system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: As they polar ice caps melt why does the sea level rise, isn't the displacement of the ice already accounted for.

I'm not debating that it is happening I just want to know why. I thought of this because I remembered that like 4th grade science experiment where you put ice in the glass and fill it to the top with water then wait for the ice to melt and the water stays at the same level.
gpt
Most of the ice that's of concern is sitting on land in Antarctica, Greenland and mountain glaciers.  Approximately half of sea level rise is attributed to melt from these ice sheets.  The other half is attributed to ocean water warming and becoming less dense / taking up more volume.