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During the summer of 2024, six weeks of record-smashing heat led to a record-obliterating amount of ice melting on the islands of Svalbard in the Arctic. By the end of the summer, 1 per cent of all the land ice on the archipelago had been lost – enough to raise the global average sea level by 0.16 millimetres.

“It was very shocking,” says at the University of Oslo in Norway. “It was not just a marginal record. The melt was almost twice as high as in the previous record.”

More than half of Svalbard is covered in ice. Winter snowfall adds to the ice, while the flow of glaciers into the sea and surface melting during summer leads to ice loss.

Schuler’s team has been using a combination of on-site measurements, satellite data and computer modelling to estimate how the total mass of ice on the archipelago is changing.

Since 1991, less than 10 gigatonnes of ice has melted during each summer, on average. But four of the past five years have set new records for summer ice loss. Altogether, the team estimates that around 62 gigatonnes of ice were lost last summer, almost entirely due to surface melting rather than ice flow into the sea.

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The land rose in response to ice loss by a record 16mm at one site during the summer of 2024, which is consistent with the team’s estimate for the ice loss.

The exceptional melting was due to record air temperatures, with (52°F) compared with around 7°C (45°F) in recent decades. This extreme event was, in turn, the result of warmer seas and a persistent weather pattern that brought warm southerly winds, on top of big jumps in global warming.

While this kind of extreme summer heat is unlikely at present, climate models suggest it will become common as the planet continues warming. In fact, even in a low-emissions scenario, more than half the summers between now and 2100 could exceed this level.

Schuler’s team hasn’t yet tried to estimate how much ice will be lost in the future in various emissions scenarios. Winter snowfall is expected to rise a little as the atmosphere becomes moister, but not by enough to compensate for much greater summer melting.