It’s not all bad news, however. Another paper in Nature reports that much of this plume of carbon might have been indirectly sucked up by a gigantic phytoplankton bloom in the Southern Ocean.
Worst fires on record
The unprecedented fires burnt across as much as 74,000 square kilometres of mostly eucalyptus, or gum, forest in southeast Australia—an area larger than Sri Lanka.
Previous estimates from global databases of wildfire emissions based on satellite data suggested that the fires released about 275 million tonnes of carbon dioxide during their zenith, between November 2019 and January 2020.
But the new analysis indicates that this figure was a gross underestimate, says Ivar van der Velde, lead author of the first paper. “These models often lack the spatio-temporal detail to explain the full impact these fires have,” says van der Velde, an environmental scientist at the SRON Netherlands Institute for Space Research, in Utrecht, and at the Free University of Amsterdam.
He and his team set out to get a better estimate, based on more-granular data from the tropospheric monitoring instrument TROPOMI on the European Space Agency’s Sentinel-5 Precursor satellite.
TROPOMI takes daily snapshots of carbon monoxide levels in the atmospheric column beneath it. The researchers used this data to calculate a more accurate estimate of the carbon monoxide emissions from the bush fires, which they used as a proxy for calculating carbon dioxide emissions.
Their final figure—715 million tonnes—is nearly 80 times the typical amount of carbon dioxide emitted from fires in southeast Australia during the three peak months of the summer bush-fire season.
Bowman says the figure is similar to what his team calculated from the area of forests burnt, but much higher than figures based on previous satellite measurements of emissions.
The key question is how these forests will recover, says Cristina Santín, a wildfire researcher at the Spanish National Research Council in Asturias. Wildfires have long been considered net-zero-carbon events, because the emissions they release are recaptured when the vegetation regrows—but an increase in the frequency and intensity of fires in Australia could mean that ecosystems never fully bounce back. If these fires “threaten the recovery of the ecosystem, then we really need to worry”, she says.
Reason to hope