Melting Antarctic ice may cause sea level to rise FASTER than expected,
Rapidly melting ice shelves in Antarctica could trigger global sea levels to rise even faster than expected, scientists have warned.
Antarctica’s vast floating ice shelves surround about 75 per cent of the continent’s coastline and act like a vast buttress, holding back the flow of inland glaciers.
However, Norwegian researchers have discovered that deep channel–like grooves beneath the ice are trapping swirling eddies of relatively warm ocean water.
That warm water melts ice beneath the surface 10 times faster than normal, threatening the structural integrity of the entire ice shelves.
Lead author Dr Qin Zhou, senior scientist for Norwegian research organisation Akvaplan–niva, told the Daily Mail: ‘These ice shelves may be more vulnerable to ocean warming than previously assumed.’
If the Antarctic shelves were significantly weakened or even started to collapse, it would release the gigatonnes of ice currently being held back in the ice sheet.
The ice sheet currently holds enough fresh water to raise sea levels by a staggering 58 meters (190 feet), threatening millions of people with flooding.
While the researchers don’t think the entire ice sheet will melt, they warn that sea levels are likely to be a lot higher than previous climate models have predicted.
Rapidly melting ice shelves in Antarctica could trigger global sea levels to rise even faster than expected, scientists have warned
Researchers have found that the ice shelves are melting from beneath, weakening the buttresses that hold back the flowing glaciers behind
Ice shelves are the extensions of glaciers that float out over the water rather than being anchored to the bedrock below.
As well as sheltering a diverse and sensitive ecosystem, this wall of ice is also critical for slowing the sea level contributions of melting glaciers.
The ice shelves wedge themselves between the headland and small hills on the seafloor, acting like a break that slows the glaciers’ relentless surge into the sea.
Lead author Dr Tore Hattermann, from the iC3 Polar Research Hub, told the Daily Mail: ‘This is all glacial ice that is flowing down from the continent into the ocean, and the floating part is providing a “backstress” like a cork in a wine bottle – if you pull it, all the wine flows out.’
Antarctica’s cold air and persistent heavy snowfall mean that the continent’s glaciers melt very little from the top down.
Instead, the ice is being gradually worn away from beneath at the point where they meet the ocean.
However, scientists have found that the bottom of the ice sheet is not smooth and even, but rather marked by deep grooves, channels and pits.
Using the Fimbulisen Ice Shelf in East Antarctica as a case study, Dr Zhou and Dr Hattermann investigated how this glacial topography might affect the ice melt.
Scientists found that deep channels beneath the Fimbulisen Ice Shelf in East Antarctica are causing more rapid melting (shown in red) than previously expected
They combined a detailed map of the ice shelf with a detailed computer model, comparing what would happen when the ice was smooth or pitted with grooves.
The simulation revealed that channels in the ice created ‘cells’ that hold warm water in place rather than allowing it to flow through quickly.
As the warm water melted the surrounding ice, the channels grew deeper and wider, burrowing deep cracks into the ice shelf.
This process pushes back the point where ice meets the bedrock, known as the grounding line, exposing more ice to water and melting the shelf even faster.
If the glacier is thicker further inland, this can trigger a cascading acceleration as the heavy ice sheet pushes faster towards the sea.
The fact that the researchers found this effect in the Fimbulisen Ice Shelf is extremely important because this area had previously been considered stable.
Dr Hattermann says: ‘In the Western part of Antarctica, the ice shelf cavity is already filled with warm water and the retreat is happening.
‘But there is also the ice shelves on the East coast. These have cold water underneath them right now, but that is slowly changing.
Lead author Dr Tore Hattermann (pictured), from the iC3 Polar Research Hub, says that this will likely lead to far more sea level increases than anyone had predicted
If the ice shelves destabilise and the glaciers start to accelerate, it could lead to more than a metre of sea level rise before 2100, 30 metres by 2150, and up to 50 metres by 2300
‘Most have channels beneath, and what our study shows is that if you add a little bit of warm water, it has a more severe effect. They are more sensitive to a little bit of warming because of these channels.’
While melting ice shelves don’t contribute to sea level rise since they are already floating, inland glaciers dropping into the sea do.
This is why researchers are concerned that destabilisation of the Antarctic Ice Sheet could lead to rapidly rising sea levels.
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Dr Zhou says: ‘The main global consequence would be faster sea–level rise. Antarctica contains the largest potential source of future sea–level rise, and the stability of ice shelves is one of the key controls on how quickly grounded Antarctic ice can be discharged into the ocean.’
Climate models that predict future sea level increases don’t take this effect into account, which means we don’t know exactly how high sea levels could become.
Since the effect is so uncertain, Dr Hattermann says we cannot ‘rule out’ sea level increases of up to 30 metres by 2150 and 50 metres by 2300.
He says: ‘Because of these processes that we don’t fully understand, we need to make the assumption that it could be so high.’
