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- Title
Variability in Biomass Burning Emissions Weakens Aerosol Forcing Due To Nonlinear Aerosol‐Cloud Interactions.
- Authors
Heyblom, Kyle B.; Singh, Hansi A.; Rasch, Philip J.; Hirasawa, Haruki
- 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. Plain Language Summary: Aerosols are small particles in the air that can impact the climate, but we don't know exactly how much. One reason for this uncertainty is that the amount of aerosols can change a lot over time, especially when it comes from burning things like wood or plants (i.e., biomass burning emissions). When the amount of these biomass burning aerosols changes a lot from year‐to‐year, it has less of an impact on the climate. This is because clouds react less strongly when aerosol concentrations are high compared to when they are low. If we smooth out the changes in aerosol amounts over time (as is done with most Earth System Model simulations), we will overestimate their cooling impact on the climate. Key Points: The radiative forcing due to aerosols is overestimated if emissions are temporally‐smoothedInterannual variability in aerosol emissions leads to a weakened time‐average cloud radiative effectChanges in time‐average cloud radiative effect with differing aerosol variability are due to nonlinear aerosol‐cloud interactions
- Subjects
BIOMASS burning; AEROSOLS; RADIATIVE forcing; WOOD; COMMUNITIES
- Publication
Geophysical Research Letters, 2023, Vol 50, Issue 11, p1
- ISSN
0094-8276
- Publication type
Article
- DOI
10.1029/2022GL102685