Competing roles of regional aerosol emissions on the tropical Pacific climate: climatology, trend, and decadal variability

The variation of the Pacific Walker Circulation (PWC), which plays a vital role in tropical Pacific climate changes, and the zonal gradient of equatorial Sea Surface temperature (SST) are extensively discussed to be influenced by the external forcings such as greenhouse gases (GHGs) and anthropogenic aerosols (AA). Unlike GHGs, the potential impacts of AA could be more complex because of the heterogeneity of spatial distribution during the past few decades. Here we show, using regional aerosol forcing large ensemble simulations based on CESM1, that the increasing aerosol emission over Asia (EastFF) and the reduction of aerosol emission over North America and Europe (WestFF) play competing roles in driving the Pacific Walker circulation and tropical Pacific SST gradient during the past few decades, but the EastFF forcing is more dominant. The EastFF also shows a damping effect on the climatological IPO amplitude. The competing effects of the heterogeneous distributed regional aerosol forcings are projected to be changed in the near future, which is likely to introduce opposite and more important impacts of aerosol forcing on the Tropical Pacific climate changes.