Study Reveals Record-High Carbon Dioxide Emissions From Boreal Fires In 2021

Boreal fires, which typically account for 10% of global fire carbon dioxide emissions, contributed 23% in 2021, a new study reports.

“Boreal forests could be a time bomb of carbon, and the recent increases in wildfire emissions we see make me worry the clock is ticking,” said study author Steven Davis.

Extreme wildfires – which impact the climate through the carbon dioxide they emit – have become more common. Wildfires in tropical forests have received notable attention for their emissions, while fires in boreal forests have attracted much less focus. This is despite the fact boreal forests are the world's largest land biome, and fires in these regions release 10 to 20 times more carbon per unit of area burned than other ecosystems. Monitoring fire emissions in this high-carbon density ecosystems is thus critical for understanding Earth’s temperature and risks to climate mitigation efforts.

Satellite-based approaches to monitoring carbon dioxide emissions from fires can miss emissions from little fires, while bottom-up modeling approaches can miss burning soil fires. Also, carbon dioxide is hard to pinpoint to fires specifically; it can stay in the atmosphere for hundreds of years, meaning background carbon dioxide concentrations are quite high compared to the carbon dioxide emissions released from small fires.

To better monitor fire emissions, and in boreal regions in particular, Bo Zheng and colleagues used a new approach to track fire carbon dioxide emissions indirectly. It involved monitoring carbon monoxide, which has a much shorter lifetime in the atmosphere compared to carbon dioxide.

The authors used satellite data from MOPITT (Measurements Of Pollution In The Troposphere instrument), the satellite instrument with the longest continuous time series of carbon dioxide measurements to date, to estimate global weekly fire carbon monoxide and carbon dioxide emissions in boreal regions through an atmospheric inversion system approach. This revealed a two-decade trend of expanding summer fires in boreal forests since 2000 and record-high emissions from boreal forest fires in 2021, coinciding with severe heatwave, drought, and high water deficit in boreal regions that year.

“Our data analysis implies a link between the extensive boreal fires and climate drivers (especially temperature increase or heatwaves),” they write.

They note that boreal ecosystems could become the dominant source regions of intensive fires and fire carbon emissions in the future. They also say the approach they developed to monitor fire emission estimates will be useful in developing a more integrated system capable of monitoring and evaluating global and regional fire carbon budgets, postfire land-use fluxes, and the net impact of fire emissions on atmospheric carbon dioxide.