Would melting sea ice lead to a rise in sea level? The ice is floating, so it's displacing the approximately same mass of water as it contains. If it melts the overall water level shouldn't change.
1. Thermal expansion. It's a tiny effect, you won't see it in a glass of water in science class but when you've got oceans a few kilometers deep and humans living a few meters above them it can have an impact.
2. It's a feedback effect. Less ice means less light reflected means more energy in our oceans/atmosphere. In turn this creates more ice loss that won't be sea ice.
Water crystallization is a different effect and not relevant here. It has the same mass so it doesn't effect sea levels when it's frozen and it's not a linear effect, it won't continue to shrink as it warms.
But like everything else (to various extents) it will expand when it's warmer.
The maximum density of water is at 4 degrees. If you heat it above that it starts expanding quickly. If you freeze it below that it starts expanding slowly.
This is correct, melting sea ice does not lead to a rise in sea level. It’s the melting of glaciers and ice sheets (on Greenland for example) that cause the sea level to rise.
2. It's a feedback effect. Less ice means less light reflected means more energy in our oceans/atmosphere. In turn this creates more ice loss that won't be sea ice.