New research highlights role of lightning in burning extratropical forests
A recent study revealed that lightning is a major cause of fires in intact extratropical forests. Using machine learning, the research found that 77% of fires in these areas are caused by lightning, in stark contrast to human-caused fires in tropical regions. As climate change increases the frequency of lightning strikes and the flammability of forests, forests, which are essential for carbon storage, are at risk of being increasingly exposed to fires.
The role of lightning in boreal forest fires
Lightning is the main cause of fires in boreal forests, areas of global importance for carbon storage. This frequency will increase with climate change, new research reports.
Machine learning and lightning fires
The study used machine learning to predict the main source of fires (human or ‘natural’ caused by lightning) in all regions of the world. Reference data from seven regions of the world were used to optimize the algorithm’s predictions. Researchers say this is the first study to globally attribute fire ignition sources.
The study shows that 77 percent of burned areas in intact extratropical forests are related to lightning-caused fires, in stark contrast to fires in tropical regions, which are mostly human-caused. Intact extratropical forests are those that are in a near-pristine state, with small human populations and low levels of land use, and are primarily found in the remote boreal forests of the Northern Hemisphere.
Climate change and fire risks
Climate models have also been used to investigate how lightning frequency will change as the planet warms. Lightning frequency was found to increase by 11 to 31 percent for every degree of global warming in intact extratropical forests, meaning climate change poses a risk of more wildfires.
Lightning-ignited fires are, on average, larger, more intense, and more strictly limited to remote areas and periods of extreme fuel dryness than anthropogenic fires.
Greater flammability of forests.
Previous research by the team has shown that episodes of fire-friendly weather are becoming more frequent and intense as the climate warms, meaning forests are becoming more flammable and more regularly.
The synchronous increase in forest flammability and lightning frequency is a worrying sign that intact extratropical forests will be increasingly exposed to fire risk in the future.
Carbon storage and emissions from fires
Extratropical forests are of global importance because they store large amounts of carbon in vegetation and permafrost soils. About 91 percent of these forests in the northern hemisphere are under permafrost. When fires occur in these regions, large amounts of carbon dioxide (CO2) and other greenhouse gases are emitted compared to other regions.
Despite occupying only about 1 percent of the Earth’s surface, fires in intact extratropical forests emit more than 8 percent of total CO2 emissions from fires globally.
amplified emissions and global warming
It is estimated that wildfires could amplify greenhouse gas emissions from thawing permafrost by 30 percent by the end of the century, under a moderate emissions scenario.
Dr Jones, a researcher whose work focuses on the carbon cycle and climate change, said: “Extratropical forests are important globally because they contain dense stocks of carbon in vegetation and soils, which helps maintain CO2 out of the atmosphere and moderate global warming.
“However, when fires occur in these regions, more CO2 is emitted 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 a greater probability of lightning strikes.
“Future increases in lightning ignitions threaten to destabilize vast carbon stocks in extratropical forests, especially with warmer, drier and generally more fire-friendly climate conditions in these regions.”
Relevance to recent fire seasons
The research is especially timely in light of Canada’s record wildfire season in 2023, when wildfire emissions were more than four times higher than the 2003-2022 average. Preliminary reports have indicated a large presence of lightning-caused wildfires in Canada this year.
Dr. Thomas Janssen of VU, lead author of the study, said: “Although our research did not focus specifically on this year’s extreme fire season in Canada, it helps us understand this year’s events. Extreme fire seasons in boreal forests, like the one we saw this year in Canada, will be more likely in warmer climates due to hotter, drier weather and more lightning strikes.
“The fires in Canada this year closely follow record fire seasons in Siberia’s boreal forests in 2020 and 2021.”
Feedback and climate change
The authors warn that greenhouse gas emissions from wildfires can contribute to rising carbon concentrations in the atmosphere and drive further warming, further exaggerating the likelihood of wildfires and other negative climate impacts. climate change in the future.
Professor Sander Veraverbeke of VU said: “Increasing greenhouse gas emissions from fires reinforces the problem of climate change, as more fires break out as the climate warms and more fires are released. more greenhouse gases emitted by fires.
“This ‘strengthening feedback’ is particularly important in boreal forests, most of which lie beneath carbon-rich permafrost soils that take many centuries to form if lost to fire.”
Dr Jones said: “Our work has shown that the risk of lightning ignition increases dramatically as the planet warms, meaning that every tenth of a degree of warming we can avoid will directly translate into a reduced risk of fires.
“Limiting greenhouse gas emissions from fossil fuel use and land-use change is critical to avoiding the worst additional fire risks in many regions, but especially in boreal forests, where fires are so common. sensitive to warming”.
