neufer wrote: ↑Sat Feb 29, 2020 3:12 pm
Opposing the tidal deceleration of Earth is a mechanism that is in fact accelerating the rotation. Earth is not a sphere, but rather an ellipsoid that is flattened at the poles. SLR has shown that this flattening is decreasing. The explanation is that during the ice age large masses of ice collected at the poles, and depressed the underlying rocks. The ice mass started disappearing over 10000 years ago, but Earth's crust is still not in hydrostatic equilibrium and is still rebounding (the relaxation time is estimated to be about 4000 years). As a consequence, the polar diameter of Earth increases, and the equatorial diameter decreases (Earth's volume must remain the same). This means that mass moves closer to the rotation axis of Earth, and that Earth's moment of inertia decreases. This process alone leads to an increase of the rotation rate (phenomenon of a spinning figure skater who spins ever faster as they retract their arms). From the observed change in the moment of inertia the acceleration of rotation can be computed: the average value over the historical period must have been about −0.6 ms/century. This largely explains the historical observations.>>
This doesn't make sense to me. I'm tempted to say that the reasoning doesn't hold water.
(No offense, Art, I'm taking issue with Wikipedia, not you directly.)
The article is claiming that because of the loss of ice at the poles, the earth is rebounding there and being lifted up, so that more mass is closer to the axis of rotation than before.
The article is implying that the ground is rebounding because
of the loss of mass on top of it. And, if this is the reason, it will only rebound to counter the loss of weight on top of it. Meanwhile, that great mass of ice has migrated from the poles, and is now causing an increase in sea level at lower latitudes.
If anything, then, the warming climate and melting of polar glaciers should increase the amount of mass near the equator and increase the moment of inertia for the Earth.
It's possible I'm misunderstanding what exactly the article is claiming. They may be talking about a temporary situation that would only cover part of the time of the melting. But so far, their claim makes little sense to me.
Meanwhile, there are lots of other effects of a warming atmosphere, so the reality of Earth's moment of inertia and tidal deceleration will be quite complex. (But if one can determine the actual
distribution of mass, and how it has actually
changed, then the venerable equations are not that complex.