Tidal friction and global warming

• mattrix
mattrix
User has been reminded to post references, not "They say..."
Ignoring global warming, the Earth will spin progressively slower.
But how will global warming affect this?

THEY say,

LESS water, LESS slowing. > slowing spin is all about the FRICTION from the action of WATER on the LAND, when the water is gone the slowing of the spin will ceased (or at least become negligible).

LESS water, MORE slowing. > the sea floor in deeper water is less affected by weather than at the coasts. So with less water it will be shallower and the friction will be acting over a greater area, and spin will be slowed down MORE.

MORE water, MORE slowing. > water doesn't resist deformation, the Earths slowing spin is all about how FAR the tidal BULGES extend into space. spin will be slowed down FASTER.

MORE water, LESS slowing. > Despite the above, as the ice caps melt, the planet will become more spherical, spin will be slowed down LESS.

I don't know if I agree with all of that. In isolation each seems sortof reasonable, but when put together, ...., a waterless, spherical planet will never be tidally locked.

The moon is tidally locked, but it doesnt have any water. So WATER doesn't seem necessary, but maybe it accentuates the effect. But point 2 suggests that more water acts as a buffer reducing the effect of friction.

Mass and hence gravity are not changing, so why would water be pulled further into space (disk shaped). But maybe more mass will make up the bulges.

I don't know. What do you say about the change in the Earths spin?

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mattrix said:
THEY say,
Who says that ?

berkeman
Sorry that my wording upset you.

The propositions can't all be correct, can they?
I take the lack of response to the content of the question to indicate that none of the propositions show any merit.

mattrix said:
Sorry that my wording upset you.

The propositions can't all be correct, can they?
I take the lack of response to the content of the question to indicate that none of the propositions show any merit.
Unless you can supply references that make those "statements" your question cannot be answered here.

renormalize said:
Unless you can supply references that make those "statements" your question cannot be answered here.

I see.

The ideas came from a range of places and have been floating around in my head for a while. They came from things I've read, not necessarily equally reliable. Most papers are behind paywalls, so I only have abstracts and reports by people who supposedly have read the papers.
Things I've heard, though I'd be hard pushed to remember when a particular astronomer gave an interview on the radio. And some comes from my high school teachers, I can't even remember their names, but I guess I can contact the school. I have never skated, we don't have large sheets of ice here, but THEY tell me that if you pull your arms in you will spin faster.

The ideas just seemed inconsistent, and I thought it a good idea to sort the wheat from the chaff. It is not a trick question.
If I had a good reliable reference, there would be no need for the question, although that would only be one persons opinion.

mattrix said:
The ideas just seemed inconsistent, and I thought it a good idea to sort the wheat from the chaff.
The rate of Earth rotation due to weather differences is typically ±1 second per year.

In 600 Ma, the Earth has slowed from maybe 450 days PA in the Cambrian, to 365 days PA today, so tidal friction is adding something of the order of 0.01 seconds per year. Tidal friction is insignificant compared to the changes of mass distribution due to climatic change.

The effects of Tidal friction and global warming, will not significantly interact. They are on different timescales by more than two orders of magnitude. Tidal friction is a more insidious, and secondary effect. It is slow, but steady.

Global warming can be expected to melt the icecaps, which will move mass from the poles to the oceans, so the Earth will slow back down slightly, to its interglacial rate. Then during the next glaciation, when we are gone, it will speed up again.

mattrix
Baluncore said:
The effects of Tidal friction and global warming, will not significantly interact. They are on different timescales by more than two orders of magnitude. Tidal friction is a more insidious, and secondary effect. It is slow, but steady.
Thankyou, though I don't think its as steady as you suggest.

Your answer does raise a few other questions, but I will refrain from giving any elaboration if I ask them.

mattrix said:
when the water is gone
Why would the water be gone? Unless it escapes into space there's nowhere for it to go.

mattrix said:
I don't know if I agree with all of that. In isolation each seems sortof reasonable, but when put together, ...., a waterless, spherical planet will never be tidally locked.
There are no truly spherical planets, moons, or other bodies:

1. There are no bodies that are entirely homogenous. That is, all objects in space have some difference in composition, density, shape, or other asymmetry. This creates the equivalent of bulges even if the material was perfectly rigid.
2. Because there is no perfectly rigid material, gravity will always distort an object into an ellipsoid and create bulges. This is why the Moon has become tidally locked to Earth.

mattrix said:
The propositions can't all be correct, can they?
I have no idea if the propositions are accurate or not, but assuming they are, then they certainly could all be true if they are all contributing different amounts to slowing/speeding Earth's rotation.

mattrix said:
But how will global warming affect this?
Not in any significant amount. It's possible all 4 effects exist, but they are all negligible. The average ocean depth is ~4000 meters. Long-term sea level rise might be a few meters. So maybe we change the slowing rate by 0.1% in either direction for 1000 years or something like that, equivalently to one year more or less of slowing. That's a difference of 20 microseconds per day we might cause.

mattrix
mattrix said:
Thankyou, though I don't think its as steady as you suggest.
If redistribution of the oceans and atmosphere, by the changing weather patterns, can generate a 1 second per year change, then that is 1 part in 31,557,600.

Let's say global warming causes 100 times that, being 1 part in 315,576.

Then the tidal friction, which is now a loss of 10 ms per year, might be changed by a similar proportion, that is by 0.01 / 315,576. = 32 ns per year. After 1000 years it will have accumulated a difference of only 32 μs.

In the presence of the redistribution of the oceans and atmosphere, you will be unable to measure a 32 μs change over a millennium.,

The change in tidal friction will be minuscule.

Thank you, every one.

However, you seem to suggest that the spin of the earth cycles between established limits, an interglacial rate, and a glacial rate?

PS Am I allowed to think out aloud on this (sub)forum?

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