With the Arctic warming at up to three times the pace of the global average, more lightning storms will invade the High North, igniting wildfires that release carbon dioxide and speeding the transition of flat mossy tundra to brush and forest landscapes that absorb more solar heat energy.
Yang Chen, an Earth scientist with the University of California, Irvine and lead author of a study released today in the journal Nature Climate Change that projected the increases in lightning strikes, said the findings were somewhat unexpected, and intensify wildfire concerns in the High North because lightning is the main ignition source in the Arctic.
“The size of the lightning response surprised us because expected changes at mid-latitudes are much smaller,” he said. More lightning-caused fires would speed a vicious circle of climate-warming changes already under way in vast areas of tundra and permafrost across Siberia and Alaska, he added.
A surge in the frequency of large Arctic fires in the last five years spurred the research, which is based on 20 years of NASA satellite data showing the relationship between lightning and the climate, he said.
Linking that data with climate projections through 2100, the scientists estimated the number of lightning strikes will grow by about 40 percent for every 1.8 degrees Fahrenheit of warming. By late in the century, the IPCC projects the Arctic could warm by 4.5 degrees to 8 degrees Fahrenheit, depending on emissions.
The study also shows that the region that experiences lightning will shift, with future flash rates in the far northern tundra areas equal to the current rate in boreal forests, 300 miles to the south.
The increase may cause “a fire-vegetation feedback whereby more burning in Arctic tundra expedites the northward migration of boreal trees,” that will absorb more heat from the sun, accelerating the Arctic cycle of warming,” the authors wrote in the study.
More Lightning, More Fires, More Carbon in the Sky
The other part of the story is the vegetation is getting drier, and consequently, more flammable. That increases the odds that any individual lightning strike will ignite a fire. “If you have more lightning and drier fuels you will have more ignitions,” said co-author Sander Veraverbeke, a climate researcher with Vrije Universiteit Amsterdam. “What I found quite intriguing is the relative increase becomes higher the farther north you go, lightning increasing 85 percent in boreal forests but 150 percent or more in tundra.”
In recent years, some of the largest, longest-burning wildfires ignited by lightning in Arctic tundra and forests burned deep into soils of carbon-rich peat, which have been documented to release large quantities of carbon dioxide when they combust. As much as 90 percent of the carbon emissions from an Arctic wildfire come from the smoldering soils, he said, with only a little bit coming from the burning trees.
“Burning peat can release 2.5 to 3.5 kilograms (5.5 to 7.7 pounds) of carbon per square meter of ground,” he said. “That’s a lot, two or three times as much as from a fire in the savanna or the Mediterranean.” Arctic fires can scar the land so deeply that emissions from the disturbed permafrost and peat continue for decades or even centuries.
“It takes a really long time to recover, if it even does recover,” he said, “and if not, it becomes a long-term net flux of carbon to the atmosphere, contributing to more global warming.”
In some parts of the tundra, shrubs and trees start to grow after a fire. While those plants do store carbon, the new growth can also warm the climate because the patchwork of shrubs and trees, which is darker than an unbroken blanket of white snow, absorbs more of the sun’s heat.
Related: Global Warming to Spur More Fires in Alaska, in Turn Causing More Warming
Michelle C. Mack, an Arctic ecologist at Northern Arizona University who was not involved in the study, said the new research highlights important consequences of some more profound changes a rapidly warming climate is bringing to the Arctic, like treeline migration and permafrost thaw.
“I think that the lightning is a moderate worry, while the consequences for permafrost thaw are profound and should stimulate lots of worrying,” she said. Broadly, across northern Alaska and Canada, the dryness of vegetation is crucial to predicting fire severity and carbon emissions, she added. “If tundra is wet, cold, and soggy, it doesn’t matter how many lightning strikes hit it,” she said. “It is unlikely to burn.”
Study co-author Jim Randerson, an Earth scientist at the University of California, Irvine, said tundra fires burn layers of moss and organic debris that insulate the frozen ground below them. So even deep soils that don’t burn can thaw and release carbon dioxide and methane, “which will drive even more warming,” he said.
The new findings bolster other recent research on Arctic lightning, said Rick Thoman, an Alaska climate specialist with the University of Alaska Fairbanks who was not involved in the study. The potential for fire-sparking lightning strikes will increase most in tundra zones where fire is still mostly a stranger, he said. Another study published last month in Geophysical Research Letters showed a tripling of Arctic lightning strikes globally between 2010 and 2020, increasing “linearly with the temperature anomaly.”
Related: Alaska Chokes on Wildfires as Heat Waves Dry Out the Arctic
Challenges and Opportunities for Firefighters
The series of large fires in Alaska and Siberia the last five years were all preceded by weeks and months of record heat that turned normally soggy bogs into tinder for the lightning storms. While the new study highlights the double whammy that global warming is for Arctic wildfire ignitions—supercharging the atmosphere with moisture and warmth needed for lightning storms while at the same time drying out the surface of the tundra in some areas—it also hints at some opportunities to better confront the fires.
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Projecting changes in lightning patterns could help identify where to look to put out fires before they get too big, Randerson said. Tundra fires sometimes smolder at low intensity for several days before spreading, providing a time window to put them out before they explode in size.
“We do want to keep fires out of Arctic tundra, so we have to look seriously at that element,” he said. “Keeping fires out will protect permafrost and keep trees from moving into the tundra. How many carbon credits would you get if you could put out some of those fires?” Satellite instruments and ground-based detection networks dedicated to measuring lightning activity should be fortified to help pinpoint where the biggest dangers are, he added.
But Mack, at Northern Arizona University, said efforts to try and extinguish tundra fires “would take a massive redirection of fire-fighting resources” that are already spread thin and concentrated on protecting rural communities. The long-term benefit of fighting remote fires to keep carbon in the ground and the urgent demands to protect communities and infrastructure will be increasinging difficult to balance throughout the Arctic. That puzzle is complicated even more by the fact that, in some ecosystems, putting out fires today magnifies the potential for bigger fires in the future.
Veraverbeke, in Amsterdam, said that, even if the main goals for fire managers in Canada and Alaska are preserving life and property, there could be some low-hanging fruit for management of the tundra fires that have the potential to release massive amounts of climate-warming methane and carbon dioxide.
“We know that if we have a lightning strike it can smolder for several days, so there is a window for fighting them,” he said. And better lightning detection could also identify “the zombie fires that smolder all winter and then flare up in the spring. You could extinguish them before they blaze up again.”
University of Montana fire ecologist Phil Higuera said suppressing fires to limit greenhouse gas emissions might be a worthwhile trade-off in a world with human-caused climate change pushingfire into ecosystems where it has been historically rare.
“Big picture,” he said, “it’s also key to keep this in context. Limiting human emissions of CO2 is the much more impactful action in terms of mitigating and reducing anthropogenic climate change.”