Andreassen looked at the Barents Sea, but the same thing may have happened in other places when ice sheets retreated at the end of the Ice Age. Scientists have also found pingos in the Beaufort Sea north of Alaska and craters in the North Sea west of Norway.

And something similar may also be happening on land. In 2014, a number of huge craters appeared in Siberia. It was one of the hottest years on record in Siberia, and permafrost was melting. The craters were also found in areas rich in natural gas, and satellite imagery revealed mounds along with more craters. Russian scientists found clods of dirt that looked like they had been thrown from the craters. Irina Streletskaya, a geographer at Lomonosov Moscow State University who studied one of the craters, wrote in an email that she thinks trapped methane explains both the Barents Sea and Siberian craters.

New craters may be forming in the Barents Sea today, too. The smaller craters, says Andreassen, may be the younger ones. But the bigger potential threat to climate change is not small methane blow-outs in the Barents Sea; it’s massive blow-outs that could happen in areas currently covered by ice. If ice sheets keep retreating in places like Greenland and Antarctica, it could leave more land bare and release long pent-up reservoirs of methane.

This study adds to existing uncertainty about the behavior of methane trapped near the poles. Methane is worrying because it can have an accelerating effect: As ice and permafrost melt, they release more methane, a powerful greenhouse gas, which makes the Earth warmer, so more ice melts, and more methane is released and so on. Scientists have mostly studied the gradual and continual seeping of methane in places like the Barents Sea. In those cases, microbes in the water use up the methane before it reaches the atmosphere, so it’s not a huge concern. But how much methane is being released in these blow outs, and does it work any differently? Carolyn Ruppel, who studies gas hydrates at the U.S. Geological Survey, poses the question this way, “If you’ve got a huge burp of methane, can that methane get to the sea-air interference before it can be destroyed by microbes in water column?”

The answer will likely lie in ice cores taken in the Arctic from 12,000 years ago, when the Barents Sea ice sheet melted. If the retreating ice sheet really did release a burst of methane into the atmosphere, you’d find it in the ice cores. Andreassen says they are now looking into such a study.

And if polar ice keeps melting, well, we’ll eventually see the consequences for ourselves.