2021 wildfires: NASA satellites reveal 150% increase in CO2 emissions

Wildfires across North America and Eurasia emitted around half a gigaton of carbon (or 1.76 billion tons of CO₂) in 2021, a record-breaking 150 percent more than the average annual CO2 emissions between 2000 and 2020, according to a report published in Science on March 2.

"According to our measurements, boreal (northern) fires in 2021 shattered previous records," said senior co-author Steven Davis in a press release.

"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."

He also added the boreal wildfires released nearly twice as much CO₂ as global aviation in 2021. 

How do wildfires contribute to global warming?

The researchers claim that the worsening fires result from a 'climate-fire' feedback system in which CO₂ emissions warm the Earth, causing conditions that encourage more fires and emissions. 

It's challenging for Earth system scientists to evaluate the volume of CO₂ released during wildfires for several reasons. For instance, smoke-covered terrain makes it difficult for satellites to observe a burning event.

Furthermore, the precise resolution of space-based observations is insufficient to identify the specifics of CO₂ emissions.

The scientists overcame these difficulties by examining carbon monoxide released into the atmosphere after fires.

They reconstructed changes in worldwide fire CO₂ emissions from 2000 to 2021 by combining CO measurements from the MOPITT (Measurements Of Pollution In The Troposphere satellite instrument) with preexisting fire emissions and wind speed records.

As CO doesn't linger in the atmosphere as long as CO₂ does, when scientists find an unusually high amount of CO, they can infer that this is evidence of fires. 

With the help of data sets provided by NASA's Moderate Resolution Imaging Spectroradiometer on board the Terra and Aqua satellites, the team independently verified the occurrence of extreme fires in 2021.

A review of the researchers' data showed relationships between widespread boreal fires and various climate variables- particularly rising annual mean temperatures and short heat waves.

They discovered that higher northern latitudes regions and areas with greater 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," Davis stated.

Around 80 percent of these CO₂ emissions will be offset by the regrowth of plants, while 20 percent are almost irreversibly lost to the atmosphere.

"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," he concluded.

The full study was published in Science on March 2 and can be found here.

Study abstract:

Extreme wildfires are becoming more common and increasingly affecting Earth’s climate. Wildfires in boreal forests have attracted much less attention than those in tropical forests, although boreal forests are one of the most extensive biomes on Earth and are experiencing the fastest warming. We used a satellite-based atmospheric inversion system to monitor fire emissions in boreal forests. Wildfires are rapidly expanding into boreal forests with emerging warmer and drier fire seasons. Boreal fires, typically accounting for 10% of global fire carbon dioxide emissions, contributed 23% (0.48 billion metric tons of carbon) in 2021, by far the highest fraction since 2000. 2021 was an abnormal year because North American and Eurasian boreal forests synchronously experienced their greatest water deficit. Increasing numbers of extreme boreal fires and stronger climate–fire feedbacks challenge climate mitigation efforts.