I am not an earth scientist but for many years I have wondered about the following. I am curious if this has already been explored by scientists? If so, what is the theory formally called? and what is the consensus of the scientific community about such a theory?

CONCEPT: When you have new tires put on your car the mechanic will put the tire on a machine to check the balance and then add small lead or zinc weights on the rim to correct any wobble. Even though the weights are tiny by comparison they play a critical role in effective lifespan of the tires.

For the past couple hundred years humans have been moving "tiny" amounts of weight around the surface of the earth. We add weights when we build large cities, or dam rivers. We take away weights when we excavate and overdrafting.

There also of course are natural events that move "tiny" surface weights around, such as glacier movement, island formation, caldera eruptions, and meteor strikes. This last of course also imparts a vector of kinetic energy change due to impact force.

THEORY: I call this personal idea the "Wobbly Tire Theory" on the presumption that Earth has for millennia been dealing with axis wobble but has usually had time to adjust/stabilize between significant changes. However, in the past 200 years or so we have been making a lot of man-made changes in these weights in a timespan that is a geologic blink-of-an-eye.

I speculate that these rapid changes may be affecting the earths rotation in subtle ways. For example, I wonder could such changes affect the core's rotation vector in any way?

So back to my original Question: Does this theory (including OR excluding the last about man-made effects) already exist among geophysicists and others? What name(s) does it go by? And what details, if any, are there on the scientific consensus of this concept?


1 Answer 1


I don't know if this theory has any formal name, but of course you are correct in assuming that any mass redistribution on or in the planet will affect it's axis of rotation, causing a wobble. Small re-distributions are happening all the time with growing and melting ice, ocean currents sloshing water from one side of an ocean to another (as in the El Nino). Theoretically, a whale swimming across an ocean will create an axial wobble, albeit far too small to measure. Earth and sea tides, climate change, plate tectonics etc... The list goes on and on, with multiple processes each causing a slight tilt in the Earth's axis. This ranges from barely detectable sub-milimetre range to thousands of kilometers (over geological time - hundreds of millions of years).

In addition to the above random fluctuations there is also the 'Chandler wobble' which is a predictable cyclic wobble in the Earth's axis, of about 9 metres, over a period of 433 days.

As for human impacts, until recently I would have said that they were puny compared to natural processes. However, recent research points to significant and growing change in the Earth's rate of spin due to human induced climate change. This could have interesting 'knock-on' effects upon the spin axis. The effect is absolutely miniscule, but as the Earth's spin slows, there is likely to be further de-coupling of spin rate between the Earths crust/mantle and core which could well be an additional component to the axial wobble.

  • $\begingroup$ Many examples of earthquake incidents changing the duration of a day can be found by simply Googling something like day longer earthquake (Google is smart enough to also give you the 'shorter' results) $\endgroup$
    – Jan Doggen
    Commented Aug 30, 2016 at 14:49

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