Warmer water gnaws away at Antarctica

Ocean warming caused by climate change is causing the Antarctic Filchner-Ronne shelf to melt. The more ice that melts, the more it flows into the ocean and the more it contributes to global sea-level rise, reports Elke Bunge. These are the findings of a new study from the Potsdam Institute for Climate Impact Research.

Scientists have uncovered the melting process for the Filchner-Ronne shelf in Antarctica. Unlike other ice shelves, it reacts linearly to ocean warming. (Photo credit: NASA Visible Earth)

Scientists have uncovered the melting process for the Filchner-Ronne shelf in Antarctica. Unlike other ice shelves, it reacts linearly to ocean warming. (Photo credit: NASA Visible Earth)

The good news is that if humankind succeeds in curbing greenhouse gas emissions, this would prevent further warming of the ocean around Antarctica. In such a scenario, the Filchner-Ronne ice shelf would remain intact and even serve as a natural barrier against melting of the Antarctic ice sheet.

In their study published in the most recent edition of the journal Nature Climate Change, the scientists at the Potsdam Institute for Climate Impact Research (PIK) describe their observations on the melting process of the Filchner-Ronne shelf. Due to oceanic peculiarities, the melting process of the 422,000 square kilometre ice shelf – the second largest in Antarctica – behaves differently than other regions on the ice continent.

Protected by a cold water wall

The Filchner-Ronne shelf is surrounded by cold water masses near the freezing point, which create a cold water wall and prevents the ice from melting. But a scenario in which global greenhouse gas emissions continue to rise could change this natural barrier. The behaviour of the current in the South Atlantic is such that water from the southern tip of the South American continent drifts past the north western tip of Antarctica, precisely where the Filchner-Ronne shelf is.

“While for other parts of Antarctica unstoppable long-term ice loss might be provoked by a single warming pulse, caused by nature itself or human action, ice loss in the Filchner-Ronne region increases directly with ocean warming,” explains lead author Matthias Mengel.

Normally, climate change and ocean warming do not have a linear relationship, which makes the behaviour of the Filchner-Ronne so unique. But if climate change continues unabated for 200 years, melting of the Filchner-Ronne shelf alone could contribute up to 40 centimetres to global sea-level rise within just 200 years. This would affect coastal regions in Japan, India, America and even Europe. Cities such as Toyko, New York or Hamburg would be at risk.

Barriers could collapse

Until now, sea-level rise is mostly caused by thermal expansion of the warming oceans and by the melting of mountain glaciers. But as the latest PIK study shows, the greatest contributors to future sea-level rise will be the ice sheets of Greenland and Antarctica. The situation of the Antarctic ice sheets is unpredictable because the ice shelves – which float far into the ocean and are just extensions of the ice sheet – act as natural barrier for the underlying masses of ice and water. If this barrier collapses due to ocean warming around Antarctica, the ice shelves would melt and increase the risk of high sea-level rise.

Warming could uncork the ice

Back in 2012 oceanographers from the Alfred Wegner Institute in Bremerhaven warned about warming of the Weddell Sea and melting of the ice shelf. They compared the Filchner-Ronne shelf to a cork in a bottle, which holds the ice back.

“It is in our hands to determine how much the region contributes to the global sea-level rise,” says Mengel. As the Filchner-Ronne region responds linearly to global warming, limiting greenhouse gas emissions will limit ice melt. One thing is completely clear for co-author Anders Levermann: “The more warming we cause by burning coal, gas and oil, the more expensive it will be for coastal regions to adapt.”

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