The blanket of wildfire smoke that spread across much of the US and Canada in 2023 was a wake-up call and showed what climate change could feel like for millions of people in the near future. However, apocalyptic orange skies and levels of air pollution 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 aren’t just burning in trees and grasses. New research into the exceptional Arctic fire seasons of 2019 and 2020 suggests that fires are also spreading underground.
These underground fires are known as ‘zombie fires’ and there are a number of reasons to be concerned about this trend.
First, Arctic soils, which are rich in organic matter, may dry up due to changing climate conditions, causing them to burn slowly and release large amounts of smoke into the atmosphere.
Second, ground fires that spread underground are more difficult to control and extinguish, requiring more resources for longer periods of time. Firefighters in Alberta, Canada, where carbon-rich peatlands are common, have dealt with fires smoldering dozens of meters underground in 2023. Because peat fires can make the ground unstable, using heavy equipment to dig out the burn areas also becomes risky.
Finally, these ground fires do not extinguish easily. Recent research shows that ground fires in the Arctic can smolder throughout the winter and flare up again in early spring as temperatures rise. Hence the nickname ‘zombie fires’.
The Arctic is becoming 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 forest fires in the northern and Arctic regions have changed in recent decades.
One big culprit is rising temperatures: the Arctic is warming almost four times faster than the rest of the world, a phenomenon known as Arctic amplification.
<iframe title="GISTEMP Zonal Temperatures" width="900" height="506" src="https://www.youtube.com/embed/Na58YnwLz2s?feature=oembed" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share" allowfullscreen="allowfullscreen"></iframe>
While governing bodies working to curb the pace of climate change worry about crossing the 1.5 degrees Celsius (2.7 degrees Fahrenheit) threshold globally, the Arctic has already seen a 2 degrees Celsius increase (3, 6 F) exceeded compared to pre-industrial times. That temperature increase is bringing a number of changes to the environment that are making the forest and tundra more susceptible to burning, longer and on a larger scale than just a few decades ago.
Among the changing conditions that promote wildfires are changes in atmospheric circulation that cause periods of extreme heat, dry out vegetation and reduce soil moisture, and, most importantly, lead to more frequent lightning strikes that can cause fires.
Although lightning is still uncommon at very high latitudes, it is expected to increase and spread over larger areas to the far north, as the climate warms and more storms capable of producing lightning develop. In 2022, thousands of lightning strikes fueled one of Alaska’s worst fire seasons on record.
As the Arctic warms and fires move further north, peatlands rich in dead plant material are burning at an accelerated rate.
The burning peat also removes the insulating layer of permafrost, the region’s frozen carbon-rich soil. Northern ecosystems store twice as much carbon in their peat and permafrost as the atmosphere, and both are increasingly vulnerable to fire.
About 70% of the recorded area of Arctic peat affected by burning over the last 40 years occurred in the last eight years, and 30% of that in 2020 alone, demonstrating the acceleration.
What is a zombie fire?
Most people imagine forest fires as catastrophic flames that consume trees and grasses. Ground fires, on the other hand, do not flame, but burn more slowly and tend to spread deep into the ground and spread laterally.
The result is that smoldering ground fires are not only less visible, but also less accessible and require them to be dug up and extinguished with plenty 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 far and wide by the wind.
Due to the slow combustion process and the abundance of fuel in the form of carbon and oxygen, smoldering ground fires can also burn for months and sometimes years. They have been shown to ‘hibernate’, lasting throughout the cold season and then reemerging in the warm, dry season. During the 2019-2020 fire season in Siberia, zombie fires were blamed for reigniting the fires the following year.
Some of these ground fires can grow so large that they release plumes of smoke that cover large geographic areas. In 1997, peat fires in Indonesia caused dangerous smoke to spread across Southeast Asia and parts of Australia, increasing CO2 emissions. They were fueled by slash-and-burn activities to plant palm plantations and were reinforced by drought conditions during a severe El Niño event.
Some hope and caution from previous lessons
I have been studying the effects of forest fires on air and water for years, including in the Arctic. However, my work and that of many colleagues focus on the combustion of above-ground biomass. More work is needed to understand the full extent of zombie fires in the Arctic and their potential for carbon and smoke emissions on a large scale. A recent study conducted at a handful of Canadian sites offered some hope, suggesting that underground fires there burned more in tree roots than in the soil, suggesting potentially lower carbon emissions in some areas.
Meanwhile, the ongoing waves of wildfires in Canada and the US are a reminder of the impact of these fires.
More regions will need help from 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 increasing around the world.
This article is republished from The Conversation, an independent nonprofit organization providing facts and trusted analysis to help you understand our complex world. The Conversation has a variety of fascinating free newsletters.
It was written by: Patrick Louchouarn, The Ohio State University.
Read more:
Patrick Louchouarn receives funding from NASA-USDA (Carbon Cycle Science Program); Welch Foundation (student support); NSF-MALE
