In this photo taken Oct. 27, 2010, Russian scientists Sergey Zimov and his son Nikita Zimov extract air samples from frozen soil near the town of Chersky in Siberia 6,600 kms (4,000 miles) east of Moscow, Russia.

But the Zimovs' research suggests the winter re-freeze in 2017-2018 did not penetrate all the way to the permanently frozen ground beneath, leaving an intermediate layer of thawed ground sandwiched between the surface and the permafrost.

The top few layers of earth in the Arctic freeze in the winter and thaw out in the spring. But at a certain depth, the earth remains frozen solid year-round. This is aptly named "permafrost." Some permafrost has been frozen for up to hundreds of thousands of years.

Father and son scientists Sergey and Nikita Zimov found surprising slushy and muddy turf near the far eastern Russian town of Cherskiy, 200 miles north of the Arctic Circle, when the ground should have been frozen.

The new research was reported Wednesday by National Geographic . If confirmed, scientists say, this could be yet another sign of climate change in a sensitive environment, and the thawed earth could have other troubling consequences.

Some of the ground in the Arctic region is typically frozen most of the year round, but there is new evidence some of it may not be freezing at all, not even in the winter.

That unfrozen layer is surprising and potentially worrying, said Max Holmes, deputy director and senior scientist at Woods Hole Research Center in Massachusetts.

"It is a big change," Holmes told CNBC. "Is it across the Arctic? Is it going to happen this year? Those are the big questions. But it is a striking change."

The Arctic has been warming for years. The twist in the story is that an unusually large amount of snow in the region this past winter may be to blame, as it could have acted as an insulator that trapped heat in the ground. So there is a chance this may not happen again if snowfall is light next winter.

The odd thing is that global warming could be causing the higher level of snow.

One hypothesis is that the warming in the Arctic could be contributing to more evaporation from sea ice, which in turn provides the moisture in the atmosphere that makes more snow, he said.

It is important to note that the Zimovs' research has not been peer-reviewed or published and that some skeptics say more research is needed. But another scientist, Vladimir Romanovsky at the University of Alaska, Fairbanks, has seen similar evidence in his own work.

If further evidence bears out their findings, it is a sign the region is warming faster than previously thought.

Evidence has suggested that thawing permafrost has its own consequences. Scientists estimate it contains roughly twice the carbon found in the atmosphere.

There are about 1,500 billion tons of carbon locked up in the decaying plant matter found in the permafrost. That is almost twice as much as the roughly 850 billion tons found in the atmosphere, Holmes said. The frozen ground is the only thing keeping the plant matter from decaying and releasing carbon into the atmosphere.

Carbon gases are widely considered the primary contributors to global warming.

"There is a lot of carbon locked up in permafrost, and we should hope that it stays there," Holmes said. "This heightens the concern that it doesn't."

But with the ground already soft in the Arctic, the decay that comes with the spring thaw could get a head start, and it could be even harder for the ground to refreeze next winter, Holmes said.

Read the full story in National Geographic.