Melting compost heaps and the permafrost precautionary principle1

Thawing permafrost could inject enough carbon into the atmosphere to cook the planet. But nobody’s quite sure how fast it’s going to happen.

Permafrost is a giant cold-storage compost heap, stuffed full of frozen carbon. Just like you chucked out last night’s potato peelings, the planet has chucked out billions of tonnes of dead plants, trees, mammoths and, yes, polar bears, all of which is now happily interred under the Arctic wastes.

The difference is that while your compost heap ticks over at a nice warm temperature, breaking down the potato peelings into compost, the frozen ground which makes up permafrost stops that organic stew of Arctic flora and fauna from decomposing, safely locking up the carbon stored in it.

I say ‘safely locking up’ because from the point of view of creating human civilisation, permafrost has been pretty handy. While the permafrost has been permanently frozen, we’ve been busy ekeing out human life, discovering fire, developing agriculture, growing our population. While we’ve been busy nurturing the capabilities that ultimately allow the lucky few to participate in Britain’s Got Talent, the planet’s been watching our backs by keeping this massive store of carbon locked up under the frozen parts of the planet’s surface.

Of course, in these exciting climatic times, permafrost is a pretty poor name. Because as the planet warms up, the permafrost is no longer permanent – it’s taking on less of the character of a crisp winter’s day, and more of the character of a damp boggy field. Normally, every Arctic summer the very top layer of permafrost melts before refreezing in the winter. But as the planet warms, (and it’s warming faster in the Arctic than anywhere else), the melt is getting deeper and more widespread, and in some places the permafrost isn’t refreezing completely in winter.

When permafrost melts, it releases either carbon dioxide or methane into the atmosphere. Both are important greenhouse gases. Both will speed up the rate at which the planet warms. And there’s a hell of a lot of carbon stored in permafrost. Maybe twice the amount that’s currently in the atmosphere. Unlock that frozen store, the worry is, and we’re dabbling with the possibility of adding enough carbon to the atmosphere to change the atmospheric era we’re in, to something even more exciting than the Anthropocene, and by implication, seriously jeapordising our ability to watch Susan Boyle on youtube.

That kinds of suggests a bit of a doomsday scenario, or at least it does to environment journalists. But permafrost is a great example of the difficulties there are in restraining our desire for clear cut statements about how the climate’s going to behave as the planet warms (and to a certain extent, the media’s desire for screaming headlines about the end of the world), with the cautious nature of the scientific field.

Permafrost is a great example of the difficulties there are in restraining our desire for clear cut statements about how the climate’s going to behave as the planet warms with the cautious nature of the scientific field.

Talk to climate scientists who work on permafrost and they’re pretty tentative about the conclusions of their work. It’s a challenging field to make predictions in at the moment, because there don’t yet exist good, widely accepted models of permafrost melt (we’re probably at least a few years away from that), and scientists rely on a pretty small number of field researchers who arduously travel around Siberia and Alaska taking point-by-point site measurements of gas emissions, which is a pretty crude way to predict emissions on such a huge scale.

Only very recently are we beginning to get predictions about how much permafrost melt might contribute to greenhouse gas emissions. Edward Schurr, a good name to look out for if you’re interested in reading more, recently wrote a paper in Nature broadly suggesting that permafrost emissions might reach in the order of a gigatonne a year – and over a few decades permafrost could be a ‘large’ carbon source in a warmer world.  But these are still early results.

What can we say confidently? We can certainly say that permafrost represents a source of carbon emissions that are additional to what the IPCC has considered up to this point. The IPCC’s latest treatment of permafrost didn’t attempt to include any assessment of permafrost as a carbon source – they were only interested in talking about the effect large parts of the Arctic land surface collapsing might have on stuff that had been built there – houses, gas pipelines, nuclear reactors, that kind of thing. Not unimportant, and in one way you want to cut them some slack for not considering it, because they’re not really cut out for appraising rapidly changing recent science.

In another way, though, it makes you want to bang your head against a table – because in emissions terms we’re already tracking along the worst-case emissions scenarios from the stuff the IPCC did consider, even without the possibility of the north of the planet outgassing carbon dioxide and methane like a compost heap having a psychotic breakdown.

There is one way in which permafrost is really interesting. A common critique of environmentalists is that they advocate the ‘precautionary principle’ – which says we should do more rather than less to tackle climate change, just in case – without good reason. But the current level of knowledge we have about permafrost is a pretty clear-cut example of why the precautionary principle is actually a perfectly reasonable way to go about things.

Because: we can definitely say permafrost emissions will be additional to the IPCC SRES scenarios, and we can definitely say that they’ve got the potential to be huge, but we can’t (yet) say how much CO2 and methane is actually going up into the atmosphere, and we can’t (yet) say how quickly emissions are going to increase. What do you do in that situation? Ignore it, as the IPCC were forced to?  Or maybe add a bit of a safety margin to the system by being ambitious? Our understanding of the science of permafrost thaw is a great advert for the precautionary principle.

Permafrost is not a clear-cut situation. It’s also one we don’t understand particularly well, yet. But by seeing that it can only really speed up the rate at which the planet changes, we see a clear argument for not developing that understanding by actually melting the stuff.