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Record-breaking amount of CO2 released by wildfires in 2021

According to a new study led by the University of California, Irvine (UCI), carbon dioxide emissions from wildfires – which have been gradually increasing since the beginning of the 21st century – spiked dramatically to a record high in 2021. The experts report that nearly 1.76 billion tons of CO2 were released from burning boreal forests in North America and Eurasia – 150 percent higher than the annual average emissions between 2000 and 2020.

“According to our measurements, boreal fires in 2021 shattered previous records,” said study senior co-author Steven Davis, a professor of Earth System Science at UCI. “These fires are two decades of rapid warming and extreme drought in Northern Canada and Siberia coming to roost, and unfortunately even this new record may not stand for long.”

Reliably measuring the amount of CO2 released by wildfires is difficult because massive amounts of smoke often hinder satellite observations, and space-based measurements are not at a sufficiently high resolution to capture details of CO2 emissions. Moreover, since that our planet’s atmosphere already contains large amounts of CO2 from fossil fuel burning, this gas is difficult to distinguish from that released by wildfires.

To overcome these hurdles, the experts combined measurements of carbon monoxide – which provides clear evidence of fires, since it has a shorter lifespan in the atmosphere than CO2 – with existing fire emissions and wind speed datasets.

“The inversion approach employed in this study is a complementary method to the conventional bottom-up approach, which is based on estimating the burned area, fuel load, and combustion completeness,” explained co-author Yang Chen, a researcher in Earth System Science at UCI. “Combining these approaches can result in a more comprehensive understanding of wildfire patterns and their impacts.”

The analyses revealed clear associations between extensive boreal wildfires and climate drivers, such as higher annual mean temperatures and intense heatwaves. Moreover, higher northern latitudes and areas with larger tree cover fractions were found to be particularly vulnerable.

“Wildfire carbon emissions globally were relatively stable at about two gigatons per year for the first two decades of the 21st century, but 2021 was the year when emissions really took off,” Davis said. “About 80 percent of these CO2 emissions will be recovered through vegetation regrowth, but 20 percent are lost to the atmosphere in an almost irreversible way, so humans are going to have to find some way to remove that carbon from the air or substantially cut our own production of atmospheric carbon dioxide.”

Finally, the scientists identified a climate-wildfire feedback process, in which CO2 emissions warm the planet, creating conditions that lead to more fires and thus more emissions. “The escalation of wildfires in the boreal region is anticipated to accelerate the release of the large carbon storage in the permafrost soil layer, as well as contribute to the northward expansion of shrubs. These factors could potentially lead to further warming and create a more favorable climate for the occurrence of wildfires,” Chen concluded.

The study is published in the journal Science.

By Andrei Ionescu, Staff Writer

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