by The blanket of wildfire smoke that spread across the United States and Canada in 2023 was a wake-up call, showing millions of people what climate change could mean in the near future. Apocalyptic orange skies and air pollution levels that force people indoors only tell part of the story, however.
As global temperatures rise, fires are spreading further north and into the Arctic as well. These fires are not just burning in trees and grass. New research into the exceptional Arctic fire seasons of 2019 and 2020 shows that fires are also moving inland.
These underground fires are called “zombie fires,” and there are several reasons to worry about the trend.
First, as organic-rich Arctic soils dry out due to climate change, they can burn slowly and release huge amounts of smoke into the atmosphere.
Second, soil fires that spread underground are more difficult for firefighters to contain and extinguish, requiring more resources for longer periods of time. Firefighters in Alberta, Canada, where peatlands are generally rich in carbon, were dealing with fires smoldering to depths of several feet underground in 2023. Because peat fires can make the ground unstable, using heavy equipment to excavate the fire areas also becomes a risk.
Finally, these soil fires do not die easily. It is clear from recent research that Arctic soil fires can smolder through the winter and reignite in early spring when the temperature rises, hence the nickname “zombie fires”.
The Arctic is becoming more flammable
Wildfires have been a natural part of boreal forest and tundra ecosystems for thousands of years. However, the intensity, frequency and types of wildfires in northern and arctic regions have changed in recent years.
The main reason is the rise in temperature: 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 are concerned about exceeding the 1.5 degrees Celsius (2.7 degrees Fahrenheit) threshold worldwide, the Arctic has already exceeded a 2 C (3.6 F) increase by comparison. to pre-industrial times. That rise in temperature creates a number of environmental changes that make the forest and tundra more susceptible to burning, for longer, and in more extensive ways than 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 which blazes could spark.
Although lightning is rare at very high latitudes, it is expected to increase and spread over larger areas into the far north as the climate warms and generates more storms capable of producing lightning. In 2022, thousands of lightning strikes sparked one of Alaska’s worst fire seasons ever.
As Arctic warming and fires move further north, peat soils rich in dead plant material burn at an accelerating rate.
The 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 than in the atmosphere, both of which are becoming more vulnerable to fire.
About 70% of the recorded Arctic peat area affected by burning in the last 40 years occurred in the last eight years, and 30% of it in 2020 alone, indicating the acceleration.
What is a zombie fire?
Most people picture wildfires as devastating flames that consume trees and grass. On the other hand, wildfires do not ignite but burn more slowly and tend to spread deep into the ground and spread laterally.
The result is that smoldering fires on the ground are less visible but also less accessible and require digging and dousing with lots of water.
These smoldering fires also produce more smoke due to their lower combustion temperature. Ultra-fine particles in smoke are particularly harmful to the respiratory and cardiovascular systems and can be carried far and wide by winds.
Due to the slow combustion process and the abundance of fuel in the form of carbon and oxygen, smoldering land fires can also burn for months and sometimes years. They have been shown to “winter,” continuing through the cold season to re-emerge in the hot, dry season. During the 2019-2020 fire season in Siberia, zombie fires were blamed for regenerating fires the following year.
Some of these wildfires can become so massive that they release plumes of smoke that cover large geographic regions. In 1997, peat fires in Indonesia sent dangerous levels of smoke across Southeast Asia and parts of Australia and increased carbon emissions. They were ignited by slash and burn activities to plant palm plantations and exacerbated by drought conditions during the intensity of El Niño.
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. My work and that of many colleagues, however, focuses on above-ground biomass combustion. More work is needed to understand the full extent of Arctic zombie fires and their potential for large-scale carbon and smoke emissions. One recent study of a handful of Canadian sites offered some hope, suggesting that more underground fires burned in tree roots than in the soil, suggesting that carbon emissions could be lower in some areas.
Meanwhile, the ongoing waves of wildfires in Canada and the United States are a reminder of the impact of these fires.
More regions will need the help of trained firefighters, which means sharing firefighting resources. Canada has seen an unprecedented level of international fire support in 2023. Best practices for safely fighting zombie fires are also needed, along with better public education about the health risks of wildfire smoke.
As a society, we are learning to live with some of the consequences of climate change, but the risks are rising worldwide.
This article is republished from The Conversation, a non-profit, independent news organization that brings you reliable facts and analysis to help you make sense of our complex world. The Conversation has a variety of free newsletters.
Written by: Patrick Louchoarn, The Ohio State University.
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Patrick Louchouarn receives funding from NASA-USDA (Carbon Cycling Science Program); Welch Foundation (student support); NSF-REU
