AP Photo/Rick Bowmer

Last week, I reported on a serious but little discussed threat to the climate system: As the frozen Arctic soil known as “permafrost” thaws, it could release a large amount of carbon — in the form of both carbon dioxide and methane — to the atmosphere. And this new source of greenhouse gas emissions could be large enough that it could substantially undermine attempts to cut down on emissions from fossil fuels.

Now, a new overview of what we know about the permafrost carbon problem has just come out in Nature, written  by a group of 17 experts on the matter. In other words, this is probably the most thorough scientific look at the issue yet. And the researchers, led by Edward Schuur of Northern Arizona University, basically confirm that we have a serious problem — if not necessarily a catastrophe — on our hands.

The bottom line is that the permafrost carbon problem doesn’t look like it’s going to just go away as researchers better refine their estimates. Rather, it’s something that the world, and especially its leaders who are the ones making climate agreements, will have to deal with.

“Initial estimates of greenhouse gas release point towards the potential for substantial emissions of carbon from permafrost in a warmer world, but these could still be underestimates,” the study notes.

A much cited estimate from past literature is that northern permafrost contains 1,700 gigatons of carbon — a gigaton is a billion metric tons — which is a vast amount and around double what currently exists in the atmosphere.

The new study goes back closely over past estimates in light of new evidence, and comes to a broadly consistent conclusion. It finds that there are between 1,330 and 1,580 gigatons of carbon in the top three meters of global permafrost soil, in what are called yedomas (permafrost with particularly high ice content), and in Arctic river deltas.

And then on top of that, it says, there is a possible 400 additional gigatons in “deep terrestrial permafrost sediments” — not to mention a simply unknown amount in permafrost below the sea in shallow continental shelves, such as beneath the East Siberian Sea.

Overall, it’s a troubling large amount of carbon — especially in light of numbers presented by the U.N. Intergovernmental Panel on Climate Change, suggesting that if we want to have a good chance of holding global warming to 2 degrees Celsius above pre-industrial temperatures, we probably have only about 500 more gigatons of carbon in total that we can emit.

“We’ve gone back with this whole synthesis effort, looked through all the data, and synthesized, and yeah, this problem is not going away,” says lead study author Schuur.

Fortunately, the new study also finds that any sudden or catastrophic release of Arctic carbon stores is unlikely. Rather, the experts estimate that by 2100, somewhere between 5 and 15 percent of the 1,330-1,580 gigatons could  be emitted. Ten percent of the total would equate to around 130 to 160 gigatons of carbon emitted this century — which is both good news and bad news at the same time.

The good news is that the permafrost emissions are “unlikely to occur at a speed that could cause abrupt climate change over a period of a few years to a decade,” as the study puts it. The bad news, though, is that 160 gigatons, even though it’s less than we’re expected to emit from fossil fuels in coming decades, is still a large enough amount to really matter for the planet — especially given the relatively tight carbon budget that we have remaining.

And it could, of course, be more. If you assume 15 percent of the carbon will be emitted in this century, for instance, then the range becomes about 200 to 237 gigatons. Moreover, the emissions don’t end at 2100 — they continue well into the next century.

Much of the research that is synthesized in the new Nature paper has been conducted since the last official report of the United Nations’ Intergovernmental Panel on Climate Change — whose climate projections didn’t include permafrost emissions. New models, perhaps, will — and accordingly, may spit out results suggesting that reducing our emissions enough to stave off the worst climate outcomes will be even harder than previously thought.

“I think this highlights, there’s a big carbon cycle out there that we’re influencing, but we don’t control the whole thing,” says Schuur.