Fig. 1-T c. Mean summer (JJA) values of the Pacific Decadal Oscillation index, 1900-2005. The stepwise function (orange line) characterizes regime shifts in the level of fluctuations of the index. Shift points were calculated using the regime shift detection calculator, with the following parameters: target significance level p = 0.1, cutoff length l = 20 years Huber weight parameter h = 1. The autoregressive parameter (AR1) was estimated using the IP4 method with the subsample size m = 12. The estimated significance levels for the shifts in 1948, 1976 and 1998 are 0.0007, 0.00002, and 0.02, respectively