From the looks of the "General Science section", it seems GW has been done to death. May I be forgiven if I make another thread about it?

I've heard of a new one from global warming deniers.
The idea now is that if ice from Antartica all melts, then the continent will rise. True enough, AFAIK.
Now, the denier claims that this will actually cause sea levels to drop, appearently due to displacement of the water.
The person was made aware that other continents would sink, due to Antartica not displacing the molten interior. He countered that this will actually cause sea level to drop.

Here is the original place where I read this. The conversation starts at the sixth post down.

I just don't know what to make of it. I think I'm missing something obvious.
Has anyone else heard of this?

__________________
This is no fantasy. No careless product of wild imagination. - Jor-El

Godspeed, John Glenn. - Scott Carpenter

And these atomic bombs that science burst upon the world that night were strange even to the men that used them.
- H.G Wells, The World Set Free

To the conspiracy crowd, radiation is a big Boogey Man that inspires terror and death in all who encounter it. - JayUtah

I think one thing that's missing is that it takes longer for continents to rebound than it takes for ice to melt. Scandinavia and the Hudson Bay area are both still rebounding after the last Ice Age: that's a bit of an inconvenient gap for port cities and low-lying countries to wait out.

Grant Hutchison

Well, for starters, some folks got the glass of ice water example wrong. If you can keep evaporation from happening, then the water level will stay exactly the same as the ice melts. This is because ice displaces its mass in water, and the density of melted ice is the same as the density of water.

And land doesn't tend to float so the air mattress analogy doesn't hold. I haven't heard about Antarctica rebounding before, though - what's the mechanism and how quickly is it expected to happen?

I'd also want to know more about this supposed downward force of 1-2 kilometers, with estimates as high as 5 kilometers. (For the sake of comparison, the peak of Mt. Everest is about 8 kilometers high.) Would all of Antarctica be that high above sea level? Just the peaks? This claim seems astounding to me, since I'm pretty sure the average height above sea level of the continent that I live on is well below 1km.

I knew the air matteress idea was laughably wrong.

I suspect the rebounding of Antartica is that it, like the other continents, float on magma. Relieved of the weight of ice, it will rebound.
But as Grant shows, it's a slow process.

Something occurred to me; even given all this movement of the tectonic plates up and down, that's not what will change the sea level, if my surmise is correct.
Now, stop me if I'm wrong, but wouldn't sea level relate more to the volume of water than the vertical movement of tectonic plates?

I did try to read on this subject, but found no answers. I only see that the melting of ice will cause a rise in sea level. But nothing I read indicates the effects on sea level by the rebound of Antartica.

Your fact helps a lot, though Grant.

__________________
This is no fantasy. No careless product of wild imagination. - Jor-El

Godspeed, John Glenn. - Scott Carpenter

And these atomic bombs that science burst upon the world that night were strange even to the men that used them.
- H.G Wells, The World Set Free

To the conspiracy crowd, radiation is a big Boogey Man that inspires terror and death in all who encounter it. - JayUtah

Now I'm curious about this idea of whole tectonic plates being moved up and down.

If you shove a land mass down into the magma, won't much of it melt and become more magma?

The Antarctic plate appears to be one of the largest ones, much larger than the continent itself. And the plates are about 100km thick. How much of its mass really comes from ice? Nevermind. Wasn't realizing that the sinking is due to land deformation, not the whole plate sinking.

Found an abstract on measuring the rate of rebound in Antarctica:
http://trs-new.jpl.nasa.gov/dspace/b.../1/03-0952.pdf

Also found this page, which discusses crustal rebound in Scandanavia:
http://www.earthscape.org/t1/min01/min01ab.html

One tantalizing little bit from there is that the Scandanavian rebound is causing the opposite to happen in the Netherlands: "This rebound of Scandinavia has created a long-term problem for the neighboring Netherlands. As part of the asthenosphere shifted from beneath Scandinavia, it raised elevation in the Netherlands. When the ice melted and Scandinavia began to rise, the Netherlands began to slowly sink."

I find that incredibly fascinating.

It's called isostasy, and as grant says, it has been happening in the north for a long time, since the last deglaciation.

If the ice is not on land, as is the case in the arctic now, there is no compensation.

My! So many possible consequences to consider, but, which one is the most likely? I hope we never find out.

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i'm sure someone in Hollywood will find a way to accurately portray the effects of the ice melting over the course of a few days, and it will be a blockbuster..
coming to a theater near you in the summer of '08-
"2 Days After The Day after Tomorrow"
this time, it's personal...

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Classic! Kudos!

__________________
This is no fantasy. No careless product of wild imagination. - Jor-El

Godspeed, John Glenn. - Scott Carpenter

And these atomic bombs that science burst upon the world that night were strange even to the men that used them.
- H.G Wells, The World Set Free

To the conspiracy crowd, radiation is a big Boogey Man that inspires terror and death in all who encounter it. - JayUtah

so, you think i have a future in Hollywood thinking up plots for new movies loosely based on what some people think is science?

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"blacker than the blackest black... times infinity."- Nathan Explosion
The.. Best.. Thread..Ever...

What a novel idea!

I think so.

We ought to start such a thread, perhaps in Fun & Games.

__________________
This is no fantasy. No careless product of wild imagination. - Jor-El

Godspeed, John Glenn. - Scott Carpenter

And these atomic bombs that science burst upon the world that night were strange even to the men that used them.
- H.G Wells, The World Set Free

To the conspiracy crowd, radiation is a big Boogey Man that inspires terror and death in all who encounter it. - JayUtah

My "friend" raises and issue.
First, he wonders what the source is for the issue that Scandanvia and Hudson Bay are rising. He searched for it, but couldn't find it.
Second, he asks that if this region is rising, why isn't Cape Cod rising, as that area was under ice too.

I invited him to the forum. I think it'd be better.

__________________
This is no fantasy. No careless product of wild imagination. - Jor-El

Godspeed, John Glenn. - Scott Carpenter

And these atomic bombs that science burst upon the world that night were strange even to the men that used them.
- H.G Wells, The World Set Free

To the conspiracy crowd, radiation is a big Boogey Man that inspires terror and death in all who encounter it. - JayUtah

If the ice on Antarctica melted, the centre of that continent would be under water, and the continent would consist of two distinct land masses- East and West Antarctica.

Isostatic recovery would cause that land mass to rise, so that the two land masses would probably merge together to form a single land mass. I think it is obvious that the water displaced by the rise, from the central channel, would enter the ocean and contriute a small amount to the total ocean level.

Antarctica is so far from all the other continents I can't see that this isostatic rise would affect the height of any of the other land masses; so the net effect would be a sea level rise (I think it may have been estimated at a half metre or more, but I can't find a source at the moment).

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You're not suggesting that total sea level rise would be half a meter or more are you? The average ice sheet thickness on Antartica is 1.6 km. That comes to about a 60 meter sea level rise.

Other dry land masses don't need to sink for there to be any mitigation of the rebound of Antarctica. The ocean floor sinking would work, too.

but how much of th ice on Anarctica is below sea level?
only the ice above sea level that isn't already floating would cause the sea level to rise.

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Not a large portion and I'm not considering the ice shelfs in this. Although about half of Antartica would be under sea level if stripped of ice, most of it would not be a great deal under sea level. A large part of the continent is 3 kilometers above sea level.

Yes; and isostatic recovery would add another half a metre or so on top of that- but only after a very long wait, as Grant Hutchinson indicated. The UK is still experiencing isostatic recovery in some places, more than ten thousand years after the ice went.

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I am trying to address the original post, or rather the 'denier' who said that isostatic recovery would make the sea level drop. I really can't see any way that can be true. As the continent of Antarctica rises, it will displace more water.

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Allright, I'll just have to accept that you're wrong on this point. Antartica covers 13,661,000 square kilometers. The average ice sheet thickness is 1.6 kilometers. The average elevation of Antartica is 2,300+ meters. The height of the South Pole is 2,835 meters. The highest point of the icecap is 4,100 meters. Also, sea levels have been more than half a meter higher than they are now in the past.

Are you talking about the rise due to the melt of the entire ice sheet? I think eburacum45 is only talking about the isostatic adjustment effect.

It'd be helpful in untangling this if you kept the back links (or, if you're not using the quote button, if you did use the quote button to get the back link )

that's only true for the northern polar ice cap. there is ice on land in Antartica.


of course the continent raising up would be the issue - but as just about everyone else here has said, it's slower.

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Okay, lets start again. If all the Antartic ice melted sea levels would rise by about 60 meters because most of the ice is on land and above sea level. Does that sound right, Eburacum45?

I did just go to that other forum and look through the posts. Luckily, they don't seem to be as prolific as we are

That's an interesting idea about the air mattress--piling ice on an air mattress will make it displace the equivalent amount of water for the ice and air mattress both. After the ice melts, it replaces the displaced water, and the air mattress only displaces its equivalent. So the level doesn't change. (I'm not sure why he claims it might even be lower, but let's just look at first order effects anyway--melting would involve heating or cooling of various components and that would mean expansion or contraction might come into play)

As was mentioned, the air mattress thing doesn't really apply, because it is not the water providing the buoyant force that raises the continents. Rather than an air mattress, lets put a small plastic table in the pool, so its top is even with the water level. A large amount of ice will depress the table some, and when the ice melts, the table will rebound. But the effect of the rebound is a lot smaller than just the melt volume itself, and you can see it gets complicated by exactly where the top is positioned with respect to the level of the pre-melt water.

Here is an online mention of glacial rebound studies, it has a few references that cover the field. The problem appears in undergraduate geophysical texts, and shows an upper mantle viscosity of 10²¹ Pa s. For Fennoscandia, the disappearance of the ice sheets was very quick, on the order of hundreds of years, whereas the upper mantle rebound took place over thousands of years. The one controversy is the viscosity of the lower mantle--the ice sheet was so large that its effect reached into the lower mantle, and the viscosity is even higher (how much higher is contended), and the time of rebound is even longer and still ongoing.

So, Antartica's rebound won't counter the increase of sea level from melt water?

My denier pal is being stubborn. Aside from not believing that Hudson Bay and Scandinavia are still rising, he counters that the slow rise is from the fact that glaciers still exist on these areas. I haven't seen him provide a claim for how long Antartica will rebound.

__________________
This is no fantasy. No careless product of wild imagination. - Jor-El

Godspeed, John Glenn. - Scott Carpenter

And these atomic bombs that science burst upon the world that night were strange even to the men that used them.
- H.G Wells, The World Set Free

To the conspiracy crowd, radiation is a big Boogey Man that inspires terror and death in all who encounter it. - JayUtah

I see that. As ice is removed, the rebound is not instantaneous. It's a function of the viscosity of the material--and the viscosity is great enough that the material is actually considered to be solid.

The ice sheets were extensive, and thick, and they depressed the area for a long time--otherwise, the viscosity would have prevented the land from depressing. When the majority of the ice disappeared, the land started to rebound.

I don't quite understand how the rebound is supposed to somehow decrease the sea level. Is your friend suggesting that the water will flow under the rebounding land? Where will it go? Is he suggesting that Antarctica's landmass is less dense than water? Otherwise, hhEb09'1's analysis applies - you are talking about minor compression, and the water has nowhere to go and will overflow the pool.

Actually, what's wrong with this reasoning? We assume Antarctica's (2 C's, by the way, Grand_Lunar) landmass is denser than water. Then, if we perform his experiment, the pool will always overflow. This is because the ice is supported by the land (e.g., not floating) and thus will add to the total volume of water when melted. The land will expand somewhat and thus take up more volume compared to when it was compressed. Thus, if the top of the land was slightly under water, then the water level will rise without the addition of the ice. If the top of the land was at or above the water level, no change in the water level will occur without the addition of the ice. However, you have ice, and thus the pool will overflow.

The only wriggle room is that the water may flow into the land, but if we assume water is incompressible at the associated pressures for this to occur, it won't help much. So, your friend can only argue that the landmass in Antarctica is less dense than water, the compressibility effects of water is sufficient to accommodate for the water flow into the expanding land, or that the water will flow into the magma layer and fill existing cracks there. I would need to see evidence for any of these possibilities before accepting them.

Thoughts?

yea, they are grasping for straws. first it was GW doesn't exist, now they want to say it won't affect much.

__________________
"I will do my best to understand and explain the universe from big to small without invoking miracles, unrepeatable events, or divine intervention. In place of those things I will use observations, mathematics, and science."


-Cross
My travel blog

Some of my Astrophotography


Those that lack education have a hard time understanding its value. - Cross