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
Polar ice isn’t floating, it is sitting on land and elevated above the water. Since it is not already displacing water line your drink’s ice would be if it was floating, when it melts it raises the water level.
salt water vs fresh water…..the ice and glass example is actually the title of the NASA article
[https://sealevel.nasa.gov/news/261/melting-ocean-ice-affects-sea-level-unlike-ice-cubes-in-a-glass/](https://sealevel.nasa.gov/news/261/melting-ocean-ice-affects-sea-level-unlike-ice-cubes-in-a-glass/)
When thinking about sea level rise, besides the ice that sits in continental masses (outside the ocean), you also need to consider the thermal expansion of water.
[According to NASA about half of the sea level increase so far comes from thermal expansion.](https://www.jpl.nasa.gov/edu/learn/project/how-warming-water-causes-sea-level-rise/)
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.
The Arctic polar ice IS floating, but that’s not the problem. The problem is all the ice covering land in Greenland and Antarctica, and all the other glacial melt around the world on land that will make it to the sea.
Sea ice won’t raise sea levels, but land ice will, and there’s lots of ice on land.
Both will also reduce the salinity of the ocean, and disrupt ocean currents.
Warming oceans also mean the water will expand
If your ice floats on the water in your glass and is only partially submerged, the water level will increase as the ice completely melts.
ELI5: Its not the ice floating on the water melting that’s the problem. its the water thats melting off the land and *into* the water that is.
The problem is that there’s a lot of ice that is actually sitting on land, that will melt and flow into the sea, ADDING water to the oceans. Greenland contains enough land ice to raise the sea level by about 20 feet and Antarctica has enough ice to raise it by another 190 feet. Again, this is not ice that is floating in the sea, like an iceberg, but ice that is sitting on land, like a glacier.
About the melting polar caps and the rising sea. I happen to own a globe, which is like a map of the world painted on a football. Both polar caps are painted white because of ice and snow. I can see that these two white patches, together with any smaller ones scattered across the continents, would need to be stacked darn tall for the ocean to rise much when they melt. So no luck with wiping out kitschy beachfront resorts, though it might meddle with the planet’s sunlight reflection quotient because less white means less reflected light. So maybe that’ll prove to be the tricky part
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