Arctic fires ignite carbon stored for millennia

ancient carbon – New soil-core evidence suggests Arctic and boreal wildfires can release millennia-old carbon, potentially boosting warming beyond current climate estimates.

Wildfires in the far north are doing more than consuming fresh vegetation.. Soil evidence from across Arctic and boreal regions suggests many of these fires can also ignite carbon that has been locked in soils and peat for hundreds to thousands of years. altering how much heat-trapping pollution enters the atmosphere as the climate warms.

In a study centered on soil cores collected from areas affected by recent fires. researchers found that combustion is not limited to newly grown plant material.. Instead. burning at the surface can trigger slower smouldering deeper in the soil. drawing down and releasing older organic carbon that had previously been considered relatively stable “sinks” for atmospheric carbon dioxide.

The work builds on a long-standing assumption used in climate thinking: that most of what burns in these high-latitude ecosystems comes from recent plant growth.. While cold conditions help vegetation accumulate gradually. they also slow decomposition. allowing layers of organic matter to build up over centuries and millennia—most notably in forms such as peat.. In that sense, Arctic and boreal soils have often been treated as long-term storage for carbon.. The new results challenge how completely that assumption holds when wildfire regimes intensify.

Researchers collected soil cores from multiple sites where wildfires had occurred, including environments with different fire behavior and soil conditions.. The cores show a pattern in which rapid burning of surface vegetation can be accompanied by the slower smouldering of older materials beneath it.. That deeper combustion can release carbon dioxide and generate soot, or black carbon, as well as other heat-relevant particles.

Black carbon adds a second pathway to warming beyond the greenhouse effect of CO2. Because black carbon absorbs sunlight, it can warm the atmosphere directly. In cold regions, it may also settle on ice or snow, darkening surfaces and promoting additional melting that would otherwise be less likely.

The age of the carbon being burned is not uniform.. According to the study’s lead author. Meri Ruppel of the Finnish Meteorological Institute in Helsinki. the timing of combustion varies from place to place because the organic depth of soils and the depth reached by burning differ across environments.. That helps explain why some sites show deeper and older carbon being released than others.

The risk of ancient carbon release appears to rise toward the Arctic.. Ruppel said Arctic soils are often shallower. and the organic matter that accumulates there can be located closer to the surface—meaning fires have a greater chance to reach and ignite older carbon pools.. In Canada’s Northwest Territories. fires were reported to burn several centimetres into the soil. releasing carbon stored up to about 400 years ago.

Farther east and north, the pattern continues, with fires penetrating deeper on average.. In Greenland, the reported soil-core findings indicate burning down roughly 10 centimetres, releasing carbon that is on average about 560 years old.. In some locations where burning extended even farther. fires were said to have reached around 15 centimetres into the soil. with carbon dating back roughly 1000 years.

Not all environments show the same extremes.. In Quebec’s boreal forests. the team found evidence that some fires released carbon from as far back as 5000 years ago. but Ruppel emphasized that this was not widespread.. The distribution matters: it suggests that while very old carbon can be vulnerable. the extent of the deepest burning may vary considerably between fires and landscapes.

The implications extend beyond the chemistry of smoke.. Climate models currently do not account for the release of this older carbon pool.. If ancient carbon is regularly mobilized as fires spread and burn more persistently. the near-term greenhouse impact of wildfire could be larger than many projections assume—potentially strengthening the feedback loop between warming and burning.

Ruppel also framed the findings as an early step rather than a complete accounting.. The key remaining question is how much ancient carbon is actually being released overall by fires across the Arctic and boreal zone.. That scale—how often deep burning happens. and where—will determine whether the effect is a localized complication or a major contributor to future warming.

Her message resonated with other researchers in the field.. Sandy Harrison of the University of Reading in the UK. who attended the talk. noted that high-latitude soils and peatlands contain large stores of older carbon.. As fire regimes change—destroying top-soil layers and burning through peatlands—older carbon becomes more exposed and more likely to be released. according to the concerns raised.

For MISRYOUM, this research underscores a critical shift in how wildfire impacts the climate system.. In a warming world where fires are becoming larger and more frequent. understanding not just what burns. but how deeply it burns. may be essential for estimating the full climate cost of the northern flames.

Arctic wildfires ancient carbon release soil cores black carbon climate modeling peatlands boreal forest