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In the recent paper published in Nature that sugests a 60-70 years inner core rotation cycle, it is said:

Interestingly, the same multidecadal periodicity is also well observed in the Earth’s climate system, especially the global mean temperature and sea level rise.

The assertion quotes this paper published in 1994.

Is this multidecadal climate cycle well accepted among climatologists? It was maybe attributed to other causes than the inner core rotation before this study?

How can then the inner core rotation influence climate?

-Yang, Y., Song, X. (2023): "Multidecadal variation of the Earth’s inner-core rotation." Nature Geoscience. https://doi.org/10.1038/s41561-022-01112-z

-Schlesinger, M., Ramankutty, N. (1994) "An oscillation in the global climate system of period 65–70 years." Nature 367, 723–726. https://doi.org/10.1038/367723a0

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    $\begingroup$ The lay media is all over this as if it's true and are botching their reports by saying the core is switching directions. it's not. If true, the core is perhaps changing from rotating about 131851 degrees per year to a bit less than 131850 degrees per year. That's not changing direction. (The mantle rotates about 131850 degrees per year.) $\endgroup$
    – David Hammen
    Commented Jan 24, 2023 at 15:00
  • $\begingroup$ @David Hammen the media here is Spain is saying the core is switching his rotation sense $\endgroup$
    – user28185
    Commented Jan 24, 2023 at 15:14
  • $\begingroup$ It's not just the Spanish media. It's everywhere. Saying it's switching direction is more eye catching. Catchy titles result in more web site visitors and hence results in more eyeballs on their advertisements and also greater charges for those ads. Which title is more catchy is tested (it's called A/B headline testing) so as to bring in more money. $\endgroup$
    – David Hammen
    Commented Jan 24, 2023 at 15:26
  • $\begingroup$ @David Hammen Today in the newspaper I read they nuanced yesterday's headline. They say now the truth, that the rotation of the inner core only slows down. The confussion should come from main agencies first headline (they all copy reuters, EFE agency...). The fact is if you consider as reference the mantle+crust rotation, if the inner core is rotating slowly it can be said relatively it turns in the other sense toward the Weast. $\endgroup$
    – user28185
    Commented Jan 25, 2023 at 8:51
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    $\begingroup$ The only way in which the core is reversing direction is if we could look at it from the surface unaware of our own rotation. It might be rotating faster one year, so it slowly seems to go from west to east when we look at it from the surface, then the next year is might be going just a little slower than us and we "see" it going slowly from east to west. Someone viewing from, let us say, the monthly-orbiting Moon would see everything always going from west to east. $\endgroup$
    – Oscar Lanzi
    Commented Jan 25, 2023 at 23:11

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I have four things to say regarding this:

  1. The paper is far too new. I'm not saying the first paper is wrong (it is in fact rather interesting), but having been published yesterday, it is far too new to be used as the basis for anything. Publication in a peer-reviewed journal is where science starts rather than ends. Wait a bit for the scientific community to confirm or reject the claims in this paper.

  2. The two effects might be completely unrelated.

  3. If they are related, you might be confusing cause and effect. It could be that whatever causes the climate oscillations in turn causes the oscillations in the inner core's rotation rate.

  4. What the authors of the paper in question are reporting to have observed is a small differential rotation between the mantle+crust and the inner core. It could well be that the inner core rotates much more smoothly than does the mantle+crust. In other words, they're seeing variations in the rotation rate of the mantle+crust.

We know as a fact that the Earth's rotation rate is gradually slowing down. Scientists see this far in the past in tidal rhythmites locked in stone. More recent signs were ancient astronomers/astrologers (the two were the same "science" up to Kepler's time) who recorded solar eclipses at specific cities. Those solar eclipses would have happened elsewhere on the Earth if the Earth maintained a more or less constant rotation rate.

Thanks to atomic clocks and long baseline interferometry, scientists readily see seasonal changes in the Earth's rotation rate. Snow falls on the northern parts of the North Hemisphere in winter and melts in the summer. That represents transfers of angular momentum between the oceans, the cryosphere, and the crust. These variations are easy to see.

Precise measurements of the Earth's rotation rate also show what appears to be longer term oscillations in the Earth's rotation. It appears that there is a multidecadal oscillation in the Earth's rotation rate that is correlated with the 60 to 70 year Atlantic Multidecadal Oscillation (AMO). Since very good data on the Earth's rotation only goes back 60 to 70 years, it's a not quite conclusive. The same goes for the AMO; very good meteorological data only goes back 100 years or so. The cause of the AMO is debated. The teleconnections between it and other climate observations are also debated. However, the AMO does appear to impact climate, and climate in turn appears to impact Earth rotation. (We know climate as a fact that impacts Earth rotation on a yearly basis.)

The Earth comprises multiple rotating parts: The atmosphere, the cryosphere, the oceans, the crust and mantle, the liquid outer core, and the solid inner core. These different parts exchange angular momentum with one another (and also with the Moon). Except for the seasonal variations and the long term secular transfer to the Moon, teasing out cause and effect in the variations of the Earth's rotation rate is a non-trivial exercise.

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  • $\begingroup$ My first perception is it is a quick assertion so I incline myself to think you are rigth in point 2. The authors quote a study from 1994 of a 70 years climate cycle; they migth just have searched a paper that matches with their study. Interesting what you say in point 3 (climate may vary inner core rotation rate). The question became a hot one. Can you explain to the audience a bit more point 3 so the title question is answered? (How does the rotation influence climate?). $\endgroup$
    – user28185
    Commented Jan 25, 2023 at 9:09
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    $\begingroup$ @Universal_learner You have cause and effect backward again. Climate influences Earth rotation. My guess is that the inner core is simply a better clock than is the Earth's surface. (By "better clock" I mean that it rotates more uniformly than does the Earth's surface.) We learned over 150 years ago that the Earth's surface is not that great of a clock. $\endgroup$
    – David Hammen
    Commented Jan 25, 2023 at 11:44
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    $\begingroup$ I suppose the differential rotation could affect the AMO (that's the multidecadal oscillations to which the authors of the paper in question referred). This is overly speculative. The mechanism would have to be the Earth's magnetic field. Correlations between magnetic field variations and climate is a bit of a shunned subject as that comes a bit too close to electric universe nonsense for most researchers. (Electric universe woo is complete and utter nonsense.) However, the merest hint of association with that nonsense tends to shut the door on what could be legitimate research. $\endgroup$
    – David Hammen
    Commented Jan 25, 2023 at 12:07

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