by The blanket of smoke from wildfires that spread across much of the US and Canada in 2023 was a wake-up call that showed what climate change could feel like in the near future for millions of people. However, apocalyptic orange skies and air pollution levels forcing people indoors only tell part of the story.
As global temperatures rise, fires are also spreading further north and into the Arctic. These fires not only burn trees and grasses. New research on the exceptional 2019 and 2020 Arctic fire seasons suggests that fires are also moving towards the ground.
These underground fires are known as “zombie fires” and there are several reasons to be concerned about this trend.
First, as organic-rich Arctic soils dry out due to changing climate conditions, they can smolder and release large amounts of smoke into the atmosphere.
Second, soil fires that spread underground are more difficult for firefighters to control and extinguish, requiring more resources over longer periods of time. Firefighters in Alberta, Canada, where carbon-rich peatlands are common, have been dealing with fires burning at depths of tens of feet underground in 2023. Because peat fires can make the soil unstable, use Heavy equipment to excavate fire areas also becomes risky.
Finally, these ground fires are not easily extinguished. Recent research finds that fires on the Arctic soil can burn through the winter and reignite in early spring when temperatures rise, hence the nickname “zombie fires.”
The Arctic is increasingly flammable
Wildfires have been a natural part of northern forest and tundra ecosystems for thousands of years. However, the severity, frequency and types of wildfires in the northern and Arctic regions have changed in recent decades.
One of the main culprits is rising temperatures: the Arctic is warming almost four times faster than the rest of the world, a phenomenon known as Arctic amplification.
While governing bodies working to slow the pace of climate change worry about surpassing the 1.5 degrees Celsius (2.7 degrees Fahrenheit) threshold globally, the Arctic has already surpassed a 2 C rise (3, 6 F) compared to pre-industrial times. This increase in temperature brings with it a series of changes in the environment that make the forest and tundra more susceptible to burning, for longer and more extensively than just a few decades ago.
Among the changing conditions that favor wildfires are changes in atmospheric circulation that create periods of extreme heat, dry out vegetation and reduce moisture in soils, and, most importantly, lead to more frequent lightning strikes that can spark fires. .
Although lightning remains rare at very high latitudes, it is expected to increase and spread over larger territories towards the far north as the climate warms and generates more storms that can produce lightning. In 2022, thousands of lightning strikes sparked one of the worst fire seasons on record in Alaska.
As the Arctic warms and fires move north, peat soils rich in dead plant material burn at an accelerated rate.
Burning peat also removes the insulating layer of permafrost, the region’s carbon-rich frozen soil. Northern ecosystems store twice as much carbon in their peat and permafrost as the atmosphere, and both are increasingly vulnerable to fires.
About 70% of the recorded area of Arctic peat affected by burning in the last 40 years occurred in the last eight years, and 30% of that was in 2020 alone, demonstrating the acceleration.
What is a zombie fire?
Most people imagine wildfires as catastrophic flames that consume trees and grasses. Land fires, on the other hand, do not burn, but burn more slowly and tend to spread deep into the ground and spread laterally.
The result is that smoldering fires in the ground are not only less visible, but they are also less accessible and require digging up and spraying lots of water.
These smoldering fires also produce more smoke due to their lower combustion temperature. Ultrafine particles in smoke are particularly harmful to the respiratory and cardiovascular systems and can be carried everywhere by wind.
Due to the slow combustion process and abundant fuel in the form of carbon and oxygen, smoldering ground fires can also burn for months and sometimes years. They have been shown to “overwinter” and persist through the cold season to reappear in the warm, dry season. During the 2019-2020 fire season in Siberia, zombie fires were blamed for reigniting fires the following year.
Some of these land fires can become so massive that they release plumes of smoke that cover vast geographic regions. In 1997, peat fires in Indonesia caused dangerous levels of smoke across Southeast Asia and parts of Australia and increased carbon emissions. They were triggered by slash-and-burn activities to plant palm plantations and amplified by drought conditions during a severe El Niño event.
Some hope and caution from past lessons
I have been studying the effects of wildfires on air and water, including in the Arctic, for many years. However, my work and that of many colleagues focuses on the combustion of aboveground biomass. More work is needed to understand the full extent of zombie fires in the Arctic and their potential for large-scale smoke and carbon emissions. A recent study conducted at a handful of Canadian sites offered some hope, suggesting that underground fires burned hotter in the roots of trees than in the soil, suggesting potentially lower carbon emissions in some areas.
Meanwhile, continued waves of haze from wildfires in Canada and the United States are a reminder of the impact of these fires.
More regions will need help from trained firefighters, which will mean sharing firefighting resources. Canada has seen an unprecedented level of international fire support in 2023. Better practices are also needed to safely fight zombie fires, along with better public education about the health risks of wildfire smoke.
As a society, we are learning to live with some of the effects of climate change, but the risks are increasing around the world.
This article is republished from The Conversation, an independent, nonprofit news organization bringing you trusted data and analysis to help you understand our complex world. The Conversation has a range of fascinating free newsletters.
It was written by: Patrick Louchouarn, The Ohio State University.
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Patrick Louchouarn receives funding from NASA-USDA (Carbon Cycle Science Program); Welch Foundation (student support); NSF-REU
