Lightning is the leading cause of wildfires in boreal forests •

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Lightning has been identified as the leading cause of wildfires in the Boreal forests, a crucial area for carbon storage, and is expected to become more common due to climate change. This is the alarming conclusion of a new study led by Dr. Matthew Jones from the Tyndall Center for Climate Change Research at the University of East Anglia, along with international collaborators.

Using machine learning, the team predicted forest fires worldwide, determining whether they were caused by humans or natural lightning. This study marks the first time that fire ignition sources have been attributed on a global scale.

Important insights

The findings showed that 77% of burned areas in intact extratropical forests were caused by lightning. This is in stark contrast to tropical areas, where fires are mainly caused by humans.

Intact extratropical forests, largely undisturbed and sparsely populated, are mainly located in the remote boreal forests of the Northern Hemisphere.

Lightning frequency

Further insights were gained using climate models to predict changes in lightning frequency as the planet warms.

The study found that lightning frequency in these forests increases by 11 to 31% per degree of global warming, indicating an increased risk of forest fires due to climate change.

Lightning fires

Lightning fires tend to be larger, more intense, and more confined to remote areas during periods of extreme fuel drought, compared to human-caused fires.

The team’s previous work found that conditions leading to fires are becoming more frequent and intense as the climate warms, leading to greater flammability of forests.

Extratropical forests are of global importance and store enormous amounts of carbon in vegetation and permafrost soils.

Remarkably, although these forests cover only about 1% of the Earth’s land area, they contribute more than 8% of global CO2 emissions from fires. Fires in these regions could increase greenhouse gas emissions from permafrost thaw by 30% by the end of the century under a moderate emissions scenario.

Carbon storage

“Extratropical forests are globally important because they retain dense carbon sinks in vegetation and soil, helping to keep CO2 out of the atmosphere and moderate global warming,” said Dr. Jones. “However, when fires occur in these regions, they emit more CO2 per unit area than almost anywhere else on Earth.”

“Our research highlights that extratropical forests are vulnerable to the combined effects of a warmer, drier climate and an increased risk of ignition from lightning strikes.”

“Future increases in lightning strikes threaten to destabilize vast carbon stocks in extratropical forests, especially as weather conditions in these regions become warmer, drier and generally more prone to fire.”

Extreme events

The research is becoming increasingly relevant in the context of Canada’s record-breaking 2023 wildfire season, when emissions were more than four times the average of the past 20 years.

Dr. Thomas Janssen of VU, the study’s lead author, noted that while the study did not specifically focus on the Canadian fire season, it does help understand such extreme events.

“While our research did not specifically focus on this year’s extreme fire season in Canada, it does help us understand this year’s events. Extreme fire seasons in the boreal forests, as we saw in Canada this year, will be more likely in warmer climates due to hotter, drier weather and more lightning strikes,” said Dr. Janssen.

“This year’s fires in Canada closely follow the record-breaking fire seasons in the Siberian boreal forests in 2020 and 2021.”

Reinforcing feedback

The researchers warn that greenhouse gas emissions from fires could contribute to rising carbon concentrations in the atmosphere and cause additional warming, further increasing the likelihood of fires and other negative impacts of climate change in the future.

“The increased greenhouse gas emissions from forest fires are amplifying the climate change problem, with more fires occurring as the climate warms and more greenhouse gases being emitted from fires,” says Professor Sander Veraverbeke.

“This ‘amplifying feedback’ is especially important in boreal forests, most of which are covered by carbon-rich permafrost soils, which take many hundreds of years to form when they are lost to fire.”

Study implications

“Our work has shown that the risk of lightning strikes increases substantially as the planet warms, meaning that every tenth of a degree of warming we can avoid will translate directly into a reduced risk of wildfires,” said Dr. Jones.

“Reducing greenhouse gas emissions from fossil fuel use and land use change is critical to avoiding the worst additional risks from wildfires in many regions, but especially in the boreal forests where fires are so sensitive to warming.”

The research has been published in the journal Natural Geosciences.

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