Worrying time-lapse footage has revealed how streams of warm seawater are eroding the polar ice caps.
The clip is composed of satellite footage photographs spanning 15 years and shows the permanent edge of the ice receding as chunks of it breaks off.
It features the eastern side of the Getz Ice Shelf – one of the largest ice shelves in Antarctica – and the ice breaking off is contributing to rising sea levels, researchers say.
The team from the US explain that warmer water sits on top of cold water and laps against the ice, causing it to crack, erode and break off in large chunks.
They said current global warming predictions don’t account for these ‘upside down rivers’ of water which have been heated by climate change.
This satellite image, taken in 2003, shows dark line – a channel of water – appearing towards the top left corner of the ice shelf
By 2017, the ice in area in the top left where the line of water was visible in 2013 has receded after ice has broken off
‘Warm water circulation is attacking the undersides of these ice shelves at their most vulnerable points,’ said Dr Karen Alley, from the College of Wooster in Colorado.
‘These effects matter. But exactly how much, we don’t yet know. We need to.’
Ice shelves are sheets of frozen water which float in the seawater and are attached to frozen earth. This puts them at risk of breaking off and floating out to sea.
When they are held fast they slow down the flow of ice from the land into the ocean, but if the shelf retreats or breaks it cannot provide this barrier.
Therefore, ice flows more quickly from the land into the ocean and causes sea levels to rise.
At the same time, the ice shelf itself is at risk of melting and contributing to this.
Ice shelves in Antarctica (pictured, the Ross Ice Shelf) are vital for slowing down the flow of melting ice from the land into the sea. Without them, the process is faster and sea levels will rise faster
The video released by Dr Allen and her colleagues shows the footprint of the ice expanding and contracting as the years pass by, but it gradually gets smaller.
The edge of it, where the ice shelf meets the sea, progresses downwards away from the water and towards the land as the time goes by.
Warm ‘upside down rivers’ which can measure miles wide and dozens of miles long are to blame for this retreating effect, the scientists said.
While the ice is still on land, large troughs form in the shear margins – essentially gutters between moving ice and stationary ice or land – becoming thin spots when the ice flows onto the ocean.
Dr Alley explained that warm ocean water finds those thin spots along the base of the ice shelf, further eroding and weakening margins, making ice shelves more vulnerable to retreat and collapse.
Previously, researchers didn’t know that warm plumes were so common beneath ice-shelf margins.
Dr Alley’s team used satellite imagery to show that, at the ends of shear margins on many of Antarctica’s fastest-changing glaciers, warm water rises to the surface, melting sea ice and forming areas of open water.
She said the processes appear to happen on ice shelves in both Antarctica and Greenland.
The research team published earlier work focusing on the damaging effects of meltwater on the surface of the ice shelves.
Study co-author Dr Ted Scambos, from Colorado University, added: ‘Now we’re seeing a new process, where warm water cuts into the shelf from below.
‘Like scoring a plate of glass, the trough renders the shelf weak, and in a few decades, it’s gone, freeing the ice sheet to ride out faster into the ocean.’
The research was published in the journal Science Advances.
HOW MUCH WILL SEA LEVELS RISE IN THE NEXT FEW CENTURIES?
Global sea levels could rise as much as 1.2 metres (4 feet) by 2300 even if we meet the 2015 Paris climate goals, scientists have warned.
The long-term change will be driven by a thaw of ice from Greenland to Antarctica that is set to re-draw global coastlines.
Sea level rise threatens cities from Shanghai to London, to low-lying swathes of Florida or Bangladesh, and to entire nations such as the Maldives.
It is vital that we curb emissions as soon as possible to avoid an even greater rise, a German-led team of researchers said in a new report.
By 2300, the report projected that sea levels would gain by 0.7-1.2 metres, even if almost 200 nations fully meet goals under the 2015 Paris Agreement.
Targets set by the accords include cutting greenhouse gas emissions to net zero in the second half of this century.
Ocean levels will rise inexorably because heat-trapping industrial gases already emitted will linger in the atmosphere, melting more ice, it said.
In addition, water naturally expands as it warms above four degrees Celsius (39.2°F).
The report also found that every five years of delay beyond 2020 in peaking global emissions would mean an extra 20 centimetres (8 inches) of sea level rise by 2300.
‘Sea level is often communicated as a really slow process that you can’t do much about … but the next 30 years really matter,’ lead author Dr Matthias Mengel, of the Potsdam Institute for Climate Impact Research, in Potsdam, Germany, told Reuters.
None of the nearly 200 governments to sign the Paris Accords are on track to meet its pledges.