[spacetime_cmplx]

I have two related questions:

1. Global temperature is rising. Any water that used to be above 4°C (or the equivalent for salt water) now takes more volume. But what about water that's below 4°C? Wouldn't that water compress? What portion of the ocean is colder than 4°C? I'd imagine all of the Arctic zone and near Antarctica is, which is an awful lot of water to offset the tropical water. An even more nuanced perspective would be to look at the actual temperature distribution and use it to weight the dV/dT of water at different temperatures.

2. Global temperature is rising. Ice is melting into water. This is new mass entering the ocean. Why can't the sea bed, which is under more pressure due to extra mass, expand? The sea bed isn't a steel utensil, it's sand and rocks. And it's constantly shifting. And it's composition is different in different regions.

Has anyone done a detailed computer simulation of the whole earth's geology under rising temperatures? There might be feedback loops that might amplify or negate some effects so it's quite important to account for all variables. And obviously there's a lot of variables to account for.

(It's sometimes scary how little we know about our own planet. I'm not talking about the things in my comment because I'm sure it's just my ignorance.)

[Timon3]

> 1. Global temperature is rising. Any water that used to be above 4°C (or the equivalent for salt water) now takes more volume. But what about water that's below 4°C? Wouldn't that water compress?

It might marginally, but the amount of water compressed will be a lot smaller than the amount of water "uncompressed", both due to the larger range of temperatures above 4°C (below is only a bit, and then ice) and due to the fact that the densest water is at the bottom, meaning that it's easier for everything else to heat up.

> 2. Global temperature is rising. Ice is melting into water. This is new mass entering the ocean. Why can't the sea bed, which is under more pressure due to extra mass, expand?

Expand where? It can't just rise since there is gravity, and the pressure above increases with more water. It can't go down because there is already other stuff there.

[friend_and_foe]

In regard to that last point, I hadn't thought of it but there is something called post-glacial rebound, it would make sense that the increased weight on the seabed would deform it, and potentially even cause bulging of land without ocean on top, potentially negating the sea level rise effect to varying degrees worldwide.

[spacetime_cmplx]

>Expand where?

Think of the ocean bed as a trampoline. Obviously much more rigid, but that's the image in my head.

>It can't go down because there is already other stuff there.

Why not? Rocks and sand can be compressed with sufficient pressure.

[marcosdumay]

> Wouldn't that water compress?

You say it because of the extra volume on top of it?

If that's the case, not because of heating. The volume increases, the water still weights the same.

[spacetime_cmplx]

No, water is most dense at 4°C. If you take water at 2°C and increase its temperature by a degree, it will _compress_, not expand. But if you take water at 10°C and heat it by a degree it will expand. My question is what percentage of the expansion is offset by the compression.

(Note that the 4°C number is only for pure water.)

> water still weights the same

Weight has nothing to do with my first point. It's the increase in volume that spills into land.

[marcosdumay]

Yeah, my comment was stupidly about how some other phenomenon doesn't exist.

But well, water being water, I imagine this doesn't happen at pressure; just for surface water. Is that the case?

[slackfan]

Reminder that Ice takes up more volume than water.

[spacetime_cmplx]

I know, did I say otherwise anywhere?

[adgjlsfhk1]

the key point is that there is very little water below 4 Celsius because it would rise into warmer water and heat up.