Quantifying Greenhouse Gas emissions from the Australian Black Summer Megafires using the Fire Radiative Energy Emission (FREM) Approach

The 2019–2020 Australian Black Summer megafires burned over eight million hectares of vegetation and constituted an extreme perturbation to terrestrial carbon cycling, releasing an unprecedented quantity of greenhouse gases to the atmosphere. Quantifying fire-driven emissions remains a key challenge, as emission inventories typically fall into one of two categories; bottom-up approaches (such as with the Global Fire Emission Database, GFED) that rely on burned area, fuel load, and combustion completeness estimates, or top-down approaches, (such as the Global Fire Assimilation System, or GFAS) which scale Fire Radiative Power (FRP) observations to emissions using emission coefficients. Currently, the two most widely used inventories (GFED and GFAS) ultimately rely heavily on uncertain modelled estimates of broad scale biome-specific combustion completeness, which remains a major limitation in constraining carbon fluxes from fires. We apply the Fire Radiative Energy Emission (FREM) approach, a top-down framework that directly links observed Fire Radiative Energy (FRE) to trace gas emissions, thereby reducing reliance on poorly constrained fuel and combustion assumptions. FREM is derived from co-located observations of FRP from the geostationary Himawari satellite and carbon monoxide (CO) from TROPOMI aboard Sentinel-5P. A dataset of 580 cloud-free landscape fires and associated plumes across six major Australian biomes (low woodland savanna, grassland, shrubland, evergreen and deciduous broadleaf forests, and sparse vegetation) was assembled for 2019 to derive biome-specific emission coefficients relating FRE to excess CO. These coefficients, combined with a calculated small-fire correction factor and hourly FRE observations from Himawari, were used to estimate emissions from the Black Summer megafires and to compare FREM-derived fluxes with those from existing inventories (GFAS v1.2, GFED v4.1s, GFED v5.1, and the Fire Energetics and Emissions Research, or FEER). The FREM estimates exhibit coherent spatial and temporal patterns and fall within the spread of emissions reported by these inventories, indicating consistency at regional scales while retaining sensitivity to fire intensity and temporal variability. By utilizing the geostationary FRP observations from Himawari, the FREM approach provides high-temporal-resolution, near-real-time estimates of fire emissions across Australia that are directly linked to observed radiative energy release, and bypasses the need for fuel load and combustion completeness estimations.