After Fire, Arctic Permafrost Enters Positive Feedback Loop Of Thermokarst, CO2 Release, More Fires
A perfect storm is ravaging the Arctic—literally. As the world warms, 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 wildfires are exacerbating this land-gouging in north Alaska. After analyzing satellite and aircraft imagery going back to the 1950s, scientists calculated that thermokarst formation has accelerated by 60 percent since then. In the past 70 years, wildfires have burned 3 percent of the landscape but are responsible for 10 percent of thermokarst formation.
“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 creates pits of melted ice and organic matter, which absorb far more solar energy 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.
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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 as potent as 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.”
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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.
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https://www.wired.com/story/wildfires-are-digging-carbon-spewing-holes-in-the-arctic/
