Wait. Are you telling me the seas have been rising since the ice age and not just in the last 100 years?
In the example I'm most familiar with, the island of Great Britain essentially see-saw'd. Relieving the northern half of the island of this unimaginably massive weight caused the northern end of the island to rise, and the southern end of the island to sink reciprocally.
So even without glacial melt to content with, some areas that were low-lying during the ice-age would have become submerged post-ice-age.
The example I find most fascinating (I'm British, so still using GB & locale as examples) is "Doggerland"[1] - the theory that what is today an underwater topology named Dogger Bank, was previous an island, and before that the land bridge between GB and the continent. There's a strong chance there's prehistoric archeology to be found in the middle of the North Sea.
Yes, sea levels have moved before - as part of one of the largest and most defining geological events in human history.
[0] https://en.wikipedia.org/wiki/Post-glacial_rebound [1] https://en.wikipedia.org/wiki/Doggerland
(I don't want to de-stress point 1, the ice went somewhere. There's just little to expand on.)
https://slate.com/technology/2017/08/why-sea-level-is-fallin...
Which makes sense really, since we're on the same tectonic plate. Geographically there's not a huge difference between Scotland and Scandinavia. They're the parts of northern Europe that were torn up by glaciers.
It does make me wonder, tongue in cheek, who's reciprocally sinking on that side though. I know a few people who'd be disturbingly proud to find out that Sweden and Finland are sinking Denmark.