I rewatched Waterworld some time ago and got to thinking about melting of the icecaps and flooding of the Earth, et cetera. Waterworld’s IMDb entry states
I’m sure that’s correct, since the Straight Dope threads I dug up tended to agree.
However: everyone appears to agree that melting of the polar ice caps would cause the sea level to rise, even if not by Waterworld-ian proportions. That means (to me) that the concentration of water is higher on the ice caps than in the rest of the world. How did all that water end up at the Poles to be frozen in the first place?
I’ve also been told that one of the reasons that we find a frozen mammoth or two but no frozen dinosaurs is that the dinosaurs became extinct 65 million years ago and the oldest ice on Earth is a mere 50 million years of age. So it’s not like the ice has been there for aeons either. How did it get there? Why is it there today?
The north pole ice cap represenmts no extrawater, as the ice is floating- it displaces it’s own weight in water, so if it melted, there would be no net flow (apart from cold currents of meltwater which will not raise or lower sealevel)
but the Antarctic cap (and that of Greenland) is formed from snow, which is transported by the atmosphere to the point of deposit. So that is a real movement of mass.
Thanks, eburacum45, that’s what I was looking for. Another question, spawned by your answer:
So, water evaporates, ends up in the clouds, and then snows or rains down. When it falls on the South Pole, it’s in the form of snow. It doesn’t evaporate since it’s frozen, and over the millions of years a snow deposit builds up. Doesn’t it follow that the sea level must be slowly decreasing over time, since some water is continually lost into the icy mists of the Antarctic?
But ice also falls into the sea (through glaciation) from Antarctica, Greenland, etc., so it’s not entirely a one-way transaction. I don’t know the quantities involved but I’m guessing that beyond a certain basic level of ice build-up it evens out after a while.
Yes, the sea level is lower during glaciations- that is to say, when the ice on the land bulds up over Europe and North America, the sea level drops all over the world.
At the same time, the weight of the ice is so great that the centre of the ice-bound continents are pushed down, and this effect remains even after the ice melts, so that the continents slowly spring up again out of the now swollen sea.
The sea level changes associated with ice ages and glaciation are worth a study in themselves.
Not quite. Water is one of the few substances (perhaps the only one, I can’t quite remember) where the solid phase is less dense than the liquid phase - that’s why ice floats to begin with. While it is correct to say that it displaces it’s own weight in water, it does not displace the same volume. The distinction is subtle, but worth making in this case. The implication of this is that, should all of the floating ice at the North Pole melt, the sea level would actually drop. You can see the same thing in a glass of ice water. Fill a glass with a combination of ice and water and note the level. Then allow all the ice to melt. The water level will decrease.
We’ve also got the net increase of water through the impacts of comets over the years, both large and small. Some scientists have even theorized that this is how the oceans were created.
El Marko, you are slightly incorrect. It is true that ice is less dense than water, so ice cubes float. But it doesn’t float entirely under water, part of the ice floats above the water in the air. So if you fill a glass with icewater, mark the water level, and let the ice melt, the water level will be exactly the same. Yes, the total volume of the ice and water mixture is lower. But the extra volume of ice was above the water level in the glass. When the ice melts then no more ice floats above water level and the water level stays the same.
You could try this experiment at home and I am confident I will be proven correct, since I’ve done it several times.
Not really. Don’t forget that frozen water, whether as ice or snow sublimes, that is it evaporates back to the atmosphere by passing from the solid phase to the gaseous phase without going through the intermediate liquid phase. This is the basic mechanism of “freeze drying” and why those hot dogs that have been in the freezer for months taste so lousy when you thaw them out (aka “freezer burn”, somewhat of a misnomer.) Whether or not this occurs at a rate slower or faster than the rate of deposit of new precipitation, I have no idea, but it is possible there is a net loss of mass rather than a net gain.