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Radiative effects of reduced aerosol emissions during the COVID-19 pandemic and the future recovery

The pan­dem­ic in 2020 caused an abrupt change in the emis­sion of anthro­pogenic aerosols and their pre­cur­sors. We esti­mate the asso­ci­at­ed change in the aerosol radia­tive forc­ing at the top of the atmos­phere and the sur­face. To that end, we per­form new sim­u­la­tions with the CMIP6 glob­al cli­mate mod­el EC-Earth3. The sim­u­la­tions use the here new­ly cre­at­ed data for the anthro­pogenic aerosol opti­cal prop­er­ties and an asso­ci­at­ed effect on clouds from the sim­ple plumes para­me­ter­i­za­tion (MACv2-SP), based on revised SO2 and NH3 emis­sion sce­nar­ios. Our results high­light the small impact of the pan­dem­ic on the glob­al aerosol radia­tive forc­ing in 2020 com­pared to the CMIP6 sce­nario SSP2‑4.5 of the order of +0.04 Wm−2, which is small com­pared to the nat­ur­al year-to-year vari­abil­i­ty in the radi­a­tion bud­get. Nat­ur­al vari­abil­i­ty also lim­its the abil­i­ty to detect a mean­ing­ful region­al dif­fer­ence in the anthro­pogenic aerosol radia­tive effects. We iden­ti­fy the best chances to find a sig­nif­i­cant change in radi­a­tion at the sur­face dur­ing cloud-free con­di­tions for regions that were strong­ly pol­lut­ed in the past years. The post-pan­dem­ic recov­ery sce­nar­ios indi­cate a spread in the aerosol forc­ing of −0.68 to −0.38 Wm−2 for 2050 rel­a­tive to the pre-indus­tri­al, which trans­lates to a dif­fer­ence of +0.05 to −0.25 Wm−2 com­pared to the 2050 base­line from SSP2‑4.5. This spread falls with­in the present-day uncer­tain­ty in aerosol radia­tive forc­ing and the CMIP6 spread in aerosol forc­ing at the end of the 21st cen­tu­ry. We release the new MACv2-SP data for stud­ies on the cli­mate response to the pan­dem­ic and the recov­ery sce­nar­ios. Our 2050 forc­ing esti­mates sug­gest that sus­tained aerosol emis­sion reduc­tions dur­ing the post-pan­dem­ic recov­ery cause a stronger cli­mate response than in 2020, i.e., there is a delayed influ­ence of the pan­dem­ic on cli­mate.

Fiedler, S., Wyser, K., Rogelj, J. and van Noi­je, T. (2021) in Atmos­pher­ic Research, Vol­ume 264, 15 Decem­ber 2021, 105866

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