For about 20,000 years straight sea levels have steadily increased.

https://www.e-education.psu.edu/earth107/sites/www.e-educati...

Whether you like it or not, this is climate change and you cannot deny this. Obviously human activity has no impact on this.

You might look at more modern reliable data: https://www.climate.gov/news-features/understanding-climate/...

We're up around 225mm or 22cm or 8inches over the last 100 years.

https://coast.noaa.gov/slr/

So about 100 years from now another 8inches or so. Hell, just go 1 foot.

New orleans, Miami, etc are probably going to need to build something to save themselves.

This is reality, but they have a long time to handle it.