Why the Arctic is smouldering
The Arctic is transforming before our eyes: the ice caps are melting, the tree-line is shifting northwards, starving polar bears wander into cities. The region is warming twice as fast as the rest of the planet due to climate change, largely due to changes in albedo – the loss of sunlight-reflecting ice and snow, replaced by sunlight-absorbing ocean and soil. This is driving a dangerous positive feedback cycle where heating spirals into more heating.
And, now, the Arctic isn’t only losing its ice. It is being set ablaze.
Gargantuan forest fires in Siberia, which burned for more than three months, created a cloud of soot and ash as large as the countries that make up the entire European Union. More than four million hectares of Siberian taiga forest went up in flames, the Russian military were deployed, people across the region were choked by the smoke, and the cloud spread to Alaska and beyond. Fires have also raged in the boreal forests of Greenland, Alaska and Canada.
Though images of blazing infernos in the Arctic Circle might be shocking to many, they come as little surprise to Philip Higuera, a fire ecologist at the University of Montana, in the US, who has been studying blazes in the Arctic for more than 20 years.
尽管北极圈内熊熊大火的图片可能会让很多人感到震惊，但美国蒙大拿大学（University of Montana）火灾生态学家伊格拉（Philip Higuera）认为，这并不令人意外。
“I’m not surprised – these are all the things we have been predicting for decades,” he says.
Higuera and his team predicted in 2016, based on sophisticated computer modeling, that fires in the boreal forests and Arctic tundra would increase by up to four times by 2100.
A key tipping point, he says, is an average July temperature of 13.4C over a 30-year period. Much of the Alaskan tundra has been perilously close to this threshold between 1971 and 2000, making it particularly sensitive to a warming climate. The number of areas near to and exceeding this tipping point are likely to increase as the climate continues to warm in the coming decades, says Higuera.
“Across the circumpolar Arctic, the take-home message is that there are distinct thresholds above which you start to see the tundra burning – it’s like a binary switch,” says Higuera. “This threshold relationship is part of what makes the Arctic so sensitive: areas will stay below this threshold for years, off our radar for fire activity – and then all of a sudden with a change in temperature it will start to burn.”
Though fires are a natural component of all ecosystems, including in the far north – they foster biodiversity and facilitate nutrient cycling – to see them on this scale in the Arctic is unprecedented and highly unusual.
“It’s an indication of how much we humans are kicking the system,” says Higuera. “And changing [the] global climate is a very big kick to the system.”
Part of the reason for the explosion in fires is that this increased heat is drying the soil and melting the permafrost. But there are more surprising reasons, too – such as that the warming climate is leading to more lightning strikes, which are causing more forest fires.
“Working in the field in Alaska this summer in a hot and smoky environment, you could literally feel the impacts of a number of fires that were happening in different places all over the landscape,” says Sue Natali, associate scientist with the Woods Hole Research Center, a Massachusetts-based organisation that researches climate change science and solutions. “You could also see the long-term impacts of fires that had happened years beforehand. We were walking on ground that was literally collapsing as a result of permafrost thaw brought on by previous fires.”
“在阿拉斯加今夏炎热和烟雾缭绕的环境中做实地考察，你可以感受到不同地方受火灾的影响。”娜塔莉（Sue Natali）说。娜塔莉是伍兹霍尔研究中心（Woods Hole Research Center）的副研究员。这家机构位于马萨诸塞州，专门研究气候变化和解决方案。“你还可以看到多年前发生的火灾所造成的长期影响。由于之前的火灾导致冻土融化，我们正在行走的地面发生了坍塌。”
If simmering permafrost isn’t surprising enough, this summer she saw something even more shocking.
“I worked in a wetland that had burned,” says Natali.
The fires are impacting entire ecosystems in the north. The air is polluted, droughts are endemic, and in response new assemblages of plants and trees are growing in unexpected places. A report last year found, for example, that warming in the Arctic, and attendant vegetation changes, have caused caribou populations to plummet by half – due to the animals being unable to locate their normal food sources of lichen.
Fires in the Arctic also have huge implications for the global climate. Boreal forests and Arctic tundra cover 33% of the global land surface, and hold an estimated 50% of the world’s soil carbon – more carbon than is stored in all the world’s vegetation, and equal in size to the amount of carbon in the atmosphere.
Because conditions in the north are so cold, microbial growth and decomposition are much slower than in the tropics, so carbon is stored in layers of permafrost rather than recycled back into the nutrient cycle through vegetation growth.
In other words, if the forests burn and tundra melts, we could dramatically increase the amount of carbon in our atmosphere – essentially rendering useless even the most coordinated global attempts to cut global emissions.
“The north is a vast, global refrigerator for carbon that has been stockpiled from the atmosphere,” explains biologist Merritt Turetsky of the University of Guelph, in Ontario, Canada. She specialises in studying how permafrost thaws – when solid land turns into a “big soupy mess”, as she describes it. Communities in the north have for years been documenting lopsided homes and crumbling roads.
加拿大安大略省圭尔夫大学（University of Guelph）的生物学家图雷斯基（Merritt Turetsky）解释说：“北方相当于全球的一个巨大冰箱，储存着来自大气的碳。”她专门研究永久冻土层是如何融化的。正如她所描述的，固态土地变成一坨“大汤团”。多年来，北方地区一直在发生房屋倾斜和道路坍塌。
Now, we are seeing that once solid ground itself burn. Fires on the peatland are dominated by flameless smouldering combustion, which move overland through the leaf litter at the snail’s pace of half a metre a week, rather than the speedy rate of 10km per hour in a forest fire.
“These aren’t flames licking up into the trees like in Bambi,” says Turetsky. “These are slow-moving edges of ignition that move through the moss, the leaf biomass, and everything else that has fallen onto the forest floor.”
These smouldering fires not only are ignited much more easily than fiery flames by lightning strikes – they also can persist through cold and wet conditions much longer, largely because the peat holds vast stores of the combustible gas methane. As the climate warms, northern soils and peat dry out, making smouldering fires much more likely.
In a research paper from 2015, Turetsky explains how smouldering fires are actually a much greater threat to the global climate. They burn for much longer, so they can transfer heat much deeper into the soil and permafrost, overall consuming twice as much carbon-rich fuel as normal fires.
“Unfortunately, there’s just no way you can send out a bomber plane with a belly full of water or fire retardant to put these out – the tools that fire managers have at their disposal to tackle these huge scale fire events are just ineffective when it comes to smouldering,” she says.
Even more disconcerting, rainfall doesn’t always help.
“You need a huge amount of precipitation to fall to put these out – but if you get just a moderate amount of rain, that often comes with lightning, which can just blow things up thanks to the methane in the peat, and just make it worse,” she says.
Sink to source
In a new study, Turetsky and others report that the boreal forests will switch from absorbing carbon from the atmosphere through photosynthesis and growth, and so acting as a carbon sink, to releasing their carbon through drying and burning, making them a carbon source.
In other words, rather than acting as a brake on climate change, by burning, the northern forests will dramatically exacerbate global heating.
Rather than acting as a brake on climate change, by burning, the northern forests will dramatically exacerbate global heating
Not all of the soil carbon is burned during a forest fire. Over time, “legacy carbon” builds up in the soil after repeated fires. But as fires in the boreal increase in size and severity in a warming climate, the likelihood of this “legacy carbon” being released to the atmosphere increases.
“The really bad news is that big fires can move through a landscape and tap into old carbon layers that had been removed from the atmosphere thousands of years ago,” explains Turetsky. “When 100,000-year-old carbon is released back to the atmosphere, that’s the stuff of true positive feedback. And while occasional fires are a natural part of the boreal forest, it’s not a regular feature of the Arctic further north – but it may be in the future. We’re dialling up the volume.”
If conceiving of fires in the Arctic wasn’t enough of a paradigm shift, an even greater psychological hurdle is understanding that much of the fire in the Arctic is actually underground.
“A better understanding of what is actually on fire in these ecosystems – the peat and the muck and the soil beneath the surface – might change the way people understand how the Arctic can go up in flames,” says Carly Philips, Kendall Fellow for Protecting Carbon in Alaska’s Boreal Forests at the Union of Concerned Scientists, a non-profit founded 50 years ago with the aim of using science to improve the health of people and the planet.
阿拉斯加关注北方森林科学家联盟（Alaska's Boreal Forests at the Union of Concerned Scientists）的肯德尔碳保护研究员（Kendall Fellow for Protecting Carbon）菲利浦（Carly Philips）说：“更好的是要理解，是生态系统中什么物质着了火——泥炭、淤泥和土壤表层下的物质在燃烧，可能改变人们对北极火灾的理解。”该联盟是一个50年前创立非盈利的机构，旨在利用科学改善人类健康和保护地球。
Capable of smouldering beneath the surface, these subterranean fires can persist through the winter and pop up in spring in completely unexpected locations. Hence their nickname: “zombie fires”. They’re neither dead nor alive.
Taken together, melting permafrost, methane release, drying peat, vanishing ice, simmering zombie fires and of course a warming climate are all combining into an unprecedented setting for dramatic changes in the Arctic.
In a 2018 study, Woods Hole’s Natali describes a field experiment that lasted from 2012 to 2016 in Siberia, where she and her colleagues scorched patches of earth to varying degrees and waited to see how easily larch seedlings would grow. By 2017, there were five times more larch seedlings in the moderately and highly scorched earth compared to other plots – implicating that in a landscape razed by forest fires, new species would increasingly flourish.
It could mean that the Arctic landscape shifts away from coniferous forests to become more dominated by leafy deciduous trees that are found further south.
“In the boreal zone, we are already seeing a proliferation of deciduous forest across the landscape as coniferous forest fails to return post fire,” says Turetsky. “The iconic structure of how we define the boreal itself might be changing.”
Dramatic changes in the boreal and the Arctic will affect the entire planet in more ways than one.
“This is a global problem: fires in one region affect air quality in other parts of the world,” says Mark Parrington, a senior scientist at the Copernicus Atmosphere Monitoring Service (Cams) at the European Forest Fire Information System. Their monitoring has tracked plumes of smoke from Alaska reaching the Great Lakes; fires in Alberta causing red skies in Europe; a smoke plume from the Canadian Arctic reaching the European Arctic, and more.
“这是一个全球性的问题：一个地区的火灾会影响世界其它地区的空气质量，”欧洲森林火灾信息系统（European Forest Fire Information System）哥白尼大气监测局（Copernicus Atmosphere Monitoring Service）的资深科学家帕林顿（Mark Parrington）说。他们的监测跟踪了从阿拉斯加到五大湖的烟尘云团；阿尔伯塔省的大火导致欧洲天空发红；加拿大北极圈飘来的烟雾到达欧洲的北极地区，甚至更远。
Parrington says we need look at where black particulates – soot – from these fires is falling back to earth to understand the impact on the global climate. If it is deposited onto snow and ice, this would decrease the albedo and lead to more sunlight and heat being absorbed – increasing warming. Cams have some data to address this question, but urgently need more, he says.
Beyond more research, what can be done? Is there any chance of stopping these fires from spreading? Higuera, for one, isn’t optimistic. “It’s just not in the realm of possibility to say we will stop fires like this from happening in the future,” he says. “It’s like trying to stop a hurricane.”
Even fighting individual fires is extremely challenging, thanks to the remote, vast nature of the area and its lack of infrastructure. But not every fire should be fought, experts say: instead, we need to turn our attention elsewhere.
“It’s not an effective use of funds to go out and put out every northern fire – it’s just not feasible,” says Turetsky. “The most important thing we can do is overall climate mitigation – and our chance to do that is not in 15 or 10 years’ time.