Zombie fires in the peatlands of regions like Alaska, Canada, and Siberia present an ongoing enigma to scientists. These fires vanish from sight during winter, smoldering underground, only to reemerge in the spring. Traditionally thought to be remnants of previous surface fires, new research suggests that zombie fires might actually be ignited by rapid atmospheric warming, which causes the peat soils to heat up spontaneously to smoldering temperatures without any external spark. This phenomenon, potentially a direct result of climate change, indicates a new form of spontaneous combustion driven by environmental factors.
Historically, reports of zombie fires date back to the 1940s, but they were rare. Over the past two decades, however, there has been a noticeable increase in both the frequency and intensity of these fires, coinciding with the accelerated warming of the Arctic, the planet’s fastest-warming region. By the beginning of 2024, over 100 zombie fires were active in British Columbia alone, with occurrences even near Oymyakon in northeastern Siberia, the coldest inhabited area on Earth. These fires have become significant, accounting for about 3.5% of the annual area burned in these regions.
The concern is not just the fires themselves but their environmental impact, particularly their carbon emissions. The Arctic peat soils, sensitive to temperature changes, contain more carbon than is found in the entire atmosphere, and these fires are releasing massive quantities of this carbon. To understand whether sudden atmospheric warming could be directly responsible for these emissions, researchers developed a mathematical model that simulates how peat soil temperatures and carbon content respond to climatic changes.
This model led to two critical findings. First, it showed that microbial activity in the soils could generate enough heat for the peat to remain smoldering at about 80°C throughout the winter, ready to reignite in the spring without prior surface fire activity or extreme weather temperatures. This state, referred to as the “hot metastable state,” can persist for up to ten years, causing prolonged underground burning. The second finding is that this transition from a cold state to a hot metastable state can be triggered by rapid changes in climate alone, such as during summer heatwaves or under global warming scenarios. The rate of temperature increase, rather than the absolute change, is critical in triggering these fires.
While these phenomena have yet to be proven in real-world conditions or demonstrated in a laboratory setting, similar spontaneous combustion events in materials like compost, which closely resembles peat, support the theoretical model. This suggests that not just the increase in temperature but the rate of warming is the key factor in causing long-duration underground peat fires.
Given the increasing severity of climate conditions, which are likely to induce more zombie fires, there is a growing concern about entering a vicious cycle where carbon released by these fires exacerbates climate changes, leading to even more fires and extreme weather. The only feasible solution appears to be limiting the variability in climate change rates. While policymakers have focused on capping dangerous temperature levels, addressing the rate of climate change might be equally or more critical to preventing future disasters and enhancing resilience against such unpredictable natural fire events.