AMOC weakening in response to global and regional reductions in aerosol emissions

Allen, Robert J and Carson, Timothy and Liu, Wei and Wilcox, Laura J and Samset, Bjørn H and Ahmadi, Sharar and Ekman, Annica M L and Elling, Maxwell T and Fraser-Leach, Luke and Griffiths, Paul and Keeble, James and Koshiro, Tsuyoshi and Kushner, Paul and Lewinschal, Anna and MacRae, Molly and Makkonen, Risto and Merikanto, Joonas and Nabat, Pierre and Nazarenko, Larissa and O’Donnell, Declan and Oshima, Naga and Paynter, David and Persad, Geeta and Rumbold, Steven T and Swart, Neil and Takemura, Toshihiko and Tsigaridis, Kostas and von Salzen, Knut and Westervelt, Daniel M and Hassan, Taufiq (2026) AMOC weakening in response to global and regional reductions in aerosol emissions. Environmental Research: Climate, 5 (2): 025025. ISSN 2752-5295

Text (pdf.pdf)
pdf.pdf - Published Version
Available under License Creative Commons Attribution.
Download (12MB)

Abstract

In response to continued greenhouse gas (GHG) increases, the Atlantic Meridional Overturning Circulation (AMOC) is expected to weaken through the 21st century. However, AMOC impacts associated with efforts to improve air quality are less well understood. Here, eight models from the Regional Aerosol Model Intercomparison Project are examined to quantify mid-21st century AMOC changes resulting from global and regional anthropogenic aerosol and precursor gas (AA) emissions reductions (industrial and biomass burning), by comparing strong air pollution control shared socioeconomic pathway (SSP1-2.6) to a baseline with weak air pollution control (SSP3-7.0). Global AA reductions and subsequent warming yield multi-model mean AMOC weakening of 6% ( −0.98±0.40 Sv; 1 Sv = 106 m3 s−1) by the last 12 years of the simulation (2039–2050). This is ⅓ of the magnitude of the corresponding weakening associated with the high GHG emissions scenario SSP3-7.0. Of the regional perturbations, combined North American and European AA reductions drive the largest AMOC weakening, followed by combined African and Middle Eastern reductions and then East Asian reductions, with South Asian reductions yielding non-significant weakening. Across these experiments, AMOC weakening is significantly correlated with the North Atlantic Ocean aerosol effective radiative forcing ( r=−0.95) and aerosol optical depth response ( r=1.0). AMOC weakening under AA reductions is associated with a thermally driven reduction in buoyancy in the subpolar North Atlantic, which is largely driven by surface shortwave radiation increases, consistent with the forcing from AA reductions. Africa + Middle East AA reductions also involve excitation of a negative North Atlantic Oscillation pattern, which contributes to AMOC weakening. Our results show that efforts to improve air quality, particularly around the Atlantic basin but also far away in East Asia, will contribute to future AMOC weakening.