We don’t know what caused the sea to rise. We’re still fairly early in, so we’re not anywhere near understanding it. It happened 300 years before the campaign, of which only my character, Ulysse, knows about the world beforehand as she is almost 600 years old. She was there when The Rising happened. She’s the only one who has any idea what might have caused it and she wants to figure it out and set the world right.
There are columns of water that pour down onto the land below, and that’s where major towns and cities are, along with the little farming that can be done. The sky ocean covers the whole sky, so it’s thinner than the oceans on the ground were, which allows the light to come through.