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Why sea level rise will be a good thing.



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04-09-2016 18:28
IBdaMannProfile picture★★★★★
(4906)
Surface Detail,

What are you claiming is the rate of sea level rise and what are you claiming is the margin of error?
04-09-2016 20:11
Tim the plumber
★★★★☆
(1295)
Surface Detail wrote:
Tim the plumber wrote:
Surface Detail wrote:
Tim the plumber wrote:
Surface Detail wrote:
Tim the plumber wrote:
Surface Detail wrote:

Yes, melting ice from the poles would indeed slow the Earth's rotation by a tiny amount. But given the lack of any references or calculations, I'm going to assume that the tenths of a mm accuracy is just your usual bullshitting.


http://www.iflscience.com/environment/rising-sea-levels-shown-actually-slow-down-earths-rotation-0/

I would have to go and buy a scientific calculator to do it myself.


The most accurate clock ever built only loses one second every 15 billion years. Scientists have a set a new record in accurate timekeeping, creating an atomic clock that won't lose or gain a second in 15 billion years — a time span greater than the estimated age of the Universe.22 Apr 2015


Given that the precision would be better than a trillionth of the rate of rotation and th eeffect of an aditional mm is in the order of a billionth of the radius of the world it should be far more accurate than 0.01mm.

You are, of course, ignoring that fact that the speed of the Earth's rotation is affected by other factors in addition to the melting of the ice caps. This is why you cannot use changes in the Earth's rotation speed to accurately measure sea level changes.


What other factors?

Which of these factors cannot be easily modeled?

Tidal effects, continental drift, earthquakes, magma movements, for example.

Of these, I'd guess that tidal effects and, perhaps, continental drift may be modellable. Earthquakes and magma movements less so. If you're that interested, why not do a literature search and so what you can find?


Given that I am expected to believe that the best way to measure the ice mass changes of Greenland is by the deviation of satellites going over there the laval flows which do not significantly effect the mass distribution of the earth over decades would be very easy to measure with surface gravitometers.

Tidal effects would of course be inconsequential. What happened last year happened this so no change there.

Nope, you have yet to point out why there is any trouble with day length as a measure of distribution of mass between poles and general sea level.

You're the one who is proposing the technique, so you tell me.

How much would you expect a rising sea level of about 3.4 mm (some from polar ice melting and some from thermal expansion of seawater) to slow the Earth's rotation? Over what duration would this be measurable? How would it compare to the continual slowing of the Earth's rotation by tidal effects? What about continents drifting towards or away from the poles? What would their effect be?


OK,

I = (mr^2)/2

m = 5.97 x 10^24 Kg

r = 6371 Km.

For a hollow sphere of negligabe guage;

I = (2mr^2) / 3

m = 1mm of sea water over the whole earth (I'm ignoring the distribution of the land for now but using the area of the oceans. If you want to do a better job feel free.)

So that's 360 billion tonnes per mm. So 360 x 10^12kg

so; I shell / I whole earth = (4/3) x Mass (shell) / Mass (earth)

360/5.97 x 10^-12 x 4/3 -----> 80.4 x 10 *-12

x 3600 x 24 x 365 ( seconds in a year) = 32 x10^6

So about 2 millionths of a second per year per mm rise in sea level. Well within the precision of those fancy atomic clocks.

Hang on, my maths is very rusty for this sort of thing, it's 30 years since I did any of this....

It should be initial moment over initial moment plus the new shell. My calculator is not up to that but I think the result will come out to be very similar...

I expect the diffeerence of a couple of cm in the location of continents to be utterly trivial and the changes in altitude in mountain ranges small as well but either would be simple to work out.

Edited on 04-09-2016 20:20
04-09-2016 23:32
Surface Detail
★★★★☆
(1673)
Tim the plumber wrote:
OK,

I = (mr^2)/2

m = 5.97 x 10^24 Kg

r = 6371 Km.

For a hollow sphere of negligabe guage;

I = (2mr^2) / 3

m = 1mm of sea water over the whole earth (I'm ignoring the distribution of the land for now but using the area of the oceans. If you want to do a better job feel free.)

So that's 360 billion tonnes per mm. So 360 x 10^12kg

so; I shell / I whole earth = (4/3) x Mass (shell) / Mass (earth)

360/5.97 x 10^-12 x 4/3 -----> 80.4 x 10 *-12

x 3600 x 24 x 365 ( seconds in a year) = 32 x10^6

So about 2 millionths of a second per year per mm rise in sea level. Well within the precision of those fancy atomic clocks.

Hang on, my maths is very rusty for this sort of thing, it's 30 years since I did any of this....

It should be initial moment over initial moment plus the new shell. My calculator is not up to that but I think the result will come out to be very similar...

I expect the diffeerence of a couple of cm in the location of continents to be utterly trivial and the changes in altitude in mountain ranges small as well but either would be simple to work out.


I worked it out this way:

Since angular momentum is conserved, the period of rotation is inversely proportional to the square of the radius (edit: because the moment of inertia of a sphere is proportional to the square of its radius). So if the radius increases from r to r+t, where t is the thickness of the additional layer, then the period of rotation will fall by a factor ((r+t)/r)^2. If r >> t, this gives a fall in the rotation period by a fraction 2t/r. For r = 6.37 x 10^6 m and t = 10^-3 m, this gives a fractional reduction in the rate of rotation of of 3.1 x 10^-10.

In one year, this corresponds to 9.8 ms! While this is a substantial overestimate (since the radius at poles is smaller, not larger), it still surprised me that it was this large. It should be correct to an order of magnitude or so. Time for some further digging.

According to Wikipedia, a modern day is longer by about 1.7 milliseconds than a century ago. This would make successive years 6.2 ms longer on average, so comparable to the effect one might expect from rising sea levels. Then I found this interesting paper:

Reconciling past changes in Earth's rotation with 20th century global sea-level rise: Resolving Munk's enigma

It seems that the apparent lack of a signal in the Earth's rotation from melting ice actually has a name: Munk's enigma! The main claim of authors of this paper is that changes in the Earth's rotation due to glacial rebound haven't been as significant as Munk thought, leaving room for a contribution from melting ice.

TL;DR: Your intuition was right (even if your maths was a bit off
): melting ice and rising sea levels do significantly slow the Earth's rotation. However, this effect has been difficult to separate from, primarily, glacial isostatic adjustment after end of the ice age.
Edited on 04-09-2016 23:35
05-09-2016 23:00
Tim the plumber
★★★★☆
(1295)
Having slept on it the 2 numbers should be multiplied together and the result is 2.6 thousanths of a second per year per mm of sea level rise.

Any talk of glacial rebound is drivel. We know how the altitude of the ground has change and this can be factored in very easily.

The impact of 360 billion tonnes moving from the poles to all over the globe, radius 6.4 thousand km compared to a thousand square kilometers of Himalaya rising 5m ...... well, it's just the ice that matters.

Given that the day length shows no sign of altering as it should if the poles were melting then either the laws of motion are wrong or those atomic clocks are wrong or the idea of measuring the ice in Greenland by the deviation of a satellite's orbit is F.ing bollocks.

Edited on 05-09-2016 23:02
06-09-2016 01:55
Surface Detail
★★★★☆
(1673)
Hmm, after doing a bit more research, it seems we are both barking up the wrong tree, and our model was far too simple. It appears that melting ice from the poles doesn't lengthen the day, instead it tends to shorten the day! Why? As far as I can tell, it's because the Earth "rebounds" where the weight of ice is taken off it at the poles and sinks a tiny bit around the equator under the additional weight of water. The net effect is that the Earth remains the same shape, but the heavy rock is shifted down at the equator and up at the poles, giving an Earth with a lower, rather than higher, moment of inertia.

It all looks fiendishly complicated, but here is as good a place to start as any, if you're still interested: Earth May Spin Faster as Glaciers Melt

Jerry X. Mitrovica seems to be the guy who's most knowledgeable on the topic. You might give him a google!
06-09-2016 10:26
Tim the plumber
★★★★☆
(1295)
Surface Detail wrote:
Hmm, after doing a bit more research, it seems we are both barking up the wrong tree, and our model was far too simple. It appears that melting ice from the poles doesn't lengthen the day, instead it tends to shorten the day! Why? As far as I can tell, it's because the Earth "rebounds" where the weight of ice is taken off it at the poles and sinks a tiny bit around the equator under the additional weight of water. The net effect is that the Earth remains the same shape, but the heavy rock is shifted down at the equator and up at the poles, giving an Earth with a lower, rather than higher, moment of inertia.

It all looks fiendishly complicated, but here is as good a place to start as any, if you're still interested: Earth May Spin Faster as Glaciers Melt

Jerry X. Mitrovica seems to be the guy who's most knowledgeable on the topic. You might give him a google!


Fiendishly complex and bollocks.

Consider the depth where the pressure is of the equivalent of a colum of rock of of say 1km.

If the mass above it is of water (ice or liquid) it will be of a certain altitude. If that moves from the poles to the equator it will cause the rock at the poles to rise and the quator to expand.

The rock rising at the poles has no effect as it does not change it's distance to the axis of rotation. The water rising on tghe equator does change it's rotation axis and of course rises more than the rock does because it's less dense.

We can also measure the altitude of the rock and see if it's changed.

You are beginning to get the lengths that the AGW religion will go to to justify clearly wrong beliefs.
06-09-2016 20:02
Tim the plumber
★★★★☆
(1295)
Surface Detail wrote:
Hmm, after doing a bit more research, it seems we are both barking up the wrong tree, and our model was far too simple. It appears that melting ice from the poles doesn't lengthen the day, instead it tends to shorten the day! Why? As far as I can tell, it's because the Earth "rebounds" where the weight of ice is taken off it at the poles and sinks a tiny bit around the equator under the additional weight of water. The net effect is that the Earth remains the same shape, but the heavy rock is shifted down at the equator and up at the poles, giving an Earth with a lower, rather than higher, moment of inertia.

It all looks fiendishly complicated, but here is as good a place to start as any, if you're still interested: Earth May Spin Faster as Glaciers Melt

Jerry X. Mitrovica seems to be the guy who's most knowledgeable on the topic. You might give him a google!


Previous research has found that melting glaciers triggered by global warming helped cause a significant amount of global sea-level rise in the 20th century. In theory, rising sea levels — once estimated to be climbing at a rate of about 0.06 to 0.08 inches (1.5 to 2 millimeters) per year — should also have slightly shifted Earth's axis and increased the rate at which the planet spins.

When polar ice caps melt, they remove weight off underlying rock, which then rebounds upward. This makes the poles less flat and the planet more round overall. This should in turn cause Earth to tilt a bit and spin more quickly.


This is a lie. Plain and simple.

The distance away from the axis of ratation of mass at the equator will rise by the introduction of more water which is less dense than rock. The rise at the equator will be greater than the slight, and long time in happening, rise at the poles of rock which will have zero impact on the speed of rotation of the earth as it will not change the distance from the axis of rotation.

Again I point out how far some people will go to try to cover up the facts.
06-09-2016 20:46
Surface Detail
★★★★☆
(1673)
Tim the plumber wrote:
Surface Detail wrote:
Hmm, after doing a bit more research, it seems we are both barking up the wrong tree, and our model was far too simple. It appears that melting ice from the poles doesn't lengthen the day, instead it tends to shorten the day! Why? As far as I can tell, it's because the Earth "rebounds" where the weight of ice is taken off it at the poles and sinks a tiny bit around the equator under the additional weight of water. The net effect is that the Earth remains the same shape, but the heavy rock is shifted down at the equator and up at the poles, giving an Earth with a lower, rather than higher, moment of inertia.

It all looks fiendishly complicated, but here is as good a place to start as any, if you're still interested: Earth May Spin Faster as Glaciers Melt

Jerry X. Mitrovica seems to be the guy who's most knowledgeable on the topic. You might give him a google!


Previous research has found that melting glaciers triggered by global warming helped cause a significant amount of global sea-level rise in the 20th century. In theory, rising sea levels — once estimated to be climbing at a rate of about 0.06 to 0.08 inches (1.5 to 2 millimeters) per year — should also have slightly shifted Earth's axis and increased the rate at which the planet spins.

When polar ice caps melt, they remove weight off underlying rock, which then rebounds upward. This makes the poles less flat and the planet more round overall. This should in turn cause Earth to tilt a bit and spin more quickly.


This is a lie. Plain and simple.

The distance away from the axis of ratation of mass at the equator will rise by the introduction of more water which is less dense than rock. The rise at the equator will be greater than the slight, and long time in happening, rise at the poles of rock which will have zero impact on the speed of rotation of the earth as it will not change the distance from the axis of rotation.

Again I point out how far some people will go to try to cover up the facts.

I'm not lying or trying to cover up facts. I'm simply trying to get a handle on what is a much more complex issue than you seem to realise (or I did).

It is undisputed that, in the long term, the Earth's rotation is gradually slowing as its angular momentum is transferred to the moon. However, there are all sorts of shorter term effects that sometimes slow the earth even more and sometimes actually make it spin faster. Changing ocean currents, expanding and contracting upper atmosphere, interactions between core and mantle, and the like.

Over the past couple of decades the Earth's day has actually been getting a little shorter, as evidenced by the lower number of leap seconds needed to keep things in synch. I don't know why this is the case; as I say, it's a complex issue.
06-09-2016 21:44
Tim the plumber
★★★★☆
(1295)
Surface Detail wrote:
Tim the plumber wrote:
Surface Detail wrote:
Hmm, after doing a bit more research, it seems we are both barking up the wrong tree, and our model was far too simple. It appears that melting ice from the poles doesn't lengthen the day, instead it tends to shorten the day! Why? As far as I can tell, it's because the Earth "rebounds" where the weight of ice is taken off it at the poles and sinks a tiny bit around the equator under the additional weight of water. The net effect is that the Earth remains the same shape, but the heavy rock is shifted down at the equator and up at the poles, giving an Earth with a lower, rather than higher, moment of inertia.

It all looks fiendishly complicated, but here is as good a place to start as any, if you're still interested: Earth May Spin Faster as Glaciers Melt

Jerry X. Mitrovica seems to be the guy who's most knowledgeable on the topic. You might give him a google!


Previous research has found that melting glaciers triggered by global warming helped cause a significant amount of global sea-level rise in the 20th century. In theory, rising sea levels — once estimated to be climbing at a rate of about 0.06 to 0.08 inches (1.5 to 2 millimeters) per year — should also have slightly shifted Earth's axis and increased the rate at which the planet spins.

When polar ice caps melt, they remove weight off underlying rock, which then rebounds upward. This makes the poles less flat and the planet more round overall. This should in turn cause Earth to tilt a bit and spin more quickly.


This is a lie. Plain and simple.

The distance away from the axis of ratation of mass at the equator will rise by the introduction of more water which is less dense than rock. The rise at the equator will be greater than the slight, and long time in happening, rise at the poles of rock which will have zero impact on the speed of rotation of the earth as it will not change the distance from the axis of rotation.

Again I point out how far some people will go to try to cover up the facts.

I'm not lying or trying to cover up facts. I'm simply trying to get a handle on what is a much more complex issue than you seem to realise (or I did).

It is undisputed that, in the long term, the Earth's rotation is gradually slowing as its angular momentum is transferred to the moon. However, there are all sorts of shorter term effects that sometimes slow the earth even more and sometimes actually make it spin faster. Changing ocean currents, expanding and contracting upper atmosphere, interactions between core and mantle, and the like.

Over the past couple of decades the Earth's day has actually been getting a little shorter, as evidenced by the lower number of leap seconds needed to keep things in synch. I don't know why this is the case; as I say, it's a complex issue.


How much mass do you think moves how far away from the earth's axis of rotation when the upper atmosphere expands a little? Just a few guestimate numbers?

How fast are these ocean currents going and by what are they changing and why, if we can model climate 1,000 years into the future, can we not account for such changes? Let's face it it's very easy maths (well, if you have not had a 30 year break away from it, then it's a head spinner). Predicting climate/weather into the future is hard. Working out the impact on angular momentum of stuff that has already happened is easy. Also if the current/atmosphere is the same today as it was 10 years ago you can discount it, what ever happened has canceled out.

Given that the 180mm sea level rise over the 20 th century would mean a 180 x 360 billion tonne transfer of mass outwards that should be very very much larger than all the other factors.
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