Climatologists have spent decades politely warning that we are cooking our planet, but now one has decided to stop sugar coating it. Professor Jason Box of the Geological Survey of Denmark and Greenland tweeted “If even a small fraction of Arctic sea floor carbon is released to the atmosphere, we're fucked.”

Box was responding to research by Stockholm University reporting “vast methane plumes escaping from the seafloor” in the Arctic Ocean.

The scientists who made the discovery were more restrained. “This was somewhat of a surprise,” chief scientist Orjan Gustafsson wrote. Although there have been plenty of reports of methane plumes in the Arctic before, these have been a forewarning of danger, rather than a direct threat themselves. Microorganisms in the water column scavenge methane as it rises. Provided they can get to it before it reaches the surface the climate change damage is small.

However, at some locations the Swedish team saw bubbles reaching the surface. Dissolved methane concentrations were 10-50 times background levels, and expedition members report “sniffing methane”.

“While there has been much speculation about the vulnerability of regular marine hydrates along the continental slopes of the Arctic rim, very few actual observations of methane releases due to collapsing marine hydrates on the Arctic slope have been made,” Gustafsson wrote.

The methane was released from a steep continental shelf 250-500m beneath the Laptev Sea off Siberia. There is evidence that the last vestige of the Gulf Stream, which reaches this point having wrapped around Scandinavia, has become warmer in recent years, and this may be triggering the release.

Explorations of the Arctic Ocean are so recent we don't know whether such events are unprecedented, but we do know the area has warmed dramatically in recent decades.

Simultaneously, evidence is building that methane release is the cause of the craters that have suddenly started appearing in other parts of Siberia. When interviewed by Vice Box said if he knew the tweet was going to attract so much attention he would have included the methane in permafrost, since this could be equally dangerous, but says he doesn't know enough about the holes to comment on their relation to climate change.

Box is a highly credentialed scientist, whose main area of research is dark snow, snow that has had soot and black carbon fall on it, speeding its melting. He blogs at Meltfactor, where he says we need “an aggressive atmospheric decarbonization program. We have been too long on a trajectory pointed at an unmanageable climate calamity; runaway climate heating. If we don’t get atmospheric carbon down and cool the Arctic, the climate physics and recent observations tell me we will probably trigger the release of these vast carbon stores, dooming our kids’ to a hothouse Earth. That’s a tough statement to read when your worry budget is already full as most of ours is.”