Carbon dioxide (CO2) emissions from wildfires that have been gradually increasing since 2000, spiked drastically to a record high in 2021, said an international team of researchers led by University of California, Irvine.
In the study, the researchers said that burning boreal forests in North America and Eurasia in 2021 led to the release of nearly half a gigaton of carbon (1.76 billion tons). This was 150 percent higher than annual mean CO2 emissions between 2000 and 2020, the scientists said in a paper in Science.
CLIMATE FIRE
“According to our measurements, boreal fires in 2021 shattered previous records,” said senior co-author Steven Davis, UCI professor of Earth system science. “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.”
The researchers pointed out that worsening fires are part of a climate-fire feedback in which carbon dioxide emissions warm the planet, creating conditions that lead to more fires and 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,” said co-author Yang Chen, a UCI research scientist in Earth system science. “These factors could potentially lead to further warming and create a more favourable climate for the occurrence of wildfires.”
“Boreal fires released nearly twice as much CO2 as global aviation in 2021. If this scale of emissions from unmanaged lands becomes a new normal, stabilizing Earth’s climate will be even more challenging than we thought,” the researcher said.
THE HURDLES AND THE MODEL
The researchers found it difficult to analyse the amount of carbon dioxide released during wildfires for a variety of reasons. Rugged, smoke-enshrouded terrain hampers satellite observations during a combustion event, and space-based measurements are not at a sufficiently fine resolution to reveal details of CO2 emissions. Models used to simulate fuel load, fuel consumption and fire efficiency work well under ordinary circumstances but are not robust enough to represent extreme wildfires, according to the researchers.
Another roadblock of is that Earth’s atmosphere already contains large amounts of carbon dioxide from human fossil fuel burning, and the existing greenhouse gas is difficult to distinguish from that produced by forest fires, said Chen.
In a bid to overcome this, the researchers studied carbon monoxide expelled into the atmosphere during blazes. Combining CO readings from MOPITT – the Measurements Of Pollution In The Troposphere satellite instrument – with existing fire emissions and wind speed datasets, they reconstructed changes in global fire CO2 emissions from 2000-2021. Carbon monoxide has a shorter lifespan in the atmosphere than CO2, so if scientists detect an anomalous abundance of CO, that provides evidence of fires.
“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,” Chen said. “Combining these approaches can result in a more comprehensive understanding of wildfire patterns and their impacts.”
CO2 CONNECTION WITH WILD FIRE
The team in their analysis found links between extensive boreal fires and climate drivers, especially increased annual mean temperatures and short-livedheat waves. They found that higher northern latitudes and areas with larger tree cover fractions were especially vulnerable.
“Wildfire carbon emissions globally were relatively stable at about 2 gigatons per year for the first two decades of the 21st century, but 2021 was the year when emissions really took off,” David 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.”
Joining UCI’s Davis and Chen on this project was an international team of researchers from Tsinghua University in Shenzhen, China; China’s State Environmental Protection Key Laboratory of Sources and Control of Air Pollution Complex in Beijing; the University of Paris-Saclay; Germany’s Max Planck Institute for Biogeochemistry; the Netherlands Institute for Space Research; Vrije University in Amsterdam; Harbin Institute of Technology in China.
