The Time-Evolving Role of Anthropogenic Aerosols in Driving Global and Regional Climate Changes
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Date
2022-07-07
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Abstract
The overall cooling effects of Anthropogenic aerosol (AA), which mask a portion of global warming, have been the subject of many studies but still have large uncertainty. The difficulty in the quantitative understanding of AA’s climate effects is partly due to the temporal and spatial heterogeneity of the short-lived AA forcing, and thus, detailed analysis of AA at different periods are essential to understanding the comprehensive AA’s evolving role on global and regional climate change. Assessment of the mid-20th century cooling (1948–1978) based on CMIP5 multi-model results shows that AA and the Atlantic decadal variation are the main contributors to the cooling and share similar contributions at the surface. However, AA’s role is more robust in the mid-troposphere than the decadal variability. This reveals that previous detections on the surface process may underestimate AA’s climate impact in this period. The three-dimensional thermal structure should be closely examined in future attribution works. Since the 1980s, the AA emission started to decline in Western Hemisphere (WH) midlatitudes but continued to increase in Eastern Hemisphere (EH) low latitudes, which may introduce competing climate impacts between the regional AA forcings. We separated and compared the distinct roles of fossil-fuel-related AA in EH (EastFF) versus WH (WestFF) during 1980–2020 based on regional forcing large-ensemble simulations. Model results demonstrated that WestFF dominates the northward shift of the zonal-mean Hadley cell while EastFF induces the equatorward shift of the NH jet stream. The simulated competing roles of regional AA forcings highlight the importance of both zonal and meridional locations of AA forcings within the NH. In addition, we further investigated how the regional AA forcings modulate the Pacific multi-decadal variation during the recent four decades. It is shown that EastFF favors a positive phase of Interdecadal Pacific Oscillation (IPO) by driving an ENSO-like teleconnection pathway, but the pattern is offset by Internal variability transitioning into the negative phase. In contrast, WestFF drives a hemispheric asymmetry pattern with large-scale warming in NP, which resembles the second leading variation mode of IPO. Our results suggest that WestFF may partly modulate the Pacific multi-decadal Variations during 1980–2020.
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Anthropogenic Aerosol, Climate, Climate model