Michael Mann again tweeted that he doesn't think that indices such as AMO and PDO are climate modes at all.

https://twitter.com/MichaelEMann/status/1276630052273369093

Press release on this today : [Atlantic and Pacific oscillations lost in the noise](https://news.psu.edu/story/602574/2020/01/03/research/atlantic-and-pacific-oscillations-lost-noise)

He thinks it is just noise.

> "UNIVERSITY PARK, Pa. — The Atlantic Multidecadal Oscillation (AMO) and the Pacific Decadal Oscillation (PDO) do not appear to exist, according to a team of meteorologists who believe this has implications for both the validity of previous studies attributing past trends to these hypothetical natural oscillations and for the prospects of decade-scale climate predictability.

>Using both observational data and climate model simulations, the researchers showed that there was no consistent evidence for decadal or longer-term internal oscillatory signals that could be differentiated from climatic noise — random year to year variation. The only verifiable oscillation is the well-known El Niño/Southern Oscillation (ENSO)."

This may be at odds with Gavin Schmidt at NASA who tweeted

https://twitter.com/ClimateOfGavin/status/1276540221539180544

> "we have a paper summarizing the improvements that the latest generation of models have made in simulating important modes of variability (ENSO, MJO, PDO, QBO etc.) in the climate system:"

[Representation of Modes of Variability in 6 U.S. Climate Models](https://journals.ametsoc.org/jcli/article/doi/10.1175/JCLI-D-19-0956.1/348564/Representation-of-Modes-of-Variability-in-6-U-S)

This appears to be a battle of foundational ideas.