OK, I’ve always had trouble with this idea. As far as I’ve ever known, when you drop ice in a glass of water, the ice already displaces an amount of water equal to the amount of water in the ice. So as it melts, it won’t cause the water to suddenly overfull the glass. So what’s different about the polar ice that makes it so that it will raise the sea level if it’s already floating in the sea to begin with?
In: Planetary Science
The biggest issue is that water expands as it warms up, if the oceans increase even just a tiny bit the existing water will *grow* in size (losing density). The overall temperature change might be smallish, just a degree or two, but there is a lot of ocean to go around and all that ocean gets just tiny bit bigger. That’s really the big deal with warming and sea levels.
To give you an idea of this effect, water is funny, it’s “smallest” when it’s a cold liquid, like 35F. It will expand when it freezes too, if you’ve ever put a sealed bottle in the freezer you’ve probably seen the mess it can make when the bottle breaks from the swelling. And that’s *just* a single, small bottle. Now multiply that growth by the whole ocean.
As other factors the water’s salinity (fresh vs salt) plays a role here (ice is fresh water, oceans are salt) plus a lot of the ice we’re talking about isn’t bobbing around in the ocean like ice cubes, it’s already on land and then *pours* into the ocean as it melts.
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