Hidden upside-down “rivers” are eroding Antarctic ice shelves, according to the latest study that suggests polar regions are melting faster than previously thought.

As ice shelves float out into the ocean they stretch and crack along the edges, meaning they are particularly vulnerable to erosion from plumes of water from below.

Warm and fresh water is more buoyant than cold, salty water, so it goes up into the ice forming a type of “upside-down river”, scientists found. These rivers can grow miles wide and tens of miles long, eroding and weakening the margins of the ice shelf, which means it is more vulnerable to retreat and collapse.

“Warm water circulation is attacking the undersides of these ice shelves at their most vulnerable points,” said lead researcher Dr Karen Alley, who earned her PhD at the University of Colorado Boulder.

Scientists say current forecasts do not account for this “troubling” process, which is contributing to the breaking up of ice shelves in both Antarctica and Greenland.

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The Sahara heat wave that recently sent temperatures to record levels in parts of Europe has also reached Greenland. Climate change is having a profound effect in Greenland, where over the last several decades summers have become longer and the rate that glaciers and the Greenland ice cap are retreating has accelerated. (Photo by Sean Gallup/Getty Images) Sean Gallup Getty Images Climate change: Greenland ice cap accelerated retreating ILULISSAT, GREENLAND - JULY 30: In this aerial view ice floats jammed into the Ilulissat Icefjord during unseasonably warm weather on July 30, 2019 near Ilulissat, Greenland. The Sahara heat wave that recently sent temperatures to record levels in parts of Europe is arriving in Greenland. Climate change is having a profound effect in Greenland, where over the last several decades summers have become longer and the rate that glaciers and the Greenland ice cap are retreating has accelerated. (Photo by Sean Gallup/Getty Images) Sean Gallup Getty Images Climate change: Greenland ice cap accelerated retreating ILULISSAT, GREENLAND - AUGUST 04: An iceberg looms behind a boat carrying tourists at the mouth of the Ilulissat Icefjord on August 04, 2019 near Ilulissat, Greenland. The Sahara heat wave that recently sent temperatures to record levels in parts of Europe has also reached Greenland. Climate change is having a profound effect in Greenland, where over the last several decades summers have become longer and the rate that glaciers and the Greenland ice cap are retreating has accelerated. (Photo by Sean Gallup/Getty Images) Sean Gallup Getty Images Climate change: Greenland ice cap accelerated retreating ILULISSAT, GREENLAND - JULY 30: Visitors look out onto free-floating ice jammed into the Ilulissat Icefjord during unseasonably warm weather on July 30, 2019 near Ilulissat, Greenland. The Sahara heat wave that recently sent temperatures to record levels in parts of Europe is arriving in Greenland. Climate change is having a profound effect in Greenland, where over the last several decades summers have become longer and the rate that glaciers and the Greenland ice cap are retreating has accelerated. (Photo by Sean Gallup/Getty Images) Sean Gallup Getty Images Climate change: Greenland ice cap accelerated retreating ILULISSAT, GREENLAND - JULY 30: In this aerial view melting ice forms a lake on free-floating ice jammed into the Ilulissat Icefjord during unseasonably warm weather on July 30, 2019 near Ilulissat, Greenland. The Sahara heat wave that recently sent temperatures to record levels in parts of Europe is arriving in Greenland. Climate change is having a profound effect in Greenland, where over the last several decades summers have become longer and the rate that glaciers and the Greenland ice cap are retreating has accelerated. (Photo by Sean Gallup/Getty Images) Sean Gallup Getty Images Climate change: Greenland ice cap accelerated retreating ILULISSAT, GREENLAND - JULY 30: A boat carrying tourists motors past an iceberg at the mouth of the Ilulissat Icefjord during unseasonably warm weather on July 30, 2019 near Ilulissat, Greenland. The Sahara heat wave that recently sent temperatures to record levels in parts of Europe is arriving in Greenland. Climate change is having a profound effect in Greenland, where over the last several decades summers have become longer and the rate that glaciers and the Greenland ice cap are retreating has accelerated. (Photo by Sean Gallup/Getty Images) Sean Gallup Getty Images Climate change: Greenland ice cap accelerated retreating ILULISSAT, GREENLAND - JULY 30: Free-floating ice floats jammed into the Ilulissat Icefjord during unseasonably warm weather on July 30, 2019 near Ilulissat, Greenland. The Sahara heat wave that recently sent temperatures to record levels in parts of Europe is arriving in Greenland. Climate change is having a profound effect in Greenland, where over the last several decades summers have become longer and the rate that glaciers and the Greenland ice cap are retreating has accelerated. (Photo by Sean Gallup/Getty Images) Sean Gallup Getty Images Climate change: Greenland ice cap accelerated retreating ILULISSAT, GREENLAND - AUGUST 04: Humpback whales spout water as they swim next to an iceberg in the Ilulissat Icefjord on August 04, 2019 near Ilulissat, Greenland. The Sahara heat wave that recently sent temperatures to record levels in parts of Europe has also reached Greenland. Climate change is having a profound effect in Greenland, where over the last several decades summers have become longer and the rate that glaciers and the Greenland ice cap are retreating has accelerated. (Photo by Sean Gallup/Getty Images) Sean Gallup Getty Images Climate change: Greenland ice cap accelerated retreating ILULISSAT, GREENLAND - AUGUST 04: Icebergs and ice float in the Ilulissat Icefjord on August 04, 2019 near Ilulissat, Greenland. The Sahara heat wave that recently sent temperatures to record levels in parts of Europe has also reached Greenland. Climate change is having a profound effect in Greenland, where over the last several decades summers have become longer and the rate that glaciers and the Greenland ice cap are retreating has accelerated. (Photo by Sean Gallup/Getty Images) Sean Gallup Getty Images Climate change: Greenland ice cap accelerated retreating ILULISSAT, GREENLAND - JULY 31: Tourists on an excursion boat photograph an iceberg during unseasonably warm weather on July 31, 2019 near Ilulissat, Greenland. The Sahara heat wave that recently sent temperatures to record levels in parts of Europe is arriving in Greenland. Climate change is having a profound effect in Greenland, where over the last several decades summers have become longer and the rate that glaciers and the Greenland ice cap are retreating has accelerated. (Photo by Sean Gallup/Getty Images) Sean Gallup Getty Images Climate change: Greenland ice cap accelerated retreating ILULISSAT, GREENLAND - JULY 30: Inuit fishermen prepare a net as free-floating ice floats behind at the mouth of the Ilulissat Icefjord during unseasonably warm weather on July 30, 2019 near Ilulissat, Greenland. The Sahara heat wave that recently sent temperatures to record levels in parts of Europe is arriving in Greenland. Climate change is having a profound effect in Greenland, where over the last several decades summers have become longer and the rate that glaciers and the Greenland ice cap are retreating has accelerated. (Photo by Sean Gallup/Getty Images) Sean Gallup Getty Images Climate change: Greenland ice cap accelerated retreating ILULISSAT, GREENLAND - JULY 30: Water drips from ice in the Ilulissat Icefjord during unseasonably warm weather on July 30, 2019 near Ilulissat, Greenland. The Sahara heat wave that recently sent temperatures to record levels in parts of Europe is arriving in Greenland. Climate change is having a profound effect in Greenland, where over the last several decades summers have become longer and the rate that glaciers and the Greenland ice cap are retreating has accelerated. (Photo by Sean Gallup/Getty Images) Sean Gallup Getty Images Climate change: Greenland ice cap accelerated retreating ILULISSAT, GREENLAND - JULY 30: An iceberg floats in Disko Bay behind houses during unseasonably warm weather on July 30, 2019 in Ilulissat, Greenland. The Sahara heat wave that recently sent temperatures to record levels in parts of Europe is arriving in Greenland. Climate change is having a profound effect in Greenland, where over the last several decades summers have become longer and the rate that glaciers and the Greenland ice cap are retreating has accelerated. (Photo by Sean Gallup/Getty Images) Sean Gallup Getty Images Climate change: Greenland ice cap accelerated retreating ILULISSAT, GREENLAND - JULY 30: In this aerial view melting ice forms a lake on free-floating ice jammed into the Ilulissat Icefjord during unseasonably warm weather on July 30, 2019 near Ilulissat, Greenland. The Sahara heat wave that recently sent temperatures to record levels in parts of Europe is arriving in Greenland. Climate change is having a profound effect in Greenland, where over the last several decades summers have become longer and the rate that glaciers and the Greenland ice cap are retreating has accelerated. (Photo by Sean Gallup/Getty Images) Sean Gallup Getty Images Climate change: Greenland ice cap accelerated retreating ILULISSAT, GREENLAND - AUGUST 04: In this view from an airplane rivers of meltwater carve into the Greenland ice sheet near Sermeq Avangnardleq glacier on August 04, 2019 near Ilulissat, Greenland. The Sahara heat wave that recently sent temperatures to record levels in parts of Europe has also reached Greenland. Climate change is having a profound effect in Greenland, where over the last several decades summers have become longer and the rate that glaciers and the Greenland ice cap are retreating has accelerated. (Photo by Sean Gallup/Getty Images) Sean Gallup Getty Images Climate change: Greenland ice cap accelerated retreating ILULISSAT, GREENLAND - JULY 30: Visitors walk among free-floating ice jammed into the Ilulissat Icefjord during unseasonably warm weather on July 30, 2019 near Ilulissat, Greenland. 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(Photo by Sean Gallup/Getty Images) Sean Gallup Getty Images Climate change: Greenland ice cap accelerated retreating ILULISSAT, GREENLAND - AUGUST 04: In this view from an airplane icebergs float in Disko Bay at sunset on August 04, 2019 near Ilulissat, Greenland. The Sahara heat wave that recently sent temperatures to record levels in parts of Europe has also reached Greenland. Climate change is having a profound effect in Greenland, where over the last several decades summers have become longer and the rate that glaciers and the Greenland ice cap are retreating has accelerated. (Photo by Sean Gallup/Getty Images) Sean Gallup Getty Images Climate change: Greenland ice cap accelerated retreating ILULISSAT, GREENLAND - JULY 30: Flowers stand on a hillside at the Ilulissat Icefjord during unseasonably warm weather on July 30, 2019 near Ilulissat, Greenland. The Sahara heat wave that recently sent temperatures to record levels in parts of Europe is arriving in Greenland. 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(Photo by Sean Gallup/Getty Images) ***BESTPIX*** Sean Gallup Getty Images Climate change: Greenland ice cap accelerated retreating ILULISSAT, GREENLAND - AUGUST 04: In this view from an airplane humpback whales swim next to an iceberg at the mouth of the Ilulissat Icefjord on August 04, 2019 near Ilulissat, Greenland. The Sahara heat wave that recently sent temperatures to record levels in parts of Europe has also reached Greenland. Climate change is having a profound effect in Greenland, where over the last several decades summers have become longer and the rate that glaciers and the Greenland ice cap are retreating has accelerated. (Photo by Sean Gallup/Getty Images) Sean Gallup Getty Images

About three-quarters of the Antarctic continent is surrounded by these extensions of the ice sheet.

The shelves can be hemmed in by canyon-like walls and bumps in the ocean floor. When restrained by bedrock obstructions, ice shelves slow down the flow of ice from the interior of the continent towards the ocean.

As ice shelves float out to the ocean and break apart, ice on land flows more quickly into the ocean, which increases the rates of sea-level rise, according to the study published in Science Advances.

“These effects matter. But exactly how much, we don’t yet know. We need to,” said Dr Alley.

Dr Alley and her colleagues first mapped the rivers – or “basal channels” – a few years ago, spotting them as wrinkles or sags in otherwise smooth ice surfaces.

Now, they’ve put it all together, showing that large basal channels are more likely to form at the shear margins – the weakest parts – of fast-flowing ice shelves.

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 called “polynyas”.

Study co-author Dr Ted Scambos, a senior scientist at Colorado University, added: “Now we’re seeing a new process, where warm water cuts into the shelf from below.