The impact would be very non-linear though. A few metres rise isn’t a big deal for coastal cliffs but for a coastal plain, river delta or flood plain a few metr

The impact would be very non-linear though. A few metres rise isn’t a big deal for coastal cliffs but for a coastal plain, river delta or flood plain a few metres rise can translate into many dozens of kilometres of horizontal encroachment by the sea. This effect was everywhere so people in that time would constantly be getting news of flood events in other regions. Many people were nomadic too. If the sea has been rising constantly for all known and even mythic history that’s going to have a huge impact on culture. Then there’s periodic catastrophic events like glacial lake outflows, temporary dams formed from moraines and landslides collapsing, etc.