A deeper climate risk is burning beneath Arctic fires
Wildfires across the Arctic and nearby boreal regions may be contributing more to global warming than many models currently assume, because some of the material being burned is not recent plant growth but ancient carbon stored in soils for hundreds or even thousands of years. That is the warning emerging from a study of soil cores collected around the Arctic and boreal forests.
The conventional assumption has been that most wildfire emissions in these regions come from relatively recent biomass. But researchers led by Meri Ruppel at the Finnish Meteorological Institute found evidence that fires can ignite old organic material buried in soils, including carbon that in some places is up to 5,000 years old. If that process is widespread, it means the Arctic is not only losing current vegetation to fire. It is also unlocking a long-accumulated carbon store that climate systems have historically treated as a sink.
That distinction is important because it changes how the fires should be understood. Burning recent growth is damaging, but it is part of a faster carbon cycle. Burning ancient soil carbon releases material that has been kept out of the atmosphere for centuries or millennia.
What the soil cores showed
According to the researchers, the key process is not only the rapid burning of surface vegetation. In many places, that surface fire appears to trigger slower smouldering combustion deeper in the soil, where old organic matter such as peat has accumulated over long timescales. That slower burn can release both carbon dioxide and black carbon, or soot.
The study indicates that the age of the combusted carbon varies by environment, depending on factors including the depth of organic soils and how deeply the fire burns. In the Northwest Territories of Canada, for example, fires are reported to be burning several centimeters into the ground and releasing carbon stored up to 400 years ago. Elsewhere, the age of the released material can be much greater.
The work suggests that risk tends to increase toward the Arctic, where shallower soils can place accumulated organic matter closer to the surface. In those settings, fire has a more direct path to older stores.
Why black carbon raises the stakes
The concern is not limited to carbon dioxide. The smouldering of old soils also generates black carbon, which has its own warming effects. Black carbon absorbs heat from sunlight directly in the atmosphere. In cold regions, it can also settle on snow and ice, darkening the surface and causing more melting than would otherwise occur.
That means these fires may be amplifying warming through multiple routes at once. They add greenhouse gases, produce soot that changes the atmosphere’s heat balance, and can accelerate ice and snow melt when particles are deposited on reflective surfaces. The result is a feedback loop that is especially troubling in high-latitude regions already warming rapidly.
Ruppel said soil combustion could unlock long-stored carbon from soils previously considered carbon sinks. That framing captures the scale of the concern. A sink that becomes a source does not just weaken climate resilience. It actively reverses it.
What current climate models may be missing
One of the most consequential points in the report is that climate models do not currently account for the release of this ancient carbon. If fire emissions from Arctic and boreal regions are being underestimated because the age and depth of burned material are not fully represented, then projections of future warming may also be missing an intensifying contribution.
The Arctic has long been treated as a climate front line because of melting sea ice, thawing permafrost, and changing ecosystems. This study adds to that picture by emphasizing the vulnerability of soil carbon itself. Organic matter that built up slowly under cold conditions is now increasingly exposed to larger and more frequent fires. Once burned, that accumulated store is not quickly replaced.
The research also underscores how fire in the far north differs from some better-known wildfire narratives. In many lower-latitude fires, attention centers on trees, homes, smoke plumes, and immediate surface damage. In Arctic and boreal systems, part of the danger is what happens below the surface, where the most important material can smoulder out of sight.
A changing role for northern landscapes
Plants in cold regions grow slowly, but their remains can build up over long periods in the soil, especially in peat-rich landscapes. That accumulation has helped Arctic and boreal soils function as a major carbon sink. The new findings suggest that this role may be less stable than previously thought under a regime of more frequent and severe fire.
If deep-burning fires become more common, the north could lose part of its buffering function and instead contribute additional warming. That shift would have consequences far beyond the Arctic itself. Carbon released there mixes into the global atmosphere, while black carbon’s effects on snow and ice can reshape polar heat dynamics.
The result is a climate story that is both local and planetary. Local fire behavior determines how far combustion reaches into the soil. But the consequences scale outward, affecting atmospheric chemistry, surface reflectivity, and global greenhouse gas totals.
