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Is there a robust effect of anthropogenic aerosols on the Southern Annular Mode?
Author(s) -
Steptoe H.,
Wilcox L. J.,
Highwood E. J.
Publication year - 2016
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1002/2015jd024218
Subject(s) - forcing (mathematics) , aerosol , climatology , mode (computer interface) , coupled model intercomparison project , northern hemisphere , environmental science , atmospheric sciences , southern hemisphere , climate model , climate change , meteorology , geology , physics , oceanography , computer science , operating system
Abstract Historical anthropogenic aerosol (AA) changes are found to have caused a statistically significant negative Southern Annular Mode (SAM) trend (associated with an equatorward jet shift) in 14 out of 35 individual ensemble members from the fifth Coupled Model Intercomparison Project (CMIP5) since 1860. However, this response is not robust. The significance of the SAM response to aerosol is model dependent and not simply related to aerosol forcing. Multiple sources of uncertainty result in a nonrobust response that means that the model mechanism connecting remote Northern Hemisphere AA forcing remains unclear. Analysis of single forcing experiments suggests that assuming the climate response to individual model forcings to be linearly additive cannot be made without proper assessment. Our results suggest that AAs may have had a historical influence on the SAM, but its influence may be overstated by assuming linearity.