Boreal fire emissions surged in 2021, study says

Forest fires in boreal regions released more carbon dioxide in 2021 than any other year since 2000, according to a new study.

That year, fires in boreal North America and Eurasia emitted 1.76 billion metric tons of carbon dioxide.

That’s roughly on par with CO2 emissions from fossil fuels in Japan or about twice the amount released through aviation in 2021, researchers said last week at the annual meeting of the American Association for the Advancement of Science.

Although emissions in 2021 were extreme, they follow an increasing trend over recent decades.

“The fires and the emissions are really two decades-worth of warming and increasingly extreme conditions coming to roost,” said Steven Davis, professor of earth system science at the University of California at Irvine, who was involved in the research.

With wildfires projected to become more frequent and intense in a warming climate, the researchers said their findings may signal a self-reinforcing cycle, where more fires lead to more emissions and more warming.

“It’s a dangerous feedback,” said Bo Zheng, assistant professor at Tsinghua University in Beijing and another of the study’s authors.

Boreal forests cover large swaths of Alaska, Canada and Russia. They are one of the most extensive biomes on Earth and cover regions that are warming much faster than the rest of the planet.

Nonetheless, fires in the western United States and tropical forests have received much more attention than those in boreal regions, as the Associated Press reported.

In the new study, published last week in the journal Science, an international research team used satellite records to gauge carbon monoxide emissions from boreal fires. The data came from an instrument known as Mopitt on a Nasa satellite that has been measuring carbon monoxide levels since 2000.

They then converted carbon monoxide measurements to carbon dioxide emissions. Both carbon monoxide and carbon dioxide are released when forests burn, but carbon dioxide can linger in the atmosphere for centuries, making it hard to directly track using satellites, Zheng said. Carbon monoxide, by contrast, has a lifetime of weeks to months, and plumes associated with fires can be differentiated from background levels.  

Using this approach, the researchers found that emissions over boreal regions have been increasing since 2000.

In 2021, boreal fire emissions were also abnormally high. Typically, boreal fires account for 10 percent of global carbon dioxide emissions from fires. In 2021 they contributed 23 percent, the team reported.

That year, about a third of boreal fire emissions came from North America. The rest came from Eurasia.

Regions with heightened fire emissions in 2021 also coincided with areas that experienced heatwaves and low precipitation or drought, an analysis of climate drivers revealed. In fact, the link between boreal fires and water deficits explained high levels of emissions in specific years, such as those in North America in 2014 – the same year the NWT experienced its “megafire” season.

2021 may have been an anomaly because both North America and Eurasia experienced regional droughts at the same time, the researchers reported – the first time since 2000 that both regions experienced droughts simultaneously.

Kathleen Groenewegen, a planning forester at the NWT’s Department of Environment and Natural Resources who was not involved in the research, points out that 2021 was nowhere near a record fire year in the NWT. She said about 170,000 hectares burned in the territory that year, whereas the average recorded since 1965 is about 460,000 hectares per year.

“There’s huge variation annually in the Northwest Territories. But we know that in 2021, it was one of the lower burned areas on record,” said Groenewegen.

Nonetheless, the association between drought and fires does apply in the NWT, she said.

“We definitely see that correlation,” she said. “When we have extreme drought years, we do see an increase in fire severity, fire intensity, the number of fires, the overall area burned.”

Weakening carbon sink

Typically, after a fire has burned, a portion of the carbon released is taken back up by growing vegetation in the following years.

But boreal fires release 10 to 20 times more carbon per unit area burned than other ecosystems, the researchers said, and recovery is slow.

As fires become more frequent, boreal forests may not have enough time to recover carbon released, said study co-author Philippe Ciais, associate director of the Laboratoire des Sciences du Climat et de l’Environnement at Université Paris-Saclay.

According to Davis, from the University of California at Irvine, what’s really worrisome is if boreal forests stop being an effective carbon sink and instead become a source of CO2.

“That makes our job of stabilizing the climate that much harder,” he said.

Records suggest that forests in the NWT are usually a carbon sink, according to Groenewegen. Most of the time, forests absorb more carbon than the territory emits, the CBC reported last year.  

A change in wildfire patterns could shift whether the territory’s forests act as a net sink or a net source of carbon, Groenewegen said. But forest managers are still working to understand the natural range of variation in fire patterns based on past records, and whether these patterns are changing, she said.

Davis said it will be important to examine how boreal forests recover to understand the extent of the issue. He and his colleagues are working to develop a system based on their emission-tracking method that would monitor fire emissions at global and regional scales in near-real time.

The team does not yet know how much carbon dioxide boreal fires emitted in 2022, but the record year in 2021 is unlikely to remain an anomaly in the future.

“There’s not actually that much evidence that this record will stand for long,” Davis said.

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This article is produced under a Creative Commons CC BY-ND 4.0 licence through the Wilfrid Laurier University Climate Change Journalism Fellowship.