Tuesday, December 27, 2005

a layman's scientific inquiry

One hears a claim from time to time from the environ-mentally challenged individuals (of the watermelon genus), that the melting of icebergs will raise the level of the Earth's oceans. Put aside for the moment whether human beings are effectively responsible for this, and what can or should be done about this.

Just follow this simple science experiment. Put an ice cube or two in a glass. Add water to the glass until the water reaches the rim of the glass. The ice cubes will then jut above the rim of the glass. Set aside the glass for a few minutes until the ice cubes have melted down somewhat. You will notice that the glass has not overflowed its container. Go ahead and leave it and come back a half hour later when the cubes have all melted away.

Wait, that's crazy, where has the water gone? It has not evaporated away if that is what you are thinking (not enough to make a difference anyway.) The answer is simple.

Ice is less dense than water; it will take up more space than water of the same mass. IIRC, the ratio of densities of ice to water is 1/9 less. That is why ice floats on water, it cannot displace a greater mass for the same volume. It can displace a lesser mass of water though, if it lies partially out of the water. That is why a small portion of icebergs and ice cubes protrude out of their surrounding liquids.

Anyway, to get back to my initial inquiry; even if all the world's icebergs melted completely due to global warming, what do we have to worry about?


Anonymous said...

The arctic ice is not a problem, as it floats. Greenland and Antarctica cause the problem, as there the glaciers are on land, above sea level...

Vache Folle said...

What anonymous said. The ice on land will be added to the water in the sea with a concomitant rise in sea level. More problematic in my view is the surfeit of fresh water flowing into the Arctic ocean from northern rivers and melting ice. This interferes with the submarine conductor current that helps keep temperatures from becoming too extreme at the poles and equator.

Brandon Berg said...

Right. If the ice is floating, it's no problem. But if it's on land, then it runs off into the oceans without any compensating reduction in displacement.

Also, I've heard that the real concern--as far as ocean levels are concerned--is thermal expansion, not melting icecaps. When water heats up, it becomes less dense, so the same amount of water takes up more space.