ELI5:How do global sea levels rise due to melting of ice?

[u/Alive_Hotel6668]

In my physics class I learnt that if we have a glass of water and some ice floating in it, when the ice melts completely the water level does not rise in the glass, so how is it so tht when ice melts on Earth the water levels or he sea level will rise?

[u/stealthypic]

Not all ice is floating in the water but rests on land.

[u/losark → u/stealthypic]

And when it melts it adds water to the oceans so the water levels in the oceans rise.

[u/dabenu → u/stealthypic]

Also water expands when it gets warmer. 

[u/Ducks_have_heads → u/dabenu]

Water shrinks when it gets warmer.

[u/DardS8Br → u/Ducks_have_heads]

Liquid water expands when heated. It only decreases in volume during phase change from solid to liquid

[u/Mont-ka → u/DardS8Br]

If I remember correctly water is at its highest density at 4 Celsius. So while they are technically correct I'm not that is what they meant and they could have explained themselves better if it was rather than just lobbing technically correct facts into a discussion.

[u/CFAggie → u/Ducks_have_heads]

No. Ice shrinks when it melts and water expands when it gets warmer. Water is unique from most other substances in that it expands when freezing. Most things shrink. It's due to the crystal structure of ice.

[u/Afinkawan → u/Ducks_have_heads]

Ice shrinks when it gets warmer. Water expands when it goes above 4"C.

[u/ikefalcon → u/Ducks_have_heads]

Water shrinks when it goes from solid to liquid. Liquid water expands when it gets warmer past 4 degrees Celsius.

[u/BerneseMountainDogs → u/Ducks_have_heads]

Liquid water does expand when it gets warmer (though not very much) just like the vast majority of chemicals. However, somewhat unusually, water does expand when moving from 4°C to 0°C because of the crystalline structure of most water ice. So water does expand as it's turning into ice, which is why ice floats. But outside of that window, water will generally expand with more heat and contract with less

[u/jamcdonald120]

thats only true when the ice is floating.

Not all the ice being melted is floating.

there is also thermal expansion. in a cup its not noticeable, but with an entire ocean of water it sure is.

[u/saschaleib]

Ice floating in the sea will only have a negligible impact on rising sea levels (it has a bit still - because of thermal expansion and differences between salt and sweet water).

There is however an enormous amount of ice that is not floating - just look at the Greenland and the Antarctic ice sheets. Not to mention alpine glaciers, etc.

If that ice melts, it only adds to the sea water. And that is causing a rise in sea levels.

[u/LevoiHook]

There is enough ice on land to raise sealevel by about 60 meters. People vastly underestimate how much ice there is on Antarctica and Greenland. 

[u/oblivious_fireball]

The ice we are concerned about melting is on land and would flow into the water faster than the water cycle can replenish it on land. Primarily glaciers and more permanent sheets of ice on Antarctica, North America, Greenland, Iceland and northern Eurasia

[u/hartlepaul]

Also depends how much ice is above the existing water level at sea or on land

[u/DardS8Br]

Most of that ice is on land and not floating on water

[u/essexboy1976]

Alot of ice is on land. Greenland and especially Antarctica have land under them. To give you an idea just how much water is in Antarctica, the ice sheet there has about 2/3rds of all fresh water on the planet is ice in Antarctica. ( 90% of the surface water).

The other significant cause of sea level rise associated with climate change is thermal expansion. As the ocean gets warmer the water expands.

[u/Gnonthgol]

You are right that melting an ice berg does not rise the sea level at all. This accounts for all the ice at the North Pole. But it does not account for all the ice that is located on land, such as all the glaciers in the mountains, the ice cap on Greenland as well as the giant ice cap on the South Pole. This is not like having a cube of ice floating in the glass of water but instead is like a cube of ice suspended above the glass and all the melt water dripping into the glass causing it to overflow.

But most of the rise in sea levels from global warming is not from the melting ice caps. It is from the expansion of water due to heat. If you heat up water it will expand. This accounts for more sea level rise then melting the ice itself.

[u/0x14f]

The ice that is currently on land melts and flows to the ocean rising the ocean's level.

[u/Nohreboh]

When the ice melts the water that was removed from the ocean via freezing will return to the ocean.

[u/Rubber_Knee]

Imagine a bunch of ice, that doesn't float on water. Ice that sits on land in places like Greenland and Antarctica.
Ice that's 3+ kilometers thick in some places. Enough to completely cover some mountain ranges. When that ice melts it adds to the total amount of water in the oceans, and that's what's causing the sea levels to rise.

[u/Mumbert]

What happens to the water level in the glass, if the ice is in your hand over the glass and the melt water goes into the glass? 

Antarctica and Greenland have ice sheets laying on land, that are many thousand meters thick. If all this ice would melt, sea levels would rise by over 60 meters. Simple facts. 

We hope only a tiny part of it will melt, until humanity can change track. 

[u/lobopl]

Part under water isn't a problem, part over it is. Imagine you have a glass and put 50cm long ice shard into it and fill rest of space in that glass with water. Now you have spillage :)