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Q & A: Global Warming & Sea Level

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Most recent answer: 10/22/2007
With everyone concerned about global warming these days & the polar ice caps melting, I put this question to you. If some of the polar ice caps melt, will the ocean level rise,fall or remain the same? Now I’ve being told that ice caps are a combination of water & trapped air(% unknown, but I was told it was a large amount). Say for example you had a piece of ice & melted it, wouldn’t the releasing of the trapped air, cause the original piece of ice to be less dense, & therefore the original water level would decrease as the ice(now water less the air) isn’t displacing as much water as it was at the start? Also how much does the temperature of the water effect the raising of the ocean level? Thanks, Michael.
- Michael (age 15)
Michael -

There are two big ways by which increased global temperatures can cause the sea level to go up. One of them is the melting ice. You're right that the submerged ice takes up roughly the same amount of space after it melts as it does before. (Actually it takes up less, but since most icebergs are partially above water, it comes out about even.) But not all ice is floating freely in the ocean. There is a large amount of ice sitting on top of the Antartic continent and Greenland. As that ice melts, it drips down into the ocean, raising the sea level.

The other way that the sea level rises is because of the temperature of the ocean itself. Warmer water takes up more space than cooler water. It's not usually a big enough difference to matter much, but the ocean is so incredibly deep that it is actually very important.

Between these two things, if the planet were to warm up enough, the ocean level could rise by as much as several meters. That may not seem like a whole lot, but it would be sufficient to put a number of islands, coastal areas, and even some cities under water.


(published on 10/22/2007)

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