Southeast Australia experienced intensive and geographically extensive wildfires during the 2019–2020 summer season1,2. The fires released substantial amounts of carbon dioxide into the atmosphere3. However, existing emission estimates based on fire inventories are uncertain4, and vary by up to a factor of four for this event. Here we constrain emission estimates with the help of satellite observations of carbon monoxide5, an analytical Bayesian inversion6 and observed ratios between emitted carbon dioxide and carbon monoxide7. We estimate emissions of carbon dioxide to be 715 teragrams (range 517–867) from November 2019 to January 2020. This is more than twice the estimate derived by five different fire inventories8,9,10,11,12, and broadly consistent with estimates based on a bottom-up bootstrap analysis of this fire episode13. Although fires occur regularly in the savannas in northern Australia, the recent episodes were extremely large in scale and intensity, burning unusually large areas of eucalyptus forest in the southeast13. The fires were driven partly by climate change14,15, making better-constrained emission estimates particularly important. This is because the build-up of atmospheric carbon dioxide may become increasingly dependent on fire-driven climate–carbon feedbacks, as highlighted by this event16.
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TROPOMI measurements of CO can be downloaded from https://s5phub.copernicus.eu. GFED4s-based fire emissions can be downloaded from https://www.geo.vu.nl/~gwerf/GFED/GFED4/. GFAS-based fire emissions can be downloaded from https://apps.ecmwf.int/datasets/data/cams-gfas/. QFED-based fire emissions can be downloaded from https://portal.nccs.nasa.gov/datashare/iesa/aerosol/emissions/QFED/v2.5r1/0.1/QFED/. FEER-based fire emissions can be downloaded from https://feer.gsfc.nasa.gov/data/emissions/. FINN-based fire emissions can be downloaded from https://www.acom.ucar.edu/Data/fire/. Prior and posterior emissions and CO concentrations can be downloaded from https://doi.org/10.5281/zenodo.4692417.
The Weather Research and Forecasting with Chemistry (WRF-CHEM) atmospheric transport model version 4.0 can be downloaded from https://www2.mmm.ucar.edu/wrf/users/download/get_source.html. Inversion and emission preparation codes are available at https://doi.org/10.5281/zenodo.4692678. Python notebooks used to create the figures and tables are at https://doi.org/10.5281/zenodo.5060184.
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We thank the team that realized the TROPOMI instrument, comprising a partnership between Airbus Defence and Space Netherlands, the Royal Netherlands Meteorological Institute (KNMI), the SRON Netherlands Institute for Space Research and the Netherlands Organisation for Applied Scientific Research (TNO), commissioned by the Netherlands Space Office (NSO) and the European Space Agency (ESA). The Sentinel-5 Precursor is part of the European Union (EU) Copernicus programme, and Copernicus Sentinel data from 2019 and 2020 have been used here. The WRF model computations were carried out on the Dutch national e-infrastructure with the support of the SURF Cooperative. We also thank the large team of scientists and technicians who worked on the fire emission data sets available online. G.R.v.d.W. and I.R.v.d.V. are partly supported by the Netherlands Organization for Scientific Research (NWO; VICI research programme 016.160.324).
The authors declare no competing interests.
Peer review information Nature thanks Johannes Kaiser and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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Extended data figures and tables
This file contains Supplementary Methodology and additional information, including Supplementary Figures 1-6, and additional references.
Video of daily simulated and observed CO column mixing ratios. The video shows on the first row the daily prior (using GFAS emissions), posterior and TROPOMI CO column mixing ratios [ppb]. The second row shows prior minus TROPOMI and posterior minus TROPOMI, and the third panel shows the average wind direction in the planetary boundary layer from WRF-CHEM.
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van der Velde, I.R., van der Werf, G.R., Houweling, S. et al. Vast CO2 release from Australian fires in 2019–2020 constrained by satellite. Nature 597, 366–369 (2021). https://doi.org/10.1038/s41586-021-03712-y