Variability in Biomass Burning Emissions Weakens Aerosol Forcing Due To Nonlinear Aerosol-Cloud Interactions

Date

2023-06-02

Authors

Heyblom, Kyle B.
Singh, Hansi A.
Rasch, Philip J.
Hirasawa, Haruki

Journal Title

Journal ISSN

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Publisher

Geophysical Research Letters

Abstract

The 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.

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Citation

Heyblom, 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/10.1029/2022GL102685