According to an international team of researchers led by Earth system scientists from the University of California, Irvine, carbon dioxide emissions from wildfires, which have been gradually increasing since 2000, rose sharply to a record high in 2021.
Almost half a gigatonne of carbon (or 1.76 billion tons of CO2) was released from burning boreal forests in North America and Eurasia in 2021, 150 percent higher than the annual mean of CO2 emissions between 2000 and 2020, the scientists report in a paper in Science.
“According to our measurements, boreal fires in 2021 broke 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 that are sleeping away, and unfortunately even this new record may not last long.”
The researchers said the worsening fires are part of a climate-fire feedback loop, with carbon dioxide emissions warming the planet and creating conditions that lead to more fires and more emissions.
“The escalation of wildfires in the boreal region is expected to accelerate the release of the large carbon pools in the permafrost soil layer and contribute to the northward spread 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 favorable climate for wildfires to occur.”
Davis added, “Boreal fires released almost twice as much CO2 than global aviation in 2021. If this magnitude of emissions from unmanaged countries becomes a new normal, stabilizing the Earth’s climate will be even more difficult than we thought.”
Analyzing the amount of carbon dioxide released during wildfires is difficult for Earth system scientists for several reasons. Rugged, smoke-shrouded terrain impedes satellite observations during a combustion event, and space-based measurements do not have fine enough resolution to reveal details of CO2 emissions. Models used to simulate fuel loading, fuel consumption and fire efficiency work well under normal circumstances but are not robust enough to represent extreme wildfires, the researchers said.
And there is another roadblock of our own creation. “Earth’s atmosphere already contains large amounts of carbon dioxide from the burning of human fossil fuels, and the greenhouse gas present is difficult to distinguish from that produced by wildfires,” Chen said.
The team found a way around these hurdles by studying the carbon monoxide emitted into the atmosphere during fires. By combining CO readings from MOPITT – the satellite instrument “Measurements Of Pollution In The Troposphere” – with existing data sets on fire emissions and wind speeds, the team reconstructed changes in global fire CO2 -Emissions from 2000-2021. Carbon monoxide has a shorter lifetime in the atmosphere than CO2so when scientists detect an anomalous amount of CO, it provides evidence of fires.
The researchers independently confirmed the occurrence of extreme fires in 2021 using datasets provided by NASA’s Moderate Resolution Imaging Spectroradiometer aboard the Terra and Aqua satellites.
“The inversion approach used in this study is a complementary method to the traditional bottom-up approach based on estimating burned area, fuel load and completeness of combustion,” Chen said. “Combining these approaches can lead to a more comprehensive understanding of wildfire patterns and their impacts.”
The researchers said their data analysis revealed links between widespread boreal fires and climate drivers, particularly increased annual mean temperatures and short-lived heat waves. They found that higher northern latitudes and areas with greater proportions of tree cover were particularly at risk.
“Global carbon emissions from wildfires remained relatively stable at about 2 gigatons per year for the first two decades of the 21st century, but 2021 was the year emissions really picked up,” David said. “About 80 percent of this CO2 Emissions are reclaimed through regrowth of vegetation, but 20 percent is lost to the atmosphere in an almost irreversible way, requiring humans to find a way to remove that carbon from the air or significantly reduce our own production of atmospheric carbon dioxide. “