Water happens to have one of the highest, and I would argue, the most important thermal capacity of all the compounds we're likely to come into contact with daily. Water has about 5-10x the heat capacity of most common things and so heating up the all the oceans by say 2 degs average is an ENORMOUS amount of energy.
Why is this important? The reason we have climate refugees today is not the water level but rather the higher intensity storms that the warmer waters spawn. Far before ppl are forced from the shores by rising waters they will be forced from the shores by massive, frequent, destructive storms that, instead of say destroying 1/1000 homes, will destroy 1/100. Eventually it will be economically non-viable to live in storm-prone zones. And those zones will increase in size over time to go far inland (away from fresh water), causing more migration.
This is happening NOW and will be a major factor in the lives of all our children.
It's easy for ppl to dismiss rising sea levels because it doesn't seem dangerous and happens over decades. It's far harder for ppl to dismiss weather disasters that they might have some first or second handed experience of or, more likely, a visceral fear of.
Maybe we should have a different metric? So instead of sea rise/year we should have expected floridian homes destroyed/year.