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Abstract Reanalysis data show a significant weakening of summertime circulation in the Northern Hemisphere (NH) midlatitudes in the satellite era with implications for surface weather extremes. Recent work showed the weakening is not significantly affected by changes in the Arctic, but did not examine the role of different anthropogenic forcings such as aerosols. Here we use the Detection and Attribution Model Intercomparison Project (DAMIP) simulations to quantify the impact of anthropogenic aerosol and greenhouse gas forcing. The DAMIP simulations show aerosols and greenhouse gases contribute equally to zonal‐mean circulation weakening. Regionally, aerosol dominates the Pacific storm track weakening whereas greenhouse gas dominates in the Atlantic. Using a regional energetic framework, we show why the impact of aerosol is the largest in the Pacific. Reduced sulfate aerosol emissions over Eurasia and North America increase (clear‐sky) surface shortwave radiation and turbulent fluxes. This enhances land‐to‐ocean energy contrast and energy transport via stationary circulations to the ocean. Consequently, energy converges poleward of oceanic storm tracks, demanding weaker poleward energy transport storm tracks, and the storm tracks weaken. The impact is larger over the Pacific following the larger emission decrease over Eurasia than North America. Similar yet opposite, increased aerosol emissions over South and East Asia decrease shortwave radiation and weaken land‐to‐ocean energy transport. This diverges energy equatorward of the Pacific storm track, further weakening it. Our results show aerosols are a dominant driver of regional circulation weakening during the NH summertime in the satellite era and a regional energetic framework explaining the underlying processes.
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This content will become publicly available on June 1, 2026
Nonlinear Response of the Surface Energy Balance to Changes in Anthropogenic Aerosols and Irrigation Over South Asia
Abstract The regional climate impacts of anthropogenic aerosol emissions and irrigation growth in South Asia have conventionally been studied separately. These forcings have overlapping influences on surface temperature and atmospheric stability, but detection and attribution simulations typically quantify the impact of individual time‐evolving climate forcings, which does not account for nonlinear interactions between forcings or their impacts, when forcings evolve in tandem. Using transient simulations in GISS ModelE 2.1‐G, we assess the summertime surface energy balance in five different sub‐regions of South Asia by comparing the linear addition of anthropogenic aerosol and land use single‐forcing historical simulations with novel dual‐forcing simulations. We find that the combination of aerosol emissions and irrigation changes between preindustrial and present‐day increases aerosol hydration and cloud cover more strongly than does the linear addition of the individual forcings. This results in a strong nonlinear decrease in downwelling shortwave radiation, which drives subsequent nonlinearities in the surface energy balance through a relative suppression of energy availability at the surface. While aerosols and irrigation are each credited with suppressing monsoon winds and delaying onset, combined simulations of both forcings suggest that surface pressure is nonlinearly reduced over the northern Indian Subcontinent. This results in a net increase in 850 mb winds from the Bay of Bengal toward northwest India and Pakistan in combined simulations, suppressing the weakening of summer monsoon winds from single forcing results. The nonlinearities identified in our study suggest that the current framework for detection and attribution may not adequately account for potential interactions between forcings.
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- Award ID(s):
- 2235177
- PAR ID:
- 10656295
- Publisher / Repository:
- American Geophysical Union
- Date Published:
- Journal Name:
- Earth's Future
- Volume:
- 13
- Issue:
- 6
- ISSN:
- 2328-4277
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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