The Early-1990s Climate Shift in the Pacific: Evidence in ENSO Diversity and Its Linkage to the Atlantic Multi-decadal Oscillation

In this talk, we will present results from observational analyses and model experiments to show that a significant climate shift occurred across a broad region of the Pacific in the early 1990s and that this climate shift is related to a phase change in the Atlantic Multi-decadal Oscillation (AMO). A strong piece of evidence for this climate shift is the change of the El Nino Southern Oscillation (ENSO) from the traditional Eastern Pacific (EP) type to a Central Pacific (CP) type after the early 1990s. The chain of inter-basin interaction processes that enable the AMO to exert an impact on the ENSO type will be described. The changing ENSO type also caused the ENSO influences on the Southern Hemisphere circulation to change significantly. A clear early-1990s climate shift is thus also found in ENSO's relations with two major modes of Southern Hemisphere variability: the Southern Annual Mode (SAM) and the Pacific–South American (PSA) pattern. Additional evidence of the early-1990s climate shift can also be found in other phenomena, including drought patterns in China and the variability in the subtropical high in the Northwestern Pacific.