Researchers on an expedition to the Canadian Arctic have discovered that permafrost in the region is thawing 70 years earlier than predicted, Reuters reported on Tuesday.

A team from the University of Alaska Fairbanks said they were shocked at how quickly a succession of unusually hot summers has destabilised the upper layers of ice blocks in the Arctic. The ice blocks had been frozen for millennia.

“It is an indication that the climate is now warmer than at any time in the last 5,000 or more years,” Vladimir E Romanovsky, a professor of geophysics at the university, told Reuters. The group’s findings were published in the Geophysical Research Letters journal on June 10.

The team used a modified propeller plane to visit extremely remote sites in the Arctic. They said the landscape was unrecognisable from the Arctic terrain they had visited about a decade ago. Instead of sheets of ice, the terrain is now marked by waist-high depressions and ponds known as thermokarst, and flourishing vegetation.

“It’s very likely that this phenomenon is affecting a much more extensive region and that’s what we’re going to look at next,” said Louise Farquharson, a post-doctoral researcher and co-author of the study. Rapid thawing of the permafrost could release vast quantities of heat-trapping gases, eventually increasing global temperatures even faster.

“Thawing permafrost is one of the tipping points for climate breakdown and it’s happening before our very eyes,” said Greenpeace International Executive Director Jennifer Morgan. “This premature thawing is another clear signal that we must decarbonise our economies, and immediately.”

In December 2015, 195 countries had signed the Paris climate accord, which seeks to prevent global temperatures from rising more than 2 degrees Celsius, to prevent extreme events such as higher sea levels, changes in weather patterns, food and water crises and other adverse effects. Former US President Barack Obama had initiated and signed the deal.