**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