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Comment by papreclip | Hacker News Reader

It seems really unintuitive to me that there is enough ice on the globe to raise the sea level by 6 feet (let alone 230). But then if I had to guess the land area of Antarctica, I would have estimated something the size of Oklahoma or Texas (when Antarctica is 40% larger than the USA)

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Much of the Antarctic landmass is below sea level, if the Antarctic ice shield melted the continent would look like an archipelago. There is much water tied up in the Antarctic ice shield(well, it took 40 myr to accumulate, you get this much even in a cold desert), on average it's 2 km thick. The IPCC estimates that if it melts fully it would result in 50 m of sea level rise.

Any ice below sea-level will melt into water that will take up exactly the same amount of space. So any ice below sea-level that melts will not cause sea levels to rise.

Could you please elaborate on your claim? I feel confused.

I learned that ice has a (slightly) lower density than water, hence it usually floats. I was convinced that submerged ice is doing so because of an additional weight on top of it (above-water ice pack).

Maybe there is also ice that is submerged without this extra weight, but then its density should be lower than water.

Either way, I don't see how submerged ice could take up exactly the same space when melted. If it has a different density, it should change in volume (elementary physics).

Ice that is floating displaces an amount of water whose weight equals its weight. That's why a little bit floats above the water and most is under the water.

When that ice melts, it still weighs the same amount and fills exactly the amount of space that it was displacing. In other words, it fits perfectly in the space in the water that it was already occupying.

So floating ice that melts (above or below the water) doesn't change sea levels at all.

Only melting ice that is currently supported by land will increase sea level.

A reference for anyone unfamiliar with this explanation: this is Archimedes' principle.

https://en.m.wikipedia.org/wiki/Archimedes%27_principle

I've heard most of the rising sea levels will come from thermal expansion of water, not melting ice.

Liquid water is notorious for having almost no thermal expansion, but the little bit it does have will be multiplied by the volume of the ocean, then divided by the surface area of the ocean, yielding the rough vertical rise.

A chunk of it is thermal expansion and the fact that CO2 is being absorbed in

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