Aerosol Forcing Is Negligible in AR6 Due to a Smaller Diagnosed ERF: Evidence from Two Independent Data Methods and SAI Implications - Preprint

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https://www.researchgate.net/publication/399240897_Aerosol_Forcing_Is_Negligible_in_AR6_Due_to_a_Smaller_Diagnosed_ERF_Evidence_from_Two_Independent_Data_Methods_and_SAI_Implications

Authors: Alec Feinberg

Abstract 

Two independent diagnostic analyses, using AR6-consistent Earth energy imbalance constraints for the 2019 reference period and an unsaturated linear Earth energy-budget framework, converge on a smaller effective radiative forcing (ERF), leaving limited need for a substantial aerosol reverse-forcing offset. Adopting an effective net feedback parameter of approximately −1.5 W m⁻² K⁻¹ (within the AR6 assessed range), together with an EEI range of 0.5–1.05 W m⁻² and ~1.0 °C global mean warming by 2019, yields a diagnostic AR6-consistent transient net forcing of approximately 1.95–2.46 W m⁻². This forcing is largely attributable to greenhouse gases, leaving little requirement for a compensating aerosol offset and lying well below the AR6 central estimate of ~3.3 W m⁻² for the same period. This conclusion is independently reinforced by an unsaturated linear forcing upper-bound greenhouse-gas Earth energy-budget diagnostic model, which yields a comparable constraint on effective GHG forcing for 2019. Accounting for additional non-GHG contributions, including urbanization-related radiative effects, raises the diagnosed net forcing to approximately 2.3 W m⁻², but does not materially alter the conclusion that aerosol cooling is limited. Across methods, strong feedback amplification reduces the external forcing required to explain observed warming by 2019, thereby narrowing the energy-budget space available for a large negative aerosol reverse forcing. These findings suggest that reductions in anthropogenic aerosols are unlikely to produce large additional warming. While they do not preclude the effectiveness of stratospheric aerosol injection, as demonstrated by volcanic observations, they indicate that aerosol-based mitigation assumptions warrant careful reevaluation. The implications for solar geoengineering strategies are briefly discussed.

Source: ResearchGate