ON A July afternoon in the eastern Siberian town of Cherskiy, 220 kilometres north of the Arctic circle, it is a warm 27 °C. The vista features silver-blue rivers bisecting green swathes of boreal forest – Earth’s biggest ecosystem. But drive a metal rod into the soil and roughly 75 centimetres below the surface you hit a layer that’s as hard as steel – and perhaps as dangerous as dynamite.
Arctic permafrost holds more than twice as much carbon in its frozen soil as Earth’s atmosphere. Which is what brings me here, accompanying seven US scientists from various labs, led by the Woods Hole Research Center in Falmouth, Massachusetts. We have travelled 7000 kilometres and 15 time zones to Cherskiy to study a phenomenon that might hasten the release of that carbon: the rise of Arctic wildfires.
“Welcome to Cherskiy,” our host Nikita Zimov says minutes after we disembark the Antonov-24 propeller plane that brought us here. Zimov directs the Northeast Science Station. “I understand you want me to take you to that hellhole,” he says as he points to a ghost of a forest that will soon enchant the scientists, despite its bugs, muck and fallen trees.
The trees at Hellhole – the moniker sticks – were burned a decade ago and could provide an important clue in the debate over the impact of Arctic fire (see diagram). There is no question that warmer temperatures, drier conditions and, possibly, an uptick in lightning are catalysing a rise in blazes across the Arctic. This summer over 9 million hectares of forest in Alaska and Canada have burnt – a record – drawing thousands of firefighters to help.
Fires devour the organic layer of leaf litter and shrubs on the floor of boreal forests and tundra alike. As this layer offers insulation during the summer, burned sites could see an increase in the depth of the soil that thaws in summer, before refreezing in winter. More thawed soil could mean more microbial respiration of ancient Arctic carbon into the atmosphere, eventually turning the boreal forest from a carbon sink into a source.
The science on this is far from settled, however. For example, some research suggests that the uptick in fires could actually reinforce the permafrost by helping regenerate trees, which insulate the soil and prevent erosion. Larch, the dominant tree species, is fire-tolerant and its seedlings benefit from underbrush-burning blazes.
This is where Hellhole comes in. To reach the forest we take a skiff across the Kolyma river. Trees lean left and right, forming crosses one must traverse. Most are lifeless, but the place is hardly dead: thick mosses and tussock grasses are thriving.
The most striking thing is how bumpy and wet the ground is. Unlike the smooth floors one finds in normal boreal forests, the fire thawed the permafrost in a wild zigzag pattern. The low areas are where the permafrost was mostly ice, while the segments comprised of actual soil now form the high ground surrounding endless pools, each maybe a metre deep.
McKenzie Kuhn, a recent college graduate, checks one of a series of funnel-shaped bubble traps she set in the pools days ago. In the anoxic conditions found in the soil beneath the ponds, microbes can create methane, a potent greenhouse gas. The team is now trying to measure emissions from the ponds and determine if they come from the carbon locked in the permafrost.
Back in Cherskiy, preliminary lab tests of the gases emitted by the soils below Hellhole’s ponds show surprisingly high amounts of methane. So by destabilising the soil and creating microponds, the scientists hypothesise, fire may be creating a new fuse on the Arctic carbon bomb.