Scientists have been debating why Antarctic sea ice, which once seemed impervious to climate change, has shrunk dramatically in the past decade. Now research suggests stronger winds have churned up warming water from the deep ocean, breaking through upper water layers that were protecting the ice from melt.

While Arctic sea ice has declined about 40 per cent over four decades, until recently the sea ice around Antarctica was slightly expanding, confounding most climate models. Then after 2015 ice extent fell from a record high to several record lows, losing an the size of Greenland.

Some has suggested the sea ice may be melting largely due to air temperatures, which have been so high in recent years that Antarctic researchers have posed for in swimwear. Two new studies make the case that ocean warming played a bigger role in this “regime shift”.

“Plenty of people will say… that it was atmospheric warming which melted the sea ice from above,” says at the National Oceanography Centre in Southampton, UK, who wasn’t involved in the research. “Now these scientists have done the thorough analysis and have got a plausible chain of events, which says that the ocean is the key player in that 2016 melt. Nobody’s put that argument together before.”

As part of global ocean circulation, a mass of warm, salty water called circumpolar deep water flows southward from the tropics and circles Antarctica at depths below 200 metres. But it’s increasingly coming to the surface where it can melt sea ice, two decades of temperature and salinity measurements from several hundred drifting buoys suggest.

Antarctica is surrounded by a belt of strong winds and storms in the latitudes of the “roaring forties”, “furious fifties” and “screaming sixties”. Climate change has shifted this storm track southward, bringing more precipitation into the sea ice zone, according to a study by at Stanford University and his colleagues. Initially, the precipitation created a layer of fresh surface water that better insulated the bottom of the sea ice from warm deep water, allowing it to expand to its 2014 record extent.

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But the southward-shifted storm track also delivers stronger winds that blow surface water and ice forward. Due to the spinning of the Earth, water moves 90 degrees to the left of the wind direction, generating spirals like the Weddell Sea gyre. As surface water is flung to the edges, deep water wells up from below to fill the void at the centre.

Between 2014 and 2016, this wind-driven upwelling began to win the “tug-of-war” against the protective layer of increased precipitation, and the sea ice began to melt away in the Weddell Sea. When the researchers plugged the observed changes in temperature and salinity into a simple computer model, it projected sea ice would expand and then contract, as it did in the real world.

“Most signs point to a persistent and sustained decline in sea ice, because even with the precipitation potentially suppressing the deep ocean heat… the heat is still there,” Wilson says. “All it would take is a sudden reversal of conditions for that heat to come back up.”

That reversal began with a string of wind storms, according to the second study by at the Alfred Wegener Institute in Bremerhaven, Germany, and his colleagues.

Even before the additional precipitation of recent years, the warm circumpolar deep water had been kept away from the surface layer by winter water, a layer of cold, salty water created when the atmosphere cools the upper ocean in winter and sea ice forms, rejecting salt ions from its new crystalline structure.

But the deep water has been getting hotter due to global warming. Because water expands when it’s warmer, the deep water has been taking up more space, thinning the winter water. In 2015 and 2016, stronger-than-average winds brought up more deep water across the winter water barrier. The layering hasn’t recovered since.

The finding suggests that even if the strong winds were a natural fluctuation, the stage had been set by global warming.

“It’s the wind that pushes [sea ice] over into these rapid declines, but it’s the ocean that really keeps it low,” Spira says. “There’s definitely evidence that we’re in a new regime.”

While sea ice melt doesn’t raise sea levels, it could harm species that spend part of their lives on this ice, like krill or penguins. And if sea ice recedes near key ice shelves it could impact global ocean currents, including the Atlantic Meridional Overturning Circulation that keeps Europe warm.��That’s because salt rejection from ice formation close to shore helps form Antarctic bottom water, which is more dense than winter water and circumpolar deep water. The bottom water cascades off the continental shelf and flows north along the seabed.

“If you were to reduce sea ice production in those regions… you’ll have less bottom water and potentially a slowdown of the meridional overturning circulation,” Wilson says, although he notes that freshwater from glacier melt has a larger effect on bottom water.

An ice dome in northern Greenland once melted completely at temperatures the region could experience again this century, a finding that will begin to paint a more accurate picture of how fast the melting Greenland ice sheet could raise global sea levels.

Researchers drilled 500 metres down through the centre of Prudhoe Dome, a bulge of ice the size of Luxembourg in the north-western corner of Greenland, to collect a 7-metre core of sediment and bedrock. A dating technique using infrared light showed that sand at the surface of the core was bleached by the sun about 7000 years ago. That means the dome was completely melted at that time.

Summers in the area then were 3°C to 5°C warmer than today, temperatures they could reach again by 2100 under human-made climate change.

“This is very direct evidence that the ice sheet is as sensitive as we feared to even a relatively small amount of warming that happened in the Holocene,” says at Northwestern University in Illinois, who was not involved in the research.

The melting of the Greenland ice sheet could unleash anywhere from tens of centimetres to 1 metre of sea level rise this century. To narrow that prediction, scientists need to better understand how fast different parts of the ice sheet will disappear.

The Prudhoe Dome core is the first of several taken by the GreenDrill project, funded by the National Science Foundation and involving researchers at several US universities. They hope to tease information about past climates from the ground under the ice sheet, which researchers have called the least explored part of Earth’s land surface.

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Sediment drilled in 1966 from under the ice at Camp Century, a US nuclear-powered military facility that operated for eight years during the cold war, showed that north-western . A bedrock core taken in 1993 from under Summit Station, a scientific research facility in the middle of Greenland, proved the as recently as 1.1 million years ago.

But GreenDrill has taken this under-ice work further by sampling several points near the northern coast.

“This question is, when have the edges of Greenland melted in the past?” says at the University of Kentucky, part of the team behind the new research. “Because this is where… the first foot of sea level rise will come from.”

There has been some disagreement among ice sheet models about whether northern or southern Greenland will melt sooner in the future. This study adds to growing evidence that warming after the last glacial maximum was earlier and more intense in northern Greenland, says Axford.

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A possible reason could be feedbacks like the disappearance of Arctic sea ice, which could have released more ocean heat into the atmosphere in the far north.

By proving that Prudhoe Dome melted with 3°C to 5°C of warming, this study will give weight to those ice sheet models that give this result, says at the University of Exeter in the UK, who wasn’t involved in the research.

“The thing that this will help is tuning surface melt models. When will we really start to lose this ice?” says Gasson.

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Static electricity can remove up to three-quarters of frost from a surface, which could save vast amounts of energy and millions of tonnes of antifreeze currently used to defrost vehicles.

In 2021, at Virginia Tech and his colleagues serendipitously discovered that frost becomes naturally charged as it forms. They used this natural electric field to charge a nearby film of water that could then, in turn, pluck ice crystals from the frost, acting as a natural de-icer. This effect, however, was minuscule and had little effect on the frost overall.

Now, Boreyko and his team have developed a more effective defrosting system by using an extremely high-voltage copper electrode suspended above frost-covered glass or copper. This system can remove half the frost from a surface in around 10 to 15 minutes, and 75 per cent of frost if the surface is also highly water-repellent. “Instead of taking advantage of frost’s pre-existing voltage, we’re trying to turbo-boost the whole effect by applying our own voltage,” says Boreyko.

Removing 50 per cent of frost from a surface using their method required an electrode charged to 550 volts, more than double the voltage supplied by mains electricity in most countries. Unlike electrical sockets, though, the electrode has a vanishingly small current, making it relatively safe. Accidentally touching the electrode would generate an electric shock comparable to an electric fence used on farms, says Boreyko.

This small current also ensures it requires little energy, less than half the energy it would take to heat the frost directly, according to Boreyko.

As well as potentially being used in car windows and on roads, a fast and efficient defrosting method could also be helpful in the aviation industry, which uses vast quantities of antifreeze to ensure aeroplane wings are free of ice that might affect flying performance.

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“Instead of dousing hundreds of litres of antifreeze over an airplane wing to de-ice it when it’s taxiing, instead you just have this machine that can drive around airport runways with an electric wand and, as you wave the high-voltage wand over the wing, it just pulls all of that ice and snow right off,” says Boreyko.