For the second time in recorded history, the ice above Greenland — the thickest ice in the Arctic — is breaking apart and melting, according to the Guardian.

The first time came earlier this year amid another record-breaking heat spell. Scientists had thought this ice would be the last in the region to melt as greenhouse gases continue to drive global temperatures up, but they’ve been forced to revise their assumptions.  

“Open water off the north coast of Greenland is unusual,” Ruth Mottram of the Danish Meteorological Institute, told the Guardian. “This area has often been called ‘the last ice area’ as it has been suggested that the last perennial sea ice in the Arctic will occur here. The events of the last week suggest that, actually, the last ice area may be further west.”

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Because temperatures in the region have been so unusually high, the ice, which is usually packed very tightly, has been easier to push around by winds. As a result, waters that are normally frozen over are now open as ice drifts.

“I cannot tell how long this open water patch will remain open, but even if it closes in few days from now, the harm will be done: the thick old sea ice will have been pushed away from the coast, to an area where it will melt more easily,” said Thomas Lavergne, a scientist at the Norwegian Meteorological Institute.

In February, temperatures in the area were higher than 50 degrees Fahrenheit (10 degrees Celsius), when they’re normally around -4 degrees Fahrenheit. Last week, temperatures reached a record 62.6 degrees Fahrenheit (17 degrees Celsius).

#Arctic sea ice extent is above the minimum year 2012 but climate change takes not a rest: we begin to speak about circumnavigating #Greenland. Unprecedented in the satellite data record. pic.twitter.com/jVzMfy8rXv

— Lars Kaleschke (@seaice_de) August 21, 2018

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Elsewhere in the Arctic, sea ice levels are 40% below the annual average and scientists expect that the region will be entirely ice-free during summer months sometime between 2030 and 2050.

The knock-on effects of this mass-melt are already being felt on the global climate.

For example, the weakening of the Gulf Stream has kept cool airs from traveling over parts of the world, leading to heat waves and forest fires across Europe, the US, and elsewhere.

If all of the ice around Greenland melts, sea levels could rise as much as 24 feet. And as ice continues to melt, it’s accelerating a feedback loop that makes it more likely for more ice to melt.

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The feedback loop works like this: As ice melts, darker waters are opened that absorb more sunlight, causing water temperatures to rise, leading to more ice melt, and so on.

Runaway feedback loops like this are happening all around the world and threaten to tip the planet into a hothouse state.