Changes of Pacific decadal variability in the twentieth century driven by internal variability, greenhouse gases, and aerosols

This paper explores the contributions of internal variability, greenhouse gases (GHGs), and anthropogenic aerosols (AAs) in driving the magnitude and evolution of Pacific Decadal Variability (PDV) during the twentieth century by analyzing 129 Coupled Model Intercomparison Project Phase 5 model realizations. Evidence shows that PDV phase transition is dominated by internal variability, but it is also significantly affected by external forcing agents such as GHGs and aerosols. The combined effects of GHGs and AAs favor the positive phase of PDV with stronger ocean warming in the tropics than the extratropical Pacific. The GHG forcing induces the increased surface downward longwave radiation, especially over the tropical Pacific, and results in stronger warming in that area. The AA forcing results in a stronger cooling in the North Pacific region, due to the reduced surface downward shortwave radiation via cloud-aerosol interaction: this offsets the substantial warming caused by GHG forcing.