(CN) — While a number of high profile wildfires in recent years has suggested that global warming has made fire season longer and deadlier, a paper published Monday is one of the first pieces to detail how both the frequency and magnitude of extreme wildfires have doubled over the last 20 years,
"There's a growing perception among the media, and scientific articles as well, that fire is changing on Earth that we're experiencing more extreme events," said Calum Cunningham, a postdoctoral research fellow at the University of Tasmania's Fire Centre and lead author of the paper published in the journal Nature Ecology & Evolution. "But surprisingly, that hadn't actually been documented."
Cunningham and his team used NASA satellite data from 2003 to 2023 and calculated the "daily clusters of summed fire radiative power," or the energy released from fire every day. They then selected the top .1% of all fire events over the last two decades — about 3,000 wildfires.
They found that the number of extreme wildfires has increased 2.2-fold from 2003 to 2023, and that the six most extreme events have all come in the last seven years.
The total area that's burned every year has been declining during this century but researchers say that isn't necessarily a good sign.
"This trend is mostly driven by declines in low-intensity fires in African grasslands and savannas," Cunningham and his co-authors write in the study. "Globally, average fire intensity has also been decreasing this century, but burn severity, an ecological measure of a fire’s immediate effects (for example, biomass loss and mortality), is increasing in more regions than it is decreasing."
Perhaps even more troubling, the largest increases in extreme fires were located in temperate conifer forests, such as those in the U.S. Pacific Northwest, and the boreal forests found in the northern part of the world.
"That's worrying because the boreal forest is just a hugely carbon rich ecosystem, huge stores of carbon in organic soils," said Cunningham in an interview. "Those systems, they do burn from time to time, but these extreme events are likely releasing enormous amounts of emissions."
Researchers say the increase in extreme wildfires is largely due to global warming — longer summers mean prolonged dry periods, more opportunities for fire and more fuel for fires to spread quickly. When carbon-rich forests like boreal forests burn, they release tons of carbon into the atmosphere, making climate change that much worse.
But it's not just global warming, researchers say.
Fire management habits have changed drastically over the centuries. Humans don't practice controlled burns as much as they used to, decreasing the number of small fires but increasing the number of large ones.
"We have this situation where you only get wildfires occurring under the very worst conditions when they're not controllable," Cunningham said. "And we're now learning, I think, to reincorporate that into fire management with intentional low-intensity fire. That, in theory, would reduce the intensity of wildfires."
He added: "Humans have lived with fire for 400,000 years. It's not the fire itself. We need to be managing these extreme events, because they're the ones that cause major ecological damage, major societal problems and threaten to reshape the climate system."
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