Wildfires Are Feeding Huge Carbon-Spewing Sinkholes in the Arctic – Mother Jones

Christian Andresen, Mark Lara

This story was originally published in Wired and is reproduced here as part of the Climate Desk collaboration.

Perfect storm is ravaging the Arctic—literally. As the world heats up, more lightning systems are igniting more peat fires. They burn through ancient buried plant material and release great plumes of greenhouse gases, which further warm the planet. At the same time, as plant species march north thanks to a more hospitable climate, the Arctic is greening. That darkens the landscape and absorbs more of the sun’s energy, further heating the region. It also provides more fuel to burn; dried plants above ground ignite more readily than permafrost, which is made from frozen dirt or sand or gravel mixed with dead plants. But permafrost is now thawing so rapidly that it’s creating massive sinkholes in the earth, up to 100 feet wide and 10 feet deep, a process known as thermokarst.

New research shows how wildfiresThese are exacerbating this land-gouging in north Alaska. Scientists have calculated that thermokarst formation is up 60% since 1950s by analysing satellite and aerial imagery. Wildfires have accounted for 10% of thermokarst formation in the last 70 years, but only 3 percent of the landscape has been burned over the past 70 year. 

“We found that after wildfire activity, the rate in which thermokarst occurs on the landscape is higher for upwards of eight decades,” says plant biologist Mark Lara of the University of Illinois at Urbana-Champaign, coauthor of A paper describing the research published in December in the journal One Earth. The cratering results in pits of melted and organic matter. These absorb far more solar power than snow. “If you follow those pits over years to decades, they start to grow and keep growing and getting larger and larger and larger over time. And they all stemmed from that initial small depression after a fire disturbed the tundra,” he continues.

TundraAlthough it might seem like desolation, this area is actually full of life. There aren’t tall trees, but there are lots of grasses and shrubs. These typically trap a layer of snow on the ground; the snow insulates the earth by bouncing the sun’s energy back into space. This encourages the growth and persistence of permafrost, which can sequester thousands of years’ worth of carbon. 

But climate change is heating Arctic, and this insulation is being destroyed. Four times as fastas the rest. “In an undisturbed tundra ecosystem, permafrost is protected by the overlying vegetation And soil organic layers from warming climate,” says climate scientist Yaping Chen of the University of Illinois at Urbana-Champaign, lead author on the new paper. “However, when fire occurs, it kills vegetation and removes the insulating organic layers to allow heat to penetrate downward along the soil profile that melts the permafrost.” 

That’s allowing vegetation to dry out more easily and giving it more opportunities to ignite during increasingly frequent lightning storms. (More heat equals more hot air rising into atmosphere This is how thunderclouds are formed.) The thawing of thermokarst occurs when temperatures rise due to climate change. This is similar to how an ice cube might melt on your countertop. A wildfire is the same as holding a flame to that cube.

Even worse, wildfire can darken the ground by charring it. This will make it even more hot. More quickly in the sun. If the landscape is level, a neat, melted ice pit will form and grow. Water also absorbs solar radiation. All vegetation previously trapped in ice will now sink to the bottom of this watery pit, darkening the landscape even more. 

Permafrost is basically a refrigerator for organic matter—and if it warms and thaws, microbes start to proliferate within it, just as they would on your food if you unplugged your fridge. Only these tundra microbes are chewing through millennia-old organic matter, releasing methane, a greenhouse gas that’s 80 times more potent than carbon dioxide. (If there isn’t standing water in the thawed permafrost and the plant material is drier, the microbes will release CO2 instead, but that’s less likely because the craters tend to create little ponds.)

“With thermokarst you expose deeper and deeper layers of permafrost to the thawing, much more efficiently than without thermokarst,” says University of Alaska Fairbanks permafrost geophysicist Vladimir Romanovsky, who wasn’t involved in the work. “The thermokarst process can turn a surface which was relatively dry into some sort of wetland, and wetlands are producers of of methane.” 

The pit is home to new vegetation that grows and dies, which also produces planet-warming gases. So, a landscape that was once very dry with carbon stored in the ground is now actively emitting greenhouse gases. Although a gradual permafrost melt would have been slow, the creation of thermokarst speeds up the process.

At the moment, climate models just aren’t equipped to consider such complexity. “Presently, most studies—especially modeling works—are focused on gradual permafrost thaw, which releases carbon from ground surface,” says Chen. “However, thermokarst formation will expose ancient carbon deep in the soil column to active decomposition. Once initiated, the carbon loss from these horizons may never recover.” According to One study from a separate international team of scientists, without taking this kind of abrupt thaw into account, scientists may be underestimating the climate effect of thawing permafrost by 50 percent. 

Across the Arctic, hotter temperatures are already pockmarking landscapes with thermokarst pits, but climate change is also changing the wildfire “regime,” Or the way that blazes begin and behave. Higher temperatures produce more dry fuel, which causes fires to burn larger and more intensely, which can be more destructive to the ecosystem. And while the team’s modeling only looked at northern Alaska, Lara says that this tundra system is similar to others around the world, particularly in Siberia. “That region is just being lit up and really, really heavily Wildfires can cause havoc,” says Lara. “A lot of the implications for the amount of thermokarst could be applicable to what they’re seeing over there as well.”

“It’s really an upending of a system,” Lara adds. “It’s pretty crazy how fast things are changing.”