the ice flow.

“For some decades now satellite remote-sensing has allowed us to track changes and movement of Antarctic ice fronts. In some regions we have seen continuous ice-shelf recession,” said Dr .Johannes Fürst, from the University of Erlangen-Nuremberg’s Institute of Geography. “Once ice loss through the calving of icebergs goes beyond the passive shelf ice and cuts into the safety band, ice flow towards the ocean will accelerate, which might well entail an elevated contribution to sea-level rise for decades and centuries to come.”

However, there are some contrasting results across the continent as not all ice shelves have this passive ice.

“The Amundsen and Bellingshausen seas have limited or almost no passive ice shelf, which implies that further retreat of current ice-shelf fronts will have serious dynamic consequences,” Fürst said. “This region is particularly vulnerable as ice shelves have already been thinning at high rates for two decades.”

By contrast, the Larsen C ice shelf in the Weddell Sea has a large passive frontal area, where the calving of large tabular ice bergs probably won’t speed up the flow of glaciers flowing toward the sea.

The findings will help improve projections for how the meltdown of Antarctica’s ice shelves will play out as the globe warms up.