The Influence of Wildfire on Interannual Variability and Long-Term Trends in Global Aerosol Composition (Invited Presentation)

In many parts of the world, considerable progress has been made over the past 25 years in reducing aerosol emissions and precursor trace gases from urban and industrial sources to improve air quality. However, fire activity has intensified in many areas over the same period due to climate warming and land use change. Within the past decade, megafire events across multiple continents have left a distinct imprint on atmospheric composition at regional and hemispheric scales. Here, we separate fire and non-fire contributions to aerosol optical depth (AOD) and atmospheric radiation during 1997-2023 using the Energy Exascale Earth System Model version 3 with interactive chemistry. We show that the observed time series of fire emissions from the Global Fire Emissions Database version 5 explains most of the AOD variability and long-term trends across different continents. Fire is a crucial driver of positive aerosol trends across western and boreal North America, Siberia, and the Indian subcontinent, as well as a negative trend across southern Amazonia. We also assess whether the magnitude of tropical deforestation fire emissions reported in several recent syntheses is consistent with available observational constraints from Aeronet, MODIS, and VIIRS. In a final step, we explore whether model-data mismatches for AOD and carbon monoxide may be helpful as a top-down constraint in reducing uncertainties associated with emissions from tropical fires.