Scientists from the University of Alaska Fairbanks were stunned when they discovered that permafrost in the Canadian Arctic is thawing 70 years earlier than predicted.

“What we saw was amazing,” Prof. Vladimir E. Romanovsky told Reuters. “It’s an indication that the climate is now warmer than at any time in the last 5,000 or more years.” The scientists made their last expedition in 2016, visiting a remote location only accessible by propeller plane, and couldn’t believe what they saw — there were depressions and ponds and lots of vegetation, a completely different scene from what they saw during their first trip a decade earlier.

Unusually hot summers triggered the thaw, and it is likely other areas of the Canadian Arctic are also affected; the scientists are preparing to expand their study. When permafrost thaws at a fast rate, large amounts of heat-trapping gasses are released into the atmosphere, and that concerns scientists, as this will make global temperatures rise even faster. “Thawing permafrost is one of the tipping points for climate breakdown and it’s happening before our eyes,” Greenpeace International Executive Director Jennifer Morgan told Reuters. “The premature thawing is another clear signal that we must decarbonize our economies, and immediately.” Catherine Garcia