if ice takes up more room that h20, why will the oceans rise when the ice caps melt?

Answer 1

There are significant amounts of ice that are part of continental glaciers, or are currently on solid land, like the huge ice caps of Greenland or ice fields of the Antarctic. This ice is currently not part of the ocean system, and when it melts will represent brand new water to the oceans, causing the oceans to rise. It will be as if you held a huge block of ice over a bucket and watched the water level in the bucket rise as the ice melts and drips into the bucket.

Answer 2

It seems pretty clear that global ice volume is still decreasing- partly naturally and partly through man made changes to the atmospheric system. The above answers cover both of the main points related to sea level rise - a) thermal expansion of the oceans, and b) the inclusion of terrestrial ice into the ocean water budget. I do not think that accumulation is keeping pace with ablation of ice sheets, but this is not unnatural.
The 'ice-age' we live in has been regularly punctuated with warm er interglacial periods and during these the ice caps recede and sea level rises. During the icy glacial periods the ice caps expand and sea level drops. The causes of these changes are very complex - but increasingly understood. As we gather more evidence it does appear that man-made changes to the atmospheric carbon budget (in the form of CO2, CH4 etc) are likely to have an increasing impact and warm the planet 'unnaturally' probably to a few degrees celsius more than would be expected.
This may lead to the total melting of the arctic ice cap and further in the future the greenland one too. For the moment the antartic appears less vulnerable as it is shielded by the powerful currents of the southern ocean. If the arctic and greenland melt - we may see continually rising sea levels up to 20m above today's. If the antarctic ice sheet also breaks down this will add twice as much - for a total of 60-75m sea level rise.
At that point every major coastal city on earth will be in a similar state to the native american remains referred to earlier.
Will this happen? Nobody knows for sure - how hot things will get. Or whether overheating the planet will lead to a kick back mechanism that takes us back into another freezing glacial via mechanisms that at the moment are poorly understood. There are many hypotheses and some evidence - but the scariest thing about the climate system is that we know just enough to see that we ARE interfering - but we have little idea of just how bad a reaction we're going to provoke.

PS: We are living in one of those warm 'interglacials' I mentioned. During the last warm period (125,000 years ago) sea levels seem to have peaked at 20 metres above today's.

Answer 3

The oceans will rise when ice on land melts, Greenland for example. Any ice in the ocean isn't going to make a bit of difference because it's weight and volume of water is already there.

Incidently, during our last ice age around 20,000 years ago, the ocean level was around 450 feet lower than today. This was evidenced by the remains of Indian campsites 100 miles south of New Orleans, now under 450 feet of water.

Answer 4

The previous answers were right except that it is not a sure thing that the ice will melt faster than it accumulates. It has been melting for thousands of years and it is likely to continue. You are correct that floating ice will not significantly add to sea level rise. Most of the rise predicted is due to warming oceans. I am skeptical of the ocean warming significantly so if you take that away it is likely that the oceans will only rise no more a few inches in the next 100 years and is not worth too much worry.

Answer 5

If all the ice stored up in Greenland and Antarctica melt, there would be significant sea level rise (about 150+ feet). BUT...that is an extremely unlikely event (that all of it would melt).

Sea ice, which mainly comprise the north polar ice cap, would not really cause sea level to rise that much (if at all) because it is derived from sea water freezing and it would just be returned to the sea.

Answer 6

Because a lot of the ice that is melting is not IN the water. The ice in Antarctica and in Greenland is miles thick, and is on land. So are glaciers on most of the continents.

Answer 7

It's not due to the added volume of water from the melted ice (you are right, that will pretty much cancel). It's due to an expansion of the water if it gets a bit hotter (water takes up a bigger volume as it gets hotter).