Global fire emissions impact on tropospheric chemistry and radiation in the Energy Exascale Earth System Model (E3SM)

Abstract. Wildfires release large amounts of trace gases and aerosols into the atmosphere, thereby playing a significant role in structuring tropospheric composition. Understanding and quantifying the interactions between fire, atmospheric chemistry, and climate has become increasingly important as wildfire activity has intensified in many regions over the past several decades. Here, we applied the Energy Exascale Earth System Model (E3SM) version 3, coupled with an interactive chemistry module as its default configuration and GFED5 fire emissions, to assess how contemporary wildfires influence atmospheric composition and radiation. We find that wildfires increase global annual average CO and O₃ column concentrations by 16 ± 2 % and 6 ± 1 % (reported as mean ± standard deviation hereafter), respectively, during 1997–2022, with the largest increases occurring in wildfire-prone regions of the southern Amazon, central Africa, and tropical Asia. We also find that wildfires strongly promote interannual variations in CO and O₃ at tropical sites, thereby improving consistency with in situ observations. Fire emissions increase global aerosol optical depth (AOD) by 7 ± 2 %, resulting in a reduction in net radiation at the surface by about 1.1 W m⁻², primarily due to the direct attenuation of incoming solar radiation and indirect cloud effects associated with fire-emitted aerosols. These cooling effects are only partially offset by a small fire-induced ozone radiative warming at surface (+0.07 W m⁻²). Our analysis provides insight into the spatiotemporal influence of wildfires on global tropospheric trace gas and aerosol abundances and establishes several new diagnostics for evaluating coupled climate-wildfire models.