posted
I am in middle of a new book called The Human Volcano: Population Growth As Geologic Force . It is interesting but some things bother me. I am always sick of America being portrayed as the ecological bad guy. I think pollution and environmental degradation happens as much in poorer countries as it does in developed countries. Maybe people will start to pick on China more. Anyway, I digress.
A few things about the book stuck out in my mind. The first is the fact that a few of the graphs (particularly in relation to global warming) are not labeled. The horizontal axis shows the years and the vertical axis is blank, but boy oh boy does the line shoot up!
As I was reading, the author started to talk about how the melting ice caps were causing the waters to rise....and then it hit me:
If ice expands when it is frozen, shouldn't the water recede as it melts? Or would the water level stay the same because as the ice melts more water is added to the ocean, however, since the ice cap looses some mass, it would displace less water?
Or is the ice on land and the run off is raising the ocean level? What am I missing? Smarter people then I understand why the oceans rise in global warming, but I can't wrap my mind around it.
Any thoughts you physicists?
Posts: 2445 | Registered: Oct 2004
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posted
My geo science is a bit outdated, but here goes...
1) Ice in Antartica is on a land shelf. When it melts, the water leaves the land and ends up in the Ocean.
2) Ice in mountain glaciers is also melting fast, sending much of its water down hill into the oceans.
Posts: 11895 | Registered: Apr 2002
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posted
Isn't the real question, (iqnoring the ice on the land, which would obviously add to the volume) is the displacement of the floating ice greater or less than the volume of water contained within the ice? If the displacement is less, sea levels rise, if its more, they should technically recede. Though I wouldn't bet on the former. (I suspect this is difficult to actually calculate, since the ice will have slightly different densities based on T and P).
Posts: 1621 | Registered: Oct 2001
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posted
What do you mean? Water is denser than ice, regardless of tempertature and pressure. thus if a piece of ice melts, it will take up less volume than a volume of water equal to the ice in it's solid state. yay?
Posts: 34 | Registered: Aug 2003
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posted
When ice floats, it sticks up above the surface of the water. So it actually displaces less than its total volume.
Posts: 1907 | Registered: Feb 2000
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posted
Floating ice displaces water equal to its mass, not volume. When it melts its mass has not changed so a volume of water equal to that displaced is added. The water level does not change. V = m/d.
Posts: 3243 | Registered: Apr 2002
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posted
Ignoring thermal expansion, the melting of floating ice does not change water levels. You can test this for yourself easily with a large glass mixing bowel, floating ice, and a grease pencil.
However, there are signficant volumes of ice in the Northern Hemisphere on land. Technically not the "ice cap," but if the Greenland sheet melts, it will oontribute to rising ocean levels.
posted
Thank you everyone. This is answering a lot. I kind-of imagined the polar Ice caps as giant ice bergs. I did not know on land.
I do see a dispute within the thread. A Rat Named Dog says:
quote: When ice floats, it sticks up above the surface of the water. So it actually displaces less than its total volume.
and Bob the Laywer says:
quote:Floating ice displaces water equal to its mass, not volume. When it melts its mass has not changed so a volume of water equal to that displaced is added. The water level does not change. V = m/d.
Who do I believe, the Rat or the Lawyer? Posts: 2445 | Registered: Oct 2004
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posted
They're saying different parts of the same thing. If something floats with any part of it out of the water, by definition it displaces less than it's volume.
The reason it floats is because the mass of the displaced water equals the total mass of the floating object.
Since mass is equal, and the volume of the floating ice is greater, then the density of the ice must be less than the water.
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