[RedDevil]

Most of our coast line is sand dunes and behind it lies land that is lower than sea level. The dunes used to be self sustaining, gathering sand blown up there from the beach.
Nowadays at spring tide the sea threatens to wash away the foot of the dunes, so millions of tons of sand need to be added yearly to the beaches or our coast line would wash away.

One can argue about what causes it, but sea level rising steadily in the last century is a fact.

If the sea level rises one meter adding more sand will become hard to sustain. At two or three meters it will become impossible. We can build dikes but if the sea level exceeds the ground water level too much then salt water will inevitably seep in through the sandy underground.

If the rising level is caused by our carbon dioxide emissions, if we're able to reduce that and stop this effect then we won't have to spend billions a year extra in the future.