Heyblom, Kyle B.Singh, Hansi A.Rasch, Philip J.Hirasawa, Haruki2023-06-122023-06-1220232023-06-02Heyblom, K. B., Singh, H. A., Rasch, P. J., & Hirasawa, H. (2023). Variability in biomass burning emissions weakens aerosol forcing due to nonlinear aerosol-cloud interactions. Geophysical Research Letters, 50, e2022GL102685. https://doi.org/10.1029/2022GL102685https://doi.org/10.1029/2022GL102685http://hdl.handle.net/1828/15162The magnitude of the aerosol forcing remains among the largest unknowns when assessing climate sensitivity over the historical period. Here, we quantify and explain a crucial but often overlooked source of uncertainty in aerosol forcing: the temporal variability of aerosol emissions. We show that time-variability in biomass burning (BB) emissions weakens the time-averaged total aerosol forcing, particularly in the Northern Hemisphere mid- to high-latitudes. BB emissions variability produces weaker (less negative) mean effective radiative forcing (ERF) compared to scenarios with no interannual variability in emissions. Satellite-estimated BB emissions (and associated variability) result in a June–September absolute ERF (relative to zero BB emissions) of −7.7 W m−2 from 50° to 70°N, compared to −10.4 W m−2 when no emissions variability is used in the Community Earth System Model version 2 (CESM2). This difference in forcing is attributable to nonlinear aerosol-cloud interactions. Aerosol forcing will be overestimated (i.e., more negative) if emissions are temporally-smoothed.enArticleSchool of Earth and Ocean Sciences