The earth turning slower or faster??

[rigadin]

Hi

 

Is there a chance that this can happen:

 

When global warming has made all the ice melt will the earth turn faster or slower due to the centrifugal force made my all the extra H2O in liquid form?

 

I think this because the earth's rotation will bring a lot of the water around the equator.

 

And what can this lead to???

[insane_alien]

slower, try spinning round in a chair holding your arms in close then letting them out, you'll slow down your rate of spin.

[mooeypoo]

Sorry, I might be missing somethig here but why do we assume the water will concentrate mainly on the equator?

 

I thought the tidal forces from the moon and even the sun are bigger than the effect of centrifugal force, at least in terms of the oceans.

 

But I'm not sure at all... ?

[insane_alien]

well, the sea level at the equator would rise(of course not all of the water is goign to go there but some of it would)

 

so mass migrates outwards, therefore to conserve angular momentum the earth would spin slower.

 

its not going to be a massive slowdown(maybe an extra millisecond to the day or there abouts) but a slow down none the less.

[mooeypoo]

Yeah, I didn't mean all the water go there, but doesn't the tidal force from the moon negates this?

[JillSwift]

Yeah, I didn't mean all the water go there, but doesn't the tidal force from the moon negates this?

I'd think lunar tidal effects would be increased by the increased mass of fluid water. (The moon has already shortened the Earthly day with what liquid water there is )

 

However, if I understand the amount of solid water at the pols versus the liquid water of the oceans, the overall effect would be negligible.

[mooeypoo]

Actually, this will be an excellent math exercise. When I get back home from work, I might try it.

[swansont]

As insane_alien points out, this will tend to slow us down, which would add to the moon's tidal effect.

 

Weather patterns and mass distributions affect the rotation rate, and since they are unpredictable over anything but an extremely short time, they are monitored — GPS doesn't work so well if you don't know where the satellites are with respect to the earth.

[D H]

Tides? Come off it! Think about it for just a second. Tides are a meter high, more or less. The equatorial bulge is 20 kilometers high.

 

insane_alien and swansont are closer to the mark -- maybe. You two didn't look at the whole picture. The ice piled on top of Greenland and Antarctica presses the rock on which that ice lies deeper into the Earth. As that ice melts the land rises; this is called post-glacial rebound. As rock is about 3 times as dense as water, melting of the ice might mean that mass is transferred poleward rather than toward the equator. Another effect that might transfer mass poleward is the heating of the oceans. The southern Pacific has a lot of open water, as does the Arctic Ocean (the Arctic ice cap is still water). Heating of the oceans will expand the ocean volume, so this too might transfer mass poleward. On the other hand, global warming will raise the height of the troposphere, and this effect will be greatest at the equator.

 

So what do scientists have to say about this? Let's ask a few climatologists.

Landerer, F. W., J. H. Jungclaus, and J. Marotzke (2007), Ocean bottom pressure changes lead to a decreasing length-of-day in a warming climate, Geophys. Res. Lett., 34, L06307, doi:10.1029/2006GL029106.

http://www.agu.org/pubs/crossref/2007/2006GL029106.shtml

Thus, ocean warming and the ensuing mass redistribution change the length-of-day by −0.12 ms within 200 years, demonstrating that the oceans are capable of exciting nontidal length-of-day changes on decadal and longer timescales.

 

de Viron, O., V. Dehant, H. Goosse, and M. Crucifix (2002), Effect of global warming on the length-of-day, Geophys. Res. Lett., 29(7), 1146, doi:10.1029/2001GL013672.

http://www.agu.org/pubs/crossref/2002/2001GL013672.shtml

we reach the following conclusions: (1) the models globally agree to an increase of the LOD of the order of 1 μs/year, (2) the effect is mostly associated with an increase of the mean zonal wind, of which about one third is compensated by a change in mass repartition.

 

Well, that didn't help much. The day will get shorter by 120 microseconds in a couple of hundred years. But then again, it might get longer by a microsecond. The affect will be small.

 

 

We've already had some global warming. What does the data say? This plot show variations in excess length of day from 1966 to 2001. (Length of day is the length of one day, UT1-R. Excess length of day is length of day less 86400 seconds TAI.)

 

Source: http://www.iers.org/images/figc.png

 

The data don't say much. The recent smoothed trend is that length of day is shortening. However, the longer trend is all over the place, including a multi-decadal oscillation that nobody knows the cause of (yet). The looong term effect, the transfer of angular momentum from the Earth's rotation to the Moon's orbit, can't be seen on this graph. It's too short a time span. To see that you would need a graph that spans a couple hundred years or so.

 

A couple final points.

 

Those season variations are one example of how climate affects the Earth's rotation. The Earth has more land in the Northern Hemisphere, more water in the Southern Hemisphere. Snow accumulates on the land during Northern Hemisphere winter, transferring mass poleward, and then melts, transferring mass toward the equator. Another example: Look at the residual oscillation plot. There is a huge spike in 1982-83. That is the worst El Nino on record. Changes in climate most certainly can have an effect on Earth rotation.

 

Finally, I'll put words in Mooey's mouth.

 

"Hey DH! I thought you said tides are tiny. What is that noisy-looking graph labeled 'Effects of zonal tides, periods up to 35 days'?"

 

Fair point. Firstly, that's basically a zero mean noise signal. Second, those are zonal tides. The Moon raises tides in the Earth itself as well as in the oceans. The Earth tides, rather than the ocean tides, are the primary component of these zonal tides.

[mooeypoo]

Tides? Come off it! Think about it for just a second. Tides are a meter high, more or less. The equatorial bulge is 20 kilometers high.

Seriously!? That high!?

 

Okay, okay, my mental estimations were way off. I came off it...

 

Thanks for the clarification and sources, though, D H. Most helpful, and saved me the trouble of doing the math, which is always good

 

~moo

 

 

P.S: Next time you put words in my mouth, use a puppet..