Why will the ice caps melting cause the sea level to rise?
tiamat, the level of the water does not go down if the ice cube floats unrestricted on the glass. Indeed as it melts the water level remains the same. However you are correct in your assertion that ice is less dense than water. As such if you attach a piece of lead to the ice and have it sink to the bottom of a glass of water, once that ice melts, the level of the glass will indeed fall. This doesn’t apply to the geological ice we’re talking about because much of it is supported by underlying earth and so the melting caps are not floating by gravity on water. Much of their mass is above water.
Its a good question and the answer is – it depends, depends basically on where the ice is and what its sitting on. Put simply, if the ice is sitting on top of a shelf of rock, ie: sitting in a pile above sea level, then when it melts the level of the sea will rise. Some of the icecap is like this. However, some of it isn’t and like your ice cube there is a significant volume of ice below sea level. When this melts the level of the sea will fall. Overall if I recall correctly only the Antarctic and Greenland sheets would cause a sea level rise if they melted (ie: the whole of the arctic could melt without affecting sea-level), but opinions differ … This account seems to suggest that even the Antarctic and Greenland sheets would not make much difference. Sea level rise is attributed to overall thermal expansion of the oceans and the melting of mountain glaciers.
It’s like adding more ice cubes to the glass. Much of that ice is sitting on solid ground, up above sea level. Antartica is a continent like any other. It is about 14 million km² big and almost all of it has around 2.5 kilometers of ice on top of it. Pretty big cube, eh? The Greenland Ice sheet is around 1,800,000 km². I don’t know the average depth, but it hits 3 km (two miles deep) in spots. It fell there as snow or rain and accumulated over the millenia. When it melts it will go down into the sea, and this time New Orleans is really gonna’ get it.
By the way, the increase in sea level from the ice on Greenland and Antarctica melting is 77 meters. That’s seventy-seven meters, or 252 feet. The coastline of the world looks vastly different if it’s 250 feet higher. The highest elevation in Florida, for example, is 345 feet. Basically all of Florida disappears under water. But not all the ice will melt at once, you say. True enough. Even a 20 foot increase in sea level wipes out dozens of the world’s largest cities, though. We have already put enough heat into the system to melt all that ice. The earth is now a glass of HOT water with ice cubes in it. The only question is how fast. Washington Post, March 3, 2006, page A1: Antarctic Ice Sheet Is Melting Rapidly: New Study Warns Of Rising Sea Levels.
