Few things signal something’s gone haywire on the planet quite like frozen land on fire. Researchers have discovered that Arctic fires, even those that are milder, can change the landscape for many decades. It may be even more difficult to maintain global heat levels at an acceptable level.
It’s mostly rising temperatures that are thawing out frozen Arctic ground but northern blazes — already increasing — are now understood to play a disproportionate role, according to a study published last week in the journal One Earth.
Studies in the past have shown that more fires can be caused by higher temperatures, more dry soil, more lightning and less rain. That work, with the new paper, mean that “in the future we might expect to see an outsized influence on thaw from the fires that will likely increase,” said Róisín Commane, a Columbia University assistant professor who studies atmospheric composition and wasn’t involved in the new study.
The paper might help explain small increases in methane and CO₂ from Alaska’s North Slope seen over the past 40 years, she said, but there’s been no massive increase yet from abrupt permafrost melt — a longstanding concern among researchers.
It can cause ground to melt, which causes it to become unstable and eventually collapse. This is what scientists call “thermokarst”. Sometimes the terrain appears as large round or shallow pits. Scientists who monitor them must walk carefully between them.
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Aerial images of these landscapes can be striking or beautiful as long as you don’t think about why they’ve grown by about 60% in the Alaskan Arctic between 1950 and 2015. Air temperatures are rising twice as fast as the global average, which is why most of this happened. Scientists in northwestern Alaska have found that fires from the region have an impact on climate change. They have used 70 years worth of overflight and satellite images to determine this. They burned just 3.4% of the area but are responsible for 10.5% of thermokarst in Alaska’s Noatak National Preserve, the area under study.
Global warming is making fire conditions more common near the top of the world, and the study’s results are likely applicable to the uptick in fires elsewhere around the Arctic rim. Temperaturekarst rates rise dozens of fold in the immediate aftermath of a fire. This rate has remained twice as high for 40 years and returned to normal after perhaps eight decades.
“That’s the main take-home message about this project,” said Yaping Chen, lead author and a postdoctoral researcher at the College of William and Mary, who conducted the work as a University of Illinois PhD candidate. “Many people think that an ecosystem will always recover. There is actually a threshold point after which the ecosystem may never recover.”
When dead biomass freezes, hungry microbes can’t feast on it and release carbon dioxide in the process. But that’s what happens when the thaw comes. The worst thing is that thermokarst pits may flood and form lakes, cutting off oxygen from the ground. That makes the land swampy and attracts microbes that produce methane, a much more powerful greenhouse gas than CO₂.
Permafrost is chock full of carbon and it sits underneath 20% of the world’s land, holding twice as much as the atmosphere. Scientists don’t have maps as detailed as they’d like of where all the permafrost is. Remote sensing only allows for a limited amount of depth on the surface. Scientists must therefore make general assumptions about the extent permafrost in an area based upon the type of terrain.
Ultimately, they’d like to know when, how much and how fast permafrost will release more heat-trapping gases, according to a major UN climate-science assessment published in August. It would allow them to be more exact in estimating the global warming rate and its extent. How thermokarst transforms landscapes, releasing more CO₂ or methane in the process, isn’t captured well in climate models now.
“I like to think of it as a 10% effect,” said David Lawrence, a senior scientist at the National Center for Atmospheric Research who wasn’t involved in the study. Permafrost melt “is going to make climate change about 10% harder to combat. We have to reduce emissions by 10% more to get to the same targets, or we’re going to get 10% more warming. That number could rise to 20%, but I don’t think it’s going to be 50%.”
Eric Roston is the Climate Report Newsletter author about global warming.