melting ice

[nice sax]

I have just frozen some water in a jar and marked the level of the ice in the jar, then I let the ice melt and the level has gone down showing that ice takes up a larger area than water.

Bearing this in mind can someone explain why there is so much concern about the icebergs melting and raising the sea level, as surely the sea level would go down as in my jar.

Please help me this is driving me mad.

Colin

[CT]

Not all of the ice is in the sea. Most of it sits on land masses eg. Greenland, Antarctica. Now imagine your experiment again but you have some extra ice in your hand, then you melt it into the jar. Now the water level goes up.

[honest_joe]

Have you ever froze a carton of milk. Once frozen the carton is bursting at the seams. using up more space. As icebergs are mostly below sea level if they were to thaw maybe you have a point.

[brachiopod]

Ok, Joe and sax,

if you have an ice cube floating in water, a small part of it protrudes above the water level. When it melts, the volume decrease corresponds exactly to that volume of ice that protrudes above water level. Net result - no change in water level. You can try this for yourself - flot some ice in water, mark the level - and then wait for it to melt.

If the Earth's entire floating ice melted, there would be no change in sea level - but, as CT says, there are large volumes of ice locked up in land-based ice masses. If this melts, the huge volumes of melt-water will run off the land into the oceans - hence raising sea level.

To expand your analogy, imagine you have a sink of water with large chunks of ice floaating in it.. You also have some large chunks of ice sitting on the draining board.
As the floating ice melts, it will make no difference at all to the level in the sink - however, as the ice on the draining board melts, the water will run off into the sink and raise the level of the water.

[wildwood]

The average thickness of the ice on the entire Antartic continent is 2km. At some places it is over 4.5km thick.

[rojash]

So a more appropriate thought experiment is:
Put the plug the sink.
put a little water in it
Cover the draining board in ice cubes
What happens to the water level in the sink when the ice cubes melt?

[Bert]

About half of the present rise in average sea level is caused by the expansion of the sea due to the increase in its average temperature (according to what I have read when I have Googled suitable key words). It may be hard to believe, because the sea has only warmed up a couple of degrees (maybe less, I don't have the figures to hand), but there is such a lot of it! I don't suppose the deep ocean waters have started to warm up yet, so we will be in more trouble when that happens. Also, why did Sax (Colin) type 'area' when he meant 'volume'? A lot of people say "antartic", but it is spelled "Antarctic" (for wildwood).