Late in the evening, Walton Smith sat on his front porch and watched the tundra burn. For weeks, a wildfire had been licking towards his home in St Mary’s, a town of 600 people in western Alaska. As the sun sank, he could see flames jump between trees. Smith, who is St Mary’s city manager, says that as the cones in the spruce flared, “all of the trees around it would suddenly be engulfed in flames”.
The state has been ablaze since April, torching – more than three times what normally burns in a year. “In the last 30 years, the frequency of large wildfire seasons has doubled,” says at the University of Alaska Fairbanks. Climate change is increasingly priming the land to burn, he says, with repercussions that extend well beyond Alaska.
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By far the largest US state, Alaska is nearly two-and-a-half times the size of Texas. It has many microclimates and ecosystems, from unbroken stretches of tundra to vast swathes of boreal forest, whose spruce and birch trees are crucial to many of the world’s migrating bird species.
St Mary’s sits inland on one of the Yukon river’s tributaries, where warmer springs have driven shrub growth: alder and willows thicketing river bottoms and hillsides are ready fuel for fire. Unusually before a dry spell left south-west Alaska parched. “The tundra actually crunched,” Smith recalls. “It wasn’t soggy and spongy the way it’s supposed to be.”
All it took to spark disaster was a lightning strike. Warmer air holds more moisture, which raises the risks of thunderstorms. Recently, . “In western and south-western Alaska, fire frequency has nowhere to go but up,” says Thoman.
Alaskan fires are also burning hotter and deeper. Wildfire is an important part of the boreal ecosystem – black spruce trees and release their seeds – but “if you change the frequency and intensity of fires, it has an effect across the whole landscape”, says at the University of Alaska Fairbanks.
When the land’s protective top layer is scorched, the permafrost can begin to thaw, destabilising the earth until it collapses into marshy hollows and hummocks, a process called thermokarst. In an analysis of 70 years of data from Alaska’s Noatak National Preserve, at the College of William & Mary, Virginia, and her colleagues found that . “The effect of fire can last for decades,” she says.
Permafrost is the foundation of the Arctic landscape, so its thaw has a cascading effect. In poorly drained lowlands, water pools can absorb heat, which speeds soil warming, causing more thawing. Fire has a similar effect. “A charred landscape becomes darker and absorbs more heat,” says Chen.
Permafrost also stores large amounts of organic matter and nutrients, says Bianca Rodríguez-Cardona at the University of Quebec in Canada. In a study of the Central Siberian plateau, she and her colleagues found that . This can cause algal blooms, which may harm fish by lowering oxygen levels. It can also lead to dramatic drops in dissolved organic carbon – a main food source for microbes at the bottom of the food chain – for the next 50 years.
That’s to say nothing of the greenhouse gas emissions when permafrost thaws. Collectively, it holds about twice as much carbon as is now in the atmosphere, , but most climate models overlook .
If these trends continue, “there’s a threshold after which the ecosystem may never recover”, says Chen. Many Arctic plants, like cranberries and blueberries, can survive burning above ground, but when severe fires scorch their root masses, it forces them to reseed from elsewhere and slows regrowth, says , a fire ecologist at the US National Park Service in Alaska. Spruce take decades to grow cones; if fires are too frequent, they can’t reproduce.
All of this also affects animal habitat. “We have a pretty resilient landscape,” says Barnes, but some wildlife depends on older forests, and ecosystems that have long since recovered from fire. Birds like the , for example, and caribou .
Food scarcity can ripple out to the people who rely on these animals, too. Before this summer’s fires around St Mary’s, the Yukon river salmon runs were already at record lows, probably due at least in part to ocean warming.
Research questions about Arctic wildfires tend to centre on things like carbon emissions. But in communities like St Mary’s, food from the land is an important part of culture, and expensive to replace in a grocery store. After a fire, erosion increases river sediment and debris, which can suffocate salmon eggs left without clean gravel beds and oxygenated water. With surrounding vegetation burned away, there is also less shade over the water, so rivers can get warmer, says at the University of Alaska Fairbanks. Even before the fire, river temperatures near St Mary’s could get warm enough to cause heat stress for adult salmon. “Is this just the nail in the coffin for fish returning?” asks Smith.
Another big question now will be how scientists, government and the people of Alaska come together in the face of such challenges. “Communities in regions where wildfire has not historically been a significant risk are going to have to think much more about fire than they ever have in the past,” says Thoman.
That doesn’t just mean learning how to cut firebreaks by hacking back shrubs to starve fires of fuel. Burning thousands of square kilometres generates lots of smoke. For weeks this summer, the air quality index for the interior of the state was often “hazardous” – meaning particulate pollution was often above 300 parts per million, . In the 1950s, the city of Fairbanks had a roughly 70 per cent chance that any given summer would have zero hours with visibility reducing smoke. “Now, that’s down to about 10 per cent,” says Thoman.
As fire seasons worsen, both communities and resources will come under pressure. Alaska often relies on fire crews and equipment from the mainland US states. But when everyone is facing more fires, fewer crews are available.
Fire isn’t the only growing challenge. In recent weeks, several places in Alaska have . “There is no one-size-fits-all situation in the Arctic,” says Rodríguez-Cardona.
Yet that variation is what makes Alaska so important, says Fresco. The Arctic is a vast place, and , spared from the fragmentation that human development caused in other places around the world. Animals can find undisturbed habitat even after natural disasters. Its undeveloped nature has also helped it to maintain such significant carbon stores. Alaska is a proving ground for both climate mitigation and adaptation, says Fresco. “It’s a crucial and obviously irreplaceable place.”
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