Detection of Decadal Phase Transition and Early Warning Signals of PDO in Recent and Next 100 Years

Based on the theory of critical slowing down, this study investigates the decadal phase transition and the early warning signals of the Pacific Decadal Oscillation (PDO) series using the historical monitoring data of PDO in the past 100 years (1900–2019) and the simulation data of the future century (2006–2100) model. First, the phase transition time of the PDO is determined by the moving t test technique. Thereafter, the early warning signal of phase transition is analyzed using the variance and autocorrelation coefficients, which characterize the critical slowing phenomenon. The results show that: (1) Four significant phase changes in the PDO occurred in the recent 100 years, and early warning signals can be given 5–10 years in advance. (2) In the next 100 years, the study of the PDO, which is obtained based on the CMIP5 data, shows that the PDO will have two decadal transitions around 2040 and 2080, and early warning signals can be given 5–10 years in advance. (3) Based on the study of the phase transition detection and early warning signals of PDO sequences in the recent and next 100 years, the variance and autocorrelation coefficients can be detected as the early warning signals of abrupt change several years in advance, which can be utilized to predict the climate changes that will affect the PDO in the future.