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.
Dendro’s have actually known about this issue for more than a decade now. Perhaps one issue is the definition of the PDO? Perhaps the PDO is a statistical artifact or an expression of some of manifestation of the Pacific Ocean or large climate system? Maybe what you are seeing are five [hundred] blind monks grasping an elephant?
Dendros have been aware of the recent divergence. May have missed it but I’m unaware of anything about tree rings measuring something besides rainfall this far back. I picked the Shen index because it purported to measure rainfall in northern China rather than standardize anomalies from a zone in the northern Pacific, but I didn’t pay the 25 bucks to read the paper and check their methods.
Geophysical Research Letters, vol. 33, L03702, February 2006. If you’re feeling rich.
I sense PDO is real because it was named by fisheries biologists and corroborated by rainfall in China. Everything is statistical until you understand it. ENSO and PDO are spatially very similar. This blind monk feels he has grasped that whatever allows cold abyssal waters to upwell will cool the planet, and whatever isolates them with a thermally stable cap of warm water will warm it.
The elephant is about a third of the oceans by volume, with a staggering heat capacity. It has migrated 25000 miles over the last millenium, and it is upwelling with gusto, fostering the salmon fishery off the Pacific Northwest, and cooling the planet today.
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