We’re already used to worrying about at least one set of issues when it comes to melting caused by global warming: that water entering oceans from disintegrating arctic ice may cause sea levels to rise worldwide.

Now scientists suggest that another sort of melting could not only be caused by climate change, but could in itself accelerate it. At issue is not polar icecaps but permafrost, the frozen ground found in the far north.

There, organic matter is normally held in a state of very slow decay, with carbon kept out of the atmosphere for much longer periods than it would be otherwise. But as this ground thaws, as this University of Florida article puts it, “bacteria and fungi break down carbon contained in this organic matter much more quickly, releasing it to the atmosphere as carbon dioxide or methane, both greenhouse gases.”

The article summarizes a paper in the journal BioScience in which scientists led by Florida ecologist Ted Schurr show that factoring in carbon held deep within permafrost “more than doubles previous high-latitude [carbon] inventory estimates.”

While all of this carbon doesn’t simply enter the atmosphere at once when the ground melts, Schurr has estimated that the tonnage of carbon dioxide being released each year could eventually grow to around an eighth of the amount currently produced by burning fossil fuels. (Of course, thawing ground means more space for trees to grow, pulling CO2 from the air, but Schurr notes that a new forest on previously frozen ground couldn’t hold anywhere near the amount of carbon currently being stored by the permafrost.)

Another report this week amplifies the Florida team’s concerns, focusing on vast reserves of methane that may now be escaping after being held under ice and permafrost since the last Ice Age.

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