A major new study reveals that carbon dioxide (CO2) emissions from forest fires have surged by 60% globally since 2001, and almost tripled in some of the most climate-sensitive northern boreal forests.
The study, led by the University of East Anglia (UEA) and published today in Science, grouped areas of the world into "pyromes" - regions where forest fire patterns are affected by similar environmental, human, and climatic controls - revealing the key factors driving recent increases in forest fire activity.
It is one of the first studies to look globally at the differences between forest and non-forest fires, and shows that in one of the largest pyromes, which spans boreal forests in Eurasia and North America, emissions from fires nearly tripled between 2001 and 2023.
Significant increases were seen more broadly across the extratropical forests and amounted to an additional half a billion tonnes of CO2 per year, with the epicentre of emissions shifting away from tropical forests and towards the extratropics.
Increased emissions were linked to a rise in fire-favourable weather, such as the hot-dry conditions seen during heatwaves and droughts, as well as increased rates of forest growth creating more vegetation fuels. Both trends are aided by rapid warming in the high northern latitudes, which is happening twice as fast as the global average.
The study reveals a worrying increase in not only the extent of forest wildfires over the last two decades, but also their severity. The carbon combustion rate, a measure of fire severity based on how much carbon is emitted per unit of area burned, increased by almost 50% across forests globally between 2001 and 2023.
The work involved an international team of scientists - from the UK, the Netherlands, US, Brazil and Spain - who warn that further expansion of forest fires can only be averted if the primary causes of climate change, such as fossil fuel emissions, are tackled.
Lead author Dr Matthew Jones, of the Tyndall Centre for Climate Change Research at UEA, said: "Increases in both the extent and severity of forest fires have led to a dramatic rise in the amount of carbon emitted by forest fires globally.
"Startling shifts in the global geography of fires are also under way, and they are primarily explained by the growing impacts of climate change in the world's boreal forests.
"To protect critical forest ecosystems from the accelerating threat of wildfires, we must keep global warming at bay and this underscores why it is so vital to make rapid progress towards net zero emissions."
Dr Thais Rosan, from the University of Exeter, added: "The findings of this study demonstrate the significance of fire geography and illustrate that fire disturbance represent a critical and growing threat to the global efforts to combat climate change.
"The frequency and intensity of forest fires in the extratropics are increasing, representing a significant risk to areas that constitute a substantial proportion of the global net land carbon sink.
"As fire intensity and severity rise, the capacity of these forests to continue storing carbon is increasingly threatened.
"To achieve international climate targets, it is essential to address the impact of these wildfires, which risk undermining the potential of forests to act as long-term carbon sinks and mitigate the effects of climate change."
Threats to carbon storage
Forests are of worldwide importance for carbon storage, with their growth helping to remove CO2 from the atmosphere and reduce rates of global warming.
They also play a crucial role in meeting international climate targets, with reforestation and afforestation schemes being implemented to remove carbon from the atmosphere and offset human CO2 emissions from hard-to-abate sectors such as aviation and certain industries.
The success of these schemes relies on carbon being stored in forests permanently, and wildfires threaten that.
Extratropical fires are already emitting half a billion tonnes more CO2 than two decades ago, and the long-term effect depends on how forests recover. More widespread and severe forest fires are a sign that emissions are now out of balance with the carbon captured by post-fire recovery.
Dr Jones, a NERC Independent Research Fellow, said: "The steep trend towards greater extratropical forest fire emissions is a warning of the growing vulnerability of forests and it poses a significant challenge for global targets to tackle climate change.
"We know that forests rebound poorly after the most severe fires, so there is huge interest in how the observed increases in fire severity will influence carbon storage in forests over the coming decades. This demands our close attention."
Escalating wildfire impacts masked until now
Significantly, the increased emissions from forest fires contrasts with the reduced burning of the world's tropical savannahs during the same period. Previous studies have shown that, since 2001, the area burned by all fires (forest and non-forest) fell by a quarter globally, mainly due to this.
The latest findings are important because forest fires burn more severely and release larger amounts of harmful smoke to the atmosphere than savannah grassland fires, presenting major threats to those living near fires and to more distant communities exposed to poor air quality caused by smoke.
The authors say the study debunks the narrative that falling overall annual area burned by fire globally means falling wildfire impact.
"Until now, reduced burning in the already fire-prone savannahs and grasslands has masked increases in forest fire extent and severity that are hugely consequential for society and the environment," said Dr Jones. "Our work shows that fires are increasingly happening where we don't want them to - in forests, where they present the greatest threat to people and to vital carbon stores."
Managing wildfires
Machine learning was key to unlocking new observations about the shifting global geography of forest fires. It was used to group the world's forest ecoregions into 12 distinct pyromes, allowing the researchers to isolate the effects of climate change from other influencing factors such as land use.
This knowledge also reveals new insights into which strategies can be most effective for mitigating wildfires and protecting forests. Dr Jones said: "Substantial financing is required to support strategic programs of forest management, stakeholder engagement, and public education, all of which represent a meaningful shift of fire management strategy from largely reactive to increasingly proactive.
"For example, priority areas for forest management and fire breaks must be defined based on proactive monitoring of forest productivity, particularly in the extratropics. Managing fuel loads in places where they could present greatest danger during fire-favourable weather is a key priority for limiting the severity and impact of fires when they do occur."
The paper is entitled: "Global rise in forest fire emissions linked to climate change in the extratropics."
