Forests are great and all, but in one way, they don’t come close to the raw power of peatlands. Sprawling in the Arctic and elsewhere, like tropical regions, these soils are loaded with plant matter that’s resisting decay, turning into ultra-concentrated carbon. Though they comprise just 3 percent of Earth’s area, peatlands store 600 billion metric tons of the stuff — more than all the planet’s forests combined — making them critical tools for preventing even more global warming.
On the face of it, then, we might welcome the findings of a new study that shows these carbon sinks are indeed expanding in the Arctic, as scientists have suspected. The region is warming four times faster than the rest of the planet, encouraging the growth of plants, just as precipitation up there is also increasing, creating waterlogged conditions that slow decomposition. But the carbon stored in all that new vegetation could still one day return to the atmosphere as a sort of carbon burp, and the degradation of peatlands threatens to release loads of planet-warming gas sooner than that.
“What is clear is that the more extreme climatic changes that we have, the more likely it is that they will release more carbon into the atmosphere,” said Angela Gallego-Sala, a biogeochemist at the University of Exeter and coauthor of the paper, which published earlier this month. “We see already in extreme dry years, these peatlands are going up in fire.”
Blame this on a phenomenon known as Arctic greening. As the far north warms, it loses ice on land and sea, which exposes darker earth and water, which absorb more of the sun’s energy, which drives more warming. This encourages the northward expansion of plant species, especially shrubs, which take advantage of warmer temperatures and increased rainfall. (That’s also due in part to decreased sea ice: Without that glare bouncing sunlight back into space, more seawater evaporates, loading the atmosphere with moisture.) “Things are getting greener, but they’re also getting wetter,” said paleoecologist Josie Handley, lead author of the paper, who did the research while at the University of Exeter but is now at the University of Cambridge. “That’s all really good conditions for the formation of peat.”
Extra plant material, especially sphagnum moss, is contributing to this expansion, the study found. Because peat is difficult to identify by satellite — given that it’s accumulating belowground, unlike a forest standing tall on the surface — the researchers had to venture into the Arctic, sampling the ground in transects. And because the vegetation accumulates year by year in layers, they could determine the age of the material by dating both the carbon and lead content.
Handley and Gallego-Sala found that indeed, peatlands have been expanding in these areas in recent decades, and they may now cover a greater area than anytime in the last three centuries. But there’s also a feedback loop here, in which peat becomes self-sustaining: Because sphagnum moss excels at retaining water, even when dead, it hydrates the landscape, providing conditions for yet more moss to accumulate and resist decay.
At the same time, frozen soil, called permafrost, is thawing, unlocking still more ancient carbon long locked in ice. Glaciers, too, are receding, opening more land for peat to colonize. “If you’ve got areas where you can retain that moisture,” Handley said, “and it gets more waterlogged, and then also if you’ve got the kind of fringes are greening because there’s more plant productivity and that sort of thing going on, then you meet all your components to make your peat.”
Indeed, the researchers found that peatlands can start as small “nuclei” that, if conditions are correct, expand and eventually merge with other nuclei. And as the Arctic warms, the growing season is lengthening, giving all this moss longer to grow and accumulate. “What’s really interesting is that they’re also showing that it isn’t all climate, that it’s also sort of local hydrology can help initiate the formation the peat,” said Mike Waddington, an ecohydrologist who studies peat at McMaster University but wasn’t involved in the new paper. “They’re hypothesizing that the peatlands, although they’re quite shallow, also are creating the conditions to continue to accumulate peat.”
Just as the Arctic and boreal regions are warming, extreme heat is periodically drying them out. That’s driving massive wildfires that are chewing through shrubs and trees, but also burning up dried peat. These extraordinarily persistent fires smolder for weeks or even months, releasing carbon all the while. They’re so relentless, in fact, that they’ll burn underground as snow covers them through the winter, only to pop up again in the spring. Hence their nickname “zombie fires.”
We’ve got an elemental tug of war, then: As the far north rapidly and radically changes, how much carbon will these expanding peatlands sequester in the Earth, but how quickly will that carbon return to the atmosphere if these new peatlands dry out and catch fire? Only time — and scientists traipsing through the Arctic — will tell.