The Arctic landscape is changing at an unprecedented rate. In addition to rising temperatures, climate change is causing episodes of extreme melting, which occurs when ice losses that previously took weeks or months occur over just a few days.

These increasingly frequent events are altering the normal dynamics of ice loss. They are profoundly changing the state of snow and ice, which are the most vulnerable elements of the polar climate system.

Snow accumulation during winter no longer compensates for summer losses. This annual balance has been negative for decades, but extreme episodes, which can last for days or weeks, cause much higher melting rates than usual. These are heat waves defined not by air temperature, but by high melting rates that cause snow and ice to disappear.

What was once exceptional is now occurring with increasing regularity. This pattern is observed throughout the Arctic, but there are significant regional differences. The highest rates of extreme melting are recorded in northwestern and northern Greenland, as well as on Ellesmere and Devon Islands in the Canadian Arctic. In contrast, the eastern Arctic – which includes Iceland and Russia’s Novaya Zemlya archipelago – shows smaller increases.

Greenland has been most severely........

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