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Fires have long been a natural part of forest ecosystems, but something is changing. Our new study shows that forest fires have become more widespread and severe amid global heating, particularly in the high northern latitudes such as Canada and Siberia where fires are most sensitive to hotter, drier conditions.
The implications of this are alarming, not just for the ecosystems affected or the cities engulfed by smoke downwind, but for the planet’s ability to store carbon and regulate the climate. The trend we discovered contrasts with declining fire extent in savannah grasslands, which may reflect the expansion of farming and changing rainfall patterns.
We established the leading causes of forest fires in different parts of the world using an AI algorithm. It grouped forest regions into distinct zones with similar fire patterns and underlying causes, uncovering the worrying extent to which climate change is fuelling the expansion of forest fires in Earth’s high northern latitudes.
More fires in ‘extratropical’ forests
Since 2001, emissions from fires in forests outside of the tropics, like parts of the boreal forest in the far north of North America and Eurasia, have nearly tripled. This rise is largely the result of hotter, drier weather occurring more frequently, combined with forests growing more efficiently in places where the cold once stunted their growth.
Climate change is creating ideal conditions for larger, more intense fires, which accelerate climate change in turn by releasing more carbon to the atmosphere. In fact, we found that global carbon emissions from forest fires have increased by 60% over the past two decades. The largest contributions come from fires in Siberia and western North America.
This trend shifts the focus of forest fire emissions from tropical forests, where fires set to make room for farmland have long contributed carbon to the atmosphere. Conservation policies have reduced deforestation rates since the early 2000s in some regions, particularly Amazonia. By contrast, increasing fires in northern forests, such as the taiga – the forest of the cold sub-arctic region – are driven by changing climate conditions and generally started by lightning, which makes them harder to prevent.
Not only is the area affected by fires expanding but the fires themselves are growing more severe and releasing more carbon, according to our new findings. This corresponds with an earlier study that found fires are doing more damage to ecosystems globally than in the past. Fires are burning through drier and more flammable vegetation as global temperatures rise and droughts become more frequent.
In northern forests, more severe fires can burn deep into the soil and release carbon that has accumulated over centuries. Forests can remain net carbon emitters for decades after burning and the more severe fires become, the longer it takes forests to rebound and recapture carbon lost during the fire.
What does this mean for the planet?
The steep rise in fire emissions from forests outside the tropics is a clear signal that the capacity of Earth’s forest to store carbon is at increasing risk.
Forests, particularly in northern regions, absorb and store CO₂ from the atmosphere. But as fires expand and become more severe, these vital carbon sinks are weakened. This undermines the global effort to tackle climate change as forests offset emissions from human activities that burn fossil fuels.
Forest fires, long considered part of the natural carbon cycle, are increasingly driven by human-caused climate change. Yet, international reporting standards don’t differentiate between “natural” levels of forest fire emissions and the higher emissions we’re seeing due to climate change.
This allows excess fire emissions caused by humans to fall outside the scope of national carbon budgets tracked by organisations like the United Nations. Gaps emerge between the carbon emissions we think we’re managing and the actual amount that’s passing between the land and the atmosphere.
What drives fires in different regions varies, so addressing this growing threat requires tailored approaches. Outside of the tropics, proactive forest management is essential. Carefully managed fires and thinning out vegetation can mean fires ultimately cause less damage when they do ignite. Monitoring vegetation growth, alongside fire-favourable weather conditions, can help identify and prioritise areas for intervention.
In tropical forests, reducing ignitions (especially during droughts) and preventing forest fragmentation is key to protecting these ecosystems and their carbon stocks. This may help prevent the more extreme fires that turn tropical forests from carbon sinks into sources.
Increasing fires are a symptom of climate change
Limiting the burning of fossil fuels is central to minimising future fire risk. Without drastic cuts to greenhouse gas emissions, more severe and widespread forest fires are likely, with increasing damage to ecosystems, biodiversity and the climate.
Our study also highlighted the importance of updating international reporting standards on carbon emissions. As forest fires become more closely linked to human-driven climate change, it’s crucial that fire emissions be included in national carbon budgets to provide a more accurate picture of the planet’s carbon fluxes.
There is also a risk of overestimating how much carbon is stored by reforesting areas, especially outside the tropics. Many carbon offset schemes rely on planting new trees or delaying the harvest of existing ones to absorb CO₂, but if the growing threat of forest fires isn’t properly accounted for, these projects could fail to deliver the carbon savings they promise.
Forest fires are no longer just a natural occurrence. As they shift north and intensify, these fires are a clear symptom of human-caused climate change.
It’s essential to recognise the growing role that fires play in the carbon cycle. By doing so, we can better manage fire risks, safeguard forests and ensure a more resilient future for the planet.
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Matthew William Jones receives funding from the UK Natural Environment Research Council (NERC).
Stefan H Doerr receives funding from the UK Natural Environment Research Council (NERC) and the FirEUrisk project funded via the European Union’s Horizon 2020 Research and Innovation programme under grant agreement no. 101003890.
Crystal A. Kolden does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
