Indices of the Pacific Decadal Oscillation are in close agreement for the period of the last seventy years. The NASA Multivariate Index and the Mantua Index only go back a hundred or so and they correlate very closely. These shorter indices correlate pretty well with the longer Shen Index based on rainfall records in China, which goes back to 1470. The longest index based on Limber Pine tree rings by MacDonald and Case goes back a thousand years, but differs significantly.
That these two match so well for the last hundred years after squabbling for the prior four hundred is notable. Actually there is reasonable agreement for about a three hundred year flat period with only the tree rings getting all excited now and then. The only major movements they agree on are the run up in the late 1400’s and the “hockey stick” of the instrumental era.